How tough to rebuild or overhaul a C4 trans?

66coupe351 · Aug 14, 2006

The C4 transmission in my '66 coupe is very old, but seems to work great. The shifts are fast and firm, doesn't slip as far as I can tell.

The problem is that is leaks really badly. Not sure what happens while driving, but if I park for even 5 or 10 minutes it will leave a small amount of fluid beneath it. I replaced the pan gasket a while ago and that didn't help at all.

I noticed that rebuild kits are about $200 at Summit, and that places like National Parts Depot have an 'overhaul' kit for around $60 that appears to include all the seals. I was thinking the seal kit might be all I would need since I'm happy with how the transmission works.

So, I was wondering how difficult either the Overhaul, or the Rebuild route would be. Do you think the Overhaul kit would be a good fix for a leaky transmission, or would you recommend doing the Rebuild while the transmission is out of the car? Is this a reasonable job for someone with a fair amount of experience working on their own car to attempt in their garage?

mustangman70 · Aug 14, 2006

Whoa slow down turbo lol

Have you checked to make sure the lines arent leasking? what about where the speedo cable goes in?

66coupe351 · Aug 14, 2006

Good point. No, I haven't checked any of that. I've been under the front of the car a lot lately redoing susp, etc. The transmission is a big oily mess - can't tell where any of the oil is coming from.

I suppose a good first step would be to degrease the whole thing and try to determine where the mess is coming from.

mustangman70 · Aug 14, 2006

Is it red? or is it black?

Transmission fluid is red...if its oily as in black the back of the intake may be leaking, or the rear main.

chemeng · Aug 14, 2006

Leaking C4

C4 is notorious for shifter leaks. You probably don't need to rebuild, but you do have to drop the valve body to get to the shifter seal. Messy, messy job.

66coupe351 · Aug 14, 2006

The fluid leaking onto the ground is definately red. I don't drive the car much - especially lately since the front end has been apart - but I have to add transmission fluid fairly often.

I was just refering to it as an oily mess. I can't guarantee there isn't any motor oil mixed in there, but there is definately a lot of trans fluid.

66coupe351 · Aug 14, 2006

chemeng - shifter leak? Where would that be - the top of the trans where the shifter hooks up?

You say you have to drop the valve body to get to the shifter seal. Is the valve body accessed by removing the trans pan?

bad68coupe · Aug 14, 2006

66coupe351 said:
chemeng - shifter leak? Where would that be - the top of the trans where the shifter hooks up?

You say you have to drop the valve body to get to the shifter seal. Is the valve body accessed by removing the trans pan?

Yes

dennis112 · Aug 14, 2006

66coupe351 said:
chemeng - shifter leak? Where would that be - the top of the trans where the shifter hooks up?

You say you have to drop the valve body to get to the shifter seal. Is the valve body accessed by removing the trans pan?

You'll find various pictures of what it looks like under the pan and the valve body of a 66' C4 here:

http://www.geocities.com/dennis_2685/frtpump.html

The shift lever is at the top if this pic, almost center.

66coupe351 · Aug 14, 2006

OK, thanks for the reply bad68coupe.

It just seemed a little strange to access the shifter seal at the top of the trans by going up through the bottom of the trans.

Is something that can be done with the trans in the car?

Think I found the seal you guys are talking about in the NPD catalog - does this sound right? From the catalog:

7B498-1 SEAL, Shift Shaft
65-73 C-4 and C-6, that leaky bugger on the side of the case! $1.98

chemeng · Aug 14, 2006

C4 leak

66coupe351 said:
OK, thanks for the reply bad68coupe.

It just seemed a little strange to access the shifter seal at the top of the trans by going up through the bottom of the trans.

Is something that can be done with the trans in the car?

Think I found the seal you guys are talking about in the NPD catalog - does this sound right? From the catalog:

7B498-1 SEAL, Shift Shaft
65-73 C-4 and C-6, that leaky bugger on the side of the case! $1.98

That's it. I've got one around here somewhere. I replaced it, started leaking again 18 months later. Like I said, not a fun job. I got tranny fluid everywhere, running down my arms as I dropped the valve body.
Tranny shop wanted 180 bucks in labor to do the job. (4 hours at 45 per).
Mike

mustangdave · Aug 15, 2006

Besides that, the lines often leak and most pan rails are bent and won't seal; I'm going to switch to a nice aluminum one with extra capacity and a drain plug.
If you do decide to rebuild, it's not that bad. You will need a large clean work area. Lay everything out in order and do NOT mix it up. I highly recommend the Ford manual. There a few special tools but you can get around all of that with c-clamps and a friend (for the clutch packs). You will need a dial indicator to check endplay if you want to do it right. One important thing to be careful of if you disassemble the valve body: there are some check balls that want to fall out if you disassemble and they need to go back in the correct place. I had a hard time finding where mine went so try not to let them fall out. Clean the crap out of everything: I pressure blasted and scrubbed the outside before I started and used a parts cleaner for all internal parts that needed cleaning. Soak the clutches in tranny fluid before installing.

66coupe351 · Aug 26, 2006

I've started tackling my transmission leaks this weekend. I've got the car up on 4 jack stands, and cleaned things off some. Looks like the pan gasket is leaking and the shift shaft seal. There may be more leaks, but I'm going to try and fix these two, and see what things are like after that.

Now, how do I get to the shift shaft seal? I've got the pan and the valve body removed, and can see where the shift shaft is, but not sure how to remove the shaft(s). Looks like there is an inner and outer shaft. I've removed the nut from the outside - this frees up the inner shaft, but I can remove it because it hits a drum inside the transmission. I've also removed what I think is the neutral safety switch. That's as far as I got last night, but I didn't really know where to proceed from there.

Any help would be appreciated - I'll be out there working on it again soon.

Jester67 · Aug 26, 2006

66coupe351 said:
I've started tackling my transmission leaks this weekend. I've got the car up on 4 jack stands, and cleaned things off some. Looks like the pan gasket is leaking and the shift shaft seal. There may be more leaks, but I'm going to try and fix these two, and see what things are like after that.

Now, how do I get to the shift shaft seal? I've got the pan and the valve body removed, and can see where the shift shaft is, but not sure how to remove the shaft(s). Looks like there is an inner and outer shaft. I've removed the nut from the outside - this frees up the inner shaft, but I can remove it because it hits a drum inside the transmission. I've also removed what I think is the neutral safety switch. That's as far as I got last night, but I didn't really know where to proceed from there.

Any help would be appreciated - I'll be out there working on it again soon.

Interested in this myself as I have the same leaks in the same places and I need to replace the natural safety switch.

How tough to rebuild or overhaul a C4 trans?

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My rearend needs a stud and two nuts.

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How tough to rebuild or overhaul a C4 trans?

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