Weird Clutch Problem

Hello All,

basically I'm having a weird problem with my clutch.

Last year I did a clutch system refresh, this included:

new slave cylinder (Honda)
rebuilding master cylinder (Honda)
new reservoir hose
clutch damper bypass hose (as in straight from the slave to the hard-line)

you can see in detail in this post:
http://www.stanceworks.com/forums/showthread.php?86920-My-old-Honda-NA1-NSX&p=1547244#post1547244

I also replaced the pedal with the type r version and adjusted it as per @Kaz-kzukNA1 instructions.

So all was fine and dandy, worked as expected without any fuss for months before I put it away for winter.

I got the car out from its winter hibernation a month or so ago (goes away in September/October time) and take it for a spin.

Low and behold the clutch starts to slip.

Take it home, have a look and can see a tiny pin hole leak in the clutch line.

Fix that, bleed it up, and take it out again

This time its fine when its cold, the clutch holds no matter what I do. But when its warm, all the play goes out of the clutch and it starts to slip. This goes on until I can get no drive what so ever. I can get gears fine, even when changing faster in high load.

So I have a look online, find that Kaz had posted this:
http://www.nsxprime.com/forum/showt...eird-problem?p=1753619&viewfull=1#post1753619

So I have a go at adjusting the pedal again (to Kaz spec) and its better, but still not great. The same symptoms occur (pedal slowly looses its free play until the clutch starts spinning)

So I though maybe it was air still in the system (I have bled it multiple times at this point) so I gravity bled the clutch until I had gone through about half a litre of fluid. There is definitely no air in it.

Adjusted the pedal again to the same spec. Its a lot better, but still, eventually, the free play is lost in the pedal and it starts to slip.

So I'm kind of out of ideas. Unless I'm not adjusting the clutch properly I really don't know what's going on. I'm prepared to except the clutch might be knackered but its seems weird it was fine before winter, then its broke whilst sat still. Also, there is no slip whatsoever when its cold.

I'm also prepared to accept I might have rebuild the master cylinder incorrectly, but again, its weird that it worked perfectly for so long until I got it out this year for spring. There are no leaks or anything untoward visually.

The only thing I can think of is the pin hole leak managed to pull air in the system slowly over winter. Then when I came to drive it, the air caused the pedal adjustment to be out of spec. Then I've been chasing my tail ever since. Like I said, I might have it adjusted incorrectly, but its as per the service manual and kaz video (https://youtu.be/O_e1mc7Rjbc)

Any suggestions would be good.

I think Kaz pretty much described the problem. The problem you described emerges when things heat up. When the hydraulic fluid in the system heats up it expands. Normally it would expand back into the reservoir through the connection between the MC and the reservoir. If this path is blocked because the piston has not fully retracted (common cause is the clutch push rod / free play adjustment) then as the fluid expands it presses on the slave cylinder piston causing loss of clamping pressure on the clutch.

Is it possible that during the clutch bleeding / filling process when you fixed the pin hole leak, you got a foreign object into the clutch fluid and this has now become lodged in the port in the master cylinder restricting the flow of fluid back to the MC?

Is it possible that the seal on the piston in the MC is incorrectly positioned and is blocking the port (not even sure if this is remotely possible)?

Did you ever try the kick test that Kaz described?

As an observation, the clutch damper delete will make the problem worse. However, reinstalling the damper is not a fix because fluid should be free to return to the reservoir whenever the clutch pedal is not depressed.

If you have or have access to a pressurized bleeder system, you could try this test. I will admit that it is a bit fussy and difficult to set up. When the engine has heated up and the clutch problem has emerged, install the pressure bleeder on the clutch MC and pressurize the system, jack the car up and attach a hose to the slave bleed port and open it up. If no fluid flows out the bleed port, or you get weak flow then you know that something is blocking the connection between the MC and the reservoir. If you get good flow then there is no blockage between the reservoir and the MC (which means you should not have this problem) or you just flushed out whatever obstruction was present. As I noted, the procedure is difficult because it all has to be done while the system is still hot. In the absence of being able to do this, I think you need to remove the MC to check it. Since the clutch initially worked fine and the problem only emerged after you had the leak this spring, I am thinking that the problem has to be related to an obstruction showing up in the port in the MC. You might have had something in the reservoir or the connecting line and when the leak appeared it migrated to the port in the MC as fluid flowed to make up for the leak.

