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bleeding clutch system


dehill
02-07-2004, 12:01 AM
I just replaced my clutch master cylinder (96 GST) and I'm a bit confused as to how to bleed the system. I filled the reservoir, put the pedal to the floor, opened the bleeder at the slave and closed when fluid flow slowed. I pulled the pedal up and put it back down (no pedal pressure whatsoever) and repeated this process several times. I still have no pedal pressure at all and I have not let the reservoir go dry at any time. Anybody know anything?

1qwik4
02-07-2004, 02:06 PM
Ok, I just did this two days ago. Have someone help you, you have to do this.

Fill the resovoir to the full line. Have a container half filled with the fluid you are filling it with. Attach a vacuum line from the slave cylinder bleed valve and put the other end into the half filled container of fluid. Now have someone push the clutch down and then open the valve when the clutch is still held down. Have your helper lift the clutch peddle back up by hand with the valve still open. When the peddle is up, close the valve and repeat the process. Do this about 3-4 times and make sure the resovior doesn't go empty otherwise you will have to start all over again. Hope this helps

kjewer1
02-08-2004, 06:56 AM
You have to close the bleeder before pulling the pedal up. Otherwise you are pulling air into the line. Unless you do the half bottle with the hose in it trick, in which case you are just moving the old dluid back and forth. :)

Heres the prcedure. I like to have 3 people when possible, one on the clutch pedal, one on the reservoir (to keep it full, never let it run dry), and me on the bleeder. bleeder open or close, put the pedal down to the floor. close bleeder, pedal up. Repeat. The level should drop a little each time if you do it right, noticeably after maybe 5 cycles. If the fluid wont start to move, pump the pedal 5-10 times before opening the bleeder. Sometimes this will "prime" the master. Also try to have the car level side to side. Dont jack up just one side. I learned the hard way that this car create an air lock, and you'll be bleeding for hours and not getting anywhere.

SO the key is only have the valve open with the pedal down or going down, and always closed coming up. Have fun :)

dehill
02-09-2004, 09:20 AM
Well, once I got some pressure on the pedal, I had a friend hold the pedal to the floor as I opened the bleeder. I closed it just before fluid flow stopped and repeated all of this 7 or 8 times. After the second or third time, there was no air coming out, just steady fluid. But, it still feels like their is air in the system. I'm suspecting there is an air pocket locked somewhere, even though I had the car jacked up level. I'm driving it for a few days to see if I can free that up and I will try bleeding again.

dehill
02-09-2004, 09:22 AM
oh yea, is there some reason for using the hose attached to the bleeder and submersed in brake fluid method other than to allow a one man bleed?

1qwik4
02-09-2004, 03:06 PM
The purpose of the hose submersed in the fluid is not for the purpose of the one man bleed. The purpose is that when the pedal comes up and the valve is open it doesn't suck in air, it sucks up fluid.

My way differs from that of 95 gsxracers, not saying either one is right or wrong its just different methods and I know mine works b/c I did it that way.

His way, I guess doesn't need the hose in the fluid. Depends on which way you decide to bleed it. Either way, you will need two people unless you bleed it through the slave cylinder by moving the rod in and out.

dehill
02-09-2004, 04:09 PM
The reason I ask is that I did it the way 95 gsxracers described, and I still have some air in the system somewhere, so I wasn't sure if some fluid backflow which occurs with the other method, is necessary to get all of the air out.

1qwik4
02-09-2004, 07:10 PM
IMO I would say that it is necessary otherwise it would feel like you have a mushy pedal. If you don't feel the mushy pedal, don't worry about it. I know once I drove mine for about 2 miles my pedal felt real firm.

kjewer1
02-10-2004, 08:32 AM
The only reason for the hose to be in fluid is so there isnt any air backtracking into the slave. You should never lift the pedal with the bleeder open. If you move the pedal up and down with the bleeder open the whole time, you are just pushing the fluid back and forth in the line, and not moving it anywhere. This is a very very simple hydraulic system. There have been dozens of times where I did clutch swaps and tranny swaps and no bleeding was required. So just because a method works a couple times doesnt mean its the right way to do it, or it works :) I always reserve the right to be wrong, and I dont know everything. But I have a pretty solid understanding of this type of hydraulic system, wether its a clutch or systems far more critical.

