1971 350ci/270hp 400 Transmission
The front seal leaks and the transmission does not downshift past 50 mph. I had a mechanic look at it and he said it was not the downshift switch, but in the transmission. With 80,000 miles on it I am thinking about rebuilding the whole unit while I have it out. Is this something I can do myself or should I remove it and have a tranny shop rebuild it?

 

I am not an expert, but looking at a diagram of all its components I decided against rebuilding myself, wayyyyyyy more complicated and intricate than rebuilding an engine, in my opinion.

Fortunately, I had a vendor who repairs our transmissions, and I got the rebuild for $225 :D. Not worth going through the hassle for me for that little money, and the shop took it out and put it back in :D.

 

ttt

 

Tom, I think you've got to ask yourself a couple of questions:

How much of a pain is it for you to get the transmission in and out of the car?

and,

Are you fairly good at following directions for automotive repairs?


Those are two questions coming closer and closer to the front of my brain lately because I think I'm getting close to where something has to be done. Personally, I don't think I will like the nitty gritty of pulling the engine and trans out of my car. If I didn't pull them together (and I'm not even sure if that is recommended for a Corvette), I'd end up dropping the transmission with the car on jack stands (way up on jack stands :eek: ). I don't think I'd like that, and I KNOW I wouldn't like doing it again if I screw the job up. As far as the second question, I've been told otherwise, but I think an auto trans is probably the most difficult thing to rebuild on a car. It just seems like sooooo many little parts. I'm not trying to discourage you, but I think you should investigate it a little more if you're doubting yourself at all. There are some books out there that are really detailed. I got a great book from the local library on rebuilding the TH350. Also, there was a really good thread last winter about a trans rebuild by one of the members. Hopefully, he'll see this and chime in. He had some really nice pics. Maybe it's still in the Archived topics (I didn't look).

One other thing I've thought about doing is buying a late model engine & trans and doing the work on it myself. That'd save money AND save my original drivetrain from any damage I might accidentally inflict.

I doubt this helped any, but please let us know what you decide. For me, someday's I think I'm up to the task, others :confused:

 

I have removed the TH400 & 350 eng from my ' 72 coupe together from the front, you need a good engine hoist with a 5' boom and engine tilter. Since I have the tranny out I'm going to go through it before putting it back. I ahve not done an automatic before buit bought a video and a manual along with a B & M transkit which has everything but a filter to rebuild the tranny. It has some very good directions that show mods to do along the way. So maybe this winter if I get the rear bearing finished then I'll do the tranny. Read up on it and if you have room then give it a shot. Good Luck,
Gary

 

Gary, I put a B&M kit in my TH350 (went with the HD/Towing but wish I had chosen street/strip) and just today put an adjustable vacuum modulator on it. The two work very nicely together and provide a great improvement in the performance/feel of the trans. If you haven't gotten it already, you may want to pick up the adjustable modulator.

 

Tom;

I would strongly encourage you to do a couple of simple, inexpensive things before you decide your trans needs a rebuild. First, change the transmission fluid and filter. Cost you about $35 and take a couple of hours. I'd also replace the vacuum modulator. When you remove the transmission pan, look closely at its contents. if you see more than about a teaspoon of mud-like material in the pan and you see a lot of little sparkles in it, that means signifcant wear of bushings and friction material. The only way to fix that is with a rebuild. You will save a considerable amount of money by removing and installing the trans yourself, if you do decide it needs a rebuild. When I had mine done, I checked around and discoverd that the flat rate (labor cost) for R&Ring a TH400 in a Corvette ranged from 10.5 to 12.3 hours. Most shops charge from $50 to $65 per hour shop time. If you don't have a friend or acquaintance to look over your shoulder while you do it, you're probably better off to have a shop do the rebuild. But please, do yourself a big favor and talk to several shops. Ask for the names of five recent customers who had similar work done and take the time to talk to them before you hand over your transmission. Also, i got the impression that this is the car's original transmission. Make sure you can identify it so you can be certain you get back the same transmission you gave them. I'm not casting aspersions here, just know that everyone makes mistakes, and you want to make sure they don't make a mistake with your transmission. Also, insist on a written estimate of the cost of repairs and description of exactly what will be done and make certain they understand that you expect them to abide by that. Talk to as many shops as you reasonably can before you pick one. If you take them the transmission, the cost of a rebuild should be well under $1K. Good luck!

 

Jerry whose modulator did you use? The trannny has been sitting on my work bench since 5/00 so I'm not in any hurry. Do you know how differant the two are,original vs adjustable?
Thanks,
Gary

 

gtr1999, I bought the adjustable modulator from Advance Auto ($12). It's made by Rostro Precision Instruments, Inc.. The shaft & O-ring section are identical to the old (I'm assuming OE) modulator. The adjustable modulator was a little shorter (overall length) than the OE, but they provided enough hose to make up the difference AND to replace the hose on the upper, engine end of the tube. At least I think that the tube ends up on the intake manifold just in front of the distributor (I didn't check any diagrams, but followed the tube as best I could). The hose up there was not cracked, but seemed swelled to the point where it was very loose on the manifold end (might have been sucking some air up there).

Tim H. recommended starting with 1-1/2 turns in. I used 2 full turns. Before I installed the modulator, I was turning the screw in to see what kind of range I had. After 5 turns in, I chickened out because I didn't want to damage the thing. I didn't check how far I could turn the screw out, but I could see a lot (maybe 6) threads above the starting point. I guess I was just looking to get a better "feel" about where the starting point was. There were no directions in the box and I wonder if they line that screw up at the factory in the very middle of the full range or something. Anyway, with the very wide range available, I'm 2 turns in from the setting that it came out of the box with.

 

Thanks Jerry something for me to think about when I get to that point.
Gary

 

I rebuilt my TH350 using only the Haynes automatic transmission repair manual and it worked out great. That is a really good book. Great step by step pics and everything. Highly recommended.