Clutch Diagnosis Help Needed

[wrogers55]

I'm looking for an easy way out of this, but I suspect I'm in for a long weekend. Clutch slipping problem. It's been fine for over 500 miles I have had the car, a Backdraft, 418 sb, FI, putting out north of 540HP. Problem started with a very light slip in 4th gear from about 3000 RPM, only for a second or less then it would stop slipping. Such a small slip, it was easy to mistake for wheel spin, which this thing will do whenever it gets good and ready.
Real problem started when a 2nd gear run up caused the clutch to just let go when the motor got up on the cam and the clutch slip let the motor instantly redline. I immediately backed off and it grabbed and I made it home fine. Man, what a smell. Now, for some diagnostic help beyond just adjustment. The pictures show the clutch fork tight against the shield and no free play by hand. The internal pictures show the bearing against the pressure plate fingers. I don't see any way to get free play in the fork. The Ford setup is new to me, but it appears something has gone wrong at the other end of the fork or maybe this is the way it behaves when the clutch plate is gone. Any help would be greatly appreciated before I start to pull this apart. Wayne in Gilroy, CA

[Rick Parker]

What has happend in the short time you have driven is a small wear of the clutch disc. This allows the diaphram fingers to relax a little in an attempt to maintain clamping force, the fingers move (toward the rear of the car) away from the flywheel, forcing the release lever rearward also, until it contacts the opening in the bellhousing. You may be able to purchase a shorter pivot stud that will pull the far side of the lever rearward and the other end (picture end) forward. The one you have may be adjustable, (threaded) and allow it to be shortened.


http://www.thefind.com/cars/info-clutch-fork-pivot

[mickmate]

If it has changed I wonder if the ball stud has backed out on the other side. The clutch needs freeplay or it is effectively being partially depressed all the time. That promotes slippage which you see a lot of debris from on the other side of yours.

[blykins]

It looks like that's a stock Ford Motorsports/King Cobra clutch kit. If so, they're good for about 350-400hp.

As Nick said, check for obvious signs such as a backed out pivot ball. However, I think you have way more motor than clutch which started the slipping issue.

The throw out bearing should never ride the pressure plate fingers.

Let us know what you find when you get it apart.

[jhv48]

Another possibility is that your rear main seal has begun to leak and it has gotten onto your disc. Any signs of oil on the bell housing?

[tcrist]

I have the King Cobra clutch and to get my clutch to engage it has to have pressure on the throwout bearing all of the time.

I was told by FORD that the throwout bearing (at rest) needs to hav 6-7 LBS of presure one the diaphram.

I have had it checked by the local hot rod shop and they said that everything was installed correctly but they did not like the 6-7 LB pressure idea and that they had never heard of it.

That said, I am not done with her yet so I have very few miles on her. One thing that I have noticed is if I am on the loud pedal fairly hard, 4TH does not seem to grab correctly. Seems soft like it is trying to slip.

I'll be watching this thread in hopes of some great information.

[Michael C Henry]

My brother in law had a new 84 F250 w/460 . It had no free travel. It worked but never liked it.
I've had several throw out bearing failures due to lack of free travel. Throw out bearings were not intended for continuos use only momentary use. The last go around for me my free travel kept going away. What I thought was rapid clutch wear turned out to be my old hyd. slave cylinder not returning to it's absolute bottom even with the return spring.

[wrogers55]

I started this thread and I'm at the point of knowing I don't want to continue with this clutch/pressure plate setup.

I come out of the rear engined open wheel indy car road race world, so I know clutch setups choices are like toothbrushes, everybody needs one and there are lots of good and bad options. The question for everyone is, which setup will work best for me. As far as I know, here are my priorities in order:

1. No slipping with a 550HP motor, 6,250 limit, TKO 600, 3:46 gear, 315/17 street tire, 2,300 lbs
2. No racing or hard launches, spirited street once in a while of course
3. I don't want to do this again
4. Pedal pressure medium to light hard is OK, but not desired (I can adjust pedal pressure with the cylinders if need be).
5. Might consider changing the shield also if there is a good reason
6. Cost is not that important if it meets everything else and I don't have to do it again.

I really appreciate the help and opinions
Wayne in Gilroy, CA

[Rick Parker]

McLeod has a dual disc setup that will work, BUT there are and have been a lot of 500HP engines in much heavier cars running single disc clutches but with a Long style pressure plate with great success.

[blykins]

Wayne,

I deal with clutches in Cobras all the time. RAM & McLeod both have excellent choices for your application.

For this setup, I would recommend RAM's Powergrip 10.5" diaphragm clutch kit. It's rated for 550hp, will have a light pedal and won't break the bank.

I usually don't post prices on here, but for part #98794T, it will be $315 + shipping.

I can also offer a Quicktime bellhousing if you choose to switch bells, but I see no reason to.