How to tell AT545 from MT643, w/pix & specs

[cadillackid]

anything chassis newer than about 02 will not be a 545..at least I havent see any busses 03 and newer running 545's..

the shifter on a 5 speed will be obvious.. on an MD3060 its usually a digital display..

on a 1000/2000 series conventional it will have D-4-3-2-1

if its an international you can call a dealer with your VIN and they can tell you if its a 545 or 643..
-Christopher

[Elliot Naess]

That's wonderfully useful information. Thanks!

[Blkjacksabbath]

Originally Posted by Elliot Naess

A basic automatic transmission does not have any mechanical connection between the engine and the tires. There is no clutch, as in a stick shift.
Instead, the power is transmitted by a fluid. There is a "propeller" on the rear of the engine, and an other "propeller" on the front of the transmission. These two "propellers" are very close together, inside the unit called the torque converter. This unit takes the place of the clutch.
So the engine "prop" blows the transmission oil against the transmission "prop", which is how the power is transmitted. But oil is not solid, so there is slippage -- maybe 5 or 10 percent. This slippage becomes heat (thru friction, essentially).
So we lose some of the energy that would otherwise serve to drive the bus forward; and we get heat, which is damaging to the tranny. The slippage is typically about 200 RPMs worth.

Then somebody invented the torque converter lock-up clutch. This clutch is located inside the torque converter, and is controlled by the transmission's regular valve body (I think). It bypasses the "fluid coupling" with a solid connection, so no power is wasted as heat.
The result is better efficiency, which means more driving force to the tires, and less fuel consumed. In addition there is less wear on the transmission from the lower heat. Having torque converter lockup is most important in mountains, when a plain torque converter generates a great deal of heat, which can ruin a transmission.

You can feel and hear when the lock-up clutch engages. It is almost as if the transmission shifts gears, so it can seem as if the tranny has five or six gears.

Does this help?

Thank you my man

[Scooternj]

Originally Posted by cadillackid

anything chassis newer than about 02 will not be a 545..at least I havent see any busses 03 and newer running 545's..

the shifter on a 5 speed will be obvious.. on an MD3060 its usually a digital display..

on a 1000/2000 series conventional it will have D-4-3-2-1

if its an international you can call a dealer with your VIN and they can tell you if its a 545 or 643..
-Christopher

Depends on what the original district ordered. My bus has a 545, verified by contacting my local bus dealer (Wolfington), and is an '03 Amtran.

[Elliot Naess]

My pleasure. And Welcome aboard, Black Jack!

[Blkjacksabbath]

Originally Posted by Elliot Naess

My pleasure. And Welcome aboard, Black Jack!

Thank you much, I have a lot more to learn! This forum is awesome!

[kaisersersae]

Can anyone help me figure this out. Allison md3060 1995 with Cat 3116: I have this. 0 IN SERVICE MODE 0 blinking displayed in my electronic shifter. My bus starts fine even with the shifter removed....

[kaisersersae]

Can anyone help me figure this out. Allison md3060 1995 with Cat 3116: I have this. 0 IN SERVICE MODE 0 blinking displayed in my electronic shifter. My bus starts fine even with the shifter removed.... After a while of blinking the display goes black until power is off for a while.

[rjnye79]

To those with the AT 545, what is your preferred trans fluid?

Sent from my VS930 4G using Tapatalk

[Booyah45828]

Any dexron3/mercon will work fine. If you're travelling extensively you might be interested in bumping up to a synthetic version of some sort or even a tes295 rated fluid. The at545 isn't too particular of brands as long as the fluid used is in good shape and kept clean and cool.

