Engine/Transmission (1994 - 1998) clutch slip?

[Berrigan]

I put in my 3kgsk yesterday (wow) and slid the #11 full forward. AFC housing 3/4 forward and star wheel full rich. Yes it smoked too much and ill deal with that on another day. The truck has 3. 54 gears and 31. 5 inch tall tires. The reason for this post is I went for a test drive, had the truck in 4th gear at about 1300 rpm and pushed the pedal to the floor. The clutch (original with 50k miles) sounded like it was slipping. I got out of it, slowed down and repeated the test. This time watching the tac at about 1600 rpm the engine raced to 2300. I then got out of it and the tac dropped to 1750. It was slipping! I then drove the truck to my safe highway section to do a 4th gear run with my g-tech. This time the clutch held. I did it 3 more times and it held every time.



After the gov spring install I sprayed brake parts cleaner on the block under the pump to clean off the oil that came out. Do you guys think oil or parts cleaner could have gotten on the clutch. I dont understand how a clutch could slip twice then hold 4 more times under the same conditions. Thanks for any ideas.



By the way at 8120 lbs the g-tech showed peak 598 ft lbs at 1700 and 240 hp at 1900. Both rear wheel.



Bill

 

[Berrigan]

correction

The hp was at 2900 not 1900

 

[Garry Verheyden]

Bill, I would guess you'd be more around 270-280hp with your set up. I had 275hp with #11 not full forward. You will most likely slip your clutch at that low of an rpm. I cannot get on it hard below 2000 rpm with my set up now else I'll slip my clutch. It is a dual friction clutch and holds fine at over 400hp. But will not hold up at below 2000rpm.

With your set up you should not floor it in 4th or 5th below 1600 rpm. You will slip the stock clutch. Above this rpm you'll probably be fine.

Garry.

 

[Berrigan]

I talked to Piers yesterday and he said I was probably at about 300hp flywheel with this setup. He said thats pushing a stock clutch. He also said the clutch will hold better when warmed up to normal temp.



Well going home after work I got on the freeway (clutch still cold) was in 5th at 60 mph. Pushed about 1/2 pedal to merge in to traffic and it slipped. Drove about 10 more miles and did it again at full throttle and it held.



Does anyone have any advice for me on this cold/hot deal? Any experiences? Will I be ok if I just stay out of it when its cold or is this thing just going to get worse. Also I havent even pulled the 8000lb trailer yet.



I dont want to de-tune the motor, but what good is the power if you cant use it? Im in denial about needing a heavier clutch but maybe I need to wake up. Can I just put in a heavier pressure plate. OK Spend my money for me!!!!!!!

 

[Garry Verheyden]

Bill,

Piers is right, I had the same thing happen in yhe past where the clutch would slip but if I tried it again 10 seconds after it slipped (when it was warmed up) and it wouldn't slip. Now that you have a gov. spring kit you don't have to worry about clutch slippage anymore if you shift at high enough rpms while towing. When I'm empty I will hammer it through the gears without worrying about clutch slippage, but when I tow my 15,500 lb trailer I bring the revs to about 34-3500rpm between shifts. The rpms drop to about 2100 after shifting which is out of the range where I will slip my clutch.

Garry.

 

[JGK]

Don't you run the risk of glazing the clutch material if you slip it too often, thereby causing it to slip more?



In any case, it slips. If you continue to use/overuse it (and you will!) you'll kill it.



Start saving for a SouthBend!



-Jay

 

[Garry Verheyden]

Most ceramic clutchs will glaze after slipping them. And continue to slip once they're glazed. I don't know if that's the case with the organic ones. When I had the full ceramic clutch , it was toast after it had slipped a couple of times and was glazed.

Garry.

 

[Deezul1]

The clutch slip will happen the worst at around 1600-1700 rpm with the boost almost peaked. On mine I could predict when it would slip by watching the boost gauge if I nailed it at 1400rpm or so, when the boost hit 25lbs the clutch would slip. Nail it After 2000 rpm no slippage. Look at the torque specs on your engine and see when max torque is.

 

[Berrigan]

Thanks for your ideas guys. The pedal releases right at the top so im going to check the slave and make sure it is fully released with no pedal pressure. If thats ok ill drive it easy untill I can get a new heavier clutch in there. Bill

 

[mschoenheider]

Bill,



I have basically your setup in 3/4 ton. I have never had my clutch slip, even pulling a 11,000# trailer. My original clutch has 143K on it now. I would bet that your is out of adjustment. Either that or I am really lucky, I doubt it is the second possibility. I am planning on a new clutch before 370s though.

Mark