Clutch Hydralic Hose Built In Restrictor - ZR-1 Net Registry Forums

ZR1FUN · 01-10-2010

During my wandering around on the web I came across and article on this. It suggests the restrictor in the hose be drilled out to allow more fluid to return to the slave more quicly.

I have noticed what appeared to be cluch slipping after throwing a fast shift or two in my Z.

Has anyone heard about this and have they drilled out the restrictor?

Doug
ZR1FUN

Corvette Clutch Hydraulics Safety Fix

At some of the longer NCCC autocross events (basically time-trial length) there were several cars (C5 Z06's and C5 LS1's with 6 speeds) that experienced shifting problems from 2nd to 3rd and some, found that their clutch pedal stayed on the floor, and had to be lifted up with the toe of their foot. This is very unsafe when you are trying to reign in 350-405 HP at 80 MPH and possibly find yourself stuck in neutral.
Many of us thought we damaged our clutches or overheated the brake fluid. Evidently this is a common problem Corvettes (C4, C5, C6) caused by the clutch hydraulic fluid not being able to flow as fast as it should because of a restriction put in the tubing by the factory which is supposed to smooth out the clutch operation by causing some slippage, delaying the full engagement of the clutch. When you try and do quick (banging) multiple shifts in succession, the fluid can't return fast enough and the pedal falls to the floor. Normally in a low-speed autocross, we launch in 1st and leave it in 2nd, so we have not seen this before. In drag racing and long autocross (time-trial) courses, like the Colorado State Patrol track, this is when it appears. I was blaming myself for miss-shifts and Becky was freaking out over the pedal, losing a lot of her concentration. If you slow the shifts down then you will not see the problem, but when you are fighting for 10th's of a second, you will not tend to restrain your shifting. Some folks on the Corvette and Z06 forums have removed the clutch pedal spring (about a 30 sec job) which normally helps to push the pedal IN, therefore allowing the pedal to return.

Most have success by simply keeping their brake fluid clean by replacing it often. This is easy to do as the clutch hyraulics are self bleeding, and only takes a few minutes. Suck out the reservoir, add new Dot 3 or non-synthetic Dot 4 (like Motul 600) in your C5. The C6's use Dot 4 (GM part# 88958860 (US) 889012440) exclusively. Pump the clutch pedal 20-50 times, suck it out again, add more, pump pedal, and continue to repeat until the fluid is clean and clear. You may need up to 9 passes. Don't get the fluid on any of your painted parts. Here's the kit (Courtesy of Ranger on the Z06 Forum - Keep in a one-gallon Zip-lock bag) you need :

Brake fluid for the clutch
Sealed can for storing spent fluid
Syringe for withdrawing the fluid (MixMizer)
Cup filled with paper towels to house the syringe
Funnel for use in filling the reservoir

60cc Mix Mizer Oil Syringe
Autobarn $3.99 + $5.99 SH

Evidently the best and permanant fix is to drill out the offending orifice, with an 1/8" drill bit, in the end of the braided tube that connects the clutch master cylinder to the slave unit. The problem and procedure was originally published in Chevy High Performance Magazine and repeated below

01-10-2010

Great info and thanks for sharing. I would be curious to know what the ZF Doc thinks of this too.

tomtom72 · 01-11-2010

http://zr1netregistry.com/ZR1_issues.htm#26

This is the only issue that is a built in detriment from factory parts that I'm aware of with our C4 CHS. I saw that link over at CF and if you look at our clutch hose you will see that the formed metal ends are not restricted. The tubing diameter may not be very large 3/16" (?), but there is no reducer at the ends where the flairs exist. I have no idea what the inside diameter of the s/s braided portion of our hoses are, there could be a ID difference at that point in the hose? I never cut one open to look.

