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Slave Cylinder and clutch master cylinder replacement

Discussion in 'E30 (1984-1993)' started by Zdaneman, Sep 5, 2010.

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    Zdaneman

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    I need some advice from someone who's replaced a clutch slave cylinder.

    I've been reviewing the process of replacing the clutch slave cylinder and it doesn't look to difficult. However, it doesn't menton in the Bentleys Service Manual if you have to bleed the breaks too once you finish bleeding the clutch master cylinder and slave cylinder. The brake fluid reservoir supplies both systems.

    I'm thinking if you empty the brake reservoir, shouldn't you bleed the brakes too? I know the correct order to bleed the brakes and have done this several time before. I also have a good vaccumn pump to hand all the bleeding jobs?

    Also I read that you can prime the slave cylinder with fluid prior to installation. Is this necessary?


    Thanks for info in advance

    Zdaneman sends
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    MGarrison

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    Up to you if you want to bleed the brakes or not. The line to the clutch master feeds off the side of the reservoir - I wouldn't recommend letting the reservoir get empty in bleeding the clutch line(s), but even if you do, as long as you don't push the brake pedal and also refill the reservoir, I don't expect you'd get air into the brake master cyl. or brake lines.

    I don't know if priming the clutch slave or master is absolutely necessary, but you may find it quicker to bleed if you do. Every time I bleed my clutch slave and check the clutch pedal afterwards, the clutch pedal goes to the floor without returning - presumably it gets an air lock. One fix is to simply unbolt the clutch slave from the transmission, which lets the piston extend, and then immediately bolt back to the transmission. I've had a mechanic suggest reverse-bleeding the system (force brake fluid back through the slave bleed) for an air-lock, but I haven't tried that.

    Anyway, don't drop it back down to the ground without making sure it's operational first. Never push your clutch pedal without the slave bolted into place - the piston will pop right out of the slave and you'll need another new clutch slave cyl.

    Make sure you have an 11mm flare-nut for brake line fittings; you'll need an extension about as long or longer than the slave cyl. itself, and maybe a universal-joint flex adaptor or socket for accessing the upper slave cyl. nut. 13mm. Access isn't too difficult, just a bit of a nuisance. Get the car up in the air (carefully and safely, on jacks, on solid level ground), and if it's high enough to get under the car on a creeper then you should have enough room.
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    granthr

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    I have never had to unbolt a slave cylinder to get air out of it. You should be able to switch the fluid line from the old to the new without loosing too much fluid. Or rubber band a small bag tight against the hose. This will at least the fluid lose to a minimum. Once you get the new cylinder in place and start the bleeding process, if you find the clutch pedal to the floor problem, just pump the pedal a few times by hand. This is really all you should need to get the air. Worst case have a helper push the pedal to the floor and hold while you have the bleeder open. Then close the bleeder will they allow the pedal come to it normal resting place. It is very important that the bleeder is closed during the pedals stroke to it normal resting place!!! Otherwise you will suck more air into the system!!!
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    Zdaneman

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    Thanks

    Pretty much what I thought. Don't let the reservior go dry. Once I return from the ZRX 1100 bike rally in North Georgia I'll tackle this little issue.

    Again, thanks! Now for a spirited drive in the Mrs Z-4 down the blue ridge parkway!

    Zdaneman sends
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    MGarrison

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    I have some little rubber caps (for lack of a better description) that snug nicely over a brake line fitting. Handy for capping off the line and not having brake fluid dripping continuously. Couldn't tell you where I got 'em from, have had them too long. Presumably you could dig something up out of a hardware store or home depot.

    As for the pedal-stuck-to-the-floor/air-lock issue, perhaps attributable to using a vacuum bleeder. I never got the pedal to come up even pushing and pulling it back up by hand multiple times. I suspect if one uses a pressure bleeder when doing a full fluid change or doing it with one person cracking the bleed while another pushes the pedal, then there might be no air-lock. Seems to happen every time vacuum bleeding.
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    granthr

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    I use a pressure bleeder and have never had a problem. That could be the difference. :)
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    CRKrieger

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    Maybe you'd like to talk with my E28 friend, Trey, about the phone conversation we had on the Saturday before Oktoberfest. Seems he was using a pressure bleeder to change his fluid and noticed an awful lot of fluid disappearing - until he found it on the floor in front of his seat. He was in a panic. He thought he'd blown out his master cylinder and, on one sip of coffee, I went with that theory for a few minutes, discussing some of the plastic and rubber lines I remembered under there. Then, it finally dawned on me (It was damn near dawn, after all.), in spite of my undercaffeinated state, that there's no brake parts inside the cabin. It was the clutch master I was talking about. So I told him to check on that. Turns out he'd blown the clutch supply line off the master using the pressure bleeder. Problem solved for a lot less than the brake master cylinder he was about to run out and buy. From now on, as far as he's concerned, gravity works just fine.
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    granthr

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    That is good to know! I don't give it too much PSI 15 to 20 at max. Still pretty slow at those pressures.
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    Zdaneman

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    Ok, I did it! But????

