Transmission for my hot rod trailer puller

[Crosley.In.AZ]

I have a '92 c3500 1 ton x cab dually that I use to tow. What OD trans is in that?

Dan I don't actually know, but I'd bet its the 4l80e.  My '89 K3500 is a TH400 suggesting the 1-tons had the bigger transmissions as would seem appropriate.  My '91 K2500 is a 700r4 or maybe a 4l60 and I know that because I crawled under it and looked.  The guy I got it from claimed it was the bigger transmission and I wanted to know before I laid down any money.

Wayne:  780 horse in my trailer puller.  Cool.

I have a Cadillac 500 and TH400 setting in my shop.  This evening I may have lucked into a second one.  It belongs to my son, and the car may become payment of a $1000 he owes me but likely will never pay me.  That makes Cadillac even more likely the truck motor.

Is your k2500 truck  a 6 lug or 8 lug wheel?  GM built some light duty 3/4 ton trucks with the 4L60 trans.

700 and a 4L60 are the same transmission.

LOL....... your son may pay you money owed?   That is not suppose to happen.

[58Apache]

What's a TH475? How is it different from a TH400? What vehicles did they come installed in? Are they any more expensive to rebuild than a TH400?

[OldSub]

My K2500 is 6-lug and is clearly the light duty version.  Because it weighs about what I expect my finished project to weigh, and because it is rated to tow 10,000 pounds, and because it has a 700r4, I keep wondering why I can't get away with using one of those in my project.

But if I capture this second Cadillac 500 I'll almost certainly use that cars power train and quit worrying about overdrive for at least a few years.

[Crosley.In.AZ]

I was fairly  sure you had a light duty truck 3/4 ton.  GM pulled something stupid there  with a weight rating too high for the transmission


I've seen many of the light duty 2500 series trucks eat the 700 trans up . the trans is not able to handle the weight.

A friend had a light duty 3/4 ton truck 1991...... ... when I first saw the truck , I told him to sell it since he pulled a 24 foot car trailer with various heavy loads on it.  

Two trannys later he sold the truck...he was getting the GM reman transmissions for it under  warranty

GM had a corvette servo and other items in the trans to help it do the job... it did not help .  LOL

[OldSub]

So far I've not broken the trans in the K2500, but there is always tomorrow.  I'm trying to remember if maybe there is a rebuilt sticker on the existing transmission.  Since I didn't buy it new so it could have been replaced before I got it.

You've pretty well convinced me to stick with one of the bigger transmissions that I already have.  The same math that convinces me I don't want to pay for a 4l80 suggests there is no compelling reason to spend bucks for any overdrive.

I've got two kids in college.  When that's over I might be willing to spend more on this project.  In the meantime I'm going to stay with cheap.

[Danimal]

The truckster just pulled to Columbus and back yesterday without a hiccup. Took a 20 footer and picked up a '46 4 door that allegedly runs. It has a shift kit in it, I do know. 106 k.

The guy that I bought it from builds rods just outside of Saline. He works for the road commission. I'm sure someone on here knows him.

Anyway, other than $175 in gas, it was a great trip. The one thing I'd do differently is to make sure there was plenty of insulation in the floor. That cab gets SO hot running anywhere. It is like the heater is on all the time.

Is that common the big blocks or is the pipe routing an issue on the GMT400s (88-98 trucks)?

[OldSub]

My '89 1-ton (K3500 single-wheels) was always hot in the cab and I basically ran the airconditioning pretty much year round.

[Beck]

What's a TH475? How is it different from a TH400? What vehicles did they come installed in? Are they any more expensive to rebuild than a TH400?

The 475 is a 400 with stronger shafts and gears. These were used in HD applications and behind some diesels. Some diesel transmissions don't work well with gas motors. They do not have a modulator. In its place there is just a jamb bolt with a perminent setting. The converters on the diesel are also very low stahl.

I would go with one of the transmissions you currently have. The cost of the overdrive and necessary controller adds up quickly. Then there are the hidden costs, yolk, kick down linkage, speed sensor.

If the idea of turning the 4 speed backwards behind the auto worked every one would use one for an OD. The front bearing on the 4 speed isn't much and wouldn't hold up to the abuse of a driveshaft yolk. You also would need to figure out how to put the yolk on the input shaft (now the output). If someone knows how to make this work let me know. I need an OD behind my TH475.

[enjenjo]

someone knows how to make this work let me know. I need an OD behind my TH475

I didn't say it would be easy.  you are correct about the front bearing not holding up. I think what you could do is to fabricate a housing that would bolt to the front of the trans case with a second bearing. Ideally you would replace the old front bearing with a roller bearing, install a second one in the housing you make, and preload the bearings with a fixed yoke.

On some of the heavier 4 speeds, the main drive gear is not fixed to the input shaft, and can be switched with the third gear to change ratios. In that case, you could use a modified  output shaft instead of the input shaft, with the main drive gear on it. Or switch the gears, and mount the trans with the front as it is, with third gear direct, and 4th gear over.

The only other problem that might show up, is having the thrust bearings on the wrong end of the countershaft.

[OldSub]

The work to turn a 4-speed into an overdrive almost sounds like fun.  But I think I'll pass.

Today my son left town headed for college.  As he did so he paid off a debt he owned me with his '76 Cadillac.  This truck project will get the Cadillac 500 and attached Turbo 400.

So the decision is made.

Thanks!