Toasted Tranny ?

[Mountain Gnome]

My tranny has run strong since I got my bus 4 years ago. Put it in drive and it pulls forward without pressing the fuel-pedal ... gotta ride the brakes in the parking lots to go slow, or it will build up a bit of speed. Delivers torque well though-out the power range, idle to 2600RPM.


or it did....


I drove it 6000 miles on fresh all cherry red Valvoline Full Synthetic across the country at top speed mostly (70MPH), up and down mountain passes, big mountain passes, though the desert in the summer, etc.


Last week I found a Forest Service Road on the map that was paved, and I headed that way on a narrow 2-lane winding highway up and down mountains with a lot of traffic built up behind my slow-*** bus. I pulled on the FS road, a narrow 1-lane no wider than my tire tracks, with no pull outs or turn arounds. Totally committed. Before I knew it, I was climbing the steepest hill I ever attempted with a vehicle not in 4-wheel-drive. I got down to maybe 1200 RMP in 1st gear, but I made it. I think if someone came the other way and I had to stop, I would not have been able to go forward again, and backing up was not much of an option either!


I left that spot the next day, went downhill a few miles back on the main 2-lane highway, and hit another FS road that followed a creek, so I figured it was flat and it was. I stayed there in a really nice spot, but had to put a double-stack of 2×8 boards under one rear tire to get level. I could barely get the bus to climb up on one 2×8 (like up 1.5") let alone a stack of 2 (they were stepped, so one at a time). I had to rock the bus back and forth; but the ground under the front tires was soft and full of debris, so I figured that was the problem, but began to worry.


On the way back out of there I had to climb back up that mountain, and the bus was really going slow up the hills. I stopped at the next little town and checked the fluid for the first time in 6000 miles (yea, smack me). It was low and brown and thin and smelled burnt. No surprise in an AT545 after driving it like I did, eh?


I limped it back to the big city 70 or so miles away, going over small hilly mountains, and it was having trouble getting up the hills.


I drained the fluid and refilled with more fresh Valvoline Full Synthetic and got the level correct when checked hot. But it started acting worse.


Sometimes it wouldn't pull from a stop anymore without giving it a lot of fuel. Then sometimes it will. But all of the time, it no longer likes to upshift. The RPMs used to hit a hard redline at 2600 RPM, and only when the pedal is floored and I'm going uphill. One time going just slightly downhill on the highway I got to maybe 2650 in 4th gear at near 80 MPH (then backed off when I saw the speed!) Now they hit 2700 RPM before shifting, and like 1st goes to second, which only drops the RPMs to 2550, and that quickly goes back to 2700 RPM while the actual speed increases, and then 3rd is similar but not as severe, and 4th maxes out now at 55 MPH on flat ground (at 2600 RPM), 60 MPH on a shallow downhill slope. It's quick to downshift when needed, though.


Driving it today, it seems like it pulls fine from the stoplight like it always used to, but the more the RPMs go up, the more it likes to slip, in any/all gears at all times. Also, there seems to be a noticeable "bump" or "clunk" when it shifts from 1st to 2nd, but the other transitions are smooth. Downshifting is smooth.



Stopped at a tranny shop, and of course the scoffed at a vehicle my size ("the tranny is too big" - what a load of horse-hockey from a primadonna; caddalackid did his alone - one guy in a parking lot), and definitely did not want to do a tranny swap to another model. He seemed to be familiar with Alison trannies, and said each "gear" has it's own clutchpack. But first he said I burned up the clutch-pack. If I did, why is the problem in all gears? Should only be in 1st, from climbing that big long steep FS road.


I think my fluid was too old, and I changed it, and the new high-detergent fluid loosened some crud and clogged a valve? Or the new fluid viscosity is higher and won't go through the clogged old spin-on filter and is screwing with the "line pressure" that should tell the tranny to upshift? I don't have a clue what I'm really talking about here, so maybe I'm way off base????? I wish I could rebuild trannies, and want to learn (I'd get up early for that job).


