Clutch Pedal Height question

[watchdogd]

I had both the Clutch master cylinder and slave cylinder replaced on an 2005 NSX and it seems the pedal is taller than before, but I am not sure if its because the old Master Cylinder hydraulics were starting to fail and the factory position should be higher as it is now. Ive had the car for about 7 months and put 4000 miles on it so I never knew what it was like with a new clutch cylinder.

The clutch engagement doesnt feel any different but when I let the pedal its definitely more "springy" and returns frimly but I sometimes bump the bottom of the steering wheel with my leg. I've always had the steering wheel rather low but never remember bumping. I did compare it to my s2000 which its clutch pedal is also higher than the brake pedal but its considerably old and has a bunch of free play.

One other thing i notice now is there is no real freeplay like other clutches. I've thought maybe the clutch was already going but before the new cylinder it had some freeplay in it.

So should the clutch pedal be higher than the brake pedal from the factory and can the height be adjusted without affecting engagement ? I figure I would ask here before bothering the shop again for something that isn't a problem.

Thanks,

 

[Old Guy]

There must be some free play in the clutch pedal. Unfortunately, the description of the pedal play values in the service manual is rather confusing. Probably the best thing to do is to check page 12-5 of the service manual which briefly describes setting the clutch pedal height. The service manual specifies the height of the pedal at rest as 176 mm (distance to the sloped part of the floor, not vertically). You adjust the clutch pushrod to obtain the correct 'at rest' height off the floor and everything else supposedly falls into place - because there is nothing else to adjust!

The service manual specifies the brake pedal height (vertically) differently from the way the clutch pedal height is specified so it is not possible to determine whether Honda intended the perceived heights to be the same or different.

 

[watchdogd]

Thanks for the input.

I just out driving again and noticed at around 7000 rpm the clutch slips and triggers a burning/plastic type smell. Whats funny is I had noticed an identical type smell months prior to having the cylinders replaced coming from the rear hatch by the driver side but couldn't find any leaks.

Update I found this thread which has a diagram.
http://www.nsxprime.com/forum/showthread.php/179052-Clutch-slipping-but-no-smell

I went ahead and loosened the Locknut A and and Clutch Pedal Switch A and adjusted the Switch out further. It feels like there is a very tiny amount of play now and it no longer slips. Even though I did nothing with LockNut B or C should I be ok or am I still potentially putting excessive wear on the clutch even though it engages and grabs as expected all the way up to red line?

 

[Honcho]

I would go through the whole pedal adjustment procedure so you can eliminate it as a potential issue. Make sure you take the rubber cover off of the pedal to do your pedal height and free play measurements.

I wonder if there is air left in the line? The slipping at 7000 seems to indicate the clutch is not fully disengaged when the pedal is up. In my mind, that could mean the piston in the slave cylinder is not retracting fully when you release the pedal. Might also be a bad/defective slave cylinder? One thing you could do is remove the rubber boot covering the clutch fork and watch the movement as someone presses and releases the clutch pedal.

 

[watchdogd]

When Looking at the diagram, If LockNut C is loosened for the push rod, is that simply for height or does it also affect engagement ?

For anyone who might be interested I include another link directly to the PDF.

https://beta.nsxshop.com/nsxb12004a-pdf/

 

[Old Guy]

I can't go out and look at my car to confirm this because it is now in winter storage; however, it seems to me that if you created some free pedal play by loosening locknut A and backing off the clutch switch, you may have just treated a symptom rather than fixing the problem. If hitting switch A is what is establishing the upper limit of pedal movement that is a serious problem.

I think you need to follow the advice of @Honcho and go through the adjustment procedure for the push-rod / locknut C to establish the correct distance C in the diagram then check your free play measurement. If nothing is bent and the MC was reinstalled correctly and the switch A adjustment is not really screwed up then you should end up with the correct free play. Once the distance C is set you go back and check the operation of switch A and adjust as described. Hopefully you don't need to mess with switch B because that is going to be a world of physical hurt adjusting that puppy!

@Honcho s comment about removing the rubber cover is interesting. Since the service manual was silent on that I had presumed that the measurement was with the pad in place. Because of the location of the pivot, if you adjust the pushrod to establish pedal height without the pad, the rod length will be longer than it would be with the pad. I think this just increases the 'risk' that you will have less free play if you use pedal height as the test. Of course, wear on the pad surface adds uncertainty to the height measurement. Also, given the curve on the pad surface the whole measurement thing is fraught with error. I find it slightly amusing that Honda specifies a pedal height of 176.2 mm. 0.2 mm implies a measurement accuracy of better that +/- 0.1 mm - as if! I think you are going to be lucky to get an accuracy of 176mm +/- 2 mm.

