od trans vs lower rear gear or?

[Booyah45828]

What kind of drivetrain mods have you guys done to lower cruise rpm? I'm not looking to go faster, I'm just tired of being redlined when I want to drive on the highway anywhere. Anyways, I'm either looking at either changing the at545 out for an o/d 6 or 7 speed manual. Or swapping rear gears and maybe a tighter torque converter. My local craigslist stinks when it comes to these parts so I'm struggling to find anything. Anyways, let me know what you guys have done and what it cost you if you don't mind.

[dalez]

Getting rid of the at545 for either a lockup automatic or a manual will improve your economy and cruising speed a bit. I'd do that before changing the rear end personally. A tall overdrive wont reduce your rpm as much as a drastic rear gear change, but taller gears with an AT545 is asking for trouble and poor performance. Put in a good tall overdrive manual and you might be happy without needing a gear change. Just my opinion based on what I've read about that trans and my test drive of a bus with one. So sluggish!

[opus]

I agree with Dalez.

[frank-id]

The AT545 is a very good trans. The best choice to to improve the engine operating rpm's, is to change the rear axle ratio. To drive at a lowered rpm, there is a need for more horsepower. Frank

[dalez]

The AT545 is a fine transmission... for a smaller, lighter vehicle. In a full size skoolie behind a DT466, it's entirely inadequate. Just looking at the SAE adapter going from 2 to 3 the transmission looks small. Not only that, but the dang thing doesnt even build enough hydraulic pressure to fully engage at full load until the revs are high. It'll never let your engine build torque down low, it just shifts out of the way. Performance on hills, especially loaded down heavy, is terrible vs my MT643. I can mash the pedal and everyone and everything inside not tied down gets thrown to the back of the bus as the torque converter grabs with authority, and the turbo is spooled up and the engine making torque by 1200rpm. The dt360 with AT545? I had to rev it halfway up just to get the bus to *start rolling*, with the engine not acting like it was really loaded till ~2200+rpm. A real slushbox, the AT545.

AT545: 267lbs, 200hp, 445ftlbs, GVW 30,000lbs
MT643: 510lbs, 250hp, 640ftlb, GVW 73,280lbs

That said, I still want a Fuller RTOO9513 "triple overdrive" in my bus

[Kubla]

For a manual tranny, I would want the spicer 6+1 that I drove in medium trucks in 94 and 95 overdrive and synchronized, DT466 has a wide enough operating range that a 13 speed is overkill and I did enough double clutching in 13 years of truck driving to last the rest of my life

[Booyah45828]

With a naturally aspirated idi, I doubt I exceed the power level of the trans. The at545 shifts good in mine. But I did go through it and adjust the shift points and the throttle cable. The converter it has in it seems like a 2000 rpm stall. If I could lower that I think its be alright.
I found a guy with a spicer 6543 that seems reasonable. Have to find a donor truck/bus to get clutch pedals out of and get a flywheel.
An rtoo9513 would be sweet, most of the gears would be unnecessary. But it has a really low overdrive that's desirable.

[porkchopsandwiches]

Is the 6.9 all mechanical? And is the MT643 an electronic trans? Fitting an electronic trans to a mechanical engine would be tough to get right. I would say Allison MD3060 6 speed swap because that is what my bus has, I love it, and it is overkill even for a fully loaded bus with a more powerful motor, but getting that to work with an old mechanical engine would be difficult. Not to mention the unit is real expensive. I would try a manual box swap. I recall putting bids on an international bus with a 7 speed manual (could be the same that Kubla is referring to) which would be a nice box, but just a quick ebay search showed $2800+ for a reman one and $1000+ for a used one. I saw a few 6 speeds for cheaper. But then you have to make sure bellhousings match, get a new flywheel that fits, get the balancing on the current flywheel matched to the new one, get the right driveshaft yoke, modify the shaft if the trans is a different length, fabricate mounts, and it just ends up being a whole can of worms.

What is redline on that motor, and what speed is redline at? I do get your frustration with that, I just recently got the 6th gear enabled in my bus which dropped engine speed to 2000 rip-ems at 65 mph. Haven't measured fuel consumption yet, but it is hella quieter and feels less stressed.

[opus]

643 is not an electronic transmission.

[nat_ster]

I just found a 95, 40 foot TC2000 with a mechanical 8.3 Cummins and the allison MD 3060.

So what was being said about mechanical engines and electronic auto transmissions?

I'm currently working a good deal on it. I will post pics when I bring it home from the shop.

This will be the drive train for my Four Season Prime.

Nat

[porkchopsandwiches]

Originally Posted by nat_ster

I just found a 95, 40 foot TC2000 with a mechanical 8.3 Cummins and the allison MD 3060.

So what was being said about mechanical engines and electronic auto transmissions?

I'm currently working a good deal on it. I will post pics when I bring it home from the shop.

This will be the drive train for my Four Season Prime.

Nat

I meant to change it over yourself. That is built from the factory with everything required. It may not be as bad as I think, but you need to add a TPS, and if the trans came off a vehicle with an electronic engine, you would likely need to change the software in the TCM. Just speculating but there is likely more to the swap than meets the eye.

