Need advice on clutch failure please

[NSX2398]

So, my clutch 'failed' the other day and I'm looking for advice on what the problem might be. The car is a '91 with 191k miles and there's about 100k miles on the clutch but it hasn't been slipping and still pulls hard when it's engaged. I was turning a corner from a stop light and got on it a bit (maybe 5k rpm) and went to shift into second. The clutch just suddenly went to the floor .. very little resistance and although I was able to shift to second, it was quite hard to move the shifter. So, now I'm in problem diagnosis mode but continued on at about 30 mph for a few blocks with no issues and decided to turn into a shopping mall parking lot instead of gamble that I might stall at a light if the clutch wouldn't disengage.

So, I come to a stop with the clutch in and the motor running but having slid the shifter into neutral (not sure if I did this with the clutch's help or by brute force). But now I can't get it into any gear with clutch in and motor running. So, I shut the car off; shift into first; and try to start the car with the clutch in (not sure if that did anything) .. and it starts. But when I let the clutch out, the car doesn't move and the engine RPMs don't change. I was within blocks of home so we towed it home. I checked the clutch fluid reservoir and it seemed to be ok. No obvious leaking of hydraulic fluid in the driver footwell (which I gather is a sign of a leaking master cylinder). So, off to the dealer on a flatbed.

Based on several threads here lately, my first suspicion is either clutch master or slave (or both) or hydraulic linkage is gone. I know that there's probably not a lot left in the clutch but the high mileage is mostly highway and I never do any hard, clutch-slipping launches. Had the clutch imploded, I don't think I would have been able to drive it after it failed and there were no strange smells or noises. I did notice a slight audible chirp noise days earlier on a light load shift from second to third .. and duplicated it at constant road speed (no shifting) by just depressing the clutch and letting it out again. The thing that's a little odd is that I was able to start the car in gear with clutch depressed .. which I wouldn't have expected with a master/slave failure unless I don't understand how it works.

Current plan is clutch master/slave is on order and will likely be replaced later this week. No surprise with that mileage .. plus people are suggesting here that you do them both together. But I'm wondering what people's educated guesses are on whether this should fix things or not. Otherwise, the next step will be a new clutch and lots more $$. And I'll probably switch to aftermarket as I'm thinking of upping the HP next year.
Thoughts? Tks ...Ian

 

[JD Cross]

Ian
I think the car will start with the clutch pedal depressed regardless of whether the master, slave or clutch itself is working.
The safety switch is on the clutch pedal and as long as the switch is open (or closed, old guy will know) the starter circuit will work.

With 100 K miles on the clutch I'd say do the clutch, the master, and the slave and be done with it.
BTW I've never got even close to 100K miles on one of my clutches.

 

[davidf]

I agree with JD here. I also agree both clutch master and slave should be changed at the same time. Is the clutch master and slave original? If so you've been blessed. Do it all a enjoy another 100,000 miles.:wink:
You may want to replace that rear main seal too.

 

[Old Guy]

JD is correct. Pressing the clutch pedal down allows the clutch interlock switch to close which energize the starter cut relay which allows the starter motor to engage. Its all in the pedal action, doesn't matter whether the clutch is working or not.

My initial reaction was also dead / leaking hydraulics; however, the part where you get it into first gear, let the clutch out and nothing happens is a mystery. If the car was truly in first gear it should have moved forward when the engine started. A long time ago I drove a car home about 10 km with a failed clutch cable using that technique. If the engine is running and the transmission is really in first gear and its not moving, the clutch itself is broken or something happened to the release mechanism that is causing the clutch to hang up in the disengaged position (I have no clue as to how that might happen). If the pressure plate failed just as you pressed down on the pedal, that might have felt the same as a hydraulic failure; however, I would have thought that would have been accompanied by a fair amount of noise.

Short answer is that I am not so sure that it is a hydraulic problem. It should be relatively easy to confirm that by having the service tech watch the slave while somebody presses on the clutch pedal. If the slave actuates, the problem is probably not hydraulics. If the slave does not actuate, then it probably is a hydraulic problem. Even if the problem is non hydraulic, a new master and slave would not be wasted money if yours are original.

 

[NSX2398]

Tks for the comments guys. It's always good to have other opinions .. like or unlike your own. I'm happy to have some support with the theory that my master/slave is the issue. I hadn't thought of the clutch interlock switch angle .. although I'm not sure it sheds any light on why I was able to start the car when it was already in gear.

My simple understanding of how the clutch system operates is that when I step on the clutch, it compresses some hydraulic fluid which travels via a hose from the master to the slave where it is converted back to motion and moves the fork in the clutch housing which then disengages the clutch from the flywheel. So, if my master or slave seals have gone, I'm no longer able to develop enough pressure to move the fork and disengage the clutch. Yet if I have the shifter in first with clutch in and then start the car, presumably pressing the clutch in does nothing but close the interlock switch and the clutch should still be against the flywheel and the car should almost lurch ahead as it tries to start.