[SashaRosen]

Originally Posted by autoqual

I have a 1983 ford b600 with a 370 and an Allison 545 I am at a crossroad and thinking about a engine swap as I understand this model year also offered the bus with a Detroit Diesel 8.2 and the DD 8.2 turbo. can I up engine without changing the transmission or its location. My 370 is a little long in the tooth and may be at a place of needing head work rear main leaks all the normal ailments of an older gasser etc... and the bus is of sentimental value to the family so chucking it for a newer model isn't an option. Plus we might want to head south thru the mountains and follow nascar a bit, and I am a little sketchy if it can climb up mountains well. I am not married to the DD 8.2 willing to listen to all advice on this subject I think if I do this I want to go diesel, and not a bunch of lg modifications. i would consider a more modern engine but not sure about the electronics. like the idea of keeping it simple I am a reasonable skilled mechanic but large trucks are anew area for me so I take it slow and figure it out as I go. new to schoolies but love every minute of it. And any easy way to figure out rear end gearing without taking it out?

Looking to purchase my bus in one week, it has the AT545 with a Dt466. Does the AT545 perform well? I just started reading about them and became concerned having it in a bus that will get consistent wear and tear. We intend on living on the road. Any major downfalls?

[EastCoastCB]

I have a 545 in my shorty. Had one in a forty footer back in the day. Its *ok* in the shorty, still not ideal. They suck in a full size bus.
If you want "life on the road" I'd insist on overdrive. I'd simply insist on it. And air ride.

[Elliot Naess]

Many of us have recently reported good experience with the AT545.
But it WILL cut your top speed by 200 RPMs, which is... something like maybe 3 or 4 MPH (I have not paid much attention to this).

I bought a bus five days ago, with Cummins 5.9 and AT545. It tops out at 53 MPH unless there is a tailwind or downhill. Rear end is 4.78, and tires are 11R22.5.

You can pick up several MPH by turning the governor up two clicks, which is a couple hundred RPMs. (Neverenuffhp did this for me. Thanks!)
But the AT545 will still steal the other 200.

The MAIN risk is overheating. Since the torque converter is ALWAYS "slipping", it generates lots of heat. That can fry a transmission on a long up-hill. So an auxiliary cooler is advisable.

Also.... IT HELPS TO install a manual switch on the fan clutch! And start that fan at the first glimpse of an up-grade. I can explain that, but not today, as I am in a bit of a hurry.

[Versatile]

Originally Posted by SashaRosen

Looking to purchase my bus in one week, it has the AT545 with a Dt466. Does the AT545 perform well? I just started reading about them and became concerned having it in a bus that will get consistent wear and tear. We intend on living on the road. Any major downfalls?

The AT545 gets a lot of bad press but i just yesterday saw posts about being in Colorado and pulling trailers and saying they get along just fine..

Can we inquire more about the bus it self. Opinions around hear are free and frequent.

[cadillackid]

Originally Posted by Elliot Naess

Many of us have recently reported good experience with the AT545.
But it WILL cut your top speed by 200 RPMs, which is... something like maybe 3 or 4 MPH (I have not paid much attention to this).

I bought a bus five days ago, with Cummins 5.9 and AT545. It tops out at 53 MPH unless there is a tailwind or downhill. Rear end is 4.78, and tires are 11R22.5.

You can pick up several MPH by turning the governor up two clicks, which is a couple hundred RPMs. (Neverenuffhp did this for me. Thanks!)
But the AT545 will still steal the other 200.

The MAIN risk is overheating. Since the torque converter is ALWAYS "slipping", it generates lots of heat. That can fry a transmission on a long up-hill. So an auxiliary cooler is advisable.

Also.... IT HELPS TO install a manual switch on the fan clutch! And start that fan at the first glimpse of an up-grade. I can explain that, but not today, as I am in a bit of a hurry.

MANY, in fact MOST school busses dont have electric fan clutches.. the RE's do and the newer FE's and CE's do.. but the rest have viscous clutches that are often bad..
-Christopher

[gbstewart]

Originally Posted by Elliot Naess

Many of us have recently reported good experience with the AT545.
But it WILL cut your top speed by 200 RPMs, which is... something like maybe 3 or 4 MPH (I have not paid much attention to this).

