Clutch slipping question - HELP PLEASE!

[Juggernaut]

Ever since I got my Cobra on the road about a month or so ago, I noticed the clutch seemed to be slipping.

It seems to slip a little going into each gear when I get on it AND seems to slip a little while I'm adding gas to go up a hill. I've adjusted it three times now & of course I bled it when I installed the slave cylinder. The pedal free play seems okay.

Since it's slipping a little going up a hill, I think the problem may not be an adjustment or air in the system but the pressure plate. Unfortunately I don't know what brand pressure plate or clutch it is, when I bought it locally, I just told them I needed one for a 289 with a T-5. I'm thinking I bought a "generic" clutch & pressure plate that I probably shouldn't have. Maybe I need a stronger pressure plate?

If so, any recommendations?

Please steer me in the right direction if I'm going down the wrong path. I don't have much experience with transmission/clutches/pressure plates, but I want to learn.

Thanks,
Randy

[jhv48]

It's either a weak pressure plate or oil leaking from the rear main seal onto the disc.
Either way, you'll have to replace the pressure plate and disc.
Preferably with a racing unit.

[SSSammy]

Randy, even if your new pressure plate and organic disc are light duty units, they should not cause these symptoms in street driving. So it is either oil on the disc, like jhv48 says, or your throw out bearing is applying too much pre-load to the pressure plate (negative free play so to speak).

If you have a fork actuated t/o bearing, then you can feel the free play by wiggling the fork by hand. If you can't wiggle the fork or move it toward the slave cylinder by hand, then it is still under load and the threaded rod needs to be backed off.

If you have a concentric hydraulic t/o, then it could be applying too much preload to the pressure plate. These things are usually threaded on a collar, and you have to spin it around one or two revolutions to back it off. Unfortunately, you may not be able to do this without removing the tranny from the bellhousing

If fiddling with the throw out mechanism doesn't do the trick, you will have to pull the tranny and bellhousing and diagnose what's going on. Whatever it is, the solution will become apparent.

Sam

[jwd]

Sounds like an adjustment problem. Are you sure it's releasing completely? Adjust it so the T/O bearing is just off the fingers of the pressure plate (ie: not touching it). Since this has been a problem from the start, I doubt it's a contaminated disc.

Jim

[Juggernaut]

Thanks for the input guys! All good replies!!

jhv48, my oil level still shows full, so maybe the rear main seal is okay & it is a weak pressure plate?

Sam, I have a fork actuated t/o bearing, I know the way it is now, completely hooked including the return spring, I can't wiggle the fork with the pedal not depressed. I'll try adjusting that again.

JWD, how can I tell that the t/o bearing is just off the fingers of the pressure plate? I can't see the t/o bearing.

I hope these aren't stupid questions but as I said, I'm trying to learn this tranny stuff.

[Roush #1]

Juggernaut,

If the rear seal is leaking, it would have to be really bad to show up on the dipstick. Your delima doesn't sound like a rear seal leaking, but more like an adjustment problem. You should be able to see the oil if the seal is leaking.

Try to adjust the clutch where there is no pressure on the clutch fork at all when the clutch pedal is at rest.

Cobras are not notoriosly hard on clutches mainly because of their light weight. A generic clutch should work well behind a basic 289 ... at least for a while.

Good luck!

Jody

[fsstnotch]

I will highly recommend the spec clutch if you go for a replacement. I ran the stage 2 in my mustang. It was awesome, and not overly expensive!

http://treperformance.com/c-180-spec-ford-clutches.html

[Juggernaut]

Jody, thanks for the response, yep, it appears that I need to adjust it the right way this time, unlike the last time I adjusted it & see what I got.

fsstnotch, thanks for the recommendation, I'll keep that in mind if I wind up replacing parts. Stay safe!

Randy

[Michael C Henry]

You will have to keep up with the adjustments as your clutch wears. The more you slip the clutch the more wear more adjustment. You are lucky that you havent taken out the throw out bearing . The throw out bearing is intended for only momentary use. If it continues to spin under tension. The bearing will heat up ,spin out its grease ,and then lock up taking out the forks in the pressure plate. You need a little free travel for throw out bearing release. As you look at the linkage there should be a spring that pulls the throw out bearings' fork forward. You can check the free play by pulling the fork arm rearward through the springs pressure untill the trow out bearing contacts the pressureplate fingers with your bare hand. you need about 3/16 or so movement. You will only have so much travel potential in your clutch linkage, so the more free travel the less to actually release the clutch. If you cant get complete clutch release gears wiil grind or resist shifting. I have a tilton hydraulic clutch system . with slave cylinder ,throw out fork arm and so on. I had a 7/8" ID master cylinder and had just enough volume to have just a very small amount of free travel and just barely clutch relase. I didn't keep up with the adjustments and ended up ruining my pressureplate. I ended up changing out the master cylinder to a larger 15/16" ID diameter master cylinder. I gained more slave cyilnder travel and have lots of free travel and complete clutch release. It takes a little more foot pressure now.