This link shows the NSX guru Kaz measuring free play.

http://www.nsxcb.co.uk/entry.php?1165-CL-Master-Cyl-Pushrod-Free-Play

Kaz appears to adjust the push rod to establish correct free play in which case the pedal height should fall out correctly. The link is good because it does explain the reason for the slightly confusing two values for free play in the later service manual.

Kaz's link alludes to this. If you do not have sufficient free play in the clutch pedal you may be blocking the free return of hydraulic fluid to the reservoir. As the clutch hydraulics heat up as the car is used the fluid in the system expands. If it can't escape back to the reservoir it will start to push on the slave cylinder piston leading to the potential for clutch slippage.

Given that you have experienced some clutch slippage I would be inclined to sort out the free play issue before you do any more driving. Since you are sort of new to the NSX, if you were not aware a clutch replacement using the dual mass OEM style clutch is rather mungo $$. Not a place you want to go if you don't have to.

 

[Old Guy]

When Looking at the diagram, If LockNut C is loosened for the push rod, is that simply for height or does it also affect engagement ?

For anyone who might be interested I include another link directly to the PDF.

https://beta.nsxshop.com/nsxb12004a-pdf/

Yes to both. If you adjust the free play it will affect clutch pedal height and vice versa. If you can accurately set pedal height the free play should come out correct. If you adjust the push rod to establish free play, the clutch pedal height should come out correct.

That said, the service manual specifies a range for acceptable free play; but, only one value for height. If you have an acceptable range for free play it seems to me that there has to be an acceptable range for height; but perhaps I am missing something. Perhaps the best way to do it is to use a pedal height measurement to get you in the correct initial range then check the free play as shown in the video from Kaz. If you lack free play then you need to shorten the push rod to establish the correct free play and accept what ever the pedal height is.

Free play is what is really important. Insufficient free play = clutch toast for breakfast.

All of this presumes that you have an OEM style clutch pedal mechanism in good condition. A worn pivot point or modified clutch pedal seriously messes up the measurement process.

 

[watchdogd]

Thanks for that video and detailed explanation, this is very helpful.

I think it makes sense that I only addressed the symptom and not the root of the problem.

Even though there is no more slip or burning smell I will adjust the push rod.

Is there a trick to easily loosening Locknut C. I was trying earlier to get a wrench on but was having difficulty getting the right angle.

 

[Speedmaster]

How fortuitous I ran across this new post!

I am about to (at least I am considering) replace my clutch master. I'd love to send it to my guru in Wisconsin but truck charges alone will be painful - so I will attempt this myself.

One thing I'd like to ask. If I setup the replacement MC exactly as the one coming out...wouldn't that suffice?

 

[Old Guy]

Is there a trick to easily loosening Locknut C. I was trying earlier to get a wrench on but was having difficulty getting the right angle.

I have seen the push rod; but, I have never had to actually adjust it. If the problem is getting an open end wrench to slip over the flats of the lock nut, there are different open end wrenches with different angle offsets on the head. I have some flare wrenches that have a different head angle compared to my regular Proto box-open wrenches and I have used them in tight spaces when I couldn't get the regular wrench on a nut. Unfortunately, I cannot advise on a particular brand / type that I know will fit in there.

 

[Old Guy]

One thing I'd like to ask. If I setup the replacement MC exactly as the one coming out...wouldn't that suffice?

Hypothetically - yes. I believe that the new MC comes with a new clevis attached to the push rod. If you count the number of turns that the clevis is threaded on to the push rod on your original and then apply the same turn count to the replacement, that should get you 'in the money'. If I were doing an MC replacement I would certainly try on that basis and then check the free play to confirm correct adjustment. Of course, if during the production run the length of the push rod got altered by a mm or two or the thread pitch got revised then that screws everything up.

 

[Speedmaster]

Hypothetically - yes. I believe that the new MC comes with a new clevis attached to the push rod. If you count the number of turns that the clevis is threaded on to the push rod on your original and then apply the same turn count to the replacement, that should get you 'in the money'. If I were doing an MC replacement I would certainly try on that basis and then check the free play to confirm correct adjustment. Of course, if during the production run the length of the push rod got altered by a mm or two or the thread pitch got revised then that screws everything up.

Thanks for the feedback Old Guy.

I watched Kaz's video and looked at the instructions on the pdf (next step, to break out the actual service manual)...but I am curious...when dealing with 1-5MM...that could be the difference in measuring with or without the carpet. So...I presume that all measurements are with carpet in and rubber pedal covers on.

BTW, I do get the occasional clutch slip even though my clutch is less than 10K old. I wonder if that was the culprit all along.

Now...I wonder if any of our discount parts houses offers Black Friday deals...ha ha.