I bought a bus five days ago, with Cummins 5.9 and AT545. It tops out at 53 MPH unless there is a tailwind or downhill. Rear end is 4.78, and tires are 11R22.5.

You can pick up several MPH by turning the governor up two clicks, which is a couple hundred RPMs. (Neverenuffhp did this for me. Thanks!)
But the AT545 will still steal the other 200.

The MAIN risk is overheating. Since the torque converter is ALWAYS "slipping", it generates lots of heat. That can fry a transmission on a long up-hill. So an auxiliary cooler is advisable.

Also.... IT HELPS TO install a manual switch on the fan clutch! And start that fan at the first glimpse of an up-grade. I can explain that, but not today, as I am in a bit of a hurry.

that's a great ideal about the switch for the fan, I had to put one on when we where on a trip, and somehow a wire broke from the temp sensor, I couldn't find it at the time , so to get us home I wired in a switch to the fan with a solenoid, got us home and I found and fixed the problem, but I did leave the wire harness that I made, now I think ill hook it back up and use it the way you said. thank you for that ideal, I will be towing with my at545
gbstewart

[DoubleO7]

Originally Posted by Elliot Naess

I bought a bus five days ago, with Cummins 5.9 and AT545. It tops out at 53 MPH unless there is a tailwind or downhill. Rear end is 4.78, and tires are 11R22.5.

You can pick up several MPH by turning the governor up two clicks, which is a couple hundred RPMs. (Neverenuffhp did this for me. Thanks!)
But the AT545 will still steal the other 200.

Loss of a couple hundred rpm is true, but your bus is topping out at 53 due to engine rpm/hp not because it has an AT545.

[Elliot Naess]

Originally Posted by cadillackid

MANY, in fact MOST school busses dont have electric fan clutches.. the RE's do and the newer FE's and CE's do.. but the rest have viscous clutches that are often bad..
-Christopher

Really! Wow! That is soooo sad. Both my Blue Birds have electric. (And of course, every 18-wheeler I ever drove.)

[Elliot Naess]

Originally Posted by DoubleO7

Loss of a couple hundred rpm is true, but your bus is topping out at 53 due to engine rpm/hp not because it has an AT545.

Correct, for that half of the equation. "You can pick up several MPH by turning the governor up two clicks, which is a couple hundred RPMs. (Neverenuffhp did this for me. Thanks!)"
Specifically, from 2,400 to 2,600, approximately.

And as you confirm, the AT545 is guilty of the other half of the equation.

The governor does not seem to be a "brick wall". Rather, it seems to reduce power gradually over... wild guess, let's call it 100 RPMs. And while in that realm, wind and slope are good for a couple MPHs.

[cadillackid]

what is the max RPM of that engine?

my DT-360 with 4.78 gears and 11R22.5 tires is good got a solid 65 on flat ground and 68 with slope and wind.. that engine maxxes at 2700-2800 RPM..

I dont like driving it that fast but it will do it..

you earlier bluebird is definitely a higher spec FE.. and your other one is newer.. seems Bluebird was much better about putting electric clutches in their FE BUSSES..

the electric horton clutches have been optional for many many years.. they just added 500-600 bucks to the cost of a Bus.. so esp up north where the busses rarely saw hot weather.. (a little in the spring and early fall school year), the viscous clutches were spec'd esp on the dognose..

all of the RE busses ive dealt with always have actual Hydraulic fans... i dont have a lot of experience with RE kit though..

viscous clutches when installed and TUNED correctly can do a very good job... ive got the one in my DEV to turn on at 185-190 and turns off at 180 or so... that bus never gets warm.. ever.. even in the blazing florida heat with both Air-conditioners on Max...

Redbyrd suffers a bit .. someplace an electric clutch would be the tops.. or as ECCB and I have been scheming, to replace with full width radiators on our shorites insteads of the half split that IH used.. those engines under high RPM always make way too much heat...

-Christopher