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Clutch Slipping issue - need advice

Joined
7 May 2018
Messages
989
Location
San Jose
My car is a 99 with no engine mods. I've had it for 2+ years with no issues. I recently had new brake calipers (rebuilt) installed along with new hoses by a reputable shop. When I picked up the car, I noticed right away that the engine seemed to be louder at idle but didn't think too much of it. On the way home I noticed the clutch slip while I was on the freeway. This was my first experience ever of clutch slippage in any car. In 6th gear, if I'd step on the accelerator pedal quickly, the RPMs would go up quickly but the car stay about the same speed. Clearly the clutch was slipping. This happened a bunch of times on my way home and in different gears. Basically I would have to be very gentle on the gas to avoid any clutch slippage. The next day things went back to normal. 100% normal. The engine didn't sound loud at idle and I got no slippage. I even did some acceleration runs with no issues. A few weeks later I encounter some slippage again. I was just driving normally but when I try to accelerate on the freeway, the clutch would slip. Again, the next day it goes back to normal. Yesterday this happened again and I'm not sure what is going on.

My symptoms are very similar to this guy but he has a high powered engine and mine is stock.

http://www.nsxprime.com/forum/showthread.php/179052-Clutch-slipping-but-no-smell

Ever since I got the car, I felt the clutch grabs high. It feels like it only grabs at the last 25% or so of travel. I'm more used to BMWs which grab at about 50%. The car has the SOS 275 clutch with less than 20k miles.

Could the mechanic have gotten brake fluid or somehow contaminated the clutch disk/pads? I just don't know enough about clutches to know what to check.

Also, I did have the Clutch cylinder and slave replaced ~ 6 months ago. Everything was working fine literally until the day I had the brakes changed. I have a dash cam and I reviewed footage of the mechanic going for a test drive. He wasn't going crazy with the car or anything but someone not used to the clutch grabbing so high could possibly burn it out I guess. But there's no smell so I don't know.

Any advice on what I should check or adjust?
 
Yeah, sounds like the clutch is going and if you keep going it will be gone.

The variation in slippage is the rivets wearing down. You are likely gouging the plates.

If you pull the clutch now, you can either rebuild it or just replace the friction discs. Keep going and you'll need a whole new unit.
 
after 4 clutches I have learned not to question why....just make sure it lasts long enough to drive it to wherever it is going to be fixed...:redface:
 
Ive had a sachs clutch and Sos 275 go after less than 50k...but that was in my track days...the skid pad at VIR didn't help....:rolleyes:....had to coast on momentum into pits and had to get a flatbed to take to NEPA......that cost me $ a second clutch:frown:
 
Clutch grabs high on pedal: normal.
When you did the master/slave did you adjust the rod length? Did you check the play in the clutch pedal?
The clutch is done, pretty sure.
 
I doubt a mechanic could get brake fluid near the clutch, even if he tried. As long as the car isn’t dragging the brakes, the brake job didn’t cause the clutch to wear out. I think you would notice the brakes dragging.

One slight possibility would be a leaking rear main seal. It wouldn’t be related to the brake job either, but is something to check while you have the gearbox out. I had an Infiniti G-20 (se-20 engine) that leaked oil out the main especially at highway speed. It started slipping the clutch on long mountain climbs. But when I went to change the clutch, the flywheel was in great shape, just needed cleanup from the oil, a new main seal and a disc and all was as good as new!
 
I have no experience with the SoS CL but here in UK, with the OEM single disc dual mass flywheel CL, at least 3 owners experienced pre-mature slip at less than 20K miles.

On the other hand, there are many owners (both the OEM single and twin disc CL) covering well over 100K miles under similar as well as different driving conditions.

These 3 people were not the original owners so don't know the main cause.
Unlike Japan, there are not many places requiring the assist of parking brake while gently slipping the CL on launch in UK.
So, quite surprised when I first heard such short CL life.


From what you wrote, very unlikely but please check the pushrod freeplay at the CL pedal.

I posted this many years ago but going to just copy it here.

While the car is still cold, just check the free play.

Then, after you drove long enough to make everything warm/hot, carry out the same check again.

If you feel the free play was significantly reduced when hot, you found the part of the cause of your slip.
However, as you mentioned that the slip happened while on freeway where enough air flow would cool down the CL Hyd system, very unlikely to be the cause of the slip.



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Without the freeplay-[ A ], the feed port would be completely/partially blocked.

When the Hyd sys gets warm, the fluid expands but there is nowhere to go and thus, the slave cyl would be pushed out.

With the proper freeplay, the expanded fluid would escape to the reservoir.

Again, unless the release bearing is not moving smoothly and reducing the pressure plate force or something else,
sounds like the slip is genuine but at such low mileage.


Kaz
 
While the car is still cold, just check the free play.

Then, after you drove long enough to make everything warm/hot, carry out the same check again.

If you feel the free play was significantly reduced when hot, you found the part of the cause of your slip.
However, as you mentioned that the slip happened while on freeway where enough air flow would cool down the CL Hyd system, very unlikely to be the cause of the slip.

Kaz


Is this test done with the engine on or off?
 
is it normal to wear out the clutch so soon? I have > 150k and 220k on two original BMW clutches with no issues.

