Clutch Slip or Something else?

[VEX]

So my slightly! modified, new to me, 04 Mini Cooper S is in for a little bit of engine work and the garage thinks the clutch is slipping a lot.

But my engineering brain tells me........

If the clutch was slipping would the revs not climb but acceleration reduce?

Mine is doing the opposite, the revs pegs at about 4000 rpm for a while, But the acceleration just keeps on going, like a train.

I know it has a remap on it, could the map be doing something to peg performance a little to help manage power to the wheels?

Thanks.

V.

Edited by VEX on Sunday 26th November 00:02

[VEX]

Ok, so how would a slipping clutch manifest its self?

As an engineer, slipping clutch to me means that rev would climb and speed wouldn’t, because the clutch can not transfer the power.

Also, would a clutch bite at the top of its peddle travel or the bottom? Again I would expect a warn clutch to bite towards the end of a push to the bottom. But I am not a mechanical engineer.

V.

[VEX]

Thanks, both useful descriptions. Thanks.

This seems to happen around 4-5k under hard acceleration but I can already be accelerating away from about 3k, as the speed climbs with no discernible decrease, the revs stagnate at 4K-ish for a couple of seconds before climbing again.

Get it back in Monday/Tuesday so will play with it a bit more.

Happy to replace it, it’s 13 years old and will be my fast weekend/meeting/track car as I have our family car and my van to use.

Just trying to understand the problem and process. (The engineer in me)

V.

[VEX]

stevieturbo said:

I'm more confused as to how both a garage and an engineer cannot recognise clutch slip !

If the engineer isnt familiar with cars....maybe...maybe, but a garage that does this daily ? Find a new garage.

No, I am the engineer reffered to in this, but I am a comms engineer, not a mechanical or vehicle one.

I just want to understand how it manifests itself, because it doesnt make sence to me at the moment.

V.

[VEX]

steveo3002 said:

doest sound like clutch slip to me

typical revs shoot up with no increase in speed is how i would describe slip..

That’s why I am asking.

It doesn’t make sense to me either, which is why I thought it could be the map holding it back to manage power to the wheels.

Get it back tomorrow so will try to replicate it with a little play time.

V.

[VEX]

Ok, that’s possible, not been able to replicate it every time.

Will play tomorrow / tuesday

[VEX]

HustleRussell said:

Old supercharged Mini
+remap
+professional mechanic says the clutch is slipping "a lot"
=clutch is slipping?

I am not disagreeing with him, just my brain is trying to take what I am seeing / feeling and apply it to a slipping clutch.

To me they don’t match, yet.

[VEX]

GreenV8S said:

With a conventional manual gearbox like you have, the relationship between engine speed and driven wheel speed will be linear while the 'box is in gear and the clutch is not slipping. The ratio between them will be fixed for each gear and determined by the gear ratio, final drive ratio and wheel size.

If it is in gear and the engine speed and road speed do not maintain this expected linear relationship then the clutch is slipping. For example, when you pull away the engine revs remain relatively constant and the road speed increases - obviously in this case the clutch is slipping and the amount of slip is reducing.

The amount of clutch slip need not remain constant. If it is increasing, the engine revs will increase by more than the geared amount. If slip is reducing, engine speed may increase by less than the geared amount - or not increase at all. You can quite easily have situations where the engine speed is going up and the road speed is going down, and vice versa.

Perfect, Thank you.

I trust them and have already priced for its replacement and a few other bits that make sense while it is being done. Just needed to understand it.

V.

[VEX]

Ok, I have been out for a spirited drive and yes, it is deffinately the clutch.

What I wasnt aware of is it slipping at around 2000rpm and then it seems to catch up with itself and fully re-engage at around 4500rpm.

So revs climb without linear speed at 2k and then speed climbs and revs stall at about 4.5k, then all is good above.

So research on clutch kits and get it booked in for the next stage.

Thanks for all the advice.

Edited by VEX on Tuesday 28th November 13:25

[VEX]

I agree, but as you say, it was the missing 2k slip I was missing.

If I enjoy it now, whats it going to be like with a fully engaged clutch at 2K!