So my C4 has 41k original miles on it and it has been sitting awhile. For two weeks i’ve been driving it and its shifted okay except now when in drive it does not want to upshift to third. Also, it is leaking about a pint of fluid out of the bellhousing/inspection plate when parked and shut off and leaking a little while driving. It has a new modulator with good vacuum, all new fluid (converter drain too) and filter. I was wondering what the cheapest possible way to fix this problem is/ what should be replaced if I pull it apart to fix the pump seal. Could that seal be causing low hydraulic pressure so it’s harder for drive to operate? I was thinking of just replacing the TC and the seal. Has anyone else gone about this and how did it go? Thanks
I’d opt for a total rebuild since ALL of the seals have been hardened with age. Then at least you’d have all-new seals/frictions/steels that should last you another 40 years!!!
Slow, draggy shift or doesn’t shift until a hi rpm?
If the shift is slow/draggy and seems to take too long to get into third, I would suspect the hi-gear clutches/blown forward piston seal.
If it shifts normally at a very high RPM, maybe a sticky governor or a bad modulator.
How does the fluid look?
The fluid was brown when i got the car, but it wasn’t driving around with it. I drained it completely and filled it exactly. It’s more of a will not shift into third unless i hold the rpms for awhile then sometimes it will eventually shift. I’ve never taken out one of these bad boys before, is there anything i should watch out for? Thanks
Why don’t you try a new modulator and a quart of Lucas trans fix. You probably need an overhaul but these inexpensive parts may buy you some time. Worked for me before!
That worked for you? Did you have a leak as well, cause it’s worth a shot if that worked fixing a leak too. Thanks i’ll try it
The Lucas swells the rubber seals, while it won’t give you a new transmission it will probably slow the leaks noticeably.
im going to try putting in a little sea foam first to maybe loosen up some stuff, then i’ll try the lucas. But eventually i will be rebuilding this old dog. Thanks Art. I’ll let you know how it goes, i’m curious to see if it works.
If you’re still in Boston, or somewhere in New England, consider joining the Cougar Club of New England. One of our members owns a transmission shop up in North Adams (Berkshire Transmissions) and would probably be willing to advise you. I had him fix my transmission when I first got my current Cougar.
Thanks catvert i might do that. Alright so yesterday after a complete drain and refill with new filter and half a pint of seafoam trans tune, the thing starts shifting great and no leaks! I put a good 15 miles on her. Now this morning, leaking again… What gives?! At least i know it’s shifting well 
I rebuilt a C4 for my car here:
http://www.classiccougarcommunity.com/forum/viewtopic.php?f=41&t=219
You can read it and ask any questions you want.
If you decide to rebuild it, I HIGHLY recommend the 4 DVD set from Badshoe production on the C4 transmission. That guy makes it way too easy, but as you will see, I still screwed up one step of reassembly and going back and watching his DVD cured my problems.
Alrighty, sorry it has taken awhile but i finally went at it and pulled her out. After a small battle and a broken cooling line i got the seal replaced and the tranny back in. No more leaks! Now for the bad: after a couple days of driving okay one morning it wouldnt go into gear and was whining (i thought the pump) but if i shut it off for awhile it’ll start up and no whining and will go into gear fine… For about a mile then more whining…if anyone has some advice on something to check before i condemn it for a rebuild that would be greaat thanks!