On the other hand, if the master/slave is fine but clutch itself suffered a catastrophic failure, then it would be consistent with me being able to start the car in gear but doesn't explain why the clutch pedal suddenly lost all resistance nor does it explain how I was able to continue to drive for 3 or 4 blocks at 30 mph or how come I couldn't shift gears with the engine running when I stopped. Also no unusual sounds or smells. It's that inconsistency between either of the two failure scenarios .. and the symptoms that I experienced, that I'm struggling with. Old Guy had an interesting 3rd possibility of the clutch hanging in an unengaged manner but if that were so, I shouldn't have been able to drive normally for 3 or 4 blocks until stopped .. I should have been immediately dead in the water.

And to answer some of the other questions .. to my knowledge, it's the original master/slave. First clutch (two owners) made it to about 90k miles; current clutch is a little over 100k miles (this is a US car). But part of the longevity explanation is that the first owner put about 80k miles on it, a large part of which (I was told) were highway miles. Likewise, my 100k+ mile contribution was probably over 80% highway as well which may explain things. However, on the flip side, the car has been in Canada for the last 15 years and I've put 25-30k winter miles on it at temperatures down to -40F which I presume isn't great for the seals.

Tks again for the comments.

 

[Albert86]

Crawl on your belly and look at where the clutch pedal goes to the master cylinder, look at the fire wall - do you see evidence of oil.
If so master is the issue - pretty common.

Mine went bad - but when it failed I could pump and pump to get it working.

I replaced both master, slave, and all hoses at the same time.
(It was one of my last drives of the season)

Hope your clutch it still with you,

 

[Old Guy]

I hadn't thought of the clutch interlock switch angle .. although I'm not sure it sheds any light on why I was able to start the car when it was already in gear.

• The clutch interlock switch operation just explains why the engine started with the clutch pedal pressed down. It doesn't explain any of the other mysteries.

My simple understanding of how the clutch system operates is that when I step on the clutch, it compresses some hydraulic fluid which travels via a hose from the master to the slave where it is converted back to motion and moves the fork in the clutch housing which then disengages the clutch from the flywheel. So, if my master or slave seals have gone, I'm no longer able to develop enough pressure to move the fork and disengage the clutch. Yet if I have the shifter in first with clutch in and then start the car, presumably pressing the clutch in does nothing but close the interlock switch and the clutch should still be against the flywheel and the car should almost lurch ahead as it tries to start.

• Pretty much correct. The clutch fork moves the release bearing back and forth on the transmission input shaft and the release bearing presses on the diaphragm spring in the pressure plate causing the spring to release its pressure on the clutch disc which is splined on to the transmission shaft. When the spring pressure is released (foot down on the pedal), the pressure plate and flywheel rotate as one and the clutch disc is free to stay stationary. To your final point, yes, if the spring/pressure plate is clamping the clutch disc, then the car should lurch forward. That is why I think that your pressure plate may have failed unless the transmission was not really in first gear or popped out of first gear just as you started because the teeth were not fully engaged.

On the other hand, if the master/slave is fine but clutch itself suffered a catastrophic failure, then it would be consistent with me being able to start the car in gear but doesn't explain why the clutch pedal suddenly lost all resistance nor does it explain how I was able to continue to drive for 3 or 4 blocks at 30 mph or how come I couldn't shift gears with the engine running when I stopped. Also no unusual sounds or smells. It's that inconsistency between either of the two failure scenarios .. and the symptoms that I experienced, that I'm struggling with. Old Guy had an interesting 3rd possibility of the clutch hanging in an unengaged manner but if that were so, I shouldn't have been able to drive normally for 3 or 4 blocks until stopped .. I should have been immediately dead in the water.

• The inconsistencies remain a mystery!

Final note - was the 2nd clutch still the original multi disc clutch arrangement? I am not particularly familiar with the NSX multi disc arrangement so there might be some oddity in its arrangement that could explain your problem.

 

[NSX2398]

Tks again for people's feedback. The car is currently at the dealer so I don't really have the ability to do any further diagnosis at this point. I did check the driver's footwell for leaks but not under the master cyl .. dumb on my part.

To answer Old Guy's question about the current clutch .. yes it's an OEM multi-disc unit and it was installed in about 2000 by Mark Basch who at the time was an experienced and well-respected independent NSX tech. I was planning to do some perf add-ons in the next year or two so if it truly is the clutch, I think I'll invest in something able to handle more HP although I'm a little leery as there have been some mixed reviews recently about what's on the market. Need to get doing my homework.

