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Heavy clutch - how do I know if it's normal?

 
Old 10-30-2005, 12:54 PM
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Patrick L
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Default Heavy clutch - how do I know if it's normal?

I though my heavy clutch is due to a modified SPEC setup, but after reading some transmission articles recently, I started to think maybe something wrong inside that made the clutch so heavy.

I installed LWF with SPEC clutch kit (I believe it's modified from a 996 turbo/GT2 SACHS clutch) when I had my engine rebuilt (~1000km now). It feels very heavy that everyone tried my clutch said it's the heaviest they ever seen, included 965, 996, and Supra (600hp+) owners and also Porsche technicians.

What I read about heavy clutch are caused by either worn master or slave cylinder, or clutch cable. Also guide tube or some other problems.

My car runs fine in gears but it's hard to get into 1st gear and from 1st to 2nd. It can be done but need much more effort than other gears.

My question is, how do I know if the heavy pedal is normal, only because the pressure plate is modified to be heavy, or there is something wrong in the system? I just had brake / clutch fluid changed few weeks ago but made no difference.

If it's normal, I'll live with it, maybe more excerise or my legs... otherwise I would like to fix whatever gone wrong and make it easier to drive...

Thanks!
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Old 10-30-2005, 02:48 PM
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Patrick,

I am sure you have read this thread:

https://rennlist.com/forums/showthre...ferrerid=10545

I don't know whether my clutch was so heavy because of the pressure plate or wear in the parts or lack of lubrication. Its a hard call. You have the added benefit of at least knowing what setup was installed in your car. Mine was done by the previous owner so I can only guess.
You may be able to check with sachs and find specs on what the spring force on your model pressure plate is compared to the factory pressure plate and gauge from that where the problem lies.

If you find the info somewhere online I would appreciate it if you posted the link so I could check the numbers off my stuff as well.

I find it interesting you are having difficulty shifting gears, (usually a sympton of incomplete clutch disengagement) on a new setup. I have similar problems but I figured it was because of wear on the parts.

As you will read in the above thread my solution is going to be to restore the car to factory specs.

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Old 10-31-2005, 08:42 AM
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Kirk,

Thanks! I will do the flexible hose first to see what happened.
"Always starts from the cheapest one!"
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Old 10-31-2005, 08:24 PM
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Agreed.

I did slave cylinder, bleed, master cylinder, bleed, flexible hose, bleed.
I just wasnt lucky enough to have it fix my problem. Sigh!

I noticed in the thread someone mentioned lubricating the guide tube, spline etc. That might make the difference. Do you think the last shop might have assembled it dry? (Page 30-3 vol II workshop manual)

The correct porsche grease is #000 043 024 00 Olista Longtime 3EP, although I imagine any standard extreme pressure grease will be fine.

I would recommend a little heat on the flexible hose connection when trying to remove the old one. Mine was a real bear.

good luck,

Kirk
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Old 10-31-2005, 11:30 PM
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Originally Posted by KirkF
I noticed in the thread someone mentioned lubricating the guide tube, spline etc. That might make the difference. Do you think the last shop might have assembled it dry? (Page 30-3 vol II workshop manual)
After March 30, 1993 Porsche added a ribbed polyamide insert to the regular DMF-version release bearing and specified a dry install of the guide sleeve. I'm still waiting for more info on the OE genuine LWF version of the release bearing, the OEM Sachs version does not have the insert and needs to be greased.

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Old 11-01-2005, 12:57 AM
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Good point, it really depends on which release bearing is being used.

Looking at the spec clutch site:

http://www.specclutch.com/specMain.php

It might just be that a higher stage kit was installed. I was hoping they would include a little more info on the parts included, or possible the installation instructions online but it doesn't look like it.
(Maybe they should spend less effort on marketing their T-Shirts and more on providing detailed information!)

Do you know which kit was installed patrick?


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Old 11-01-2005, 06:34 AM
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My clutch is also heavy with only 10K miles on it so I think its normal.....
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Old 11-01-2005, 07:45 AM
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Kirk,
Not sure which kit I installed but I guess it's stage 1, according to the look of friction plate.

Christer,
Are you using SPEC as well?
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Old 11-01-2005, 07:53 AM
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Hi Patrick

No, I am not. And Imust confess to making a lame comment like the above purely to illustrate that this subject is sooo subjective that I don't think you can really ever resolve this sort of thing on the internet. You need to find some other 964 owners perhaps and compare physically with theirs...

Apologies for any confusion.
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Old 11-01-2005, 08:14 AM
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Christer,

Yes, your are right, it's very subjective. So I tried some other 964 and ask some people to try my car. All shows my clutch is HEAVY!
Actually it's heavier than my previous clutch, which was standard and worn to rivet. But since it's smooth, I guess it's normal. Anyway, I'll change the hose and see.
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Old 11-01-2005, 10:38 AM
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Just got the reply from SPEC:

The difference in the hydraulics will make the setup in the 964 feel different. Our pressure plate is 400psi stronger than the GT2/3 pressure plates. So I would expect it to be heavier for no other reason but that the 964 hydraulics were designed for a weaker setup. Keep me posted if it changes,.

Looks like it is supposed to be heavier...is 400psi on a clutch a lot? No idea on the scale...
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Old 11-01-2005, 02:12 PM
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I wish we could find a site that listed the PSI ratings of these different pressure plates. I searched for something on SACHS pressure plates yesterday but I couldn't find anything. I would like to look up the number from the one in my car and see what it is, and how it compares to the factory pressure plates supplied from SACHs. (Maybe it is factory with just a lightened flywheel.)

The higher pedal pressure does not explain your difficulty with 1st / 2nd gear shifting, which points towards the clutch not fully disengaging with the pedal in. (Or maybe just really worn synchro)

Do you notice the car trying to creep forward at all when stopped in 1st gear with the pedal in?


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Old 11-01-2005, 09:41 PM
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Kirk,

Car won't creep and there is no cruching nosie when engaging gears, so it didn't seem like clutch not fully disengaged. However, it's smooth when car is cold, and getting harder to engage when hot. Maybe shifting mechanism problem?
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Old 11-04-2005, 11:54 AM
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Kirk,

Asked local SACHS office about the clutch, the lady is very helpful and help me to get the clutch spring rate from Germany. The 996 turbo clutch I used has clamping force of diaphragm spring 14000N, and release pressure 4500N. Maybe you can try to ask on SACHS website, just give them part number. However, no idea how to compare 4500N or 14000N to SPEC's 400psi.....
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Old 11-04-2005, 08:06 PM
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Patrick,

I don't know how we would compare those numbers either.
14,000 Newtons is 3147 lbf (pound-force)
4,500 Newtons is 1011 lbf

I think to relate the PSI (lbs per square inch) given by SPEC we would have to know the total contact area on your clutch face??

I think this is becoming one of those questions where we shrug and slink away!


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