Gillig school bus transmission model

[Adarian]

I just purchased a 1978 gillig school bus, 636d model.
Does anyone know about the 4 speed Allison transmission that were put in Gillig school buses?
If they more than one type was offered, how do you identify the which model it may have?
Bus has a cat 3208 non-turbo version.


I searched the skoolie.net web site and couldn't any information.

[luvrbus]

The one's I have seen here all have the AT 545 Allison one has a 644 Allison and I was told it was a transplant when they installed a new 3208T 


good luck

[TomC]

Fairly easy to tell by just driving it.  If it sounds like it upshifts 3 times and it revs all the way up when on the freeway, then the RPM's just drop off when you release the accelerator, then you have a AT545 since it does not have a torque converter lockup clutch.  If it sounds like it upshifts 4 times (one will be the torque converter locking up) and the rpms stay put at freeway speeds whether you are accelerating or not, then you have the MT643 transmission.  If you do have the AT545, although it is an excellent transmission for under 45mph, if you're going to do alot of highway driving, the AT545 will use alot of fuel and create alot of heat.  If possible, look for an Allison 2000 series transmission since they are a little brother of the B400 and B500 transmission.  The first four gears of the 2000 series are the same as the AT545, but then you have the possibility of two overdrives (Freightliner only uses them as a 5 spd since the 6th gear is a bit weak).  But even at 5 speeds, the 2500 (the heaviest duty of them all) has a .74 overdrive.  Then you'll get some fuel mileage.  Good Luck, TomC

[gus]

Adarian,

Before you invest a lot of money in the bus do some good research on the Cat 3208 engine. It is not one of the best.

I have one in a fire truck pumper and it has the worst diesel exhaust smell of any engine I've ever been around. It is also a low mileage engine for a diesel. I've heard it called a "throw away engine".

Nobody told me all this before I bought it!!

[RJ]

Adarian -

There should be an ID tag on the side of the transmission that will help you determine what you've got.

Since that bus has metal springs, you should be able to slide underneath easily w/o fear of becoming a pancake during your search.

FWIW & HTH. . .

[TomC]

The main reason the 3208 was not so great an engine-the cylinders have no liners.  You have pistons with just two rings rubbing on a cast iron cylinder wall.  What happens is the cylinder wall gets mushroomed out at the top of the cylinder because of the combustion and the fact that the cylinders are not induction hardened (like they are in today's engines without cylinder liners) causes the rings to start bouncing and prematurely wear out around 200,000 miles.  The fix is to bore the cylinder out and install a steel cylinder liner-problem fixed.  Also if you overhaul the engine, if you upgrade to a turbocharged engine (and I believe to more recent pistons on non turbocharged engines) you'll have more standardized 3 ring pistons that seal better.  The 3208 can be an excellent engine-just have to have an expert on the engine upgrade it, and then you'll have an engine that's good for 3-400,000 miles.

Much is the case of the 8.2 liter Detroit Diesel V-8 4 stroke engine (like a smaller cousin of the 3208).  There are intricate nuances that are needed to be known to properly overhaul the 8.2 to get proper engine cooling and decent engine life out of it.  Once again, a knowledgeable mechanic that has done numerous rebuilds on these engines should be used.  Good Luck, TomC

[Adarian]

I just drove the bus 750 miles.
It average 10mpg, didn't smoke except for some black smoke for going uphill in 3rd gear. I would ease off the throttle a little and no more black smoke.
I will climb underneath and take a closer look at the transmission id tag.

RPMS stay up at freeway speeds, it takes a while for it to downshift when climbing a steep hill.
I would just manually shift it to 3rd.

I wasn't able to get another transit bus, so I opted for a skoolie.
It is more of a short term solution and short term being a year or two.

Seats have been removed, it was painted gray.

[Adarian]

Transmission is an Allison MT 643 with the deep sump oil pan.

[TomC]

Good going with the transmission.  They typically shift like this: 1C-2C-3C-3L-4L.  The MT643 locks up in 3rd gear rather than 2nd gear like the HT740.  At least you don't have the infamous AT545.  You can go places with the MT643.  I had a manual torque converter lockup switch installed (requires an extra external solenoid valve) on my HT740.  Maybe you could do that with your MT643 to get better low speed braking control.  Good Luck, TomC