Automatic transmission upgrade

[machmeter62]

I've never saw a th350 in a 1 ton. Does your trans have a kick down cable, or a wire with a solenoid (at the carb) going from the trans to the carburetor? If it's a cable it's a th350 if it's a wire it's a th400

Well, I checked and double checked, from the left side of the carb looking forward, a short rod runs from the attached carb. into an enclosed housing, that must attach to a cable, which flexes its way around the bell housing down into the right side of the transmission meaning it's a TH-350(?).

I had the transmissiion fail on a snow skiing trip in the Sierra-Nevada's Mtns. The vehicle would back-up only, after sitting all day in freezing weather. We were unable to drive it, and had it towed down the mountain to a GM dealer. We followed in a rental car, and retrieved the vehicle about a week later. Maybe the trans. was traded-out??

 

[carpenter383]

Yup if it has a cable running to the trans and not a wire it's a th350. It's possible someone switched the trans, but the driveshaft yoke would have to be changed too, cause a th400 has a larger output shaft than a th350. Which is something you would have to do if you replaced a th350 with a 4l80e.
A th350 is a lighter duty trans than a 400, but they are still a good reliable trans if not abused or used for alot of heavy towing.
A 700 r4 was based off the th350, and it has 30% overdrive VS a 4l80e 26%? (I'm not positive on that)and a low 3.06 first gear. VS a 4l80e 2.42 first gear? (again not positive) which is a noticable gear ratio difference.
700's had a bad rap early on as did all the early O/D trannies, I personally like 700's and they can be built to handle good power and can be had pretty cheap.
The cable on a 700 is not a kickdown cable, it's a TV (throttle valve) cable, it HAS to be hooked up and adjusted properly or the trans won't last. The only wires it has are for converter lockup, which don't have to be hooked up but trans temps would stay lower if you used lockup.
A 700 is the same length as a long tail th350 so if that's what you have it would be an easy swap, the drive shaft yoke and all will be the same. You might have to drill new cross member holes in the frame.
If your van has 4.10's the spedometer won't be accurate with a 700 trans but you can get a "thingy" to go between the spedo cable and trans to correct that.
If you wanna post a pic of the trans pan I can tell you for sure what you have, but it sounds like you have it figured out.

 

[Stimw]

Here is the easiest way to identify your transmission- Chevrolet Car Club - GM Transmission Identification & Decoding
I had two 700R4's fail in a 1989 1/2 ton Chevy in less than 100K miles and I drove it normally and towed very little. First one started slipping, second one broke in final drive, got off of interstate, stopped and truck would not move! I'm not crazy about 700R4's!

 

[machmeter62]

Yup if it has a cable running to the trans and not a wire it's a th350. It's possible someone switched the trans, but the driveshaft yoke would have to be changed too, cause a th400 has a larger output shaft than a th350. Which is something you would have to do if you replaced a th350 with a 4l80e.
A th350 is a lighter duty trans than a 400, but they are still a good reliable trans if not abused or used for alot of heavy towing.
A 700 r4 was based off the th350, and it has 30% overdrive VS a 4l80e 26%? (I'm not positive on that)and a low 3.06 first gear. VS a 4l80e 2.42 first gear? (again not positive) which is a noticable gear ratio difference.
700's had a bad rap early on as did all the early O/D trannies, I personally like 700's and they can be built to handle good power and can be had pretty cheap.
The cable on a 700 is not a kickdown cable, it's a TV (throttle valve) cable, it HAS to be hooked up and adjusted properly or the trans won't last. The only wires it has are for converter lockup, which don't have to be hooked up but trans temps would stay lower if you used lockup.
A 700 is the same length as a long tail th350 so if that's what you have it would be an easy swap, the drive shaft yoke and all will be the same. You might have to drill new cross member holes in the frame.
If your van has 4.10's the spedometer won't be accurate with a 700 trans but you can get a "thingy" to go between the spedo cable and trans to correct that.
If you wanna post a pic of the trans pan I can tell you for sure what you have, but it sounds like you have it figured out.

My next question, since my gear indicator is on the steering column, will I still be able to use that since it is totally a mechanical method, or just us a "WAG" with my ears, or tach?

 

[carpenter383]

Yeah the shifter linkage would be funky since it only has 3 positions for forward. You could still set the linkage so "D" is actually O/D and "1" would be second. You just would'nt be able to have manual first, this way the neutral saftey switch would work right too.

 

[machmeter62]

Why don't you go with a 700R? You get O.D. and don't need a controller. Just asking.

There has been some conjecture on the 700R, so I haven't given it much thought, but thanx for reminding me. I want the 4th speed, and a minimum amount of adaption to make the upgrade. I have learned on modified vehicles over my years of experience, sometimes these upgrades take value out of the resale potential? I will check it out.

 

[carpenter383]

There has been some conjecture on the 700R, so I haven't given it much thought, but thanx for reminding me. I want the 4th speed, and a minimum amount of adaption to make the upgrade. I have learned on modified vehicles over my years of experience, sometimes these upgrades take value out of the resale potential? I will check it out.

I thought we were discussing a 700r4? That's what I've been reffering to in the past few messages anyway

 

[MossRoad]

There has been some conjecture on the 700R, so I haven't given it much thought, but thanx for reminding me. I want the 4th speed, and a minimum amount of adaption to make the upgrade. I have learned on modified vehicles over my years of experience, sometimes these upgrades take value out of the resale potential? I will check it out.

Just remember to never tow in OD with the 700R. But with no load, the OD is a great fuel saver and quiets the ride down when the RPMs drop.

I have read about the early 700R problems. However, you can have them rebuilt to be really strong transmissions. And no electronic controller is a big plus on older vehicles that don't already have a controller. I have a 1985 700R with only a few thousand miles on it waiting to go into a 1971 Toyota Land Cruiser some day. I also have a 4L80E out of a 1993 Chevy van sitting in my garage. That is a spare for my 1993 Suburban with about 75K original miles, should that one ever break. The controller out of the van is also identical to the one in my Suburban, so I saved that, too (and the starter, throttle body and some other stuff). Well, come to think of it, I saved pretty much everything except the body and the engine block. :laughing:

 

[machmeter62]

Gentlemen:
I am truly elated with all the help you provided me, and expansion of my options too. The 700R looks like it maybe the easiest, but will maybe need the cross-member modified? I will check out the dimensions.

 

[carpenter383]

Gentlemen:
I am truly elated with all the help you provided me, and expansion of my options too. The 700R looks like it maybe the easiest, but will maybe need the cross-member modified? I will check out the dimensions.

You might have to drill new holes in the frame for the cross member. The cross member itself won't need modified.