Anyway, the pan plug had a bit more metalic dust on it's magnetic tip that I would hope for this week. I just pulled the pan and cleaned all the magnets less than 20K miles ago (I think it was 12K-15K miles ago).


Today I got a new spin-on filter, and tomorrow I will swap it in and hope for the best, but I suspect it to be worse.


Then I gotta find a new tranny, and figure out how to get it installed. MT643 or a 1000/2000 series? Which has lower 1st gear, since I have 3.56 rear-end gearing? Do I even need overdrive with that rear-end? Gotta run the "final drive ratio" calculator to find some figures. Then find the tranny. These are all beginning questions I will look into before moving forward, and hopefully I don't find myself stranded.


Gotta go, my carriage is about to turn into a pumpkin, but I'll be back tomorrow.

[cadillackid]

It sounds like the 545 is just worn out. At some point the friction material wears off the clutches similar to how the pads on brakes wear down. It’s not quite 1 gear per clutch as they operate in conjunction with each other to create your 4 different ratios and reverse. Engaging the combinations of planet gears and spinning drums (or stopping them so the gears inside spin).

The heat probably sped up the decline as did the fresh detergent fluid. Now that it slips it will get much hotter and decline fast. Try to baby it if you drive it.

You are geared like my red bus. It has 3.54 gears and 19.5” tires. So it maxed out somewhere around 70 with the 545. Then I threw in a double overdrive . Now I’m well over geared. I borderline lug that engine anytime I’m in an incline and below 65.. at 70 in 5th the bus is happy as can be now that I tuned the engine. I’m actively getting ready to do a 4.10 or 4.30 gear swap.

You climb hills so if you swap to a 1000/2000 I’d also plan on a gear swap which would help you in the hills as it effectively lowers your drive ratio for your lower gears giving you better pulling power for off road or steep scenarios. Trick with a 1000 / 2000 is going fast enough to shift to 2nd where it can be programmed to lock the converter and avoid heat.

The other alternative is to realize you’ve done far better with a 545 than the odds say (or I have since I wasted 2 of them). And just replace it with a reman.

Put on a big aux trans cooler with a thermostat or toggle switch fan and go. If you get another 5 years out of it like you did this one you have a bargain. Last I knew LKQ I’m marsh field Missouri had reman 545 with converter for $550.

Mt643 is a heavy beast and designed to take a beating but unless you can get lucky enough to find a 653 which has a granny gear you still have similar ratios to a 545.

Pulling hills with a 643 can be more like driving a stick. My little 5.9 dt360 struggles on steep hills and the 643 don’t like to downshift out of 4th till it’s lugging along.. the 545 is the same but the TC slip on the 545 keeps the engine in its power rpm. So I do a lot of manual shifting in my 643 in the hills.. granted I found a nasty exhaust leak on my dt360 pre turbo so I’m guessing I have little boost till I fix that lol..

If it were mine I’d prob regear and a 1000 6 speed swap my de ision was also made knowing my bus is purely a hobby and it was home. I don’t live in it or rely on it for transportation so taking it apart for weeks at a time was no issue..

Maybe you slap in another 545 and plan for the upgrade when you can work o. Your terms and schedule

[Ronnie]

I agree with Christopher, and would likely toss another 545 in till you can plan a swap which will likely need a gear change in the rear to get the best out of any trans with a overdrive.


Mountain driving really is best with a manual trans, just saying....

[magnakansas]

There is a 653 in my area. Facebook marketplace. Let me look for the ad. Be right back.

Parsons Kansas. Mt653 used. With torque converter. Guy bought it cause he wanted PTO stuff from the transmission. Selling as a core. $500

Also $750. Mt643. Out of a Cummins 5.9 bus. Supposed to have all the parts needed to bolt to a Cummins. Topeka Ks.
William

[Mr4btTahoe]

I'm a bit confused...


