Cummins 5.9 with AT545 85mph?

[Thunder]

Originally Posted by Versatile

No trouble for me to get 78 mph on freeways @2800 rpm

What type of gearing do you have on yours?

[mmoore6856]

No tag on rear axel and no info in all the paperwork i got including the line sheet from chevy as to ratio ill just have to figure it. Cat did try to make better fuel milage by increasing torque and using higer ratios. Im running in the 10mpg range so i figure it must be a higher one

[Larrybird]

I noticed you wrote “ I drove my 40 ft tc 2000 today and had no problem going 70 on the flats at 2k rpm. I averaged 11mpg”.
I just bought a 34’ 98 tc 2000 with a 12v 5.9. Im riding 55 at 2500 rpms with a 3 speed at545 transmission. Looking for input on safe way to get up to 65mph and safely sustain that to drive cross country with the family. Any input would be greatly appreciated.

[cadillackid]

first off if your AT545 is really a 3 speed then theres a big problem.. it should be 4..



you feel 3 distinct "shifts" or "surges" as you speed up.. but you should have gears 1-4 in it..



if in fact you have all the gears and are topped out at 55@2500 RPM then your rear gear ratio is low and would need swapped to gain more speed for the same RPM.. this would also put more stress on the transmission esp in the mountains..



at a minimum you would need to re-gear and add a bigger transmission cooler.. ( if you can find a 3rd member and do all the work yourself you may have a grand).. couple grand if a shop does it..



swapping a rear third member is not a huge job.. the rear unit is usually a couple hundred pounts.. you dont even have to take the tires off the bus.. you pull iout the axles, take off the rear driveshaft.. unbolt the 3rd member and bolt in the new..



first youd calculate what you want as far as a new one.. i cant calculate since we dont know your tire size on the bus.. if you post that we can surmise what your current and desired gear would be..





optimally youd swap in a different transmission with overdrive and a lock-up converter.. lots of work if you do it yourself and prob a couple grand.. double that if a shop does it with used parts,,



thirdly you could realize you bought a bus thats not fit for your travels, sell it and go buy one that is..

[Larrybird]

Thanks for all the insight. I bought the bus a month ago and just emptied the interior. I do have an uncle that is a retired diesel mechanic who can help me in the spring when he gets back to Massachussetts from Florida. Tire size is 10r22.5. Im open to replacing the transmission (what tranny would you recommend) if it will give me the power for the mountains,65mph on flat highway and give me longevity for the bus as I am contemplating a small roof raise and complete solar etc.($$$$) I went with the 5.9 12v because I was under the impression it was easy to work on, reliable and good mpg, and easily able to add power to it. I paid 4000 for the bus so if you feel its not the right bus for my travels then so be it I can sell and look elsewhere. In that case any input on a bus, motor, tranny combo 30+ft lol. Thanks again for everything

[cadillackid]

If trans swaps interest you there are several threads on them. I’ve done a couple with great results on my own busses. They can be expensive. Sometimes you can get lucky and buy a donor bus that has all the parts you need . I went with new parts on mine because I drove my busses all over the place lots but that was the priciest option ..

[Larrybird]

Thanks for the reply. Sounds like youve got a good understanding of the busses. So you think my 5.9 would be good with a new tranny?

[Jay Brand]

Originally Posted by Thunder

I am not the most knowledgeable with drive trains and stuff. So please tell me if I am dumb. But I am currently looking at a 2000 Bluebird TC2000 8 Window.

The guy says that it is governed at 85mph and was driving it at 85-90 across the country. From my understanding a governor limits to that exact speed. But also would a year 2000 TC2000 Cummins 5.9 with an AT545 and 4.44 gearing even get to these speeds? The speed he listed was also in MPH not KMH.

Also it is supposed to consistently get 15 Miles Per Gallon. (Which I know is Plausible.)

Any thoughts and suggestions are always helpful!

I have the exact same bus. A 2000 8 window TC2000 with a 5.9 Cummins At545 with a 4,44 rear dif and I can tell you that the bus will NOT be happy at 80mph and the fuel mileage will be more like 6-7 mpg at those speeds. The best speed for my bus is around 63 mph and if the ground is flat, you might get 13-14 mpg if you baby it the whole time.

[Larrybird]

Jay brand, how did you get it up to that speed and how does it do in the mountains/long hauls? Also what rpm at 63mph? I was governed at 55 and 2500rpms and was told to stay away from sustained rpm of over 2700 or ide kill mpg and tranny

[Jay Brand]

First thing first, get a additional trans cooler for it and mount it before the stock trans cooler. This is the single best thing you can do for a AT545.
A plus for us is that we have the same drive train as the full sized Bluebird but with a lot less weight.
Hills, the bus is not a big fan of hills but will climb them pretty good with the additional trans cooler.
My first real drive in my bus was 600 miles and it ran perfectly the whole way. I ran it between 55-70 mph and it had no real issues with lack of power.
I usually hover around 2100-2300 at 60-63 mph.
I ran it at 2600 for a short bit but at 70mph, the engine temp will start to creep up. I'd advise 65 as your top speed but for max fuel economy, keep it between 55-63.
2700 rpms is on the higher side as far as I'm concerned and I don't think I'd ever want to turn that many rpms in my bus for any amount of time.

