4x4 Automatic Trans???

[72 Green Monster]

OK folks. I've got a 72 GMC half ton 4x4 that just ate its second transmission. Truck has a small block pushing almost 500hp and is sitting on 35's and definitely is not happy with the th350 trans in it. I'm really not happy with RPM's I'm pulling on the highway with the th350 and am looking to get something with an overdrive. I really don't want a trans that requires anything electric because I'm not any good at wiring. Wondering if y'all have any input on the situation, thanks

[hugger6933]

First off welcome to this website. Then an overdrive is probably the answer to the problem but, it is gonna be hard to get a 700 to live in that truck with that kind of power. You can have one beefed up to with stand some pretty heavy stuff so that may be your only alternative at this point, just make sure it is not a junkyard find or a regular rebuild or it will not stay. You also need to take into consideration differences in the drive shaft lengths the front will need to be longer and the rear will need to be shorter. Good luck Jim

[72 Green Monster]

Thanks Jim, this forum seems to be pretty informative so far. Yeah I've talked to a couple ppl about slapping a 700 in but most of them say that it probably won't hold up to the hp or torque that the motor is producing. I've also had other's tell me to install a 4L80E, and that I shouldn't have anymore problems. My knowledge is better at tearing up vehicles than it is in fixing them but if I'm not mistaken, a 4L80E and even some 700's are electronically controlled. Do you or anyone else know of a good stout overdrive trans that doesn't require this, or am I gonna have to bite the bullet and go that route? Thanks again

[Chrome8]

I've tossed this same situation around in my head for a while. I'm just planning a future build though. If you go to randy's ring and pinion he has some great calculators on there for different types of transmission, ratio and tire combinations that will give you your RPM at any given speed. I hashed and re hashed the issue because I really wanted to just drop a th400 in my truck and forget about it. In my opinion the only way to get tame rpm's is to use a 4l80e. If you don't have a newer LS or fuel injected motor you may have trouble getting a speed sensor reading to the trans unless someone makes a kit for this, I didn't dig around. The other option is really tall tires or a th400 and a seperate overdrive. Good luck

[special-K]

A 700r4 can be built to take 500hp. A TH350 can take about anything you give it. There must have been issues with those you blew up,or your torque convertor is the culprit,or the trans is not being cooled properly. They didn't blow up just because you have a 500hp motor. But,you want overdrive,so the strongest/most reliable non-electronic way to go is a TH400/Gear Vendors.

[D.PASSMORE]

Originally Posted by special-K

A 700r4 can be built to take 5r00hp. A TH350 can take about anything you give it. There must have been issues with those you blew up,or your torque convertor is the culprit,or the trans is not being cooled properly. They didn't blow up just because you have a 500hp motor. But,you want overdrive,so the strongest/most reliable non-electronic way to go is a TH400/Gear Vendors.

I agree...

[Bigdav160]

I figure I've built a couple thousand 700R4/4L60/4L60e's. The design is inherently weak in a couple areas. Even the "heavy duty" parts are just a patch.

I say get over your fear of wiring or stick with a TH400.

[Fitz]

Originally Posted by 72 Green Monster

OK folks. I've got a 72 GMC half ton 4x4 that just ate its second transmission. Truck has a small block pushing almost 500hp and is sitting on 35's and definitely is not happy with the th350 trans in it. I'm really not happy with RPM's I'm pulling on the highway with the th350 and am looking to get something with an overdrive. I really don't want a trans that requires anything electric because I'm not any good at wiring. Wondering if y'all have any input on the situation, thanks

What's your budget? A 700 R4 probably won't live behind that motor of yours but a built turbo 400 or even a turbo 350 backed up by a gear vendors overdrive will likely do just fine. The problem with a separate Overdrive unit is price. The alternative is a 200R4. They don't get a lot of respect here but they are stronger than one of the early 700's. The good thing about the 200r4 is it will slide right into the spot your TH350 occupied without changing the driveshaft and it will take about the same abuse. It's all a matter of your budget and how hard you beat the truck.