OP stated that their bus used to pull at an idle so much so that they would need to drag the brakes. That doesn't sound right for a 545 considering it's loose converter.


Also the trans dragging the rpm down to 1200 or so doesn't make sense. The converter should have been stalling out higher keeping the engine rpm up even under severe load.


Am I thinking wrong or does it sound like there was an issue with the converter before this happened?


Either that... or maybe my 545 is more tired than I thought. Lol.

[turf]

howdy!
i'd echo what the others say.

just my opinion.... but running a synthetic adds to slipping.
with a slipping 545, i'd run cheap dex3.

imo - slicker fluid makes clutches slicker

[Booyah45828]

Sounds like you smoked the forward clutch. Slipping in all forward gears, the fluid being low, brown, and smelly also says that. Time for a rebuild or replacement, no magic elixir is going to fix this.

Easiest would be like for like with a fresh 545.

Second easiest would be a donor with an mt643. Rebuild the 643 if you'd like, but the donor is important so you can scavenge the different parts between the two. This could be considered an upgrade, as it's more robust then the 545, it's got better ratios for your deep geared rear end, and a locking torque converter to lower your highway cruising temps.

3rd easiest would be finding a donor with a 2000 or 3060. Both of those units became more and more common until the 545 was finally phased out of service. With a donor you can swap out and in the different parts, pieces and harnesses needed to get it to work. The additional electronics and the possible headaches associated with them is why this option is behind the 643. Also having OD might be a benefit, but with yours already being geared the way it is, it's not really needed.

I don't think I can recommend what chris did as an option though. I don't believe he had a donor vehicle for his swap, and thus spent a lot of time and money sourcing parts for his build. There's no doubt it was an upgrade, but it's not something the average guy could pull off without a lot of help from dealer techs and parts managers. Having a nearly identical donor vehicle is easier and is what most of the other swappers on here have done.

[Booyah45828]

I'm also in agreement with turf. The fancy fluids are super cool and light years ahead of the old stuff, but swapping them into a transmission that's used isn't a recipe for success. The old transmissions worked with dex3, and some places used tractor hydraulic fluid and motor oil in them as well, so try not to reinvent the wheel here. Use cheap fluid, and change it often if you have to.

[Mountain Gnome]

Thanks for all y'all's replies. I got 12.0V in my battery now, so this is quick.


Y'all talk down good synthetic fluid, say to use cheap stuff. In my experience, the opposite has happened. Used cheap Super-Tech fluid, and my tranny got worse (didn't have problems shifting before). Upgraded to Valvoline Max Life Full Synthetic for "older vehicles" in that vehicle, and the tranny came back better than before. Just saying....


Thanks for the tranny leads magnakansas. Looking at a hotel this week to hide from the 100°+ temps, so hopefully I can do some research online then.


Aloha for now, and thanks again all!

[magnakansas]

Start local, use face book marketplace and Craigslist—- use “Cummins Allison “ or “Allison transmission “ or “bus transmission “ as search words, my experience says you will find some near you, I am in Kansas I would help do a trans swap if you are near,

William

[mhaisten]

I am also in the same boat. I took the bus up the Dalton Highway to the Artic Circle, bucket list trip. Now a I have a toasted AT545. 11+% grades are not this busses cup of tea. Had I known about them in advance I would not have done the trip. Anyway luckily for me after calling and going to many shops I found one that had just done the same job and can get me going again within a week. Once all the goodies are gathered up they will do the work in one day so I don’t have to get a hotel.

[Mountain Gnome]

Originally Posted by cadillackid

The heat probably sped up the decline as did the fresh detergent fluid. Now that it slips it will get much hotter and decline fast. Try to baby it if you drive it.

You climb hills so if you swap to a 1000/2000 I’d also plan on a gear swap which would help you in the hills as it effectively lowers your drive ratio for your lower gears giving you better pulling power for off road or steep scenarios. Trick with a 1000 / 2000 is going fast enough to shift to 2nd where it can be programmed to lock the converter and avoid heat.

