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TH350-c Transmission on a 1982 Chevy G-20, Engagement problems,

I have recently run into a problem with my transmission on my van, mainly that it won’t drive forward, however reverse seems to work just fine.

Prior to the problem:

Before it stopped working all together, there were a few symptoms that I should tell you before we get started.

First, upon starting the vehicle and putting it into drive the vehicle acted like it was in neutral, or barely crawled forwarded. If you waited a few moments, or pressed the accelerator, it would quickly engage and once it had been driven for 5 minutes no more problems shifting gears would occur.

I attributed these problems to low fluid and/or cold fluid (as the problem would noticeably become better/worse with warmer/colder conditions respectively) So I was content with topping off the fluid and seeing if the problem persisted consistently when it got warmer.

2.) There would be at times a loud clunk when the gear finally engaged after pushing the accelerator. I have a repair manual for the van which has a trouble shooting guide and it said to check the universal joint. I did, and it seemed intact, rust free, and fine. I researched it a little more and did not see any indications that this was an awful horrible problem, so again, I decided to wait until the weather changed to investigate further.


One day I drove the van to north Austin and left it in a parking lot for a few hours while I went inside. When I came back out and started the vehicle it would not engage ‘drive’ no matter what I did. It has since been sitting in the parking lot for about 2 weeks and the owner finally gave me the boot so I pushed it out onto the street.

What I have tried:

I found a leak where the transmission fluid connects to the radiator (a hose was clamped too hard) and seemed to have fixed that problem. So that solves the problem of why there was low fluid in the first place.

I took the doghouse apart and replaced a few vacuum lines that were extremely worn and damaged. At one point this was causing the van to stall immediately after starting, but have since been fixed.

I checked the shift linkage where it connects to the transmission housing and, luckily, was able to view the dial on the transmission case where it connected; all moves of the shifter do in fact engage the dial and turn it.

I pulled the two electrical connections off of the transmission housing to inspect them for burns or corrosion, although I would doubt reverse would work if they were damaged, and found none. They seemed to be in fine shape.

The throttle cable seems to be fine.

The speedometer cable is missing I believe because I can’t find it and the speedometer doesn’t work. However, unless I’m missing something this wouldn’t cause the problem.

Fluid seemed dirty, but I did not feel that is had be roasted over a fire pit (indicating burned out parts?)


I am going to drop the pan today I hope and investigate a little further inside the transmission, but before I did, I wanted to post here and see if anyone else was familiar with this problem.

Here are some other information that might help:

The transmission fluid does NOT seem to be getting any hotter than luke-warm. From what my manual tells me this should not be. Transmission fluid should get to a point where it is too hot to comfortably touch.

I am wondering if this could be caused by one of three things

a.) Broken pump not circulating the fluid

b.) Clogged filter - fluid unable to circulate

c.) No vacuum - not allowing the pump to get adequate air pressure to operate (I’m unsure how the vacuum effects the transmission so this is a complete guess, if you can help inform me I’d be thankful.)

I am wondering if, maybe, the fluid is not being warmed enough to expand correctly to let the transmission operate.


Could the problem originate with the vacuum modulator? I have heard that these go bad, but are cheap and easy to replace. I have put this option off because I’d assume the regulator controls more than one thing and so if it were broken something like say, the fuel system would be effected as well.

Maybe I’m wrong? Could it also be the hose itself?

I think there is also a short somewhere in the electrical system, although I think it’s located in the heater wiring, because the battery will drain heavily when it rains and the heater is engaged. I have read somewhere that this may cause the transmission not to operate properly, but it seemed to me like it is something else.

In any case, I have been stuck in Austin now for quite some time, don’t have money to pay a shop 2,000 to diagnose, over charge me for parts, and charge 10 hours of labor for a rebuild when you can buy these transmissions, it seems, for relatively cheap. I am hoping this is a relatively simple problem that someone here would be able to recognize and diagnose, or at the very least be able to say:

“Check and fix these 4 things and come back.”

I’m trying very hard to learn this car inside and out and the repair manual I bought doesn’t want me playing with the transmission at all - simply says “take it to a pro chump”

Thank you for reading and any help you can provide.

Well, the reason I’m going to say “take it to a pro chump” is that what you describe sounds like almost dead internal seals. They’re only “almost” dead b/c apparently after they warm up they soften up and expand enough to seal up. The only real remedy for that is to tear the thing down. Getting to know the vehicle inside & out is a great idea but not so much the transmission.

Hmm, thank you for the comment. And I agree, a problem with the transmission such as this is grounds for saying “take it to a pro”. When I drop the pan today is there anyway I can check on these seals? Or are they located deeper in the transmission? I would still like to learn about the transmission in general, and I plan on keeping the old transmission if I end up buying a used one from a junkyard and learn how to rebuild it over the next few months as the rebuild kits seem relatively cheap. Thanks again for the reply, and let me know if there is anyway I can check on these seals myself so I can learn what they look like and what they look like broken.

For the want of a nail…

A stitch in time…

Too little too late…

etc, etc, etc…

Drop the pan, change the fluid and filter, add a bottle of Trans-Medic or Trans-X and idle the engine in Drive until it moves or you give up and call a wrecker. Good luck.