To put things in perspective I run a built TH400 and Gear Vendors OD unit behind a ZZ572. Just about 100 passes at the drags and 15k miles without a failure. That motor puts out a bit more HP and torque than yours and I drive my truck like I stole it!

[mrein3]

Originally Posted by Fitz

What's your budget? A 700 R4 probably won't live behind that motor of yours but a built turbo 400 or even a turbo 350 backed up by a gear vendors overdrive will likely do just fine. The problem with a separate Overdrive unit is price. The alternative is a 200R4. They don't get a lot of respect here but they are stronger than one of the early 700's. The good thing about the 200r4 ia it will slide right into the spot your TH350 occupied without changing the driveshaft. it's all a matter of your budget and how hard you beat the truck.

I believe the swap between the 200-4r and the th350 is only true on 2 wheel drive vehicles.

If I was tearing up transmissions I would consider one of Bowtie Overdrive's units. They cost a bit more but they have pretty stout claims to what their trannies can handle.

My 383 is no where near 500 hp and I don't beat the snot out of it but I do pull some pretty stupid stuff with it. The transmission I run is a th350. I bought it out of a '72 Blazer because I wanted to get away from my 3-speed manual. All I did is have it rebuilt by a local place before I did the swap.

Bowtie Overdrives and other similar companies will sell you what they claim is an improved 700r4 with the correct output shaft to mate to your transmission adapter. I just clicked on their website and notice they have something new. "HUGE HP GIANT TQ EXTREME 4X4" th400s and th350s.

To go with a direct replacement you need to stick with a th350. EVERYTING else is more work. th400s have a 32 spline output shaft which won't work in place of your 28 spline th350. A 700r4 is almost two inches longer so you'd have to move the engine forward that distance or leave it where it is, move the transfer case back, lengthen the front drive shaft and shorten the rear.

[72 Green Monster]

Thanks a lot everyone so far with all the advise. Guess I should have put in a little more info. I have only had this truck for a little under a year and as soon as I got it ordered the 383 for it. While waiting for the motor to come, I went ahead and had the th350 trans rebuilt and beefed up. Well finally the day came, and I had my first test drive and everything was good! But after about 25 miles (and of corse a little of me whooping on my new power) the trans didn't wanna go into second gear without me letting off the gas, and it sounded like a herd of Chee Chee birds were in my transmission fighting.
After pulling the transfer case and trans again, and taking trans back to the "Reliable" transmission guy. It was determined that the hardened steel sprag in second gear had broke, and pretty much chewed everything else in second up with it (I was on scene for the tear down and determination or else I wouldn't have believed it myself). Now me and the trans guy know my motor doesn't put out enough power to break this hardened steel sprag so we chalked it up to faulty manufacturing, and he once again rebuilt the tranny.
So after about 4000 miles in my new found love affair, my transmission (after a little smoke fr

[72 Green Monster]

Thanks a lot everyone so far with all the advise! I have definitely gotten a couple good leads on what I'm gonna do next. For everyone saying that a th350 or th400 is the way to go, I believe your right. These are suppose to be the toughest transmissions GM has to offer for my truck (without making alot of modifications). I still dont know why or how I cratered the last ones. However, I'm gonna find the some kind of racing transmission shop to rebuild the next one. Next, Im probably gonna get a bolt on overdrive from Gear Vendor or somebody else, and that should make me happy with my RPM range on the highway. I actually called Gear Vendor yesterday and spoke with a guy named Nick about all their products, and he too was very helpful. They are by no means cheap, but I think in the long haul an overdrive system from them (or a company like them)would pay off. Lets just hope it holds together better than my previous transmissions.
If anyone else has some more tips or advise, I'd love to hear it. The Ole Love Affair is gonna be parked in the garage, so I'll have plenty of time to change my plans again while I search around for a reputable transmission shop, and start saving some cash. Thanks again everybody.

