-----Original Message----- Date: Thu, 21 Mar 2002 10:53:16 -0500 From: "Hansen, Ron" Subject: Clutch pedal pressure problem Noticed this morning the clutch pedal is acting weird. Initial contact point is almost at the floor, when pedal is released, it seems to hang up halfway, takes 1-2 sec for it to spring all the way out to normal resting position. After driving the car 30 min, contact point seems to be at the top of the pedal and distance required for engag/release is almost full distance of travel (full release clutch is engaged, pedal touching floor, clutch disengaged). Show just did work on MC and brake booster. Said new brake booster was initially leaking a little in the pedal area. Was this just spilt fluid from the install, or did they screw up something putting it in? Any idea what's causing the clutch pedal differences (wondering if they did something while doing the brake booster)? TIA, Ron rhansen@stk.com '82 928(s) '00 aprilia milleR-CF From: Dan [dbrindle@kondratyev.com] Sent: Friday, March 22, 2002 1:37 AM To: 928 Subject: [928] RE: Clutch pedal pressure problem Ron, Here is what is going on. The engine when it is hot heats the fluid causing it to expand. Normally the fluid backs up into the reservoir. When it cools it contracts and the fluid pulls back down from the reservoir into the system. Fluid being thicker than air it will not leak out of small holes, but air can leak in. So when the system cools instead of the fluid being sucked back down from the reservoir air get sucked in from an air leak. Thus when you go to start the car in the morning air has filled the system and you have a low pedal. As the fluid heats up it expands pushing the air out of the system through the same holes in came in through. If you bleed the system first thing in the morning it will work properly again, until the car sits over night and the cooling cycle sucks back in more air. The most likely culprit is the flex hose that runs from the Clutch Master to the Clutch Slave. Since you just had work done in this area it is possible the mechanics disturbed an old hose just enough to cause the problem. Not the mechanics fault since the hose is probably more than a coupe of days old and with German rubber hoses this is old enough. Since you are getting some fluid inside the car it is also possible the clutch master is shot. If the Brake Master was bleeding back through the push rod the fluid would show up on the garage floor and not inside the car since the brake booster is in between. The bad news is the clutch master is a pain to replace. The best and easiest way is to remove the brake master and brake booster to gain access. If you replace the clutch master be sure to replace the flex line to the clutch slave and the blue supply hose from the reservoir. If these parts are not bad when you start the job they will be in a short while. The good news is unless the clutch slave is leaking (most likely it isn't) then you can save by not replacing it. If later on down the line it does start to leak it is very accessible and easy to replace. Most shops will want to sell the complete system but you can save a few bucks by skipping the clutch slave. As much as I work on my car this is one job I am more than happy to leave to the professionals - but when you do be sure to get a fixed bid up front and not get talked into time and materials. Hope this helps Dan the Pod Guy Portia's Parts -----Original Message----- From: Dr. Bob [mailto:dr.bobf@worldnet.att.net] Sent: Saturday, March 23, 2002 2:12 PM To: 928 Subject: [928] re: Clutch pedal pressure problem Ron wrote to the list: > Noticed this morning the clutch pedal is > acting weird. Initial contact point is almost > at the floor, when pedal is released, it > seems to hang up halfway, takes 1-2 sec > for it to spring all the way out to normal > resting position. After driving the car 30 > min, contact point seems to be at the top > of the pedal and distance required for > engag/release is almost full distance of > travel (full release clutch is engaged, pedal > touching floor, clutch disengaged). Show > just did work on MC and brake booster. > Said new brake booster was initially leaking > a little in the pedal area. Was this just spilt > fluid from the install, or did they screw up > something putting it in? Any idea what's > causing the clutch pedal differences > (wondering if they did something while > doing the brake booster)? The car is an '82, but the cause is common to all years. In a nutshell, the problem is likely related to the length of the pushrod going to the clutch master cylinder. If the pedal or pushrod adjustment does not allow the piston in the master cylinder to retract completely with the pedal at rest position, the cup inside the cylinder does not retract past the bypass port. With that port still covered, there's now way for fluid from the reservoir to fill the front of the master cylinder. As another lister points out, the fluid grows as it warms up, eventuially making enough volume to release the clutch when the pedal is fully depressed. What to do: You can verify the dr's diagnosis by checking the pedal freeplay. From the top of the pedal stroke, you should be able to move the pedal slightly before the rod starts to press on the piston. There's also the part of the travel where the rod pushes on the piston prior to where the TO bearing actually presses on the release mechanism, so don't get them confused. If in fact the rod is too long, it is adjustable and should be shortened. Your mechanic/tech almost undoubtedly had the pedal assembly out for the booster replacement. Adjusting the position of the pedals after installation includes a check of the rest position clearance between the rod and the piston. It's easy to forget that the clutch master needs to be checked at that time. Another proof of the problem is to try to bleed the clutch circuit; with the bypass port covered, you won't get any fluid make-up after the first or second pedal press. Have you mechanic do this for you, since you will have no pedal at all until you can get fluid to flow into the cylinder again. As far as the fluid leak in the pedal area-- There is not supposed to be fluid at the back of the brake booster. However, there is fluid at the back of the clutch master cylinder if you pull the piston out with the housing installed, or if the rear cup on the cylinder is damaged. -------- Anybody having this work done: The clutch master cylinder is a snap to replace with the brake booster out. Do it. The infamous 'blue hose' needs to be replaced at the same time; It supplies fluid from the main reservoir at the top of the brake master cylinder, and is often damaged during the brake master cylinder removal process. Replacement is cheap insurance. Lastly, a reminder to flush the fluids in this system on a regular basis. Although it won't help directly with most booster failures, swapping out old fluid will reduce or eliminate hydraulic problems related to corrosion in the systems. If the booster failed, full of fluid sucked out the back of the brake master, corrosion due to moisture in the old fluid is a possible cause. 5-Speed cars need the clutch system flushed at the same time as the brake circuits are flushed. Good luck! dr bob