Oldsmobile Diesel Transmission Questions
 

Does anyone know anything regarding the maximum engine input horsepower and torque specifications for the TH200/C, TH200-4R, TH350/C and TH400/C whenever they're used with the Oldsmobile 4.3L V6 (LT6), 4.3L V8 (LF7) or 5.7L V8 (LF9) diesel engines?

The gear ratios are:

TH200/C, TH200-4R
1st: 2.741:1
2nd: 1.568:1
3rd: 1.0:1
4th: 0.674:1 (TH200-4R only)
Reverse: -2.07:1

TH250/C, TH350/C
1st: 2.52:1
2nd: 1.52:1
3rd: 1.0:1
Reverse: -2.07:1

TH400/C, 3L80
1st: 2.48:1
2nd: 1.48:1
3rd: 1.0:1
Reverse: -2.07:1

It is known that many Oldsmobile diesels were given the TH200/C (direct-drive) transmissions in the early 1980s, which may be perceived as one reason why the Olds diesel was so bad (other than the engine's own issues like head bolts, gaskets, and no fuel/water separator): The metric-specification transmission wasn't exactly designed to handle engines with such immense torque. Now this would've been a better fit with the smaller 4.3 liter diesels (both the V6 and V8 versions), but not the 5.7.

The TH200-4R, by comparison, was a much better transmission partly because of the overdriven 4th. Starting in 1983, it was often specified in place of the TH350 which was also a better transmission for the diesel 5.7 than the TH200/C.

I also wonder whether any of the Oldsmobile diesel engines ever used the TH250/C, dependent on whether or not that transmission was available with the BOP (Buick-Olds-Pontiac) bellhousing?

~Ben

Re: Oldsmobile Diesel Transmission Questions
 

Never a 250C.
A 200C is best suited for carbed V-6.
2004R is good for a 5.7 diesel, kind of light on torque capability but a good gear spread to take advantage of the diesel's torque on the highway.
TH350 with highway gears is a fair match.
TH400 will last forever and is overkill unless you're towing.

Re: Oldsmobile Diesel Transmission Questions
 

The "200", "350" "400" are related to the torque capabilities of the transmissions. The difference in the diesel versions of the transmissions usually had to do with the damper springs in the lockup clutch and valving/pressure controls.

The 4.3 V6 was offered in the FWD cutlass. I'm pretty sure it had a TH125C behind it. I don't remember ever seeing a RWD version of that engine.

I did work at an Oldsmobile dealer in the 1980's doing driveline work.

Re: Oldsmobile Diesel Transmission Questions
 

The later 3L80, 4L60/E and 4L80E transmission nomenclature, adopted by GM in 1987, was different in that the first number indicated the number of gears, and the letter indicated powertrain mounting (L=longitudinal; T=transverse), and last two numbers were the GVW rating x 100 (meaning: for example, both the 3L80 and 4L80E could be used in vehicles weighing up to 8,000 lbs. GVW). The "E" at the end of 4L60E and 4L80E indicated electronic controls.

~Ben

Re: Oldsmobile Diesel Transmission Questions
 

Officially, GM calls those two digit numbers the "product series based on relative torque capacity". The 4L60e has a maximum engine input torque of 350 ft/lbs. and a maximum gross vehicle weight of 8600 lbs. The 4L80e has an engine torque capacity of 440 ft/lbs and a gross vehicle weight capacity of 16,500 lbs

We were taught in GM school the numbers were torque input values. The 700R4, to differentiate itself from the TH350 used 2 times the torque input because of the multiplication factor of the torque converter.

Re: Oldsmobile Diesel Transmission Questions
 

The TH200 is a decent trans when modified, They are fairly popular in NHRA Stock Eliminator class. Building one that a Olds diesel can't break is easy.