Tom W

I had my first track outing in my '92 964 at Laguna Seca a couple weeks ago. Before I bought the car I had the PO fix the 3rd gear synchro. Well during day 2's driving fun I started to have problems shifting for 2nd to 3rd (in the corkscrew, of course) and this progressed to difficulty shifting from 3 to 2 or 3 to 4 (but not on all shifts). Sometimes it would shift fine/normally and sometimes it was like the clutch had not disengaged.

Well, I drove home without any problem and work got in the way of any further thought about the issue. However, last weekend I went to move the car and found that I couldn't shift it into gear from neutral. A bit of poking around and I found the pedal was stuck at about 1/2 height and not returning up the full travel. When I pulled it up all worked fine. This made me remember one time on the track when I had difficulty shifting and the pedal "popped" back up to my foot and then alll was fine.

What should I look for in trying to determine what is broken with my clutch? I know in the 993 the revised kinematic pedal could address an issue like this - is there a similar issue and fix for the 964?

Adrian

Dear Tom,
I would be checking your brake fluid level. You may have boiled your brake fluid. The hanging pedal is an indication of this. The difficulties you experienced on the track I bet are related to the brake fluid temperature.
This is the area I would look at as well as bleeding the clutch circuit.
The slave cylinder does not work well when it is overheated.
Ciao,
Adrian
964C4

Tom W

Thanks Adrian. And I believe your book includes the procedure to bleed the slave (at least I thought I saw it there)? This makes sense as I had bad fade at the end of day 1. I bled the brakes and that helped a lot but started to have the shifting problems on day 2.

If I bleed the slave and the problem persists, do you have a next step that I should investigate? Do I have to bleed the master too?

Jeff Curtis

Nope, bleed the slave cylinder at the transmission bellhousing, left side.

Get a sports bottle and some flexible tubing, preferrably clear...so you can see the fluid changing colors as you go from SH__ fluid to new.

As for problems thereafter, start with changing the slave cylinder, it is the least expensive of the two and lives in a horrible environment...read as: heat, oil, heat, road debris, heat...etc.

Get the picture?

Only item after that is the actual clutch master cylinder...it's a bit more expensive, and harder to changeout.

Get a new hose for the slave cylinder when/if you replace it...from memory, it cost about as much as the replacement slave cylinder ~$45 each??

Tom W

Jeff,

Thanks. I've got all I need to bleed it, I've just not done it before. It will be interesting to see if it's blue or not at the start of the bleed.

Adrian

Dear Tom,
I would just do the bleed and make sure the right fluid is used. The G50 and G64 transmissions do get stiff when they are hot.
I very much doubt you have a problem with the master cylinder. I know of one failure but that was fairly obvious the pedal was on the floor and there was brake fluid everywhere.
You might want to also consider some serious brake cooling. This reduces brake fluid temperature problems as well. Not just air channeling but some serious airflow over the brakes.
Ciao,
Adrian
964C4

Tom W

Adrian,

I'm looking at two approaches to cooling: (1) getting big reds so I have greater surface area and (2) ducting. The metal backing plates have already been removed.

The car already has the nearly useless air intakes instead of the fog lights, but lacks any ducting to deliver the air to the rotors. However, I'm a bit sceptical that I'd get that much air to the rotors with ducting though due to the limited clearance to route the ducts due to wide front tires. Hence the probable switch to big reds.

I was expecting better from the brakes as the fronts have been upgraded to 993 fronts (rear are supposedly 965 rears). The stopping power was much less than my 993, even when fitted with stock pads. I have a month or more before my next event and will, at a minimum, replace the pads on the car now. They did not perform well and created 3-5x more dust than stock pads.

tonytaylor

All this sounds horribly familiar; I was having persistant problems with the shift from 2nd to 3rd that got worse as the trackday went on. The problem was cured by bleeding the clutch slave and the gearchange was fine on the road but the problem re-appeared at the next trackday. I was getting about 140 track miles before the shift became truly awful. It would appear the problem was overheating of the clutch slave cylinder.
With hindsight the problem appeared at the same time as fitting MSPC which would work the brakes harder. The brakes , while getting hot, never faded on track ( big reds F and 965 R ) but after pulling into the paddock I often noticed the pedal had gone soft ( through not using the brakes and hence not pumping fluid through the slaves allowing the calipers to overheat the slaves), so the fluid was getting quite hot.
The end result of the poor shift and my subsequent abuse of the gearbox was a broken gear selector fork, so be careful when the shift is poor.
On dismantling the clutch the pressure plate was warped and 75% worn after 8k miles indicating the clutch had been getting a work out as well. ( clutch was an RS unit)
My new 993RS box has clutch cooling but shift quality does drop during a long dry day and the box doesnt want to leave neutral the day after but improves with use thereafter.
I don`t fancy the disc "air-scoops" as I`m sure I`ll knock them off on the kerbs and the foglight conversion is apparently useless, so is there any other way of gaining cooling?