[nat_ster]

Originally Posted by porkchopsandwiches

I meant to change it over yourself. That is built from the factory with everything required. It may not be as bad as I think, but you need to add a TPS, and if the trans came off a vehicle with an electronic engine, you would likely need to change the software in the TCM. Just speculating but there is likely more to the swap than meets the eye.

Thx

I look forward to digging into it and learning as I go. I will post as much info as I can.

Nat

[Kubla]

I bought an MT643 and I am picking up a 4.10 ratio differential next friday, will be all set (I hope) in the drivetrain dept once installed

[Dragonpop]

Nat you scored a real good drive train. My All American has the same drive train, 8.3 with MD3060. I am also running 5.38 differential gears which in
5th gear (first overdrive) engine RPM is 1800. If I can open up 6th gear it
will bring RPM down to 2600. The Wanderlodge owners group had one of the members swap an 8.3 with a MD3060 into a Wanderlodge with real good documentation and pictures. My 1996 AARE has air throttle with TPS on it
and a mechanical engine. Make sure you get the wire harness, computer,
relay box, throttle pedal and controller. Computer is a $750 item by it's self.
Forgot to mention the Wanderlodge was built on the same chassis as the Bluebird All American and Wanderlodge had the distinction of only having one death in a rollover accident in 50 years of production.

[nat_ster]

Originally Posted by Dragonpop

Nat you scored a real good drive train. My All American has the same drive train, 8.3 with MD3060. I am also running 5.38 differential gears which in
5th gear (first overdrive) engine RPM is 1800. If I can open up 6th gear it
will bring RPM down to 2600. The Wanderlodge owners group had one of the members swap an 8.3 with a MD3060 into a Wanderlodge with real good documentation and pictures. My 1996 AARE has air throttle with TPS on it
and a mechanical engine. Make sure you get the wire harness, computer,
relay box, throttle pedal and controller. Computer is a $750 item by it's self.
Forgot to mention the Wanderlodge was built on the same chassis as the Bluebird All American and Wanderlodge had the distinction of only having one death in a rollover accident in 50 years of production.

Thx, Great info.

This one is also geared 5.38. Every one of the rear engine pushers at our shop seems to be geared 5.38. I'm getting the only one with a MD3060. The rest of the pushers are MT643's.

I was a bit concerned about the gearing because my other bus is 4.44. But now that I know it will only be turning 1800 RPM, that will be fine.

Nat

[Dragonpop]

Looks like I was posting while half asleep last night the sixth gear engine speed would
be 1600 RPM not 2600 at 60mph/100kph. Also my tire size is 12R22.5. The 8.3L has
max torque at 1300 but they say you shouldn't run them at max torque for any length of time and the best economy is 200 to 300RPM over max torque.

[nat_ster]

Originally Posted by Dragonpop

Looks like I was posting while half asleep last night the sixth gear engine speed would
be 1600 RPM not 2600 at 60mph/100kph. Also my tire size is 12R22.5. The 8.3L has
max torque at 1300 but they say you shouldn't run them at max torque for any length of time and the best economy is 200 to 300RPM over max torque.

All good, I knew it was a typo.

That's great info about the economy.

Nat

[Booyah45828]

6.9 is all mechanical. Redline, depending on the pump is either 3300 or 3800(6.9 vs 7.3 pump) I'd like an automatic, but all the ones I've seen are $2000-$3000 just to get the transmission let alone the computer to run it. Plus, I'd like an overdrive so if I would swap transmissions, regardless of an auto or manual, it'd have to have OD. As far as manuals go, all the really desirable manuals(RTOO9913, spicer 6+1, Fuller T34) are either expensive(1500 bucks for used, unknown condition) or are obsolete.

I priced some different options over the weekend:
1)The torque converter for the at545 would be about 350 bucks, couple that with used 4.78 rear gears at 650 and I'd be at 1000(about the most I wanted to spend)

2)With the spicer 6543(.79 OD) that I found. 250 for the trans and clutch, leaving me 750 to find and buy a clutch pedal/linkage assembly and shorten the driveshaft.

With the 4.78 gear, and new torque converter. I'd cruise 65mph at 2600 rpm. With my current gearing(5.57 not the 6.50 I thought I had) and the 6453. I'd cruise 65 mph at 2400 rpm.
I'm leaning towards the manual at this point because of the lower rpm and the increase in reliability. But before I buy it, I'd like to source the pedal/linkage assembly.

At the most, I'd want to spend a grand on this undertaking. I don't drive it thousands of miles a year, and the combo I have isn't all that desirable(6.9 w/ at545). So if it costs any more then that I'll just live with it and hope it doesn't blow up. I just can't see spending 2-3 thousand on upgrading what I have when newer busses are about that much. At that cost I'd just as soon buy a newer bus with the gearing that nat and dragonpop have, swap the stuff from my current bus to the new, and then sell my current bus, then blow a bunch of money on an old bus.

[nat_ster]

True if the bus is not converted yet.

If the bus is already built, we must swap what ever is needed.

Nat

[opus]

I'm not sure you'd get a 6.9 up to 65, especially with an OD.