I had an interesting conversation with a SSCA race team crew chief yesterday about clutch fluid. Cliff Notes follow:
(1) Fluid in the clutch hydraulics falls prey to the same adverse issues (heat and water) as fluid in the brake hydraulics.
(2) Race team changes the clutch fluid at every opportunity, not less than daily, doing a full bleed, often involving several quarts.
(3) Changing the clutch fluid aggressively is part of the routine for the C5R/C6R.
(4) On street cars at normal operating temps, the clutch fluid in the actuator (slave) runs at no less than 230 degrees. Under launch and high rpm shifts, the friction involved produces fluid temps over 400 degrees. Not an issue for fresh fluid. But problematic is the fluid isn't fresh.
(5) The actuator (slave) is at the lowest point in the clutch hydraulics. Therefore it collects by-products spawned by heat and water. If those aren't flushed regularly, issues will follow.
(6) The clutch master cylinder cap is vented. When hot clutch fluid cools, air is drawn in and absorbed by the (brake) fluid. Black nasty clutch fluid is a sign of deterioration by heat compounded by corruption of water. Both combine to drop the boiling point of the fluid well below 400 degrees. The dirtier the fluid is the lower its boiling point.
(7) He said we are smart to keep the clutch fluid clean. He said my protocol will work for street cars. But obviously, full bleeds are the race-car routine.
(8) He said if the slave is full of debris, it takes many flushes to get it cleaned out. And sometimes it's just easier to replace the slave altogether.
Thought several of you might derive some encouragement from the above. There is hope for clearing up some issues if you work to clean up your clutch fluid.
I had an interesting conversation with a SSCA race team crew chief yesterday about clutch fluid. Cliff Notes follow:
(1) Fluid in the clutch hydraulics falls prey to the same adverse issues (heat and water) as fluid in the brake hydraulics.
(2) Race team changes the clutch fluid at every opportunity, not less than daily, doing a full bleed, often involving several quarts.
(3) Changing the clutch fluid aggressively is part of the routine for the C5R/C6R.
(4) On street cars at normal operating temps, the clutch fluid in the actuator (slave) runs at no less than 230 degrees. Under launch and high rpm shifts, the friction involved produces fluid temps over 400 degrees. Not an issue for fresh fluid. But problematic is the fluid isn't fresh.
(5) The actuator (slave) is at the lowest point in the clutch hydraulics. Therefore it collects by-products spawned by heat and water. If those aren't flushed regularly, issues will follow.
(6) The clutch master cylinder cap is vented. When hot clutch fluid cools, air is drawn in and absorbed by the (brake) fluid. Black nasty clutch fluid is a sign of deterioration by heat compounded by corruption of water. Both combine to drop the boiling point of the fluid well below 400 degrees. The dirtier the fluid is the lower its boiling point.
(7) He said we are smart to keep the clutch fluid clean. He said my protocol will work for street cars. But obviously, full bleeds are the race-car routine.
(8) He said if the slave is full of debris, it takes many flushes to get it cleaned out. And sometimes it's just easier to replace the slave altogether.
Ranger
This is very good info.
I'm not sure if the temps listed are more of educated guess, but I think everyone is in agreement that the fluid can get pretty darn hot in the slave cylinder -- and that can create problems.
As you indicated, the particulates are heavier than the fluid and because of this, settle down to the lowest point in the system. Therefore, it brings up the question of how to effectively purge all the debris.
The clutch fluid change protocol that has been outlined is easy to do and will remove particulates that are in suspension before they settle to the bottom of the slave cylinder.
As far as totally purging/bleeding the system, any ideas on what is involved?
I have been through 3 GM clutches and there is only ONE solution to the sticky clutch woes. LS7, LS6, LS1 clutches (Luk) all have the same problem, a pressure plate that is not good enough and ends up destroying the slave cylinder. The slave going bad is the result, not the cause of the problem. An aftermarket clutch along with new master and slave is the ONLY sure fire way to get rid of the problem. I've installed a remote bleeder, changed the fluid after every track day, etc, etc. and it is NOT the solution.
I highly recommend a Textralia clutch (though I'm sure sure it will work on an LS7).
I have been through 3 GM clutches and there is only ONE solution to the sticky clutch woes. LS7, LS6, LS1 clutches (Luk) all have the same problem, a pressure plate that is not good enough and ends up destroying the slave cylinder. The slave going bad is the result, not the cause of the problem. An aftermarket clutch along with new master and slave is the ONLY sure fire way to get rid of the problem. I've installed a remote bleeder, changed the fluid after every track day, etc, etc. and it is NOT the solution.
I highly recommend a Textralia clutch (though I'm sure sure it will work on an LS7).
Well...Since resollving to maintain clean clutch fluid my three Z06 have been totally free of pedal issues thru around 500 passes at the drag strip.
One of the benefits of an after market clutch is more clamping power that produces less heat from friction on launch and the shifts. That means less heat.
Might also point out that bout everyone uses the GM slave. Not aware of an aftermarket alternative.
You are correct, there is not an aftermarket alternative for the slave. Doug Rippie Motorsports will do a mod to a new slave or you can order it directly from them already modified.
I purchased a new GM master and didn't have any problems with the Textralia clutch. I believe McLeod or Cartek makes an adjustable master but I haven't tried it.
Quote:
Originally Posted by Ranger
Well...Since resollving to maintain clean clutch fluid my three Z06 have been totally free of pedal issues thru around 500 passes at the drag strip.
One of the benefits of an after market clutch is more clamping power that produces less heat from friction on launch and the shifts. That means less heat.
