Can other things act like slipping clutch?

[AL92]

My car looks like its down for the count with big engine problems but right before that happened I was noticing that when got on it hard off the line it would apparently just rev up and not go anywhere in first and second. This was not wheelspin. I did try a few tests for the clutch like putting parking brake on and then letting it out and it stalled and I did try punching the car in higher gears and the rpm didn't really seem to show slipping.

So wondering if other parts might be broken like the center diff or viscous coupling. Could failure of either of these parts give same symptoms of slipping clutch?

My clutch had maybe 4000 miles on it,no track use mabye five or six 5000 launches on stutterbox on the street. It did seem to hold at first but then noticed this revving without really going anywhere problem.

I am not very impressed with the HD 4000 if that turns out to be fubar but I also had some problems with hydraulics and changed out slave once and then master a few months later. Maybe the bad hydraulics killed the clutch in only a few thousand miles.

 

[ekanddsm]

you have less than 5000 mile on a clutch and its slipping again, perhaps a more gentle break in period would help, the disc material is quite similar to brake pads and brake will do the same thing if you cook them first time out.

 

[boostnhard]

some times people make the mistake of just replacin the clutch assembly, without worrying about the flywheel.
If the flywheel is cristalized which is normal if should be resurfaced by your local machine shop or replaced with a new one.

 

[ThingyNess]

It's not likely for the viscous coupling or center diff to fail in a manner that would act similar to clutch slippage. In my experience, viscous couplings when they fail tend to lock solid, rather than start slipping. Center differentials will pretty much either work or they won't.

If you have the newer HD4000 that uses an organic disc, heat buildup may be your culprit. Organic friction materials have their temperature coefficient decrease rather sharply with temperature. In addition, their dynamic friction coefficient is significantly less than their static friction coefficient.

Since holding power of a clutch is directly proportional to the friction coefficient, then when you're launching it hard, you have two things working against you.

1) The difference in speed between the clutch facing and flywheel is going to be highest at this point, and the lower dynamic friction coefficient is going to make the poor clutch more likely to slip. This leads to a lot of heat production which leads us to....

2) The coefficient of friction becoming even lower as the organic friction material heats up from the launch. This is unfortunately a bad case of positive feedback, in which the material heats up, which makes it slip more, which makes it heat up more, which makes it slip more, and so on. Once you get past 1st and 2nd gear, the clutch has more time to cool down during your pull (once it's actually managed to grab and equalize speed between the disc and the flywheel), so it doesn't slip anymore.

Basically, your clutch is sized properly for your needs in a static sense - when doing a dyno pull, 5th gear pull, etc -- it won't slip. From a dynamic perspective though, if you're going to be launching it hard, it likely won't be too happy.

This is why people often move to different friction materials on the clutch disc. The metallic/paddle type discs actually have a friction coefficient that increases with temperature. This makes them much, MUCH less likely to slip on a launch. In addition, they usually have a dynamic friction coefficient that's closer to their static coefficient than an organic disc. Again, their properties are much more favourable under hard dynamic loading.

Of course, the reason why most people don't use these discs is that their lack of slippage tends to grenade driveline parts, and they wear much quicker in normal street driving.

AL92: I know a lot of this is likely not news to you, but it's good to have the information around in case anyone stumbles upon this thread in a search. I'm not trying to spoon-feed you.

 

[ekanddsm]

I love technical info on a minor problem.

 

[AL92]

Wow nice technical info for sure. I broke in the clutch for 500 miles and mine is the year or so older Hd 4000 which is six puck sprung disc from what I can remember.I did not track or hard launch it for 500 miles and my boost was kept under 10psi. I did however have a slave cylinder fail first even though I put in a new slave when put in my new 2.4 and all my other mods pretty much all at same time about 5000 miles ago.

The slave fell off the trans I guess from vibration on the slave bolts. I put in new slave and loctited it on . Clutch worked so so but finally had to put in a new master recently and then the clutch would shift gears properly.I do think its possible thought that pump up maybe made the hd 4000 slip all the time from the first master. That is about only thing I can think of if my center diff is not the problem unless axle can also go and cause slippage.
All I do know is that I can't launch my car and get any decent time out of it. I did manage a 1.78 once though not too long ago. But my mph was awful for my combo and clutch slippage is the most likely cause..recent time was 13.3 at 106mph with a 1.94 60ft.
Car did that same time at 108mph at 1bar just after break in and was now at 1.4 bar.

Now engine is shot anyway I think have some checking to do ,possibly jumped timing belt or spun bearing or something. Not having much luck with my dsm lately. course dsms are cursed.