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MG MGB Technical - Clutch hydraulics revisited...again

I've read through the archives, followed all the advice and still have a problem, so I thought I'd ask anyway.
Car is a 1974 CB roadster 4 speed

Just installed new clutch and seals due to a very leaky main oil seal that eventually soaked the clucth plate. Everything looked great until I decided to replace the clutch fluid. Bad decision.

I followed every bit of advice as far as bleeding the system, nothing worked to get rid of all the air. I filled it from below, filled it from above, took the slave off to put the nipple at the highest point, etc, etc. Everytime I thoought the air was all out, the clutch still felt mushy and would only move the slave pin about a quarter inch or so. I do not own an EZ Bleed.

The clutch hydraulics worked perfectly prior to all this, so my question is: is it possible to have somehow wrecked the seals in the master or slave cylinders such that they would allow air to enter the system (so that you can never remove all the air)? I saw no evidence of any fluid leaking anywhere as I attempted to bleed the thing. I believe these are the original hydraulics.

Also, I've read that rebuilding the clutch master cylinder is easy and recommended, but that you're better off replacing the slave with a complete new unit. True?

Many thanks,
Tony
Tony Grasso

Here are some areas to look at:

The flexible hydraulic line leading to the slave cylinder deteriorates on the inside and will flex with pressures and will clog up the slave cylinder with debris.

The seals in the master cylinder are easy to replace and the process provides a good look at the cylinder's condition. The replacement seal kit is cheap. I keep one in the trunk (slave kit too) along with fluid.

The slave cylinder can be rebuilt if it's still in good shape, but at $46 it's a good idea to change it out.

You have only one clutch hydraulic system and it's not fun when they fail on the road (always at night in the rain). At least with the brake duel brake system you can get home.

Good luck, Chuck



Chuck Hassler

I rebuilt both the slave and master, both were simple and successful despite some heavy corrosion in both. It seems sometimes on bleeding its impossible to get the mushyness. Have you tried simply pumping the crap out of it for a minute or two with the pedal, with the lid on, after bleeding it your best. I've had this work more than once, don't know why it works but it does.
Greg
Greg

Like Greg, "I rebuilt both the slave and master, both were simple and successful despite some heavy corrosion in both"

I bleed the clutch-system by letting it run by itself; open the nipple on the slave cilinder, let the fluid drip into a suitable cup, fill the mastercilinder as the fluidlevel drops.

It even worked as a roadside repair, I didn't fasten the slave-nipple properly after a clutch replacement...., I used fluid from the brake-mastercilinder-reservoir (in Holland a seperate, larger, see-through reservoir is compulsary so I had enough left for the brakes!)
Willem van der Veer

Some advice on clutch hydraulics: (I've got a 69B and just went through it myself)

Just got a slave rebuild kit and the piston cup was "flimsy" compared to the one in there to begin with. Had to take apart the newly rebuilt slave and swap back in the "old" piston cup - but the old cup was great and did not leak.

Regarding bleeding the system, if you have a little leak anywhere, it will suck air in and you won't be able to get rid of that air.

Check the union of the flex hose to the steel pipe (mounted on the inside of the fender, somewhere in the area below the coil). This has to be tight, and can be a trick to get just so - as tightening the flare connection you will find there is almost NO room to turn the wrench.

TO BLEED THE SYSTEM: What worked for me.....

Initial run-in of fluid: Open bleeder screw, step on pedal, close screw, let up pedal. Avoid the "harsh" bleeding procedure of tromping on the pedal repeatedly, holding the pedal down real tight, and then opening the screw under pressure - this might be OK towards the end, but to run the fluid in just doesn't seem to work.

TAP ON THE LINES - gently pump the pedal up/down, and tap the hydraulic line gently with a wrench - all the way from the master, down the line (including flex hose) to the slave. This will liberate any bubbles in the lines, and encourage them to accumulate in the slave cylinder.....pay special attention to the long vertical pipe on the firewall.

PS - anybody know where to drop off old brake fluid, let me know. I've got more than I know what to do with at this point - bleeding the brakes/clutch is not my idea of fun!!!!!!

MGB Girl

This thread was discussed between 26/09/2004 and 01/10/2004

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