: Transmission not shifting out of first..?



slaya786
05-04-11, 06:59 PM
Hey whats up guys, I got a 1975 coupe deville, and it's not shifting out of first gear. It'll run just fine in first and reverse, but it won't upshift for some reason.

Any idea's what the problem could be..?

thanks

sven914
05-04-11, 08:17 PM
What creates the up-shift to second is the intermediate band, inside the transmission. The band has friction material on it that can wear off and cause it to slip and prevent the transmission from up-shifting.

Here are somethings to try:

1. Check you fluid with the engine warm and running. If the fluid is low or burnt, then it can cause slipping in the gearbox. If the fluid is low, refill the transmission and test. If no change, go to the next step.

2. Drop the transmission pan and replace the filter. If the filter is clogged, it will cause the transmission to malfunction. When you get the filter out, cut it open and check it for metal shavings. Refill the transmission and test. If no improvement, go to next step.

3. Take the car to reputable transmission repair facility. Have them diagnose it and ask them if a flush might help. The fluid lines may be clogged with debris, which could be loosened by a flush. More than likely, the transmission will need to be rebuilt to repair the intermediate band.

cadillac_al
05-04-11, 09:50 PM
TH400 failure is pretty rare in my experience. I'll bet it isn't getting enough vacuum or the vacuum modulator is malfunctioning or it is just low on fluid. If you just got the car then I would change the fluid and filter anyway.

slaya786
05-04-11, 11:53 PM
Fluid's been changed, so that isn't the issue.. i've had the car for a while, just happened recently..

I've heard that it could be the governor? I have another long tail tranny which I pulled the governor from and it's in good shape, i'll have a look at the governor from this tranny and see what condition the gear is in.

I'll look into the vacuum aswell actually. any easy way to diagnose that issue?

sven914
05-05-11, 12:56 AM
Your right, the governor could be the cause. When you check it, look for any plugged oil holes or a leaking "O" ring.

As for the modulator, replace the hose. Then get a vacuum pump (the hand-pump kind with the little gauge on top) and see if the modulator can hold a vacuum.

cadillac_al
05-05-11, 08:28 AM
I have never had a governor fail in any transmission that I have ever owned or worked on. I suppose it could be but i would have a hard time believing it. However, if the fluid is full and the vacuum is good and the modulator is good, I guess I would look at the governor next or look very closely at the valve body. It could have gotten loose or somebody could have put a shift kit in it years ago and something may have come loose. Good luck

deVille33
05-05-11, 10:16 AM
It could be that your trans needs a new seals. The intermediate band will not activate if the power piston seals leak.

aplascen1a
07-07-11, 04:56 PM
i have a similar prblem to this but my mechanic says the problem is electical thats why the car wont shift to higher gears and u should check circuits to the trany if u pull data loss codes

jayoldschool
07-07-11, 05:31 PM
His car is a 75, no electronics.

I do know for a fact that the TH350 will not shift out of first (unless at full throttle) if the vacuum line from the intake to the trans is disconnected. I would suspect that the TH400 in slaya's car would be the same. Check the vacuum connection at the trans, and at the manifold behind the carb.

albymangled
07-07-11, 07:09 PM
+1 for a vacuum leak.

creeker
07-07-11, 08:39 PM
Hey whats up guys, I got a 1975 coupe deville, and it's not shifting out of first gear. It'll run just fine in first and reverse, but it won't upshift for some reason.

Any idea's what the problem could be..?

thanks


My 80 cdv. was doing the very same thing, an old school mechanic rearranged the vacuum hoses and it cleared up.