[flipscobra]

To check your free play on your throw out bearing you need to release the spring pulling the fork back. Then you will be able to jiggle the arm an see if you have free play. Thats the way I check mine, because that pull back spring is strong.

[nevermind65]

I had a similar problem on a Cobra I bought last Fall. It seems as though the builder of the car used a brake master cylinder for the clutch, which is not a big issue. Unfortunately, the master cylinder was for a car with drum brakes and they had left the residual check valve in the master. Although it wasn't a lot of pressure, it sure made a huge difference when you shift from one gear to the other. What type of master cylinder are you using?

[patrickt]

Originally Posted by flipscobra

To check your free play on your throw out bearing you need to release the spring pulling the fork back.

Here, I wrote this a year or two back. Maybe it will help you in adjusting your clutch.

Originally Posted by patrickt

When I say “adjust the clutch” I mean adjusting the slave cylinder to clutch fork clearance so there is no unnecessary pressure on the throw out bearing. As your clutch disc breaks in the clutch fork will move closer to the slave cylinder (with a “push slave cylinder” like we have), so you have to adjust the clearance on it. 1900 miles is a good time to adjust it since it’s probably nicely broken in now. Here’s how to do it:

1) Here is a picture of the slave cylinder on my ERA, yours is probably identical. Note the return spring, the silver looking locknut that is on the threaded rod coming out of the slave cylinder, and the brass colored fitting that is on the rod next to the locknut and that actually contacts the clutch fork.



2) Remove the return spring and back off the silver locknut and brass colored fitting about a quarter inch or more towards the slave cylinder. You will need two half inch wrenches to do this. One to attach to the lock nut or the brass colored fitting, and the second to go around the nut that is on the very end of the threaded rod behind the clutch fork. You hold that nut to prevent the entire rod assembly from just rotating as you try to unscrew the nut or fitting. Use your finger and push the end of the threaded rod back in to the slave cylinder and you should now have an obvious distance (a quarter to a half inch) between the brass colored fitting and the clutch fork. The clutch fork is now in its natural position with no pressure on the throw out bearing and the brass colored fitting is not touching the clutch fork.

3) Use your fingers and tighten the brass colored fitting until it is tight against the clutch fork. Put a .063" feeler gauge between the silver locknut and the brass colored fitting and tighten the silver locknut so there is a .063" distance between the locknut and the fitting and the fitting is tight against the clutch fork. Remove the feeler gauge and tighten the brass colored fitting back up tight against the silver locknut without moving the locknut. Thus there is now a .063" distance between the fitting and the clutch fork and the locknut is tight against the brass colored fitting. Put the spring back on.

[Juggernaut]

Thanks to all for the help! You guys are great!

Mike H. - I also have a Tilton system with a 7/8" master cylinder. Once it's adjusted correctly I'll keep an eye on it to see when it needs further adjustment. Over the winter, I might just change it to a 5/16" as you suggested.

I didn't get any garage time today (Mothers Day), tomorrow after work I must mow the grass, so my next chance to adjust it will be Tuesday night. I'll post the results.

Randy

[Michael C Henry]

You can get various sizes ( ID vary by 1/16") of master cylinders . I originally bought a 1" ID master cylinder but decided to try a 15/16"ID master cylinder first. I couldn't increase my pedal travel so I increased my volume and gave up some leverage. It is a little stiffer pedal than before, but I always wear shoes anyway. The way it was before I had very little free travel and barely enough for complete clutch release. Any wear on the clutch and I lost free travel. It was realy a fine adjustment with just the bare minum of free travel. That is how I took out my pressure plate and throw out bearing. One of the first signs that the clutch isn't releaseing is reverse is tough to get into when engine is running. When I ordered the 1" ID master cylinder I was warned to guard against overtraveling the slave cyilnder. So I backed of a 1/16" on the master cylinder ID size. The master cylinders come as a kit with various resivoirs and plumbing. The 7/8"id master cylinder was a bare minimum and the 15/16" ID master cylinder was a better fit.

[undy]

Going to a larger bore master cylinder, all things else remaining the same, will give you more fluid volume with increased pedal effort (given the same M/C piston stroke/foot travel). The resulatant effect of that will be more slave cylinder travel which yields a higher degree of clutch release. I run a 1" bore M/C on mine.

Dave

[Juggernaut]

Just wanted to thank everyone for the help.

I finally got the clutch adjusted a few nights ago & it works great!

What a difference it made, seems like a different car!

Thanks again, this forum is great!

Randy