Put on a big aux trans cooler with a thermostat or toggle switch fan and go.

Mt643 is a heavy beast and designed to take a beating but unless you can get lucky enough to find a 653 which has a granny gear you still have similar ratios to a 545.

Pulling hills with a 643 can be more like driving a stick. ... So I do a lot of manual shifting in my 643 in the hills.


If it were mine I’d prob regear and a 1000 6 speed swap my de ision was also made knowing my bus is purely a hobby and it was home. I don’t live in it or rely on it for transportation so taking it apart for weeks at a time was no issue..

Maybe you slap in another 545 and plan for the upgrade when you can work o. Your terms and schedule

My dash gauge has always shown it to be running cool compared to the temps others on this site quote for their trannies. Maybe 120°F-150°F -ish (see pic). Unless the gauge is wrong. I have an infrared temp gun, but never checked that. I took a pic, I never noticed that the gauge shows temp when the motor is off, but that is typical. It still is not getting much hotter (maybe a little, or maybe now I'm paranoid) until I climb hills (or maybe now I'm paranoid and paying attention - I didn't much to that gauge before). The other day I saw it approach the 200°F mark on that gauge climbing another hill on a FS road. That road's incline is more "normal", but it's 5 miles mostly uphill in mostly 2nd gear, with a flat spot in the middle where it shifts to 3rd. I put in the biggest aux trans cooler I could find at Summit Racing, hoping to keep my motor cooler, but it did nothing to affect the temps of either unit (as seen on the gauges).


Rear-end gear swap is more $$$ than I can pump out right now. We're talking loans here at the moment....
I don't mind the manual downshift on big hills, if I must.

But I like the idea of a lockup 2nd gear. Didn't I see you say (or was it someone else) here that the AT545 and the MT643 don't have lockup in 2nd? But like Booyah said, I really need to find a donor vehicle for all the goodies, not just a remanned unit. I was on that already, thanks to all the cool folks on this site who have tackled this problem over the years and documented it here. I would be at the mercy of the tranny-repair shops and they would be putting in another AT545 without question, I bet. Then I would be right back where I started.


Yea, I'm living in it at this point, far from any "home base". Worst comes to worst, the quick AT545 swap may have to happen if it gets worse faster than I can get my sh*t together on a swap and all the parts needed.

Originally Posted by Ronnie

Mountain driving really is best with a manual trans, just saying....

I will be considering that. Would love a 10-speed Spicer (I don't know what I'm talking about, remind you) with 2-3 extra low gears, and an overdirve gear. But where to put the clutch pedal in this beast? Doesn't look like a friendly job....lots of fabrication. But I would certainly prefer a manual tranny in almost any vehicle. My 1977 Dodge Tradesman van had a 3-speed auto with a connecting rod to the steering, so if you turned the wheel all the way (going around a corner) it would downshift and give you better handling and better performance when you hit the gas at the apex of the turn. I likes that tranny. The rest are never "ready" when the transitions are extreme.

Originally Posted by Mr4btTahoe

I'm a bit confused...


OP stated that their bus used to pull at an idle so much so that they would need to drag the brakes. That doesn't sound right for a 545 considering it's loose converter.


Also the trans dragging the rpm down to 1200 or so doesn't make sense. The converter should have been stalling out higher keeping the engine rpm up even under severe load.


Am I thinking wrong or does it sound like there was an issue with the converter before this happened?


Either that... or maybe my 545 is more tired than I thought. Lol.

I never looked at the tag until today. HA! I only had a clue from the folks on this site (thanks y'all!) from the D-3-2-1 shifter T-handle and the way 4th never locks up when driving.



So I bet this was just rebuilt before I bought the bus, because even the fluid and magnet were not very dirty when I serviced them when I first got the bus.