    Replaced the slave cylinder last night and it wasn't too much of a pain in the arse. Top bolt was a little tricky and required several ratchet extensions/universal socket, but I got it. I also had to remove the tranny protection shield plate, (afte rmarket item). Seal on the slave cylinder was shot and leaking pretty bad. I also confimed travel and lubed it correctly IAW bentley manual. Clutch master cylinder is clean and dry. Bleeding was pretty simple.

    Initial drive last night was good to go, pedal pressure, ect, no leaks but not a real test to confirm it was fixed. I decided to drive her to work today in ugly DC traffic and really put it to the test using the clutch in stop and go traffic . Once I got her parked, I looked under the car and ........drip, drip! Not much, but needless to say it causes me concern! I popped the hood and fluid level was the same in the reservoir, no change, also none of the sensor lights were tripped on the dash.

    So.........I'm thiking this leak is possibly from the bell housing and is just previous fluid that has collected from the old cylinder? New slave cylinder is dry and clean? Is that possible? Any thoughts???

    Zdaneman sends
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    CRKrieger

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    Are you sure it's brake/clutch fluid? Could be oil.
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    Zdaneman

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    CRKrieger,

    It's not oil. What ever dripped this morning is for sure brake fluid. Nothing this evening, My guess is over the last 3 weeks the car leaked about 4 to 5 ozs of fluid till I got the opportunity to install a new slave cylinder. I wasn't driving it, except for moving it in and out of the garage. Its seems very likely this much could have leaked and collected into the lower section of the bell housing around the clutch and laid in the bottom portion.

    I'm really not sure what action to take next. However, there is no loss in fluid level in the reservoir since driving it today. No sensor lights kicking on either. I plan to drive it for the next few days and see what happens. I still feel this slight fluid loss this morning is from the previous leak since the area around the belhousing / transmission was pretty saturated.

    Zdaneman sends
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    granthr

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    I think you are on the right track. If the slave was leaking severely it is possible there is a fluid puddle in there somewhere. If you can wipe down the underside of the car where ever it is damp from brake fluid and watch those areas to see if it gets better.
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    MGarrison

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    spray down the reservoir, vacuum booster, clutch master, feed lines, slave cyl. etc. with a thorough amount of brake parts cleaner to get everything cleaned off and dry. Then look for your leak. Make sure the feed line off the reservoir isn't the culprit after the cleanup, and look for rusty metal brake lines as a possibility too. Let the brake parts cleaner evaporate before starting the car; too soon and you stand a chance of having it ignite.
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    Zdaneman

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    Ok, the delima continues good & bad

    I'm 99 percent sure I've got the slave cylinder fixed. No leaks no continued dripping and every thing looks dry. Clutch pressure is fine and it shifts great. No sensor lights flipping on or off and no loss of fluid anywhere. I may have spoken too soon on the oil leak. I think I've got a gasket seeping some where, maybe the oil pan, not really sure till I get it on the lift at Ft. Belvoir. Drips I'm seeing now are from the front of the motor at least 2 feet in front of the transmission. Not much just enough to know something is not right!

    Most of this issues may have resulted from letting a one of my wife's friends husband drive the car. I think he thought the checkered flag had been dropped and he was taking a drive around Indy. After two corners of rapid excelleration and shifting and drifting the car I put a stop to it and pulled him from behind the wheel. I drove the car from Tulsa to D.C. with no issues. Maybe the rought driving / abuse started the leak, either way I've got to find the leak. The odd thing, oil level is spot on and doesn't seem to be any lower after two day and you would think the level on the dip stick would revel something?

    The other thought is maybe its a bearing seal or maybe the transmission? But that doesn't see right since its in front of it?

    Thoughts gents?
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    CRKrieger

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    Quit obsessing. Wait until you're losing a measurable amount of oil. A few drips from a 20-odd-year-old car are nothing.
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    John in VA

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    It's not uncommon for M20s to have a small oil leak at the front on the passenger's side.
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    Zdaneman

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    Yeah, your right!

    But.......obsessing raises my stress level which assist in weight loss and early heart attack!

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