Kim Moulton Miller

Hi all...I recently had the 350 L82 engine rebuilt in my 78 Corvette. New cam, bored out with new pistons (like a 355 now) When I got it back I immediately had issues with the transmission. It doesn't want to go into 3rd/high gear unless the rpms are at around 5,000. (it's an automatic, no overdrive) OR if driving on a flat surface nicely it will sometimes shift into high, but then when you give it gas it drops back into 2nd/passing gear. It's a the shop now where they said it sounded like the torque converter is loose/rattling and that it is slipping in 3rd gear. One place said they would rebuild my transmission for $750, another person has a 350 Turbo short shaft that came out of a camper/rv with very little mileage for $300 and then $200 to install. Here's the issue...maybe I'm getting too much feedback, but somebody else said it sounded fishy that trans goes out like that...that it could be another issue due to something not being done properly when engine reinstalled. Another said if reverse is working fine then 3rd should as well. Reverse works fine. I know nothing! Any advice? Kim

cobrachuck

Kim
Was the transmission ok before the engine was worked on?
Has the fluid level been checked? Transmissions normally give some warning before failure .

Kim Moulton Miller

Yes, It was fine. One mechanic smelled the fluid and said it smelled "burnt"....but have never had an issue with it before.

Mountainoakie

It sounds like you failed to reconnect the hose at the intake manifold that goes to the transmission's modulator valve or the hose came off the modulator valve when the engine was reinstalled.

Kim Moulton Miller

I just relayed that to the mechanic shop and he said he fears it has already ruined the transmission. UGH....they are going to check what you posted. I would think the shop that rebuilt the engine would be responsible for repairs/transmission??? I'm just sick about it! Thank you so much for your input....I will let you know what they say.

MelWff

try replacing the transmission filter and fluid and also make sure the transmission cable attached to the throttle is corrected adjusted. It sounds like the shop you are dealing with is not familiar with older cars. Locate a local Corvette club and find where the members have their cars serviced.

MotorHead

One of the problems you run into owning a Vette and having to take it to a shop to get things fixed is the fact the car is going to get driven and if a shady shop it will get passed around to all the greasemonkeys to have a little fun with it.

If your transmission was OK before you took it in then I would go back and ask the owner what is going on. If paid by credit card then you might have a legal angle, ask your credit card company. I am not saying the shop is directly responsible but I would look for a shop where you can talk to the owner specifically about this and have him agree not to allow any more mileage than necessary to fix the problem.

I am sorry this happened but trying to diagnose a transmission problem over the internet is difficult. But there are many knowledgeable members here that might just be able to do that.

Welcome to the forum and I hope you get things right with the shop you dealt with

Kim Moulton Miller

I am relaying all the info to the current shop. I trust them. The mechanic who did the engine rebuild and install races older corvettes in the dragway (1/4 mile)...he is supposed to be a pro. My future son-in-law referred me to him. UGH. I paid cash for the work. I have a feeling I have a very hard lesson coming to me.

MotorHead

I know the feeling, you think of the worst but in owning my C3 for 20years it is not the worst thing that has happened. For me it ends up with something easily fixable 99% of the time.

Kim Moulton Miller

I just hope the original guy will agree to pay to get it fixed.

Thank you for your comment.... :-)

MotorHead

Get a great big guy, maybe a brother to go with you

Kim Moulton Miller

OK more info just given...when we first discovered issues with high gear, my son-in-law took it back to the original mechanic who swapped out the 350 turbo modulator valve to a 400 modulator turbo valve to see if would make high gear better because sometimes when you switch to a 40 mod valve it will take up the slack from weak clutches. Also, a 400 mod valve is adjustable into making it shift harder or softer. And the mechanic said afterwards he had it adjusted tight enough where it was barking in second gear. Then he backed it off to shift regularly but it did not help high gear. The mechanic said everything was connected when he first saw it and when he was finished. This is all relayed info from my son-in-law from the mechanic today.

Kim Moulton Miller

For real!

reefrashralph

Mite look at the kick down rod on the carb to make shure it is free moving kinda far fetched but it cant hurt

Kim Moulton Miller

We checked that...was hoping it would be something somewhat simple. But it looks like I'm just going to have to get another transmission. Can't prove any issue with the original mechanic, so I guess I eat it. UGH

reefrashralph

That sucks

MelWff

If you had this problem immediately after the rebuild why didnt you go back to the shop that did the rebuild?
The original shop removed and rebuilt and reinstalled the engine?

gungatim

did your motor rebuild include and performance upgrades? could have been going out and just made worse/more noticeable with the new motor. or if using a performance cam you may need a lighter modulator but it sounds like the mech. tried adjusting it.

Did your son in law do any test driving with the new motor to "test it out" and maybe beat on it a bit?

what does the fluid look like, bright cherry red, or yellow or brown and smell like mineral oil or smell like old turpentine?

next thing after ruling out the kick down not being setup correctly. would be a stuck governor. that is easy to take out and check. also look for a vacuum leak (or kinked line) for the modulator circuit. both the vac line and the downshift cable could have easily been damaged during the engine install.

larrywalk

The symptoms you describe are caused by lack of vacuum at the modulator at the right rear of the trans. If this modulator sees atmospheric pressure (line not connected to manifold vacuum), it raises the shift points and firmness as it would for full throttle. It will also make the trans downshift very easily and at speeds much higher than are correct.

If the high rpm into 3rd is not caused by no vacuum to the vacuum modulator, it could be symptomatic of a failing 3rd gear (direct) clutch, however all shifts into 3rd would be soft and rpm would flare as you added throttle while in 3rd gear.

Please tell if the shift into 3rd at 5000 rpm is firm or soft?
It it's firm, just ensure that full manifold vacuum gets to the vac modulator and you'll be fine.
If it's a soft shift, it could a failing direct clutch.

A loose or rattling torque converter would not cause the symptoms you've described. Better find a different mechanic.

diehrd

TH350 and TH400 use the same modulator valve .. No vacuum to the valve will for sure cause the up shift issue AS WILL an improperly adjusted detent cable. ( passing gear , kick down cable)