RB25DET clutch issues

[the-31]

Hello All,

I'm trying to narrow down what my clutch issue may be, so here's some information about the car and setup.

I have an Aus delivered R31 Ti, its converted to RB25det box and Has either a clutch to suit the rb30 box/fly or rb25det box/fly, I can't recall as it's been in the while but it Is an Exedy 5 puck clutch.
R31
NSK-6797HDB
Heavy Duty Button Clutch Kit
Or
R33
NSK-7056HDB
Heavy Duty Button Clutch Kit
It has had a lot of abuse which is what the car was built for.

I had the car at a drag meet and all of a sudden it ended up becoming hard to select gears, now I'm trying to find the issue.

The master cydiner and slave are both rb30. Box is 25det as mentioned.

Fluid was abit mucky so I replaced and bled it.

The pedal was abit sloppy, a small plastic bush/shim that conect the pedel to the adjustable master cydlinder rod was shot and gave the pedal abit of play as the small pin (6-8mm) that's connects the two goes though a 10mm hole with a shot bush to pick up the slack. I made a new bush and also adjusted the pedal so it had more throw on the master cylinder.
When I release the clutch pedal I am moving the pedal abit before the clutch engages which tells me I'm getting enough travel out of the pedal?

Next was the push rod between the slave and the fork, with some help i had the clutch pedal pushed in I manually moved the fork to see how much more travel it had after the slave was fully engaged and it could move around another 10mm so i made a new push rod about 7mm longer which made the car shift into gear easily but under boost the clutch slipped.

Any other suggestions? Obviously I don't want to pull the box, do I just need a push rod 3.5mm longer than standard? Is it the diaphragm/fingers on the pressure plate?

Probably not important but the car is running a RB30DET with 350rwkw.

Thanks
Adrian

[GTSBoy]

  On 22/01/2020 at 12:09 AM, the-31 said:

do I just need a push rod 3.5mm longer than standard?

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That would never be the case.

It is either hydraulic (ie, master or slave bypassing), or the clutch has a mechanical problem.

[the-31]

  On 22/01/2020 at 12:48 AM, GTSBoy said:

That would never be the case.

It is either hydraulic (ie, master or slave bypassing), or the clutch has a mechanical problem.

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Is there any difference between 25 and 30 slave cylinders?

 

When i first did the conversion the orgnial/factory pushrod didn't suit so I made another one and that has worked for around 7 years. Untill my current issue.

 

I have no fluid leaking from slave or master.

 

As mentioned it still engages the clutch soild without slipping but not great when changing in any gears.

[GTSBoy]

  On 22/01/2020 at 3:50 AM, the-31 said:

Is there any difference between 25 and 30 slave cylinders?

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I don't know. Well, actually, if the RB30 slave is for the NA box, then probably yes, because that box is related to the RB20 boxes and they are definitely different to RB25. The RB30 turbo box is basically the same box as the RB25, and so there is a better chance that the slaves would be same-ish.

  On 22/01/2020 at 3:50 AM, the-31 said:

I have no fluid leaking from slave or master.

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Bypassing is an interval event.

 

  On 22/01/2020 at 3:50 AM, the-31 said:

 but not great when changing in any gears.

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Which tells you that it is not disengaging sufficiently. Which is either lack of hydraulic effect, or something broken at the clutch itself.

 

The reason that it slipped under power when you lengthened the rod was that you were always applying load onto the clutch release, which is a no-no and wears shit out real fast.

[the-31]

  On 22/01/2020 at 4:07 AM, GTSBoy said:

Which tells you that it is not disengaging sufficiently. Which is either lack of hydraulic effect, or something broken at the clutch itself.

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Once the hydrulics are at full stroke the fork doesn't move back in on it own as if there is fluid bypassing? 

[the-31]

  On 22/01/2020 at 4:07 AM, GTSBoy said:

The reason that it slipped under power when you lengthened the rod was that you were always applying load onto the clutch release, which is a no-no and wears shit out real fast.

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I under stand the slipping. 

 

Just don't understand how it's such a fine line between crunching gears and having traction or shifting smoothing but slipping clutch, with the length of the push rod. 

It could be something in the clutch itself but I hope not.

 

By the sounds of what information you have given the pushrod shouldn't affect it and should never have been changed?

 

[GTSBoy]

  On 22/01/2020 at 8:23 AM, the-31 said:

Once the hydrulics are at full stroke the fork doesn't move back in on it own as if there is fluid bypassing?

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No. Master and slave cylinders are pistons with seals. When the seals are f**ked, the hydraulic fluid is not all pushed along in front of the seal, it slips past the seal, reducing the hydraulic power.

  On 22/01/2020 at 8:28 AM, the-31 said:

It could be something in the clutch itself but I hope not.

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If it is not a hydraulic problem, then it is something mechanically f**ked in the clutch.

[the-31]

Well it seems to be stuffed. Pressure plate fingers look to be good, still meat on the clutch but it seems to have worn the pressure plate and the flywheel.

 

Any recommendations for a new clutch? Something cheap, drivable and capable of 350rwkw. IM not looking to push more out of the engine.

 

Thanks