TM 400 Troubleshooting
Thread Starter
Melting Slicks
Joined: Sep 2000
Posts: 2,406
Likes: 418
From: Chester Virginia
TM 400 Troubleshooting
On my 73 Corvette L-82 w/ TM400 it does not shift out of first gear at WOT even up to 5800 rpm. The kickdown for 'passing acceleration' also does not respond.
I have check that 12V is going to the kickdown solenoid and that I have vaccum at the modulator. The engine has 14" Hg vaccum at idle. There appears to be no vaccum leaks: I have checked all hoses tubings, etc., had the carburetor rebuilt and the throttle plate rods openings in the base bushed, The engine idles smooth, a couple of old Chevy street rodders have found nothing wrong with the engine but believe the cam is hotter than a stock L-82 cam.
The modulator is a replacement, it has the vaccum connection pointing straight out of the housing not angled like in the pictures I have seen old old modulators.
Any suggestions on what else to check or do?
Roger
I have check that 12V is going to the kickdown solenoid and that I have vaccum at the modulator. The engine has 14" Hg vaccum at idle. There appears to be no vaccum leaks: I have checked all hoses tubings, etc., had the carburetor rebuilt and the throttle plate rods openings in the base bushed, The engine idles smooth, a couple of old Chevy street rodders have found nothing wrong with the engine but believe the cam is hotter than a stock L-82 cam.
The modulator is a replacement, it has the vaccum connection pointing straight out of the housing not angled like in the pictures I have seen old old modulators.
Any suggestions on what else to check or do?
Roger
Thread Starter
Melting Slicks
Joined: Sep 2000
Posts: 2,406
Likes: 418
From: Chester Virginia
I have had the car for about 8 years and about 5000 miles. I have never know it to upshift at WOT. Had a recommended transmission shop check the transmission last summer and he said there was nothing wrong with the transmission.
Roger
Roger
Drifting
Joined: Oct 2007
Posts: 1,317
Likes: 22
From: Marina CA
A Turbo 400 that has no 1-2 shift, here are a few items to check.
1. Governor valve may be sticking.
2. Driven gear in governor assembly loose, worn or damaged.
3. The 1-2 shift valve in valve body stuck closed.
4. Intermediate clutch plug in case may be leaking or blown out.
5. Check for porosity between valve body channels and/or blocked governor feed channels in transmission case.
6. Intermediate clutch malfunction.
In my experience the governor is usually the culprit. If it's stuck, the transmiision will not shift out of 1st gear. 1 or 2 probable cause, 3 possibly and 4-6 long shots.
1. Governor valve may be sticking.
2. Driven gear in governor assembly loose, worn or damaged.
3. The 1-2 shift valve in valve body stuck closed.
4. Intermediate clutch plug in case may be leaking or blown out.
5. Check for porosity between valve body channels and/or blocked governor feed channels in transmission case.
6. Intermediate clutch malfunction.
In my experience the governor is usually the culprit. If it's stuck, the transmiision will not shift out of 1st gear. 1 or 2 probable cause, 3 possibly and 4-6 long shots.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Most likely the governor 'driven' gear (at the end of the governor shaft) has failed and lost all of its [plastic] teeth or the pin holding it on to the shaft has sheared. In any event, my guess is that the governor has some problems. If you find that the governor is OK, the next place to check (for NO upshifts) is in the valve body....stuck shift valves, etc. If not the governor, you are likely looking at a full rebuild on the tranny.
