TH400 Transmission issues Please help!!
Thread Starter
Intermediate
Joined: Dec 2010
Posts: 39
Likes: 0
From: El Paso TX
TH400 Transmission issues Please help!!
I just put a new engine in my 73 and my auto th400 tranny was working fine before i did the swap... When I took it for my first test drive after the swap, it did not shift out of 1st and it slipped out of drive. It also does not go into 1st or 2nd.
Racer
Joined: Dec 2008
Posts: 297
Likes: 19
From: arlington TX
First guess would be the transmission cable wasn't re-installed/adjusted correctly. Your desription is a little confusing, but I would check the cable adjustment first. Then, fluid level.
Was the same engine put back in after a rebuild or is it a different one? Was the converter emptied out when the trans was pulled? If so, was the converter refilled before installation?
Good luck.
Was the same engine put back in after a rebuild or is it a different one? Was the converter emptied out when the trans was pulled? If so, was the converter refilled before installation?
Good luck.
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
Make sure you have good vacuum going to the modulator first...before doing anything else. Make sure you have atleast 10" hg of vacuum at the modulator....Then report back.....
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
Check installation of shift cable.
Shifter should match detents in tranny.
If it won't shift out of 1st, then the vacuum hose or modulator valve.
Upshift or downshift?
Downshift wire or solenoid.
Check level fluid hot first.
Shifter should match detents in tranny.
If it won't shift out of 1st, then the vacuum hose or modulator valve.
It also does not go into 1st or 2nd
Downshift wire or solenoid.
Check level fluid hot first.
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
The torque converter can't be fully filled statically, only dynamically by the trans pump when the engine is running. This will result in the level of fluid dropping by a couple of quarts or more in the trans, so make sure you check the levels while running at idle.
Although you probably have already checked the fluid level, the vacuum signal is most probably missing from the vacuum modulator due to a leak. This causes the trans to raise both the shift rpm and firmness similar to full throttle.
Although you probably have already checked the fluid level, the vacuum signal is most probably missing from the vacuum modulator due to a leak. This causes the trans to raise both the shift rpm and firmness similar to full throttle.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Intermediate
Joined: Dec 2010
Posts: 39
Likes: 0
From: El Paso TX
Ok, I think I have two problems, let me explain further, aside from it not shifting in drive(which I agree, feels like the vacuum line is leaking), the actual shiter lever does not "lock" into drive and it does not go past drive to "1" or "2"...
Burning Brakes
Joined: Nov 2006
Posts: 893
Likes: 7
From: Orange Park Florida
Check the shift cable and bracket. Did you put the bracket AND any spacers back correctly?Did the cable routing change? The shift cable has to be reconnected correctly or some adjustments will have to be made..
Race Director
Joined: Jan 2000
Posts: 13,017
Likes: 2,261
From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
C2 of Year Winner (performance mods) 2019
2017 C2 of Year Finalist
Did you try to start it with a loose or missing ground cable? If so the shift cable usually becomes the ground path and will weld itself internally and not move much.
JIM
JIM
Burning Brakes
Joined: Nov 2006
Posts: 893
Likes: 7
From: Orange Park Florida
Verify that the detente relay power source is connected! There is a plug/connector on the drivers side adjacent to the shift cable and bracket that provides a connection for the power source. Sounds like that wiring is not connected.
Racer
Joined: Dec 2008
Posts: 297
Likes: 19
From: arlington TX
http://www.zip-corvette.com/ProductDetails/ProductDetails.aspx?pid={d2d18850-015a-4798-9024-c48b19f49459}&gid={855ecadb-080b-466c-9127-3a0ec34ebe36}&GroupName=Transmission+Con trol+Cable&pname=68-82+Auto+Transmission+Shifter+Control+Cab le&Referer=&Alias=&ptct=GL1-SR&CTitle=&
Modulator will cause problems also, but it will shift even if the modulator has issues, just really rough shifts. The governor may also have problems.
Anyway, I wouldn't drive the car much if the shifter isn't adjusted correctly; it will burn up stuff inside if in 2 gears at the same time.
Good luck.
walt z.