The key thing to remember about a flat nosed bus
"If it was meant to be fast, it wouldn't be shaped like a brick"
Take your time and enjoy the ride.

[Larrybird]

Thanks for the reply but did you do any modifications to it because mine like I said rides at 2500 RPMs at 55 mph

[cadillackid]

I think the 5.9 is a fine engine.. and you can turn up the pump on it some to get some extra power.. i will say that the electronic transmissions do much better wit helectronic engines.. however there are PLENTY of resources for swapping an allison 1000 / 2000 series into a 12 valve. on ANY school bus the MPG willl likely go down the faster you go..



so let me go on to say what *I* would do if it were my bus..



personally i would build and swap in a 6 speed 4th gen allison 1000.. yes it would be expensive.. (I did this in my red international with a 73).. I had a transmission custom built and boiught a harness and Tuneable TCM to dial it in..



CAC (Custom Automatic Conversions) specializes in making bits and parts for doing 12 valve to allison 1000 swaps..



when i got mine, CAC used Suncoast to build the transmissions, not sure who they use now.. may be the same.. ive had Zero issues out of the transmission 4 and a half years in..



to do a 1000 swap you will need:


Allison 1000 6 speed with SAE3 Bell / Tail.
4th Gen TCM and wire harness.
Throttle Box to mount to your pump or throttle pedal which tells the transmission how much throttle you are giving the engine.
if you are hydraulic brake you'll need a park brake assembly (or modify the one from your 545).


doing this allows you to keep your low ratio rear end and maintain the ability for devently quick take-offs and hill climbs in lower gears.. yet drop RPMs on the higher gears for highway cruise.. the overdrive in 5th is 0.71 and in 6th is 0.61


I would then bump the pump on the 5.9 for a few more horsepower.. there are numerous resources for doing minor HP boosts on 12 valve engines.. they are popular..



you can also look for used parts out there or a donor bus if you have lots of time and space to tear apart a second bus.. or want to piece things together from various sources..



again alot depends on your future for the bus.. if its a design for one epic road trip around the country and then just weekend jaunts to the lake after then id probably travel the back-roads at 55 and put a little more fuel in. if its a rig you plan to keep for years and take on multiple many-mile trips then id do the build described to make it a true cruiser.. in my case it was worth the $$ and effort to build because for one, 6 window shorty busses are hard t ocome by, and two, I planed on (and have) driven that bus all over creation... Covid has slowed me down a little but im getting back int othe road trip game again with both busses...



The RedByrd is a highway Cruiser!

[Jay Brand]

No mods at all.
Make sure you are in drive and not 3rd when you start out. Mine is super easy to put in third and you think you are in drive.

[EastCoastCB]

Originally Posted by Larrybird

Thanks for the reply but did you do any modifications to it because mine like I said rides at 2500 RPMs at 55 mph

If you want more mph capability and more mpg's you'll need highway gearing.
I've got a 545 and with my 3.42 rear end I'm at 1750 rpm at 65 mph.
I do have a different engine but that's not really relevant. The engine doesn't determine the top speed its the trans, tires, and rear axle ratio.

[Larrybird]

Awesome man it’s people like you that make this forum what it is. I appreciate all the info. BTW my bus is not a six window it’s more like a 12 window at 34 feet, I Can’t figure out how to post a picture but Hopefully your insight still applies.

[cadillackid]

Originally Posted by Larrybird

Awesome man it’s people like you that make this forum what it is. I appreciate all the info. BTW my bus is not a six window it’s more like a 12 window at 34 feet, I Can’t figure out how to post a picture but Hopefully your insight still applies.

mine is 6 window.. it is one of the reasons I chose to upgrade it vs sell it and buy another with a better trans.. as 6 window were hard to come by..

[EastCoastCB]

Originally Posted by Larrybird

Awesome man it’s people like you that make this forum what it is. I appreciate all the info. BTW my bus is not a six window it’s more like a 12 window at 34 feet, I Can’t figure out how to post a picture but Hopefully your insight still applies.

Chris is probably the most intelligent person I've ever met.

[kulbuskid]

Not sure what one of these flat nose busses will do on top end.

The flat nose design is really pushing hard on the wind at highway speeds.


When I bought my 2000 tc2000 29 footer with 5.9 and 545 I had a chance to meet the sole operator who had driven the bus for the past 19 years.
He told me that the bus would cruise at 75 mph all day long.

I did not even ask for that information, he just mentioned that out of the clear blue on two separate occasions.

So far I have only had the rv on roads that are posted 55 mph so ive yet to get her out and see for myself.

[Jolly Roger bus 223]

it is possible with proper rear end gearing and pushing the engine HP up close to the limits of the 545.
all the slowing down will be on the brakes and is probably slow getting up to speed especially pulling hills.

[cadillackid]

Originally Posted by Jolly Roger bus 223

it is possible with proper rear end gearing and pushing the engine HP up close to the limits of the 545.
all the slowing down will be on the brakes and is probably slow getting up to speed especially pulling hills.

faster top speed = higher torque pushed againsrt the converter = lots of AT545 roasting Capacity