[Dr.Naren]

I have a stage 3 S-Cross 1.6 which does 202 HP / 438 NM. I have run 77k km and still on factory clutch. There is absolutely no clutch slip while driving normally or even if redlined in every gear.

What's strange is the clutch slips in first 2 gears only when I launch the car for 0-100 / QM timings. I had noticed this issue around 15k kms back and it's still present. The RPMs shoot with not much increase in speed and I am slower to 100 by almost a second. I have launched the car many times before and had only wheel spin in 1st gear. There is no wheel spin now and clutch just slips in first 2 gears. I understand the OE clutch wouldn't be able to handle so much torque but I didn't have this issue before. If the clutch is worn / bad, why isn't it slipping when I redline normally ? I would like to understand the technical reason for slipping clutch only while launching the car.

0-100 in 6.93s (when clutch wasn't slipping)



0-100 in 7.59 seconds (Run 1, today)



0-100 in 7.92 seconds (Run 2, today)



Oh yes, the clutch slipping gets worse if I do back to back 0-100 runs.

I plan to change the clutch when it slips during normal driving, but it's been 15k kms already since I noticed clutch slip only while launching the car.

Please help me diagnose this issue. Thanks

[tharian]

Quite sure it is a worn clutch especially since you have done launches and the power output is more than a stock engine.

Not sure how to explain it technically, but from my layman knowledge, it is because the first two gears are short gears compared to the rest which is why you don't see a clutch slip otherwise.
Actually you should see it even when doing roll on's, maybe it is not worn that much yet.

The clutch is one part you should have replaced as well along with the other performance mods.

[Dr.Naren]

Originally Posted by tharian

Not sure how to explain it technically, but from my layman knowledge, it is because the first two gears are short gears compared to the rest which is why you don't see a clutch slip otherwise.

There's no clutch slip if I normally redline in 1st and 2nd gears, it's only while launching the car .

Actually you should see it even when doing roll on's, maybe it is not worn that much yet.

Absolutely no slip. There's no drop in my in-gear acceleration timings too.

The clutch is one part you should have replaced as well along with the other performance mods.

Agreed!! I would mostly go with Sachs Performance clutch. It has higher torque rating than OE.

[corvus corax]

Have you tried starting the car from an incline?
Try starting from a steep incline, preferably with the car loaded with passengers.

[Dr.Naren]

Originally Posted by corvus corax

Have you tried starting the car from an incline?
Try starting from a steep incline, preferably with the car loaded with passengers.

Yes, I have done that without passengers. The clutch doesn't slip. Let me check if load makes a difference

[Shreyans_Jain]

I believe it is the jerk load of launch which is causing the clutch to slip. Still early signs of wear, you’ll get the redline slip as it wears out further.

[Dr.Naren]

Originally Posted by Shreyans_Jain

I believe it is the jerk load of launch which is causing the clutch to slip. Still early signs of wear, you’ll get the redline slip as it wears out further.

I was expecting the same that the clutch will start slipping at redline (without launch) soon, but it's been 15k kms already. I am curious to open it up and check, but there is absolutely no issue while driving normally...hence the delay

[Kosfactor]

Its normal.

Your clutch is behaving as expected, the clutch cover is disengaging the clutch when overloaded to avoid breaking the gearbox or something inside the engine itself.

Upgrade the clutch for more clamping force to handle the horse power increase, but you know where this is going

[Dr.Naren]

Originally Posted by Kosfactor

Its normal.

Your clutch is behaving as expected, the clutch cover is disengaging the clutch when overloaded to avoid breaking the gearbox or something inside the engine itself.

I didn't have this issue before though with the same tune. As you can see, I had done 0-100 in 6.93 seconds without slipping the clutch.

Upgrade the clutch for more clamping force to handle the horse power increase, but you know where this is going

Yes, that's the plan. Sachs has an option for S-Cross with 15 percent higher torque rating. I can ask Wolf to give me a map with lower torque just to check if the clutch slips.

[AMG Power]

Man, just yesterday I saw your post on BMW 320d equaling power! Nice.

On the issue:

1.The clutch has the highest load when you start off so a slip during starting off are typical early signs of wear.

2. Once you move, synchroniser rings (a quasi clutch) help reduce load on the main clutch so even if you redline there will be no slip.

