68pony5

I wanted to get all your advice on this but I ultimately may know the answer. I have a 1968 Coupe with a 289 C-4. The car has been stored for 8 years and the tranny was rebuilt with a shift kit installed at that time. The car was not started during my long restoration and I finally got her done for a ride around the block this past weekend. The tranny seal was leaking so I replace it and put in new fluid and filter. Now the problem..

Car runs great. started up no issues. Reverse works fine...neutral and park (of coarse) no problem. 1st and 2nd gear work fine. When I put her in Drive, the car does not want to get out of low gears and does not shift automaticly.

I am wondering is my seals are toast and I am lookig at another rebuild for letting her sit so long. Is their anything I can do to verify this? Any troubleshooting advice would be appreciated.[&o]

72rustang

I don't know a whole lot about transmissions but here are a few simple things you can check.

1) Fluid level. I'm sure you've checked this already, but doesn't hurt to check again. A few months ago my FMX started acting seriously weird, it would drop out of gear, then race and slam into gear at 2K rpm, nasty stuff, when cold. Once up to temp, it was totally normal. Turned out it was marginally low on fluid, top off fixed it. I've always found ATF dipsticks to be a little finicky in terms of getting a good accurate read.

2) Vacuum modulator. This is a little screw-on vacuum diaphragm that tells your transmission when to shift. If the diaphragm ruptures it can no longer do its job. This might be your problem since manual shifting works fine, only "D" is failing. On the FMX the modulator is near the back of the trans, but right now I can't recall where it is on the C4. You should also check the vacuum line running from the carb to the modulator for leaks. If you have a vacuum pump, you can remove the modulator and manually apply vacuum to it and see if it holds. I think 18" / Hg is the vac amount but check a shop manual to be sure.

3) Snake oil. Seriously, I'm not kidding. After the weirdness in the FMX occurred, I figured I'd try one of the various tranny snake oils, and I put like 1/3 of a can of something called "Seafoam Trans-Tune" in there. It is supposed to clean up varnish etc. inside your trans. I figure it only takes one gummed up spring or check ball to make your trans misbehave, and so I dumped this stuff in for the hell of it. My trans has always downshifted quite firmly, but I honestly believe it is even quicker and firmer now than before the snake oil. I drove it around like 100 miles or so with that stuff in there, then dropped the pan and changed the filter. It didn't look dirty at all but I figured cheap insurance.

Anyways, good luck. Hope one of these works for you, I remember getting pretty bummed out about trying to find somebody who could rebuild an FMX. So far, no need.

THUMPIN455

From the troubleshooting guide in my trans book. C4/C3 section.

[IMG]local://upfiles/14646/0A52D4706BAE4ED78AFD6DE76B165D31.jpg[/IMG]

THUMPIN455

Another one.

[IMG]local://upfiles/14646/5FA6CD906831424FB37DF7E6802518B7.jpg[/IMG]

THUMPIN455

More.

[IMG]local://upfiles/14646/4A19103552BB4A0492BD2486735FD5F2.jpg[/IMG]

THUMPIN455

OK what I think it is would be the trans has sat for a long time. Ford transmissions dont like to shift right for a while after they sit. Since it was relatively fresh when parked, it should be ok now provided no water or dirt made its way into the trans.

Why they dont like to shift is sticky valves in the valve body. Even changing the fluid can cause erratic shifts in a C4. So if the valve that controls the 2-3 is sticking, its not gonna shift.

Additionally, check your vacuum modulator and make sure it is conneted to manifold vacuum, that could allow a 1-2 and not a 2-3 as well. What I would do if it were mine, sould be drive it for a while at slow speeds and see if it loosens up. If it doesnt you will have to pull it and find the problem.

68pony5

Thanks you both for the advise and THUMPIN455 for the troubleshoot sheets. This will be a big help. I will let you all know what happens. I have a a lot of this to check this weekend.

68pony5

rigwelder

i didnt read any of the rest. but theres a vacum hose running from the tranny to the intake behind the carb. if its off or cut, cracked or whatever. it wont shift into drive.

Calixtus

My 68 289/C-4 is doing the same exact thing. I was already leaning toward a vacuum problem because my power brakes are soft and the A/C temperature selector has no effect. Since I am also having the problem described above, I think I can be 99% sure I've got a vacuum leak somewhere.

Thanks for the info, this site is great!

Bulldog66

I just had a Cruise-o-Matic rebuilt ( c-4 ) and had a laundry list of problems. I found This site to be extremely usefull for info..

The guys that answer your questions ( the ones that run the site basically ) are builders and are inside trannys daily.

Good luck.