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Clutch issues, need some advice


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Hello. Having some 'fun' with this new setup on my 1995 S1.5 R33 GTST:

I have a brand new Exedy (extra extra heavy duty) 500kw single plate ceramic clutch kit, new aftermarket throw out bearing + holder, new Exedy spigot with all parts having only 750-1000km on them.

Today while driving I gave it a fairly hard (5000rpm or so) shift from first to second gear and now I can't disengage the clutch. Limped it home in second so the clutch is engaged, but can't get it to move gears whatsoever. Goes through all gears when engine is off.

It made no noise when the clutch stopped working- nothing went bang or made any odd sounds and drove it home fine in second gear.

I checked the pedal adjustment and it's as high as it'll go (most movement of pushrod on slave) and had someone push the pedal down while watching. The slave pushrod moved about 1.5 inches which is apparently the correct amount of movement.

Decided to try and bleed the clutch to rule that out, and now all of a sudden there is no pressure on the pedal- it just falls to the floor and stays there. Tried bleeding master and didn't do anything. A fair bit of air comes out of the slave when bleeding, but continues and gets no better- with no change in pedal.

What on earth is going on? The slave worked fine before opening the bleed valve, now the pushrod won't move, and still obviously can't disengage the clutch as I have a pedal that flops to the floor. Tried compressing and bleeding master 30 times or so with no change. Anyone got any idea what is causing this? Why did the slave suddenly stop, or was this the issue all along?

Cheers everyone! Sorry for the long one.

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 Have you checked the clutch pedal box is intact ?

They are notorious for breaking the spot welds.

Sometimes it can be hard to see as you've got to flip upside down in the foot well to see it !

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Possibly broken clutch fork pivot, or something just wrong with the clutch.

Anyway I think your box is coming out, as you are somehow not pressing on the clutch pressure plate to disengage.

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I think you may have massive air pockets in the damper (the loop next to the chassis rail). Do you have a hand vacuum pump? that might help get fluid down.

 

Or like the others mentioned, snapped pivot or snapped fork (can happen with super strong pressure plates).

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On 9/29/2021 at 4:51 AM, PLYNX said:

 Have you checked the clutch pedal box is intact ?

They are notorious for breaking the spot welds.

Sometimes it can be hard to see as you've got to flip upside down in the foot well to see it !

Thanks for the advice- hsve read about this issue but mine is good, works as it should.

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On 9/29/2021 at 6:08 AM, BK said:

Possibly broken clutch fork pivot, or something just wrong with the clutch.

Anyway I think your box is coming out, as you are somehow not pressing on the clutch pressure plate to disengage.

I sadly think this is the case too- based on how sudden it is. I've decided to buy a new OEM slave cylinder just in case but that all appeared to work. The second I opened the breather however it just never bled properly, so maybe a seal in it has gone suddenly. Unlikely but trying before box is out.

Any clue if I can check clutch pivot with a boreascope camera?

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On 29/09/2021 at 10:45 AM, CLEM0 said:

I sadly think this is the case too- based on how sudden it is. I've decided to buy a new OEM slave cylinder just in case but that all appeared to work. The second I opened the breather however it just never bled properly, so maybe a seal in it has gone suddenly. Unlikely but trying before box is out.

Look, you may have air in the system and your master (not slave) may be passing, but the fact you can see your slave rod moving that much points to something not pressing down on the clutch. This comes back to something like a bent clutch fork or broken fork pivot.

Another thing to check regarding air in the system while you're doing all this,  which has happened to me in the last 2 weeks, is if your booster has had its master cylinder dump clutch fluid into it. My master cylinder seals failed, passed fluid into the booster and got sucked into the engine via the booster vacuum line. It won't be why your not disengaging, but can explain air in the system as slave cylinders very rarely fail.

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On 9/29/2021 at 9:43 AM, BK said:

Look, you may have air in the system and your master (not slave) may be passing, but the fact you can see your slave rod moving that much points to something not pressing down on the clutch. This comes back to something like a bent clutch fork or broken fork pivot.

Another thing to check regarding air in the system while you're doing all this,  which has happened to me in the last 2 weeks, is if your booster has had its master cylinder dump clutch fluid into it. My master cylinder seals failed, passed fluid into the booster and got sucked into the engine via the booster vacuum line. It won't be why your not disengaging, but can explain air in the system as slave cylinders very rarely fail.

I believed it may be the slave- it does move but apparently it must move almost the whole way, which it didn't seem to. It was close- but it could be 1-2mm off and that might be all it takes.

If it was the clutch pivot, or even fork for that matter, wouldn't it lose all feeling immediately, as it requires those parts to even move the pedal? Not after opening the slave bleeder? It felt totally normal and made no sounds until I opened the slave cylinder valve.

I suppose this doesn't rule out throw out bearing- I will get a camera in there today and update. Cheers.

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On 9/29/2021 at 2:30 PM, BK said:

For your sake I hope it is the slave, but it is very unlikely.

How'd you go with your mangled crank keyway issue ?

I have strong doubt it's the slave too- but for $100 worth a shot. Otherwise tow car then box out. Beginning to hate this car more than I love it haha. 6 weeks on road, 10+ Months off it since ownership. Expensive too...

As for the mangled keyway, bought a used crank, did new ACL race series bearings, oil pump collar, custom single keyway mod, and a ross balancer. Nissan balancers are not made properly and shred the keyways, regardless of bolt torque. It's a design/tolerance fault and I confirmed it by using a micrometer, as well as several OEM balancers- new and used. They never fit properly snug, and rely on bolt tension instead of interference fit! I can't even begin to imagine how many RB series engines are currently driving around with shredded crank snouts as a result- probably a tonne.

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Not just oem. I have shredded a keyway with a Ross balancer and Nitto billet crankshaft before - Bolt came loose eventually from crushing the crank washers, and that was at tension to 460nm.

The balancer is not supposed to rely on the key for any sort of load really as that is the bolts job.

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On 30/09/2021 at 5:19 PM, Dose Pipe Sutututu said:

Since you're changing the slave and rebleeding the entire system - might as well piss off that clutch loop line/damper.

That should be a given really.

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You may have split the clutch fork arm at the pivot ball area  happened to mine when i first upgraded to a higher rated pressure plate. Replaced it with an aftermarket fork arm and pivot ball pin.

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On 30/09/2021 at 10:43 PM, Dasmbo said:

You may have split the clutch fork arm at the pivot ball area  happened to mine when i first upgraded to a higher rated pressure plate. Replaced it with an aftermarket fork arm and pivot ball pin.

Definitely possible too and will have the same effect as snapping the pivot. Did you actually go aftermarket for the fork ? The more common 350z cd009 cast fork with a chromoly pivot is generally the fix for this. 

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On 30/09/2021 at 5:49 PM, Dose Pipe Sutututu said:

Since you're changing the slave and rebleeding the entire system - might as well piss off that clutch loop line/damper.

This should be a compulsory mod.

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