Originally Posted by turf

howdy!
i'd echo what the others say.

just my opinion.... but running a synthetic adds to slipping.
with a slipping 545, i'd run cheap dex3.

imo - slicker fluid makes clutches slicker

That's just it. The Valvoline Max Life Full Synthetic is Dex3. Not "slicker" than regular Dex3. Synthetic oil has longer molecular chains, that resist breakdown longer. Or so I read on the internet....


Thanks again for all the replies, and stuff to think about. Still running on low battery (drove 2 hours today all over town looking for Chinese food, but they were all closed ) but it did give me enough power for this reply and some more searching that I need to do.


Aloha for now (and always, come to think of it!)

[Mountain Gnome]

Originally Posted by Booyah45828

Sounds like you smoked the forward clutch. Slipping in all forward gears, the fluid being low, brown, and smelly also says that. Time for a rebuild or replacement, no magic elixir is going to fix this.

Easiest would be like for like with a fresh 545.

Second easiest would be a donor with an mt643. Rebuild the 643 if you'd like, but the donor is important so you can scavenge the different parts between the two. This could be considered an upgrade, as it's more robust then the 545, it's got better ratios for your deep geared rear end, and a locking torque converter to lower your highway cruising temps.

3rd easiest would be finding a donor with a 2000 or 3060. Both of those units became more and more common until the 545 was finally phased out of service. With a donor you can swap out and in the different parts, pieces and harnesses needed to get it to work. The additional electronics and the possible headaches associated with them is why this option is behind the 643. Also having OD might be a benefit, but with yours already being geared the way it is, it's not really needed.

I don't think I can recommend what chris did as an option though. I don't believe he had a donor vehicle for his swap, and thus spent a lot of time and money sourcing parts for his build. There's no doubt it was an upgrade, but it's not something the average guy could pull off without a lot of help from dealer techs and parts managers. Having a nearly identical donor vehicle is easier and is what most of the other swappers on here have done.

Originally Posted by Booyah45828

I'm also in agreement with turf. The fancy fluids are super cool and light years ahead of the old stuff, but swapping them into a transmission that's used isn't a recipe for success. The old transmissions worked with dex3, and some places used tractor hydraulic fluid and motor oil in them as well, so try not to reinvent the wheel here. Use cheap fluid, and change it often if you have to.

Thanks for this reply. I think I'm already on the same page. I definitely want to find an upgrade, but only if I can get the whole package at once and easy, and before this one completely craps out. Don't want to hunt around far various stuff.


I still stand by the Valvoline Synthetic decision. Like I said, I ran cheap fluid in my $500 minivan for 8 years. The first time I did, it started shifting slow/sluggish, especially into reverse. I changed it every 12K-20K miles, including cleaning the magnet. Then I went to the Valvoline Full synthetic that I used in my mom's Pathfinder, since I had it left over. It shifted better than before. Her Pathfinder had 350,000 miles on the original tranny, and it always shifted perfect, smooth, and pulled strong. I changed the fluid and cleaned the magnet at 60,000 when she got it, and every 12K-20K after that. It only had a metal screen filter, so it never got a new filter. She hit a pothole, and tore the front strut from the body, though.


Alright, down to 12.0V, gotta run. Found a few trannies local, including a MD3060! Waiting for model numbers, or to hear if they will sell separate from the motors they are bolted to.

[turf]

no argument here.

just a point - synthetic Dex3 is called - Dex6

some but not all Dex6 are also labeled TES295

[cadillackid]

I use tes295 in my allison 1000. It’s there because my trans builder extended the warranty if I used it so transynd it is..

My build was different simply because I wanted new parts and 6 gears. Donor vehicles were all over but SAE3 6 speeds werent. And 4 years ago a donor bus with an a2000 commanded a bit of a price as not too many were junked yet.

Now there’s lots of them as schools obsolete or EPA their older busses that may very well be 02 or 03 models with 2000s on them.

I also knew I would be tuning at some point. After all I’m an old hotrodder so custom builds and turning up the juice are in my blood. A stick A2000 is a great trans but the 01-04 models are not equipped for high torque high HP. Applications.