And dont rule out the fact that the adjustment rod may have to be adjusted. Its entirely possible to have a firm pedal, but the first 1/3 or so has no pressure. Screw the rod out, in effect making it longer. If it feels "normal" after this, chances are there is no air in the line. If it still feels mushy and not firm, its not the rod, and needs to be bled. Bleed with the rod still out (longer) to get more travel out of the master while bleeding. In my experience this can help in some cases. If you push that rod out too far, the master will not be able to fully retract and it will pump up. You'll feel this as you use the clutch, it will get firmer and firmer, or freeplay will become less and less. At some point it will be partially disengaged with the pedal all the way up, and your clutch will slip. Never drive any longer than you have to like this. Screw the rod back in just far enough to get rid of this issue.

It is also entirely possible that the pumping up affect may not be a result of the rod being too far out, but the upper clutch switch (used to deactivate cruise control, and used as an upper hard stop) needs adjustment. Screw that "in," or away from the clutch pedal to allow the pedal to come up higher and let the master bleed down after each use.

Also keep in mind that you want about an inch of freeplay. Use your favorite manual to the actual spec, but I like an inch. Most cases of a throw out bearing wearing prematurely can be explained by the freeplay being not enough, or the master pumpign up. This puts constant pressure on the TOB wearing it, the clutch plate, and the thrust bearing (crankwalk) whenever the motor is running. Always avoid this. All you 7 bolt guys should be going out to check this ;) And disconnect the clutch start switch while you are under there (the "lower" switch), but you didnt hear that from me. Be careful starting the car, always be in neutral and foot on the brake. Before long that will be just as natural as putting your foot on the clutch, and the brake will stop the car from starting in gear.

Its alos important to note that as you machine more and more material off a flywheel, and use stronger plates, some travel of the slave is lost. The clutch throwout fork can hit the side of the hole it comes through in the bellhousing before the clutch is fully disengaged. If you find this is happening, or you know the flywheel is getting thin (the firction surface is level with the body of the FW), shim out the ball stud the fork pivots on. Just remove it, and put a washer behind it. That will move the whole fork closer to the plate, getting you some travel back. Taboo makes a 1/4" longer slave rod, but I've never used one.

Rambling on a little bit, but the clutch hydraulic system is a simple but very widely misunderstood part of our cars.

dehill
02-10-2004, 05:24 PM
Thanks for the in-depth explanation 95 gsxracers. When bleeding, I never let fluid flow stop completely before closing, so air creeping back into the line was not possible. It's not that pedal feels mushy so much as it bites very low and is difficult to get in and out of gear, especially when cold. I didn't think of the adjustment rod possibly being off. I eyeballed it next to the old rod and assumed that should be close enough. I'll crank it out a couple of rotation and tighten the upper stop adjustment in the same.

Quick question though: what is the big advantage in starting the car with the clutch pedal not depressed (i.e. why disconnect the switch)? You're not the first person I've heard recommend that.

kjewer1
02-12-2004, 03:51 AM
Because of the location of the rods attachment point, a small change in length makes a bid difference in where it engages. So start small, one full turn at a time perhaps. Once i get it near where I want it I have used half turns in the past, its that sensitive. Just follow the guidelines above to be sure you are going to far to cover up another issue (pumping up).

I also do that, close it while the pedal is still moving.fluid is still flowing, but only on the last cycle. If you do that every time, more power to you. It can only help.

Starting the car with the clutch in puts the full force of the plate on the thrust bearing. The crank will grind against the thrust bearing for a good bit while you are cranking, with no oil between them. And we all know that excessive thrust bearing wear is also known as crankwalk :) I never start my car with the clutch in. That habbit has been transfer to pushing the brake pedal down instead. I havent had a motor CW since i disconnected that switch, but its not the magic cure either. SOmething that is certainly good to do if the safety risk is ok with you.

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