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MG MGB Technical - Bleeding Clutch System

Hello all,

Have a 71B that had a leaky clutch slave cylinder.

I replaced it (and the bloody hose!!!) and I can't get the thing bled. I've read the Haynes and all the stuff about bleeding from below by using an oil can to force the DOT4 up to the master from the bleed nipple but I still can't get it. Any suggestions as I've been doing this all day today and it is driving me mad.

Thank you.
Dave Latrell

Dave
Sign up and have a look in the archives of this Board loads in there to put you on the right track

Colin
C J Bryan

Dave, This may work. Fill the master cylinder, push the slave cylinder piston all the way into the cylinder and and open the bleeder, have an assistant push the clutch pedal down and close the bleeder. Pump the clutch pedal in and out a few times and let the car sit for several hours or overnight. Most clutches will self bleed if you give them enough time. Good luck, Clifton
Clifton Gordon

hmm...never heard of the backwards technique not working but that is interesting approach, Clifton. When you bled backwards did you start with completely empty system?

J.T. Bamford

JT, I had trouble getting the backwards technique to work a few months ago on an MGB. I had to open the bleeder, push in the slave piston and close the bleeder to get the clutch to work. I haven't really tried the self bleeding method but I know some people that have used it with good results. My son used it recently on a race car with hydraulic throwout bearing and it worked fine. FWIW, Clifton
Clifton Gordon

There has been a lot written in these archives about bleeding MG brakes and clutch systems but I must say that I have never had such a problem in these or other cars for that matter. I use the old basic method and don't have a problem. Unfortunately it is a two man/woman operation and only fails when for some reason my wife pumps the accelerator. I know there are other ways and I fancy trying Paul Hunt's method of connecting together the OSF brake nipple to the clutch one. I also have an eezi bleed but can't get on with it.

You only need a clean glass jar and a short length of clear plastic tube which will fight tightly over the nipple. Assuming that the system has no faults and this seems to be the case here, put a ring key over the nipple then attach the tube with the other end submerged in a little fluid in the jar. Top up the master cylinder then open the nipple 1/4 to 1/2 turn and ask the assistant to depress the pedal. Tighten the nipple and get asst to lift pedal. Open nipple and derpess pedal again repeating the operation until bubbles have ceased coming down the tube then a couple of extra pumps to be sure.

There are a couple of points to watch, the nipple must be closed as the pedal is lifted, the tube must be a tight fit on the nipple and it is not necessary to open the nipple more that the specified amount as any of these will result in air being drawn in, either past the tube or up the threads. In addition it is vital that the the fluid level in the master cyl is maintained otherwise air will be drawn in and it is back to square one.

I use silicon fluid in both my Bs and this method works fine here as well although it is best not to pump the pedal to forcefully as this tends to make the fluid aerate.
Iain MacKintosh

Iain,

Thank you for the excelent advise. Today, I'm putting a 51 TD back on the road after 25 years and a complete brake job. I find the EZ Bleed simple, especially that you can run a dry test on an empty system first to check for leaks. Just connect the ez bleed, and put a little soapy water on each connection. Air bubbles=leaks. That said, unfortunatly, the ez bleed will not fit the internal threads of the TD master cyl cap! Thus I will be using your method above as soon as I can round up a suitable victim, er assistant.

TDers--Moss salesman told me that they do not have an adapter for the ez bleed thus will be removing it from the TD catalog or writing a disclamer under the photo. In either case, it won't work. What might work is a spare MC cap with vent blocked, cap drilled and ez bleed conection installed. Might be a good addition to the club toolbox. fwiw

Paul
Paul Hanley

Dave,

To help get you started, I've also heard to remove the bleeder screw completely for the first couple of pumps until the fluid begins to flow. Use your finger to build the pressure, release to let fluid flow, then replace finger. Supposedly, doing this a couple of times will get the fluid moving faster. Then replace the bleeder and proceed to bleed as normal.

I personally haven't tried this method, however, it seems to make sense.

Just be sure to keep an eye on the fluid level as several others have mentioned.

Good Luck!

Mark
Mark Wasunyk

Sounds very messy to me and dangerous as it could get into your eyes. Nipple must be open ONLY as pedal is being depressed to ensure fluid can only go one route if it is open there is a risk of drawing fluid in. I just find the basic method very simple and foolproof.

I wish you luck Paul hope all goes well.

Iain
Iain MacKintosh

Dave,
I have just finished going through what you are facing. My approach was to finally remove the slave cylinder bolts and let it hang vertically. Next I used bailing wire to push the piston in as far as possible. This is where the air seems to collect. Now you can bleed the system with a hose attached to the bleed nipple and inserted into a jar of clean fluid using the two person method or an EZ Bleed. Ray
RAY

John Twist gave an impromptu demo in a parking lot some years ago:

2 person job. He was under the car:
-removed the bleeder screw
-he commanded "on", the assitant pushed and held the pedal to the floor.
-covered the opening with his thumb, commanded "off", assistant released the pedal.

Four or five reps, and it was done.
Phil Collura

I read of a procedure that eliminated the need for a second person and have found it to be quite effective. The key is to produce a "one way valve" by making a short slit in the neoprene tube near the 'open' end and then sealing this end with a tight fitting screw. When the brake pedal is pressed, the slit opens to release the fluid under pressure but closes to prevent any back flow. Usual advice re only opening the nipple a quarter turn, having the tube end in a container with sufficient fluid to cover the slit and also using a tight fitting tube since there is a small pressure built up in it when the pedal is pressed sufficient to open the slit. Open nipple, press pedal several times, close nipple, test for pedal firmness. Try it.

Barry
73B
B.J. Quartermaine

This thread was discussed between 09/10/2004 and 11/10/2004

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