Oh I was hoping not to have to lower myself to the ranks of buying fix-it bottles, but alas, you do make a good point. Thanks for the input.

I have no direct knowledge of any of them, but there are some fix-it bottles that oviously won’t “fix” it but can alleviate the symptoms a bit and help you eke out some more miles - basically a seal conditioner kind of additive might help for a while.

Yeah, that would actually be helpful though and I plan to try it. My understanding of how most of the fix-it things work is that they recondition the seals and saturate them with a liquid putty which swells and sticks in the gaps around gaskets and seals and helps them to stop leaks for a time. However, I’ve heard this is a quick fix that can lead to allow more serious problems to continue to worsen. As it stands now though, a 8$ bottle sounds like it’s worth a shot to get it to a better spot to sit for a while, or a shop if need be.

mainly that it won’t drive forward, however reverse seems to work just fine.

There would be at times a loud clunk when the gear finally engaged after pushing the accelerator

Sounds to me like you joined the broken forward hub club. That loud clunk was putting a lot of stress on the forward hub and it finally cracked. Low fluid->harsh engagement->broken forward hub

Ah, this is something I have yet to check. I don’t know much about Hubs so I went through and did some reading, albeit not a lot, and noticed that hub problems are usually accompanied by a noise turning the wheel.

This is curious because there is in fact a squeaking grinding when I move the steering wheel from left to right. However, this does not continue once the van has started any sort of forward movement, so I have always thought it was simply the weight of the engine and forward part of the van pushing down on the wheel and the noise was because they were grinding against the cement.

in hindsight however, I think your suggestion considers serious investigation. Do you know of any way to thoroughly check the hub? And can it be checked without disassembling a large portion of the car? I’m going to go grab a couple books and read some more online, but if you could a quick follow up on how I could determine if this is the cause or not it would be much appreciated. Thank you.

This is not an axle hub, it is a hub inside the transmission and it doesn’t care which direction you turn the steering wheel :wink:

Ah gotcha. Thanks again.

I will make this short and sweet. Your transmission is shot. Dead. Junk. It needs either rebuilt or replaced. The good news for you is that the TH350 is cheap and plentiful. Rebuilt units usually go for well under a thousand dollars. A torque converter, which you will also need to replace, will set you back another couple hundred or less. You could also look into a used one. Place an ad on your local Craigslist under auto parts that you need a TH350. I know of a half dozen or so guys who have plenty of these things laying around doing nothing, so they’re not hard to find.

A couple details you will need to know before you get a different transmission for this beast: You will need to know the length of the tailshaft. There are short tail TH350’s and long tail TH350’s. The tailshaft on the one I have in my garage (Hey, I told you those things are easy to find. I go out to my garage and, lo and behold, there’s a TH350!) is about 10" long, which is a long tailshaft. The short tailshafts are about 5" long. You also need to know whether or not you have a lockup torque converter. If you have a square, four pin wiring harness on the side of the case (not all pins are necessarily used on all vehicles), you have a lockup torque converter.

Keep in mind also that if you buy a used transmission, it may be difficult to find a shop to replace it. If you do the job yourself, which is not terribly difficult to do, be very careful while working on it. Transmissions are heavy and having one fall on you will change your life forever. Also, if you do this yourself, having a second person there will make things a whole lot easier. While it is possible to do this by yourself, it is not advisable. It’s a two person job, period.

I am very glad to hear this from a real person. I have been searching through hundreds of forums and articles and books and have been coming to the conclusion of either a.) too many things could be broken or b.) what you said.

I have also noticed that the TH350 is available, and apparently used quite often for hot rods, but it is great to hear from a person like you that this is indeed the case.

My repair manual, although refusing to give repair details on transmissions, does have a step by step walk-through on replacing one - and yes it says 2 people period.

You also brought up another question I have been wondering about - the lockup - so thank you. I do believe it has this connection, however I’m not 100% if it’s what you are talking about. I will get a camera and post a picture and maybe you can give the thumbs up or thumbs down a little bit later.

As for finding a transmission, I was tinkering with the idea of going to a scrap yard to get one, but three problems enter my mind that you might be able to confirm:

1.) I’d assume most junk yards are either going to pull the pan and drain the fluid and leave it open to the elements or just drill a hole through the pan, in which case I’d have to reseal it or buy a new pan.

2.) How good it is, I have no knowledge in my head that would allow me to know if a transmission is good from a scrapped car, is there an easy way to tell other than hooking it up or taking it apart?

3.) I don’t like the idea of lowering one off a junk car with soft ground. Like you said, heavy - fall on you - ouch.

So I guess what I’m asking is, should I even bother with a junkyard, or actually get off my butt and do a week of searching around town and craig’s list? Do you have any other tips on places to look outside of craig’s list? Such as talking to mechs at shops etc.

Thank you again for the response it was very very helpful.

It needs to be rebuilt. You have to remove the transmission and take it apart to actually fix it. Best bet is to ask the transmission repair person how much it will cost to rebuild.