[mrein3]

Originally Posted by 72 Green Monster

Thanks a lot everyone so far with all the advise! I have definitely gotten a couple good leads on what I'm gonna do next. For everyone saying that a th350 or th400 is the way to go, I believe your right. These are suppose to be the toughest transmissions GM has to offer for my truck (without making alot of modifications). I still dont know why or how I cratered the last ones. However, I'm gonna find the some kind of racing transmission shop to rebuild the next one. Next, Im probably gonna get a bolt on overdrive from Gear Vendor or somebody else, and that should make me happy with my RPM range on the highway. I actually called Gear Vendor yesterday and spoke with a guy named Nick about all their products, and he too was very helpful. They are by no means cheap, but I think in the long haul an overdrive system from them (or a company like them)would pay off. Lets just hope it holds together better than my previous transmissions.
If anyone else has some more tips or advise, I'd love to hear it. The Ole Love Affair is gonna be parked in the garage, so I'll have plenty of time to change my plans again while I search around for a reputable transmission shop, and start saving some cash. Thanks again everybody.

A couple of points to ponder.
You are going to be pretty hard pressed to make an overdrive of any type "pay off" if you are just looking at dollars and cents. You can buy a LOT of gas for what it costs for overdrive in these old beasts. OD does however give you other things like WAY less noise in the cab when you are driving down the interstate at 70+ mph because you'll be running way less r's. Less vibration from the engine and if you are running loud exhaust, way less exhaust noise.

Gear Vendors probably does have a unit that will work with a 4x4 however I doubt it will work in four wheel drive. It probably bolts to the back of the transfer case, in front of the rear drive shaft. The resulting drive shaft is going to be pretty short but I'm sure they have that all figured out. You probably will only have overdrive while in two wheel drive while going down the slab at higher rates of speed. But you probably will never do that in four wheel drive anyways.

Just some thoughts.

[72 Green Monster]

Oops, didn't mean to send out the incomplete post earlier. I'm trying to delete it but can't figure out how.
The Gear Vendor does bolt on to the back of the transfer case as do all the other overdrive systems I've seen so far. And yes it would only work while in 2wheel drive, but that's the only time I'd wanna use it. Like you said, it's loud in the cab of my truck. When I get anywhere near 3000rpm's I just turn my radio off cause I can't hear it. I would have to shorten my rear driveshaft by 6". I have given that some thought, but my truck is a long bed so I'm thinking the pitch change with the shaft being shorter shouldn't affect my U joints too much. I am still pondering the idea, cause $3000 is alot on money. One things for sure, I'm gonna have to get my th350 rebuilt first. Anyone know of a GOOD transmission shop down here near San Antonio I can take it to?

[Fitz]

Originally Posted by 72 Green Monster

Oops, didn't mean to send out the incomplete post earlier. I'm trying to delete it but can't figure out how.
The Gear Vendor does bolt on to the back of the transfer case as do all the other overdrive systems I've seen so far. And yes it would only work while in 2wheel drive, but that's the only time I'd wanna use it. Like you said, it's loud in the cab of my truck. When I get anywhere near 3000rpm's I just turn my radio off cause I can't hear it. I would have to shorten my rear driveshaft by 6". I have given that some thought, but my truck is a long bed so I'm thinking the pitch change with the shaft being shorter shouldn't affect my U joints too much. I am still pondering the idea, cause $3000 is alot on money. One things for sure, I'm gonna have to get my th350 rebuilt first. Anyone know of a GOOD transmission shop down here near San Antonio I can take it to?

I'm in Arizona now but I used to live in Merritt Island Florida. The best trans shop east of the Mississippi is JW Performance Transmission in Rockledge Fl. If you don't recognize the name that's Johnny Winter Racing. His TH350, TH400 and powerglide boxes are available through JEGS, Summit Racing and several racing trans shops in the Ft Worth and Houston area. If you check their website you can get the numbers and addresses. Nothing near San Antonio, though. Sorry. He built my TH400 up in 2006 and it has never let me down!

Good luck with your truck.