Hi all,

I own a C3 1975 Auto TH400 transmission and have been experiencing a strange issue.

The transmission engages into 1, 2, 3 and neutral with normal operation however:

The park and reverse are not working at all. Through the shifter in the interior of the cabin I am able to engage them, but the transmission does not engage them, meaning the car does not go into reverse and park.

FYI, the transmission went through a rebuilt before this happened, was filled with fluids properly along with having normal operation for 3 to 4 drives and then this issue was encountered.

Any feedback from your end would be highly appreciated, as I am looking forward to continue enjoy this beautiful car.

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First thing I'd suspect is the shifter cable, especially for park but unusual for reverse. Where the shifter detent isn't match to the trans detent.
If you hold the button down and put the car in neutral and then shift ahead feeling for the next detent from the transmission and not the shifter will it go into reverse?
When the car is in park, does the key come out normal and when shifted just a little out of park it won't? There is also a possibility that the cable is bending when being pushed all the way for R and P and it's not shifting.
Next thing i would check would be the lever on the trans that the cables connect to. If the nut that holds it onto the shaft is loosened off it possible that it's just going crooked instead of rotating the shaft.
Beyond that it would most likely something inside
Anyways, a couple of easy things to check to eliminate the obvious first
M

 

Park doesn't engage like in won't hold it on a hill ? like it's in neutral ?

 

First suggestion: Take it back to the guy who did the work and have him fix it. Why are you even screwing with it if you had the work done by somebody else?

If you're really wanting to get into it yourself, get the car up on jackstands and disconnect the shift cable from the selector lever on the tranny. Manually rotate the selector lever to the "Park" position. Verify that it is, or isn't, going into "park" by attempting to rotate the driveshaft. If you can rotate the driveshaft, it is not going into "park." If you cannot rotate, it's in park. Then, have someone in the car, with foot on the brake pedal, start the engine. Manually rotate the selector lever one "notch" into "reverse." Verify that it is, or isn't, going into reverse either by the "jolt" of the tranny going into gear, or by having the driver gently release the brake pedal. If the wheels turn, you're in reverse. Apply the brakes gently, manually shift back to park, shut engine off, and re-verify that you cannot turn the driveshaft (with driver's foot off the brake pedal). If things work without the cable connected, you have a cable and/or shifter problem. Adjust, repair, or replace the shift cable or shifter. If nothing works when shifting the lever manually, you have an internal tranny problem - take it back to the guy who built it (not sure why you haven't taken it back to him already and made it his problem rather than yours...).

Lars