Might also point out that bout everyone uses the GM slave. Not aware of an aftermarket alternative.
13K trouble free miles. I change the fluid anytime at starts to change color.
Thanks Ranger
Tim
That's again for this tip last week on the clutch fluid. I will religiously follow Rangers regime in the matter. And thanks a ton Ranger...I read your posts all the time!!
that is weird, when WayneT changed his clutch fluid the one time he didnt need to then still looked brand new...maybe yall should stop slipping your clutches at the strip.
Ranger......Ok now I have a question. I just picked my car up from the dealers. Having normal service oil and filter.
I told them to change the clutch fluid and the check the axle nuts. I even printed a copy of the thread where you list the step by step info and gave it to the service guy to show the mechanic.
When I picked up the car the service guy gives me a bottle of GM Hydraulic Clutch Fluid to take home so I can do it myself in the future and save $$..no problem but when I look at the bottle it says DOT 3 #12345347 with friction Modifiers.
I told the service counter man why didn't you use DOT 4? He called the mechanic who had left for the holiday weekend and he said that the DOT 3 is what GM uses and recommends for the car.
What is the difference between DOT 3 and DOT 4? Why do you recommend 4 over the 3? If you could please explain, I would appreciate it.
Ranger......Ok now I have a question. I just picked my car up from the dealers. Having normal service oil and filter.
I told them to change the clutch fluid and the check the axle nuts. I even printed a copy of the thread where you list the step by step info and gave it to the service guy to show the mechanic.
When I picked up the car the service guy gives me a bottle of GM Hydraulic Clutch Fluid to take home so I can do it myself in the future and save $$..no problem but when I look at the bottle it says DOT 3 #12345347 with friction Modifiers.
I told the service counter man why didn't you use DOT 4? He called the mechanic who had left for the holiday weekend and he said that the DOT 3 is what GM uses and recommends for the car.
What is the difference between DOT 3 and DOT 4? Why do you recommend 4 over the 3? If you could please explain, I would appreciate it.
Thanks
Frank
Hi Frank,
Chevy specifies GM-Branded DOT4 for the C6 clutch. See the thumbnail of the owners manual.
The can of fluid they gave you is what's spec for the C5s.
Chevy change to DOT4 on the C6 due to recognition of heat issues with clutch fluid. Note they also heat-wrap the clutch hydraulic lines.
I image they charged you $100-125 for bleeding the clutch. Seems like they ought to redo it with the correct fluid. Question is will they (actually) redo it.....
I have been changing the clutch fluid every couple of days and have just about got it clear I bought my Z06 used with 9K miles, and they replaced the flywheel/clutch assembly per a TSB. It is funny to note that they never even bothered to change the clutch fluid
Since I have a new clutch I now have the fluid clean. I plan to change the fluid everytime I go to the strip and upon completion of same. Other wise It will be monthly, unless I notice it getting dark sooner. I use the GM Fluid, order several can's at a time.
Chevy specifies GM-Branded DOT4 for the C6 clutch. See the thumbnail of the owners manual.
The can of fluid they gave you is what's spec for the C5s.
Chevy change to DOT4 on the C6 due to recognition of heat issues with clutch fluid. Note they also heat-wrap the clutch hydraulic lines.
I image they charged you $100-125 for bleeding the clutch. Seems like they ought to redo it with the correct fluid. Question is will they (actually) redo it.....
Good luck; let us know how it turns out.
Ranger
Hi Ranger
So they used DOT 3 for C5's. I see the mistake they made.
Your right on target as far as what they charged $94.00. I think they will do it over at no charge they are nice to do business with. It was their mistake. I did bring in a copy of your to do list for them to follow...but I guess they haven't worked on many C6 Z06's.
I will copy your responce to me and bring it in and some dounuts I'm sure they will fix it.
It turns out that it's not just GM clutch hydraulics that produce pedal woes when the clutch fluid is allowed to degrade from the ravages of heat and moisture.
Have worked with some Infiniti G35 owners who are starting to affirm the cure of the fluid change protocols on their cars too. Here's one such report from an Infiniti board:
Quote:
Originally Posted by mal_TX
Ok after 4 days of driving my clutch has not acted up not one time since I did this. Previously it acted at least mushy no less than once a day.
Since the fluid change (using Ranger's method and prestone dot4), the pedal has been slightly stiffer, more linear, smoother and easier to control modulate. And most importantly, it hasn't stuck not once, nor has it changed in character at all, it always feels the same. The car is much more enjoyable to drive now!
Yay, two thumbs up, thanks a bunch Ranger. I recommend anyone unhappy with how the clutch feels to try this. :JAMIN:
Ranger
I changed my clutch fluid out and it was clear but within a day or so it was black again. Am I not getting enough fluid out during the flush? I did it four or five times, with the last two times both being clear but changing anyway. Is there a way to use vacuum at the reservoir so as to get all the fluid from the system? I know that I will have to force the pedal back up a couple of times if I do, but are there any other issues with using vacuum? How much fluid is in the rest of the system anyway?
Cheers
Randy
__________________
Randy Goss
2006 Z06, Velocity Yellow, LGM Long Tube Headers, G7X4 Heads and Cam Pkg, Exedy Twin Disc Clutch, KN Cold Air Intake, LG Ported TB, C5 Half shafts, LG Radiator, and tuning. 571.5 RWHP and 523.6 RWTQ
2002 Z06, Black on Black, LG Motorsports G7 SOLID ROLLER 427 C.I., 530 RWHP and 524 RWTQ on Motor Sold, sad to say.
Corvette Store
I'm sure they will fix it.
Same here on both