 

[Old Guy]

Indeed, you identify an obvious problem. The pedal height measurement is an absolute measurement so if the pedal pad rubber is worn or if your carpet thickness and underlay are compressed relative to that of the factory fresh NSX that the measurements are based on, the measurement is unlikely to be correct (or what the service manual editors intended when they drafted the manual). However, the free play measurement is a relative measurement. You don't need the absolute reference of the floor location. All you are doing is measuring the pedal movement so it doesn't matter how thick the carpet is or whether the pedal pad is worn. If you can hold the tape measure steady and measure the high and low of the free play region you should have an accurate measurement.

Having thought about clutch pedal adjustment more in the last 24 hrs than in the total period of my NSX ownership, I probably would be inclined to base the clutch rod adjustment just on the basis of the free play measurement using the technique demonstrated by Kaz. Adjusting using the pedal height just seems to have too much uncertainty in it.

 

[watchdogd]

I assume if you were add too much play in the pedal it would it simply not return all the way causing other possible problem ?

Indeed, you identify an obvious problem. The pedal height measurement is an absolute measurement so if the pedal pad rubber is worn or if your carpet thickness and underlay are compressed relative to that of the factory fresh NSX that the measurements are based on, the measurement is unlikely to be correct (or what the service manual editors intended when they drafted the manual). However, the free play measurement is a relative measurement. You don't need the absolute reference of the floor location. All you are doing is measuring the pedal movement so it doesn't matter how thick the carpet is or whether the pedal pad is worn. If you can hold the tape measure steady and measure the high and low of the free play region you should have an accurate measurement.

Having thought about clutch pedal adjustment more in the last 24 hrs than in the total period of my NSX ownership, I probably would be inclined to base the clutch rod adjustment just on the basis of the free play measurement using the technique demonstrated by Kaz. Adjusting using the pedal height just seems to have too much uncertainty in it.

 

[Old Guy]

I assume if you were add too much play in the pedal it would it simply not return all the way causing other possible problem ?

There is an upper limit to the free play established by the full retraction point in the MC piston and the slop in the pedal linkage. Once you reach that point as you shorten the push rod you will start to lower the pedal height. There is a return assist spring on the pedal assembly that attempts to bring the pedal back to full height; but, once it reaches the limit on the MC piston travel and takes the 1-7 mm of mechanical slop out of the pedal mechanism it can't raise the pedal any higher. Get the push rod short enough and at some point it may not be possible to adjust switch A properly which will interfere with cruise control operation and the clutch signal to the ECU (idle control). Also, if you get the push rod short enough it may be possible that the pedal hits its limits (or you run out of leg length) before you get enough travel on the master cylinder piston to cause complete disengagement of the clutch. At that point shifts are going to be difficult or you may experience grinding during shifts.

If the pedal height is in the 175 - 180 mm range and the free play measures out as described in Kaz's video, you should be good to go (you may have to check the switch operation if you fiddled with the switches). If your carpet is particularly squished you might want to add 1 or 2 mm to that number. Just don't beat yourself up trying to get a pedal height at exactly 176.2 mm.

 

[Honcho]

I'm pretty sure it was LarryB who advised me to adjust free play/height with the pedal rubber off and the bare metal floor. Over 10 years ago at this point- memory is fading lol. But, it makes sense intuitively to me regardless. The rubber can wear down and the carpet can compress, so you would never have a uniform measurement across different NSXs. Makes sense to take them out of the equation.

 

[watchdogd]

Thanks to all the feedback, diagram and video, last night, I was able to adjust the push rod and it now makes an unbelievable amount of difference.

When there was no free play the pedal felt considerably harder to push and super springy. So adjusting from Locknut A by itself was not the correct solution at all. I moved it back a few threads from my original adjustment.

And as for the push rod adjustment, I do not know if I got exactly the amount, but based on the video its pretty close. If anything I went on the slight conservative side. Figure ill drive around for a few days to see if it continues to engage as expected.

Something strange that might be another benefit from this whole experience. For about 4 months I've noticed a slight burning plastic or belt type smell coming from the rear hatch on the drivers slide. No visible signs of leaks or smoke. It would usually be a little noticeable at a stop light or after coming back from the drive. I looked on the forums and saw a range of answers from Cam Plugs, Gaskets seals or Clutch. When the clutch slipped the other night, it was that exact same smell multiplied by 1000.

I no longer experience that smell even in the slightest amount at all now. I figure for the last 4 months even though I never experienced any slipping there was probably premature wear on the clutch maybe due to master or slave cylinder. So if anyone else experiences that type of smell it might be related to his/her clutch as well.

Thanks again to all the responses I would not have been able to figure this out otherwise. :smile:

 

[silver2002]

I experienced this myself - if there is inadequate free play, the pressure doesn't fully release from the slave, so the more you pump it, the more pressure is left on the slave.
The result is pressure on the clutch fingers when the foot is not on pedal. It will release overnight.
I didn't drive that hard to create slippage but i could hear the throw out bearing spinning in neutral, at idle.
That was the clue.