We do have a restriction built into the bung on the slave cylinder as the linked article indicates....however that issue is the least of your potential problems if you need to start replacing C4 CHS parts. Your bigger worry is getting parts that have good quality control! See the links below:

http://zr1netregistry.com/ZR1_mastercylinder.htm

http://zr1netregistry.com/clutchmaster.htm

http://zr1netregistry.com/ZR1_troubl....htm#clutchact

Tom

01-10-2010	#1
ZR1FUN Join Date: Sep 2006 Location: Olympia Posts: 161	Clutch Hydralic Hose Built In Restrictor During my wandering around on the web I came across and article on this. It suggests the restrictor in the hose be drilled out to allow more fluid to return to the slave more quicly. I have noticed what appeared to be cluch slipping after throwing a fast shift or two in my Z. Has anyone heard about this and have they drilled out the restrictor? Doug ZR1FUN Corvette Clutch Hydraulics Safety Fix At some of the longer NCCC autocross events (basically time-trial length) there were several cars (C5 Z06's and C5 LS1's with 6 speeds) that experienced shifting problems from 2nd to 3rd and some, found that their clutch pedal stayed on the floor, and had to be lifted up with the toe of their foot. This is very unsafe when you are trying to reign in 350-405 HP at 80 MPH and possibly find yourself stuck in neutral. Many of us thought we damaged our clutches or overheated the brake fluid. Evidently this is a common problem Corvettes (C4, C5, C6) caused by the clutch hydraulic fluid not being able to flow as fast as it should because of a restriction put in the tubing by the factory which is supposed to smooth out the clutch operation by causing some slippage, delaying the full engagement of the clutch. When you try and do quick (banging) multiple shifts in succession, the fluid can't return fast enough and the pedal falls to the floor. Normally in a low-speed autocross, we launch in 1st and leave it in 2nd, so we have not seen this before. In drag racing and long autocross (time-trial) courses, like the Colorado State Patrol track, this is when it appears. I was blaming myself for miss-shifts and Becky was freaking out over the pedal, losing a lot of her concentration. If you slow the shifts down then you will not see the problem, but when you are fighting for 10th's of a second, you will not tend to restrain your shifting. Some folks on the Corvette and Z06 forums have removed the clutch pedal spring (about a 30 sec job) which normally helps to push the pedal IN, therefore allowing the pedal to return. Most have success by simply keeping their brake fluid clean by replacing it often. This is easy to do as the clutch hyraulics are self bleeding, and only takes a few minutes. Suck out the reservoir, add new Dot 3 or non-synthetic Dot 4 (like Motul 600) in your C5. The C6's use Dot 4 (GM part# 88958860 (US) 889012440) exclusively. Pump the clutch pedal 20-50 times, suck it out again, add more, pump pedal, and continue to repeat until the fluid is clean and clear. You may need up to 9 passes. Don't get the fluid on any of your painted parts. Here's the kit (Courtesy of Ranger on the Z06 Forum - Keep in a one-gallon Zip-lock bag) you need : Brake fluid for the clutch Sealed can for storing spent fluid Syringe for withdrawing the fluid (MixMizer) Cup filled with paper towels to house the syringe Funnel for use in filling the reservoir 60cc Mix Mizer Oil Syringe Autobarn $3.99 + $5.99 SH Evidently the best and permanant fix is to drill out the offending orifice, with an 1/8" drill bit, in the end of the braided tube that connects the clutch master cylinder to the slave unit. The problem and procedure was originally published in Chevy High Performance Magazine and repeated below

01-11-2010	#3
tomtom72 Join Date: Dec 2004 Location: Jacksonville, FL USA Posts: 4,609	Re: Clutch Hydralic Hose Built In Restrictor http://zr1netregistry.com/ZR1_issues.htm#26 This is the only issue that is a built in detriment from factory parts that I'm aware of with our C4 CHS. I saw that link over at CF and if you look at our clutch hose you will see that the formed metal ends are not restricted. The tubing diameter may not be very large 3/16" (?), but there is no reducer at the ends where the flairs exist. I have no idea what the inside diameter of the s/s braided portion of our hoses are, there could be a ID difference at that point in the hose? I never cut one open to look. We do have a restriction built into the bung on the slave cylinder as the linked article indicates....however that issue is the least of your potential problems if you need to start replacing C4 CHS parts. Your bigger worry is getting parts that have good quality control! See the links below: http://zr1netregistry.com/ZR1_mastercylinder.htm http://zr1netregistry.com/clutchmaster.htm http://zr1netregistry.com/ZR1_troubl....htm#clutchact Tom __________________ 1990 ZR-1, Black/grey, #2233, stock. ZR-1 Net Reg Founding Member #316 & NCM member

01-10-2010	#2
HAWAIIZR-1 Guest Posts: n/a	Re: Clutch Hydralic Hose Built In Restrictor Great info and thanks for sharing. I would be curious to know what the ZF Doc thinks of this too.