Transmission Not Shifting
 

Now that the 68 stang is finally restored, I took it out for its first test drive in over 8 years yesterday. I've mentioned this before but the 302 and C-4 automatic transmission were completely rebuilt in 94, had about 50 or so miles put on them and then it sat all these years. Was cranked about every weekend, oil changed regularly and I personally changed the transmission fluid 4 times over the past 2 years (while attempting to stop the pan from leaking). Drove it about 3 miles down the road, but it took forever to shift to 2nd and never shilfted to 3d. On the way home, it shifted about normal to 2nd and finally did shift to 3d but took a long time. Anyone know what I should check first? Does it possibly just need to run several times or could all my seals and everything else have hardened or gone bad? Everything is new, lines, modulator, etc, and hooked up properly. I know my Edelbrock 600 cfm carberator is not adjusted properly (idle sounds fine but the mixture screws are bottomed out clockwise) so could that be affecting the vacuum? The first I'm going to do is check the fluid as I know I've lost some due to the transmission pan leak. Hopefully, that's my problem. I'm also taking the cheap piece of crap $20 chrome pan off soon and putting on an aluminum one with rubber gasket to hopefully stop the leak. Yes, everything else has already been checked and it's only coming from the pan. I'm clueless as usual. Thanks for the help.

Whats the temp like when your running it. Like all cars, if it's cold it sometimes takes a while to shift since fluid is not warmed up. It very well could be a bad seal but I don't think they would have roughted over that short of time.

There's a strong possibility that your problem is it sat for so long, and the seals being hard. But, your shift problem sounds much like a bad modulator, wrong modulator or a vacuum problem. I would check that area first.

Drive it some, maybe you'll get lucky and the seals will supple up some.

Run a good strech in reverse. Sometimes it will clear out the gov. and trash laying in the v-body.

As Maroon stated your mod valve could be bad also. That controls your shift points Its on the rt back side of your trans. If the vacum line to the valve is cracked or loose it can cause a shift problem. Check the lenght of it and its vacum.

Trans oil will come out when it wont shift. Alot of pressure builds and it will push out the vent hole.

As far as the temperature goes, it was pretty cold the only time I drove it down the road. I'll let it warm up next drive. The modulator is brand new (replaced about a year ago, but guess it could have been bad to begin with). The lines and rubber are all new, correction reproduction length and bends, and not kinked anywhere. I'll do as suggested and drive a ways in reverse. Would anyone recommend I add some kind of seal conditioner or what that do more harm than good? I also know the vacuum coming out of the back of the engine will determine the shifting points so I guess I need to figure out how to check that. Time to dust off the shop manual again. After I drive it quite a few more times, I'll post an update and hopefully it'll will be working much better.

is it bad on the transmission to manually downshift an auto transmission (FMX) from 3rd to 2nd, like passing gear? I know not to ever downshift into 1st, but is it okay to downshift it into 2nd?

Cause i cant get my kickdown linkage to work correctly right now. So i always just knock it down into second gear by hand to pass and what not. Just checkin if that was bad or anything. lol.

i dont have a shift kit or anything in it, but it seems to shift fast and firmly. Especially upshifting from 1st to 2nd, it kicks in hard. 2nd to 3rd is a little smoother.

When you redid the tranny, did you put in a new torque convertor? Or drain the old one? I had the same problem with an FMX. I couldn't figure out why it wouldn't shift to 3rd. It needed fluid. Yeah I know DUH! lol While ideling the dipstick read right between add and full. OK right? Rev the engine and the fluid goes into the convertor, leaving nothing in the pan to shift. Stop revving and it goes back to the pan. It took almost 2 full quarts of fluid. Thirsty little devil it was. Now the convertor is full and alls well that ends well. I hope your fix is as easy as mine was!

Start simple
 

everyone on here has said some really good ideas, but look to the simple ones first.
Obviously like was just mentioned, check the fluid level. After that, I think the thing being cold could be part of the problem. Mine sits sometimes for 8 months of the year. I always start it and let it warm up, but the tranny fluid does not really start to warm up til u drive it. After mine has sit for that long, it takes it forever to shift but finally will. After that, it should start to shift more normal. It should only do this when it has sit for a long period of time (a month or more). After checking these few simple things, then the other things might come into play if u still have shifting probs. It took me a long time to realize, it was something stupid and trivial, cause I was always thinking the worse (big money items).
good luck
Ryan