My 1000 is built for 500 HP and over 1000 ft lbs.. way more than I’ll ever push out of that 7.3 in the bus..

My plan worked I’ve had zero transmission issues other than the growing pains of making it all work in the beginning and me learning to tune an allison. (I built tuners for 4L60E for years). But tuning an allison is an art all its own..

My swap def isn’t for everybody. But remember my busses to me are like the classic cars and street rods are to those guys.. they are play toys, they are cool-factor, they are an escape for me from work, they are my art instead of a canvas or a guitar..

Sure they also do serve a purpose such as transporting work equipment or being a mobile dev lab / dining room / CoVID-coffee-house. But ultimately if I were stuck out somewhere and my bus was my home and my transportation I would likely slap a reman 545 in and a big cooler and be on my way.. a 643 with all the adapters and plates would be a nice upgrade but only if that’s all included.. then pretty much the only fab to do is sending the driveshaft off for shortening . If you have hydraulic brakes you’d want to make sure the 643 comes with the full park brake assembly intact as those are a bit pricey and sometimes difficult to find. At 643s lived on air brake trucks / busses.

[HamSkoolie]

Originally Posted by Mountain Gnome

Y'all talk down good synthetic fluid, say to use cheap stuff. In my experience, the opposite has happened. Used cheap Super-Tech fluid, and my tranny got worse (didn't have problems shifting before).

The current manufacturer of SuperTech automatic transmission fluid Dexron and Mercon, is CITGO. That's a good name in the lubricants industry so just because it's labeled "supertech" doesn't mean it's bad stuff. It WILL MEET OR EXCEED the specification to which it is labeled.



[/QUOTE]Upgraded to Valvoline Max Life Full Synthetic for "older vehicles" in that vehicle, and the tranny came back better than before. Just saying....[/QUOTE]
As would be expected from an organic lubricant designed "for older vehicles" as well. Such lubricants have different lubricity and while they may "bring an old tranny to life" they aren't generally good for them. But if yo get another 5000 or 10000 miles before total failure it could be worth it.

[Booyah45828]

Originally Posted by Mountain Gnome

My dash gauge has always shown it to be running cool compared to the temps others on this site quote for their trannies. Maybe 120°F-150°F -ish (see pic). Unless the gauge is wrong. I have an infrared temp gun, but never checked that. I took a pic, I never noticed that the gauge shows temp when the motor is off, but that is typical. It still is not getting much hotter (maybe a little, or maybe now I'm paranoid) until I climb hills (or maybe now I'm paranoid and paying attention - I didn't much to that gauge before). The other day I saw it approach the 200°F mark on that gauge climbing another hill on a FS road. That road's incline is more "normal", but it's 5 miles mostly uphill in mostly 2nd gear, with a flat spot in the middle where it shifts to 3rd. I put in the biggest aux trans cooler I could find at Summit Racing, hoping to keep my motor cooler, but it did nothing to affect the temps of either unit (as seen on the gauges).

Your trans temps were likely fine. The fluid is burned due to localized heat inside the unit. The temp in the pan probably read fine, which is likely where your gauge was. But your forward clutches really hated life when you were in 1st gear at 1200 rpm pulling that hill. That's a lot of torque being applied.

Originally Posted by Mountain Gnome

But I like the idea of a lockup 2nd gear. Didn't I see you say (or was it someone else) here that the AT545 and the MT643 don't have lockup in 2nd? But like Booyah said, I really need to find a donor vehicle for all the goodies, not just a remanned unit. I was on that already, thanks to all the cool folks on this site who have tackled this problem over the years and documented it here. I would be at the mercy of the tranny-repair shops and they would be putting in another AT545 without question, I bet. Then I would be right back where I started.

MT643 only has lockup in 3rd and 4th. MT644 has lock up in 2nd 3rd and 4th. The gear ratios are the same between the two.