 

[NSX2398]

Just thought I should update this thread in case it comes up in someone's search results in the future. It's been about 3 weeks and I finally picked up the car today. Due to the high mileage on the car, we decided the first step would be to replace the clutch master & slave but unfortunately that didn't get rid of the problem. There were noises coming from the clutch so I decided to order an SOS 350 sport clutch as I may be doing some motor work in the next couple of years. SOS was initially out of stock on the 350 but more were on the way and I got one pretty quickly. Once the mechanic opened things up, there were a couple of seals that made sense to replace .. more delays but worthwhile doing. It turned out that one of the clutch discs had a metal fatigue failure which allowed one of the springs to 'escape' and cause minor damage as well as the noises. In the attached photo you can see where the metal broke and allowed the spring enclosure to open up. I want to point out that this clutch has about 105k (mostly highway) miles on it and still has a little life left had the spring enclosure not come apart. I'm no clutch expert but the mechanic said that this would definitely explain why I couldn't get it into gear. So, the good news is it's fixed; the bad news is the VISA account took a big hit .. but I can't really complain .. the clutch didn't owe me anything after 14 years and 105k miles.

 

[Old Guy]

That is not a failure that I would ever have expected. I would have expected a fair amount of noise (other than a slight chirp) and great potential for collateral damage when that spring dropped out of the disc. What is odd is that it is not obvious to me why the clutch would not release unless that spring got caught up in the release fork mechanism. Those springs are just damper springs and have nothing to do with the clamping or in this case unclamping force applied to the friction disc. Was the release fork or bearing damaged at all?

I hope you VISA card has rewards points!

 

[neuronbob]

That is one of the stranger clutch failures I've seen. Thank you for updating the thread and I definitely learned something today.

 

[NSX2398]

Was the release fork or bearing damaged at all?

Neither. When it happened, there were no odd noises from within the car and I drove about 5 blocks at about 40 kph before turning left and then right to enter a small shopping strip mall. As reported, I came to a stop in neutral and couldn't shift into any gear with clutch in. At this point I didn't have my door open (but probably should have) but no unusual noises in the car. However, after changing the master/slave unit, the mechanic said he could hear rattling noises (he was probably in the shop with the door open). You can sort of see some dings in the clutch picture but nothing severe. I left the rest of it at the dealership so can't comment on other damage but mechanic didn't mention any.

 

[FF Drifter]

NSX2398, glad to hear you got the problem resolved. I had the exact same symptoms and the same problem with my Acura Legend sedan actually. Sometimes I would go into gear easily, but usually it was a grinding and gnashing ordeal and it was inconsistent so we could not pin down the problem easily. Replaced the clutch master and the clutch slave with little to no improvement. Eventually we took the entire car apart and lo and behold, two springs in my clutch had somehow dislodged themselves. Really a weird failure, but interesting to look at. I've got my clutch sitting on a shelf now.

Hope this never happens to the NSX =(

 

[asylum]

The same happened to my clutch some years ago.

 

[Larry Bastanza]

This is a very typical NSX clutch failure. Seen over ten of these over the years....

Regards,
LarryB

 

[NSX2398]

The same happened to my clutch some years ago.

Wow, your clutch is a lot less rusty looking than mine. Maybe that's what I get for driving it in the winter. How many miles on yours?

Tks for the feedback on clutch experiences Larry.

On a more general note, I should give props to SOS for getting me the clutch so fast... plus they had their year end sale just when I needed it .. tks guys. As advertised, the sport 350 clutch is a heavier pedal feel .. which I'm sure would be a pain in LA stop & go traffic .. but I'm not minding it. The engagement starts earlier (might be an adjustment thing) so starts are a bit of an adventure until the muscle memory in my leg gets retrained.

 

[Old Guy]

The same happened to my clutch some years ago.

Based upon where the damper spring ended up, I could see that messing up the operation of the release mechanism.

- - - Updated - - -

This is a very typical NSX clutch failure. Seen over ten of these over the years....

Regards,
LarryB

Typical failure on just the early multi plate clutch design or are there similar problems with the later dual mass flywheel design? My recollection is that the dual mass design does not have damper springs in the friction disc like the more conventional clutch design; but, has a bunch of damper springs between the two flywheel masses. The upside is that it doesn't look like a broken spring could fall out on the dual mass design.

 

[Larry Bastanza]

Yes on the earlier twin disk. The single disk, as you mention has the springs in the flywheel. The only issue with the single disk clutch is you need to take a loan out for the replacement flywheel. List price on the single disk flywheel alone is $2757.35!!

Regards,
LarryB

 

[Old Guy]

The only issue with the single disk clutch is you need to take a loan out for the replacement flywheel. List price on the single disk flywheel alone is $2757.35!!

Regards,
LarryB

That would be over $3500 Cdn based upon where the $ is trading at right now. Excuse me while I run upstairs to grab a tissue to stop the nosebleed :smile: !!!!!

 

[docjohn]

one of my sachs comptech clutches also had a similar spring failure.....you think they would modify the construction...