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  • 1 Post By Aussie Mike
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  #1 (permalink)  
Old 11-04-2015, 11:29 PM
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Default What is wrong with my clutch?

Something weird going on....after driving it for the first few weeks and starting to fang it at the nationals, I noticed that the fluid has gone "dark". It is the same Penrite race fluid as in the brake reservoirs, from the pic below you can see the difference. Fluid in the brakes has not changed at all.

I contacted Tilton and asked them for any possible causes, the only thing they could think of is that there was excess rubber grease in the cylinder from manufacturing assembly and it has tainted the fluid.

I drained the fluid, replaced, and bled out all the old stuff, and within 50kms of mostly freeway driving, it has happened again. If it is rubber grease in there then it must be a large amount !?!?!?!?!

The bite point has moved up the pedal too as this has happened - after ditching the first load of coloured fluid the bite point was very near the floor as I would expect with a brand new clutch and fresh fluid, now after the 50kms it is higher up slightly. Also when changing the fluid there was one air bubble in there which came out first.

Obviously I will change it again, but any thoughts?

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Old 11-05-2015, 12:08 AM
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Optical illusion? Swap lids.... Just a punt.
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Old 11-05-2015, 12:21 AM
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Originally Posted by spookypt View Post
Optical illusion? Swap lids.... Just a punt.
hahah - very funny spook. The fluid came out plenty "dirty" when I changed it.
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Old 11-05-2015, 12:34 AM
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This is a common thing I've seen on LS engined cars. Commodores do it too.

I suspect it's to do with the design of the hydraulic throwout. Here's my theory:

Most cars with a clutch fork and slave cylinder have the slave on the outside of the bell housing. The cylinder bore of the slave is protected from the elements with a rubber boot over the pushrod.

The LS motor has a hydraulic throwout with a large ring shaped piston about 2" in diameter. There is no dust seal protecting it from the ingress of dirt and dust. There is also a lot of surface area on the sides of the piston and piston bore compared to a conventional slave cylinder. A lot more area for dust and dirt to collect. Each time that piston moves back and forth it tracks some of that dust and dirt back into the areas behind the piston seal. This discolors the fluid.

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Old 11-05-2015, 01:06 AM
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I would put it down to your flamboyant driving style
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Old 11-05-2015, 02:13 AM
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Quote:
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hahah - very funny spook. The fluid came out plenty "dirty" when I changed it.
I did suggest I made a better grid girl!!!
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Old 11-05-2015, 02:17 AM
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Originally Posted by Aussie Mike View Post
This is a common thing I've seen on LS engined cars. Commodores do it too.

I suspect it's to do with the design of the hydraulic throwout. Here's my theory:

Most cars with a clutch fork and slave cylinder have the slave on the outside of the bell housing. The cylinder bore of the slave is protected from the elements with a rubber boot over the pushrod.

The LS motor has a hydraulic throwout with a large ring shaped piston about 2" in diameter. There is no dust seal protecting it from the ingress of dirt and dust. There is also a lot of surface area on the sides of the piston and piston bore compared to a conventional slave cylinder. A lot more area for dust and dirt to collect. Each time that piston moves back and forth it tracks some of that dust and dirt back into the areas behind the piston seal. This discolors the fluid.

Cheers
that sounds logical enough Aussie, but I wouldn't think this would happen after a mere 50kms where 40km of it was freeway ?!?!?
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Old 11-05-2015, 02:17 AM
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Mike would that show evidence after only a short distance like that which Modena suggested? I'm curious now.....
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Old 11-05-2015, 02:20 AM
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I thought first that it is heat related. The cat is right under the cylinders although about 40cm below, and it gets mighty hot in there. The clutch line also passes somewhat near the headers but not really that close.

I plan to put another heat shield over the cat to keep the heat away. The clutch line is braided stainless.
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Old 11-05-2015, 02:26 AM
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some info here:
The Reason Your Clutch Fluid Turns Black - LS1TECH
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Old 11-05-2015, 02:43 AM
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Something to do with the Dark-side ?
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Old 11-05-2015, 03:16 AM
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The rubber grease in the slave cylinder they mention in that thread could be believable too.

I know mine had gone dark when I checked it after only a few miles.

It doesn't seem to affect it's performance.
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Old 11-05-2015, 03:49 AM
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Following Mike's first suggestion. I wonder if it takes some time for dust to accumulate in the bellhousing from an initial 'clean' build. Fluid from re-bleed is however quickly contaminated by the existing dust deposits in the bellhousing?

Can you flush out the bell housing next time you replace the fluid and see then how quickly it darkens.

Last edited by PeterAllen; 11-05-2015 at 03:51 AM..
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Old 11-05-2015, 12:26 PM
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Mine did the same thing followed by a Master Cylinder failure.

Masters are over my headers and the heat boiled out the fluid to the point oxidation took place. I was getting the rust from the failing cylinder.

Put in heat shield and replaced the unit.

Not sure if this is the same as yours.

Tru
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Old 11-05-2015, 04:08 PM
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I'm reluctant to think it's heat related in our cases. All 3 master cylinders are above the headers with no discoloration in the other two. The brake lines run down the foot box and past the headers too.
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Old 11-05-2015, 04:11 PM
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could it not be discolouration from the rubber lines going from the master to the slave cylinder ? just a though
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Old 11-05-2015, 04:39 PM
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Quote:
Originally Posted by deano59 View Post
could it not be discolouration from the rubber lines going from the master to the slave cylinder ? just a though
I run a braided Teflon line from the MC to the Clutch. I think Ben does too.
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Old 11-05-2015, 04:46 PM
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I don't have a clutch but my master cylinders are directly above the headers and the fluid doesn't discolor. It's not heat.
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Old 11-05-2015, 04:52 PM
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Personally I think you are worrying over nothing.
Next you will be chasing answers as to why the engine oil goes black so fast.

I have done 12000kls now and not changed the fluid, it is darker than the brake fluid (But I used a dark green colored fluid), it still operates perfectly well.
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Old 11-05-2015, 05:06 PM
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If the " Bite point" has changed this may indicate that MC piston is dragging on one side of MC bore. If pushrod from pedal is poorly aligned this will happen quite readily, followed by failure of the seal. Result is like scrubbing that old aluminium pot in the sink........goes black pretty quick.
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