If you're going to be driving steep grades frequently, or dealing with soft soils, the extra low gear in a mt653/mt654 might be of interest. Pull the shifter down into first when stopped and you get a 8.05:1 ratio vs the 3.58 you'd normally have, or the 3.45 in the at545.

[Mountain Gnome]

Thanks again for all y'all's replies!


At this moment I'm leaning heavily toward the MT653. I found one rebuilt for a price that doesn't make my eyelashes singe when I saw it. I need to check with local shops about the price of rebuilding one if I find a core locally cheaper.


I really like the idea of the granny gear. A lot!


But the MT654 would be the unicorn it seems, with the lockup in 2nd. Most of my hill climbing is in second gear on most of the FS roads I'm on, in this area where I'm at, likely to be my new home area. Maybe. At least for the summer. Maybe.


My other favorite area seems to have all flat forest service roads, or very gentle inclines, from what I've seen there. But the campsites can have steep access drives, where the granny gear would be invaluable.


Anyway, I have more to say in replies to others, but I'm burnt out right now. It was after 4AM this morning before it was cool enough to sleep. Amazing how much heat that steel box with such little insulation can hold. It was cool outside at 10PM. And I had the roof hatch and 2 windows open.


What I'm really here for at this moment in time is this confounding question I just coughed up:


I went to Summit Racing's vehicle speed calculator to find some answers:
https://www.summitracing.com/newsand...tio-calculator
and put in 3.54 rear end gears (the plate on the front wall by the door says so), 33-inch tall tires (measured from the pavement to the tire top was 32.25", but they are low on air right now, and I haven't seen a place to fill them in several states....gotta hit a tire shop soon), and 70MPH, and it comes out to about 2523RPM. That was what my AT545 with its non-lockup TC does ..... ? Weirder, is that at 80MPH, I get about 2883RPM, but I've done 80MPH on flat land (or seemed flat) and it was only about 2600RPM. I let off the fuel and slow down, so gravity was not pulling me (it has done that on some big hills, and I would have easily hit 90MPH+ without brakes). My speedometer matches what those roadside radar-speed-signs say (the ones telling you to slow down when you are speeding).



What am I missing here? Anybody? God, I thought I was smart enough to use a vehicle calculator!


If this is correct, then I want the overdrive for sure! I saw torque peaks in my engine at about 1600RPM. It climbs fast to that, and then very slowly, insignificantly falls only a bit after that up to redline. Horsepower peaks near 2000RPM if I remember correctly, and if the graph I saw was correct. So I'd like to cruise at 70MPH at 2000RPM, but then I'd need 2.81 rear-end gearing. No.


I'd likely be better with overdrive and a higher rear-end gear ratio. So maybe the 1000 series after all?


uuuugh! I really like that granny gear!


What I also want is smaller steps between gears, so 5 gears from starting at 3.58:1 up to 1:1 and then an overdrive gear or 2, plus the extra-low granny gear. An 8-gear automatic unicorn transmission.



Or how about that 10-speed Spicer manual?

[cadillackid]

uktimately more gears = more control.. what is the printed size on your tires? mine with 3.54 gears are 225/70R19.5 and I topped out in my AT545 right about 70-71 at 2600 RPM . the computer when the engine was on a very slight decline and a little tail wind would let my engine go to its "no-load" RPM of 2700 so I was in the 72-73 range then.. downa steep hill foot to the floor and that bus would get up i nthe mid 70s and im guessing at some point the engine actually started pulling me down a little.



ive seen alot of those handi-busses with the same tire size or the 245/70R19.5, again not sure what you have..



ultimately the completely correct way to calc this is real world rolling distance.. you lay a tape on the ground, chalk the tire and drive exactly one revolution of a rear wheel.. thats your distance travelled per tire rev.. and it goes down with tire wear..



