My C4 has a mind of its own............

[crushnut]

it chooses to shift at different speeds sometimes, but it doesnt do it all the time. I know it will shift different depending on how much throttle you give it, but it will shift at different speeds sometimes giving it the same amount of throttle. Any ideas as to what is up, and why it is doing this?

Thanks

 

[golf4283]

maybe the vacuum line is loose??? try pushing it in farther. and u can adjust the shift speeds by twisting the part where it goes in I believe so try and adjust that too. see what happens.

 

[10secgoal]

Start by testing your line that goes from you modulator to motor(should be hooked to manifold vacuun) for leaks. If it's fine pull out your modulator and get a pair of needle nose. Pull on the valve behind the modulator, make sure it moves freely. I would change to tranny fluid and modulator. Something is causing your mainline pressure to change.That's how the c-4 knows when to shift. The modulator is what controls the main line pressure. Something might be jamming the valve. See where I'm going with all this ? Trannies are the same as motors. ( A clean motor is a happy motor) Almost forgot, check to make sure motor doesn't have any vacuum leaks either. Get a guage check that first. It's the easiest.

 

[GaPonyFarm]

Check your vacuum line and replace your modulator valve. The modulator valve basically sets the shift points on the C-4. Is this a recent problem? Does it shift particularly hard or soft? Any slippage? At what speeds is it shifting? When in 1st, does it feel like its in forward & reverse at the same time?

I always look to the modulator valve (its the part that the vacuum line attaches to on the tranny) for shifting point problems. Answering the other questions can help identify other possible problems. I'm assuming that you have checked the trans. fluid level and it is correct.....

 

[dodgestang]

it chooses to shift at different speeds sometimes, but it doesnt do it all the time. I know it will shift different depending on how much throttle you give it, but it will shift at different speeds sometimes giving it the same amount of throttle. Any ideas as to what is up, and why it is doing this?

Thanks

And check your fluid level at operating temp. a low or high fluid level will cause the tranny to shift 'weirdly'

 

[crushnut]

Thanks guys, i fixed it. I had a vacuum leak at the manifold, damn vacuum leaks..........

 

[EvilAirman]

I am having similar problems? Also is there any links you guys can give me where i can get specs on this car, I have a 289 2v 2bbl 66 stang with a 3 speed auto. It only slips from first to second if i am going around at the right speed where the it can't decide between which gear. How could i check for a vaccum leak. But if I am giving it gas to go through the 3 gears it will never slip. For any links or specs on transmission maintainance as far as type of fluid and capacities I would be greatly appreciative.