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No reverse in C4 and Slipping?
Hello all. I have been trying to get my Mustang back on the road and have run into a issue with the tranny. The car has been sitting for sometime and I remember the trans working fine when I originally parked it, then it sat for about 5 years with no work on it. Since then I have replaced the fluid and the large filter in the pan, I didnt know about the small filter until I searched for issues in the forums so I will check that later. The tranny was rebuilt sometime ago (dont know how long) by my grandfather who has rebuilt many engines and trans.

The tranny will engage reverse when cold, but when it heats up it will not engage at all. I have adjusted the low reverse on the side of the tranny per my Chilton. I am also running into an issue that when I have it down shift the engine revs but it doesn't speed up one bit, seems like its slipping.

Any help with this would be greatly appreciated, and I hope I dont need to rebuild/replace it.
My guess is that it’s getting past o-rings or seals when the fluid heats up. I would probably rebuild it.

My 2 cents

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Had a similar issue about 1983 or so with a C4, after rebuilding it and we installed it, my buddy said he filled as per the Haynes manual, but he forgot that we also drained the torque converter. After feeling like it wouldn't move, or just did neutral drops when it would finally catch, I checked the fluid and it was way low. Good luck and let us know what you find out.

Did you try driving it before you replaced the fluid and filter?
I did drive it before the fluid swap with the same issues. I was hoping the new fluid would help, but it didn't.

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(10-22-2018, 10:48 PM)71killshot Wrote: I did drive it before the fluid swap with the same issues. I was hoping the new fluid would help, but it didn't.

Fluid changes rarely fix transmission issues and fresh fluid can often make things worse. 

Said it before and I'll say it again, if your auto trans is sensitive to temperature, it's time for a rebuild. That said, the C-4 is the easiest transmission I've ever rebuilt. Did my first one in the kitchen of my apartment at college.  Chin

I buy my auto trans parts at BulkPart. Great selection and service. The stuff you buy from them is the same parts that rebuild shops use. Just be sure what year your C-4 is, as they did change things up over the production run.



I had 2 different trannies with similar issues
1st trans, I added a qt. of kerosene, drove is a while and did a trans service, got reverse back!
2nd trans, I dropped the valve body, cleaned the grooves with Q-tips and it shifted much better and at the proper intervals
the seals are most likely dried out and leaking. you could drop in some lucas transmission fix. maybe it kind of gets you moving but you need to rebuild the trans.

fresh fluid causes more problems in a old transmission that was on its way out where the fluid was never changed from new for maintenance. the older fluid would of been thicker full of metal and debre from the clutches. it would of been harder to push through a leaking seal so the trans would of acted a more like normal.
lucas thickens up the fluid and has some anti leak that clogs up some small leaks.

if the clutches and bands are still decent then it just needs a refresh. pull the trans apart change the seals check for wear or additional issues then reassemble if the clutches are still ok and then new fluid will work as normal.
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