building to use all 6 speeds is ultimately the best.. your engine is an inline 6 , mine is a V8, the torque curves are different.. that 1600 RPM I get at 65 in 6th gear on mine is too low.. i watched the EGT gauge spike when I give the engine any work to do.. your I-6 would be happy as a camper at low-moderate load.. the step down from 6th to 5th is small so it will put your engine right into probably its happy place for all but true mountains.. ..


lets talk ratios!. first electronic overdrive units..



here is my Go-to DOcument on all things current-model electronic allisons.. a few pages down you find the gear ratio charge for 1000-4000
https://www.allisontransmission.com/...sn=5ca6051d_13


the 1000 series runs a 3.05:1 first gear and its 2 OD gears are 0.71 and 0.61
the most common 2000 series found in a school bus is a 2000 series ,specifically the 2500 PTS (Pupil Transport System). it runs a 3.51:1 first and its OD gears are 0.74 and 0.64 (Note 6th gear only available on 2006+ year units.. otherwise 0.74 is it)


the 3500 which generally i see in city trucks like trash trucks has a nice 4.59:1 first. those are wide ratio units. 4000 series units are SAE1 and not going to ever bolt up to a medium duty engine like a 5.9, they are heavier applications like class-8 and coach bus. technically a 3700 which is a 7 speed could be bolted to an SAE2 engine, ive never actually seen on e in the wild..



now we are in the completely custom built territory. I will say that I have seen 3000 series (3060) in blue-bird busses behind a 5.9, its not the most common but that means the parts exist to bolt up a 3000 series to a 5.9.






Mechanical Non overdrive units.

your AT545 has a first gear of 3.45:1
an MT653 has a standard first gear of 3.58:1. granny is an 8:1
an MT643 has a first gear of 3.58:1


Brakes on these bigger trannies are a concern.. is your bus hydraulic brake or air? meaning do you have a drum on the back of your transmission? which transmission you choose, manual or auto needs to be abke to accomodate the type of parking brake.. if you have air brakes in the bus you are home free because the park brake isnt affected by the transmission you install.



again my perspective may be different because i set out to build what I wanted and have the time and $$ to do it..



im just throwing out info..

[Booyah45828]

Originally Posted by Mountain Gnome

I went to Summit Racing's vehicle speed calculator to find some answers:
https://www.summitracing.com/newsand...tio-calculator
and put in 3.54 rear end gears (the plate on the front wall by the door says so), 33-inch tall tires (measured from the pavement to the tire top was 32.25", but they are low on air right now, and I haven't seen a place to fill them in several states....gotta hit a tire shop soon), and 70MPH, and it comes out to about 2523RPM. That was what my AT545 with its non-lockup TC does ..... ? Weirder, is that at 80MPH, I get about 2883RPM, but I've done 80MPH on flat land (or seemed flat) and it was only about 2600RPM. I let off the fuel and slow down, so gravity was not pulling me (it has done that on some big hills, and I would have easily hit 90MPH+ without brakes). My speedometer matches what those roadside radar-speed-signs say (the ones telling you to slow down when you are speeding).

My calculator says the same. No idea how you hit 80 doing 2600 rpm. Magic I guess. You'll gain a couple hundred rpm or so with the lock up torque converter. Once it's above the stall point the slippage is 10% or less depending on converter health and tightness. Slippage amount also depends on how much hp you're putting through the thing.

I think an OD would suit you well, But I think a granny gear would be better though, as 1200 rpm pulled down into 1st is where I feel you created your issues with the current trans. You're already doing 70. Yes it would be nice to optimize your cruise rpm, but it's not completely necessary. You've said it yourself the granny gear would be invaluable for where you like to go, so go with a granny gear.

I think you're on a truncated time table with your current trans. Not sure what your finances look like, but you need to get after this sooner rather then later. As much as I'd love to see you do an upgrade, rebuilding/replacing your at545 might be the best route. Anything outside of that would require you to source different parts, and if you don't have a "home base" to sit at for a few weeks(or months) to source these parts your list of options gets thin.