Clutch or Slave Cylinder?

[benm]

Car: 1995 R33 GTS-t (200rwkw)

Clutch: Daiken Exedy Organic Sports Clutch (~18mths old, ~25,000km)

Problem: Have to double-clutch to get in/out of gear (sometimes, see below)

Well this first came apparent to me whilst drag racing. Around 1 in 5 runs i'd have problems getting into 2nd gear and just thought it was me being an average driver whilst trying to give it my all. But since fitting Nitto Drag tyres the problem has become alot more obvious and common (atleast 1 in 2 runs). If I do a very small burnout (basically just scrape the water off the tyres) and then launch from 5,000rpm (dump the clutch) I can take off fine but when I go to change to 2nd gear i'd say 50% of the time I have to press the clutch 2-3x just to pull it out of gear and then another 2-3x to put it into gear with 2nd gear being the worst followed by 3rd gear. The clutch doesn't smell at all and I can't feel it slipping either and under the foot it still feels very heavy compared to a stock skyline clutch. If I do no burnout at all and launch from only 3,000rpm the problem is no where near as common.

At my last trackday (Oran Park) I'd do the main straight in 4th and the rest of the track in 3rd without any issues at all. But soon as I dropped back to 2nd gear for the last corner (coming up onto the straight) i'd be doing around 4,500-5,500rpm going through the corner and when trying to change into 3rd gear it would crunch again and i'd have to get off the power and double-clutch again. Soon as I went back to holding the last corner in 3rd gear the problem basically disappeared.

When just street driving in a casual manner the clutch is fine with the odd crunch (using 1yr old redline shockproof gear oil which probably would be worth changing).

I've ready some threads on here and from that I believe it's the slave cylinder (worn or too hot I don't know). But every mechanic I talk to (clutch specialist or otherwise) all say the same thing "not too sure what the problem is until I get the clutch out and look at it" which is an exspensive exercise if the clutch turns out to be fine. The problem seems to occur when either high rpm or high levels of heat??

I believe a new genuine nissan slave cylinder is around $100 + fitting.

Thoughts?

[Duncan]

actually Ben I think the problem might be your synchros instead.

Their job is to match the revs to the input shaft as you grab each gear, as they wear they can't get the job done in time. Wrong revs and no synchros mean it just won't engage the gear.

As you said, if you double declutch or try a few times it works, what is probably happening is that while you are trying you are off the accelerator, so the revs are falling to the right level...once they get there you can pull the gear.

If it is worn sycnhros you can try the good oil (redline, I think you already have it?) on downshifts make sure you blip the throttle up so the revs are higher and the synchros don't work as hard.

However, theres not much you can do about upshifts with worn synchros, the revs have to fall, and to give it time for that to happen you have to shift slowly and be off the gas. Not much use for drag racing I think.

If you can get it into gear from neutral at idle without a crunch, it is unlikely to be the clutch master or slave cylinders....you can have a look by getting someone to move the clutch and watching how far the fork/slave cylinder moves on the gearbox, it only needs to move a couple of cm.

[Cubes]

Get under the car and flick the rubber boot off the slave cylinder.

It should be perfectly dry inside the boot. If you are getting a little fluid inside the boot you are up for a reco'd or new slave cylinder.

Check the master cylinder isn't leaking fluid inside or outside the car.

Inside, reach up under the pedal box and follow the clutch pedal back to the firewall. Check the firewall clutch opening for any wetness.

Outside, look under the mastercylinder for any wetness or signs of paint damage.

If there are no leaks give the system a complete bleed, ensuring you bleed the little square box under the car. I had a similiar problem when I had a small airlock in the little box. I think the box is there to smooth out pedal feel or something. Unsure exactly.

[benm]

You know I was actually thinking that also Duncan until I read some other threads on here with the exact same problem (being fixed by a new slave)

Cubes, I might get my mechanic to do that

[benm]

Update...

Had a mechanic from UAS (new guy, didn't catch his name) take a look at it along with some other things and he bled the slave cylinder and adjusted the clutch pedal (outwards about an inch or more, it feels weird and slower to change gears until I get used to it I suppose).

The gearbox hasn't been notchy or crunched once when changing up/down in the 200km i've driven it since the adjustments. The clutch pedal is very stiff (gets softer all the way in past the friction point) it feels brand new and is very consistent.

I haven't tried any launches yet, still getting used to the pedal feel, it's like driving a different car altogether. Hopefully the problem just needed this simple adjustment