Old Guy said:

I think Kaz pretty much described the problem. The problem you described emerges when things heat up. When the hydraulic fluid in the system heats up it expands. Normally it would expand back into the reservoir through the connection between the MC and the reservoir. If this path is blocked because the piston has not fully retracted (common cause is the clutch push rod / free play adjustment) then as the fluid expands it presses on the slave cylinder piston causing loss of clamping pressure on the clutch.

Is it possible that during the clutch bleeding / filling process when you fixed the pin hole leak, you got a foreign object into the clutch fluid and this has now become lodged in the port in the master cylinder restricting the flow of fluid back to the MC?

Is it possible that the seal on the piston in the MC is incorrectly positioned and is blocking the port (not even sure if this is remotely possible)?

Did you ever try the kick test that Kaz described?

As an observation, the clutch damper delete will make the problem worse. However, reinstalling the damper is not a fix because fluid should be free to return to the reservoir whenever the clutch pedal is not depressed.

If you have or have access to a pressurized bleeder system, you could try this test. I will admit that it is a bit fussy and difficult to set up. When the engine has heated up and the clutch problem has emerged, install the pressure bleeder on the clutch MC and pressurize the system, jack the car up and attach a hose to the slave bleed port and open it up. If no fluid flows out the bleed port, or you get weak flow then you know that something is blocking the connection between the MC and the reservoir. If you get good flow then there is no blockage between the reservoir and the MC (which means you should not have this problem) or you just flushed out whatever obstruction was present. As I noted, the procedure is difficult because it all has to be done while the system is still hot. In the absence of being able to do this, I think you need to remove the MC to check it. Since the clutch initially worked fine and the problem only emerged after you had the leak this spring, I am thinking that the problem has to be related to an obstruction showing up in the port in the MC. You might have had something in the reservoir or the connecting line and when the leak appeared it migrated to the port in the MC as fluid flowed to make up for the leak.

Click to expand...

I did try the kick test but couldn't get it to work, although im fairly sure there was still air in the system at the point so maybe worth trying again

yeah that's a good idea, I never thought of that. Ill give that a try if I can rig up a decent cap that seals properly

Air in the hydraulic system is not your problem. Air is compressible, fluid is not compressible. If you had air in the system it would compress as the fluid heated up and you would not have the problem with the slave pushing on the clutch actuating fork. You would have the opposite problem, inability to get the clutch to release.

As an additional observation about my comments on using the pressure bleeder. Its not just an obstruction in the MC port that could cause the problem. If the MC piston isn't retracting sufficiently then this will also block the port. The test with the pressure bleeder will confirm that the port is or isn't blocked. It won't tell you what is blocking the port.

problem sounds like port is blocked ,this port is called a compensating port ,next time pedal loses play just crack the bleeder fitting on slave cylinder,if the play returns then remove m/c and check your rebuild . the fluid will actually squirt as if its under pressure which is a clear indication fluid can not return.

ralph cerbone said:

problem sounds like port is blocked ,this port is called a compensating port ,next time pedal loses play just crack the bleeder fitting on slave cylinder,if the play returns then remove m/c and check your rebuild . the fluid will actually squirt as if its under pressure which is a clear indication fluid can not return.

Click to expand...

yup I did that, and that's exactly how it reacted

I might just go ahead a buy a new one rather than stripping that one down again.

Old Guy said:

Air in the hydraulic system is not your problem. Air is compressible, fluid is not compressible. If you had air in the system it would compress as the fluid heated up and you would not have the problem with the slave pushing on the clutch actuating fork. You would have the opposite problem, inability to get the clutch to release.

As an additional observation about my comments on using the pressure bleeder. Its not just an obstruction in the MC port that could cause the problem. If the MC piston isn't retracting sufficiently then this will also block the port. The test with the pressure bleeder will confirm that the port is or isn't blocked. It won't tell you what is blocking the port.

Click to expand...

yes I understand that, my thought was however that air like everything else, expands under heat. If the air was the master cylinder side and unable to get to through the return port, then the expansion of such would create pressure on the pedal. But like you said, I wouldn't be able to get gears.

I hadn't thought about the piston return causing the problems so that's for that. I think I may well just replace it and see what happens rather than stripping down the one I've got.

cheers for all the help

hkz286 said:

yup I did that, and that's exactly how it reacted

I might just go ahead a buy a new one rather than stripping that one down again.

Click to expand...

Something to be said for experience , been doing this for along time {50 yrs}. Had a similar problem like this ,friend rebuilt his brake m/c ,i was able to view the seal blocking the port ,got another kit ,same problem . put in a new m/c ,no problem ,turns out the seal was not correct size . He did nothing wrong in his rebuild ,kit was defective .