3. The fact that it happened 15,000 Kim’s ago is an indication that you probably drive without too much stress on the clutch during normal driving.

4. As the slip has started, be careful of 0-100 launches as that is when the maximum load will come on the car. It is best to replace the clutch early.

5. Do Note that it could also be that the clutch is unable to handle such power so if you’re unlucky even a change may not help in reducing the initial slip.

[Dr.Naren]

Originally Posted by AMG Power

Man, just yesterday I saw your post on BMW 320d equaling power! Nice.

Thank you

1.The clutch has the highest load when you start off so a slip during starting off are typical early signs of wear.

2. Once you move, synchroniser rings (a quasi clutch) help reduce load on the main clutch so even if you redline there will be no slip.

This sounds very convincing.

3. The fact that it happened 15,000 Kim’s ago is an indication that you probably drive without too much stress on the clutch during normal driving.

Possible. I drive mostly on highways. There are many stock cars which needed clutch change at 40k kms, most of them driven in city traffic.

4. As the slip has started, be careful of 0-100 launches as that is when the maximum load will come on the car. It is best to replace the clutch early.

I didn't launch the car after the clutch started to slip. I tried it again today as I was curious to see the improvement post Garrett intercooler, but no luck .

5. Do Note that it could also be that the clutch is unable to handle such power so if you’re unlucky even a change may not help in reducing the initial slip.

Unlikely as the clutch was able to handle this before. Anyways to be on safer side, I will go ahead with the Sachs performance clutch.

[viXit]

At launch, that cracker of an engine is sending all that torque to the clutch.

Clutch assembly has two surfaces where rotational energy is transferred from one surface to another, The flywheel and the clutch plate. They grip to each other because of the frictional material on the clutch disk. The Flywheel is on the engine side, and the clutch disk on the gearbox side. The job of the pressure plate is to push the clutch disk onto the flywheel to help it stick and maintain grip.

Case 1 , Launch.
At the clutch, the angular momentum is higher on the engine side (Clutch disk), and nil at the gearbox side (pressure plate). Nil because the wheels are stationary and hence gearbox is too. So when you dump the clutch there is a very high difference in rotational inertia of both plates. Because one is stationary, and the other is rotating at a high rpm. It is likely that the frictional force is not enough to bring both sides to the same rpm immediately, especially when the load of entire mass of the stationary car is on the second plate. Hence the slip at launch.There is a great load on the system.

Case 2 , Redlining
The car is already rolling, so the pressure plate on the gearbox side is also rotating, now when the engine is redlined, the difference in rotational/angular momentum between both surfaces is within limits, and the grip between both surfaces is enough to transfer the torque without any slipping.

EDIT: Buy a new clutch, man

[abhi9044]

It could be a failing clutch. Slipping in the first gear is because the car is at rest when you dump the clutch. We all know that it takes energy to put a body in a different state of motion than its present state of motion. So when we start the car and dump the clutch altogether, it has to move a stationary car and that translates to greater power required to be transferred by the engine to the gearbox via the clutch. In general cases, stock clutches would take that much abuse, but with those massive torque figures along with the clutch being 77k kms old, I think your clutch is showing up its age.


Also, I don't know if I am right, but I think you should avoid dumping clutch till the time you get a new one, because, with a weak clutch, the synchronizer rings in the transmission would be taking the hit every time you will be doing a quick launch.


PS- I'm a great fan of your S-Cross and all the mods that you have performed on it.

[keroo1099]

Originally Posted by Dr.Naren

Thank you
Unlikely as the clutch was able to handle this before. Anyways to be on safer side, I will go ahead with the Sachs performance clutch.

Your clutch is on its way out. I had the same issue when I shoved a baleno 1.6 in my 1000 and enjoyed power launches, which was great for me but not so much for the poor car. I don't know if you can get a Centerforce clutch for the Scross, but that was the one that finally held up for me.

I'm amazed that your drive shafts have held up with all that extra torque.

Great mod.

[Dr.Naren]

Thanks for the valuable input guys

As I mentioned before this issue was noticed 15k km back and clutch is holding good under normal driving or redlining even now. I guess OE clutch is pretty strong, it's the same clutch used in 2.0 MJD SX4 / Sedici.

I wanted to rule out if it's something minor and could be easily fixed, looks like it's an early sign of failing clutch as you all have suggested