clutch slipping

[chpr1972]

The car is a 66 Lemans conv with a 489 BBC estimated between 575/600 hp. It had 2900 miles at the time. It is 10:1 compression with large valves extremely ported closed chambered stock heads. The cam is a Comp roller with .510/.520 lift with .230/.236 magnum cam. I have dual throttle body TPI tunnelram. It has a Lakewood bellhousing with Centerforce steel flywheel and a Ram performance clutch rated to 550rw hp. It runs through a TKO600 and Ford 9" with 3:50 posi and 25.5 " 275/40R17. It has an American Powertrain hydraulic clutch with .145 clearance.
On my way to Daytona Beach during speed week I was driving on a 2 lane highway. I was passing in 4th gear with no problem. I also passed in 5th gear a couple of times. A 302 Mustang passed me and I followed him around 3 or 4 groups of cars. When I went to pass him I was going fast enough that I did not down shift and powered around the Mustang. All of a sudden the clutch let go and slipped badly blowing blue smoke.
I looked inside the bellhousing and can see clutch dust. I can see no sign of an oil leak inside. There is still free clutch play. Is it possible that the clutch braided hoses got too hot and put pressure on the throw out bearing. The guy at Ram clutch just gave me silence and NO SUGGESTION on what to do or look for. They claim it is for high performance use and the guy said it was rated to 550 rwhp. Is it possible that at 2300/2600 rpm it is producing so much torque the clutch can not handle it? It has not slipped since then. It is still works good and does not chatter any more that when new. The say that a small amount with this clutch is normal.
An Ideas, I can not afford a super clutch!

[SSLance]

I had that same RAM clutch behind my 340 hp small block and it only lasted a year before it started slipping on me coming out of corners on the autocross course. It was fine everywhere else, loading on and off the trailer, every day driving...even aggressive street driving. But once it got some heat in it and pushed hard on course, it wouldn't hold either.

I just replaced it with a Mcleod Street Extreme PP and disc. So far only have about 500 street miles on it but I like it. I have an autocross test n tune scheduled for April 9th which will be the real test for it. I also considerably upped the HP in front of the clutch over the winter.

Hope that helps, if any questions just ask away.

[TheJDMan]

Is it possible that you inadvertently had your foot on the clutch pedal without realizing it? I have had that happen before and it only takes a very light pressure to cause the clutch to slip. You see people driving around all the time with the brake lights on because they are resting their foot on the brake pedal.

[chpr1972]

No. I drove over 3,000,000 miles in a big truck. I have driven manual transmission cars all my life. In 1968 I bought a 66 Goat 4 speed and drove it till about 15 years ago when it fell apart from rust.[Illinois and Florida beach]
SS Lance, ya that is similar to what I experienced. It was the only time I had a problem. But a 340 built coming out of a corner would have a high rpm and high torque. It would not have low in torque at a low rpm that would change clamping force or am I thinking wrong?

[Centerforce]

What is your torque output vs the rated torque of the clutch? That is the force that is actually working on the clutch. It's possible it just didn't like the heat, which caused it to slip. It should be okay to continue using the clutch if its driving normally, you're just going to be limited on how hard you can drive and further upgrade the car.

[chpr1972]

I called Ram and found out the clutch was only for 550 hp. So much for hight hp street. I called Centerforce and their clutch that I used was good to 630LB torque. After 2 tries of aligning the clutch, I put the manual linchage back in and now the clutch takes a lot less leg preasure and the transmission shifts smoother and I do not have to put the trans in a forward gear before I put it in reverse. The hydraulic caught about 1 1/2 / 2 inches up and the manual linchage catches at about 1 "It is a lot easier to drive. The Centerforce instructions breakin period is 100 take off so I have not hit the clutch hard. Almost time for an other trip to Daytona and do some passing going across hwy 40

[Centerforce]

I called Ram and found out the clutch was only for 550 hp. So much for hight hp street. I called Centerforce and their clutch that I used was good to 630LB torque. After 2 tries of aligning the clutch, I put the manual linchage back in and now the clutch takes a lot less leg preasure and the transmission shifts smoother and I do not have to put the trans in a forward gear before I put it in reverse. The hydraulic caught about 1 1/2 / 2 inches up and the manual linchage catches at about 1 "It is a lot easier to drive. The Centerforce instructions breakin period is 100 take off so I have not hit the clutch hard. Almost time for an other trip to Daytona and do some passing going across hwy 40

We're glad to hear the clutch feel is much better now with the new clutch and linkage!

[TheJDMan]

I am a big advocate of mechanical clutch linkage provided there is sufficient header clearance. The feel of a mechanical linkage can be dramatically improved over stock by installing this Speedway Motors HD clutch fork which allows you to use linkages equipped with rod ends.

http://www.speedwaymotors.com/Speedway-GM-Heavy-Duty-Clutch-Throwout-Fork,37080.html

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