Several owners have reported shorter clutch life on the SOS versus the OEM twin disc. Not enough data for the NA2 cars, since there are so few out there. No chance of brake fluid on the clutch disc at all, since it is almost entirely encased by the clutch housing. Either your clutch is worn out or there is a problem in your hydraulic system.. As others mentioned, I would check the pedal free play first and make sure it is set correctly. I would also bleed the system again and make sure there are no air bubbles in the line. See if that fixes it. Much easier than pulling the trans.
 
If the clutch slips as described in high gear with no pedal engagement, it is not a hydraulic issue but a worn clutch. It is time to open it up and replace the clutch. I would also replace the master cylinder and slave (over 20 years old) and set pedal height as part of the process
 
Is this test done with the engine on or off?
No need running the engine as we are just looking at the pushrod freeplay.

Check it before starting the engine when everything is cold.

Compare it against my video above.
Mine has Type-R CL pedal and adjusted to minimise the mechanical freeplay so normal to see extra play on yours as per caption in the video.

Drive the car for a while to cook everything nicely.

On return, stop the engine and check the freeplay again while everything is hot.

But, as mentioned in my post, if it happened while on the freeway with lots of airflow to cool down, your slip could be genuine….
I hope not but....


Kaz
 
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So I brought the shop back to the shop and had them take it for a test drive / diagnosis. On the way there it was slipping on the freeway again. The tech took it for a spin then came back and made some adjustments and said I should be good now and that I didn't need a new clutch. I asked what he did and he said he basically adjusted the clutch engagement point. He said that the way it was set up previously was as if I was driving with my foot on the clutch slightly so it wasn't able to fully bite down. The clutch now grabs at about 50% of the way up while in the past I would say it grabs at about 75%. It feels way better and I couldn't get it to slip in any gear I tried. The grabbing point feels like my other cars now. It's been a couple of days now and still no issues so I assume my problem has been solved. Thanks!
 
Glad you got it solved! Adjusting the clutch engagement point. Is that done through the pushrod or did they have to adjust something on the actual clutch assembly?

I'm actually quite impressed Kaz was able to fit his hand, camera, and a ruler down there. I have barely enough space to fit my head under!
 
Glad you got it solved! Adjusting the clutch engagement point. Is that done through the pushrod or did they have to adjust something on the actual clutch assembly?

I'm actually quite impressed Kaz was able to fit his hand, camera, and a ruler down there. I have barely enough space to fit my head under!

Honestly I have no idea how he did it. But it took less than 10 minutes after he drove it back into the garage. I wasn't able to see what he was doing.

There's a bit more free play now. It probably dips 1/4 inch with very little pressure and then another 1/2 to 5/8 inch with more pressure like in Kaz's video. I would say before this it was closer to 1/8 inch with little pressure....never paid attention to the second step down.
 
The video in #17 shows pushrod free play which is one adjustment you can make, and you can also adjust free play by screwing in/out the clutch pedal switch and locknut on the pedal bracket which is easier IMO. Both accomplish the same goal which is placing the pedal (and by extension the master cylinder piston) in a resting position that is right before clutch disengagement begins.

When I installed a new master cyl and clutch kit, I left the factory pushrod adjustment alone and used the clutch switch to adjust free play. Kaz's video he posted was very helpful to illustrate how to measure free play, you should do it with just one finger and a metric ruler to feel the difference in resistance.

Too little free play (or zero/negative play) and the clutch might slip or partially disengage even with the pedal at resting position which sounds like your issue. This is what the tech meant by "resting your foot on the clutch slightly", essentially removing the needed free-play from the system. Basically just repeating what Kaz said in #8 . Naturally, applying the gas and producing more engine torque through the clutch assy is when you're most likely to experience slippage.

Too much free play and you'll have to press the pedal further to disengage/engage the clutch at all, and you might not be able to disengage it fully with the pedal all the way to the floor which can cause gear grinding and accelerated clutch wear.
 
From this i would assume that the more free play in the clutch pedal the lower the grab point would be right?
When I installed a new master cyl and clutch kit, I left the factory pushrod adjustment alone and used the clutch switch to adjust free play. Kaz's video he posted was very helpful to illustrate how to measure free play, you should do it with just one finger and a metric ruler to feel the difference in resistance.

Too little free play (or zero/negative play) and the clutch might slip or partially disengage even with the pedal at resting position which sounds like your issue. This is what the tech meant by "resting your foot on the clutch slightly", essentially removing the needed free-play from the system. Basically just repeating what Kaz said in #8 . Naturally, applying the gas and producing more engine torque through the clutch assy is when you're most likely to experience slippage.

Too much free play and you'll have to press the pedal further to disengage/engage the clutch at all, and you might not be able to disengage it fully with the pedal all the way to the floor which can cause gear grinding and accelerated clutch wear.

Thank you! ill be checking out if this would help lower my clutches engagement point
 
From this i would assume that the more free play in the clutch pedal the lower the grab point would be right?

Yes but I'm not sure how much it would really change with just another few mils of free play. I do know that changing the lever arm of the master cylinder rod on the clutch pedal (by using an NSX-R pedal or modifying the pedal to have a different rod/pin location) can lower the grab point, as well as deleting the clutch damper. I have both the R-spec pedal and damper delete and the grab point is nice and low.

I referenced this Kaz post http://www.nsxcb.co.uk/entry.php?430-Type-R-Header-Tank-Cover&goto=next and this one http://www.nsxcb.co.uk/entry.php?1653-Health-Check-Brake-OH-Koyo-Rad-etc-09. Unfortunately the R pedal is only for RHD cars but you could modify your own, I think there are some FB posts about it.
 
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