Noisy Master Cylinder

Post by **mof** » Wed Nov 05, 2008 4:59 pm

I've bled brakes many times before, but seem to have lost the knack!

New wheel cylinders and shoes fitted after many months under a sheet.

Bled system until no bubbles present.

But

First pedal application drops to about 1 inch from boards. Subsequent pumps bring up the pedal resistance. Leave car for a couple of minutes and pressure is lost once more.

Master cylinder makes 'squishing' noise as you press the pedal. I don't remember hearing this before. Also, if you press the pedal with the filler cap off the cylinder you get a small fountain of fluid jumping up.

Wondering if the master cylinder seals are duff now.

Snail cam adjusters are only about one click from max and the shoes are brand new. I wonder if the drums are worn out?

Suddenly I'm not enjoying Minor ownership any more.

Help!

Post by **mike.perry** » Wed Nov 05, 2008 5:06 pm

You can try adjusting the push rod on the end of the master cylinder to see if that helps take out some free play. Not too much or the brakes won't release fully when you take your foot off the pedal.
Don't know about the squishing noise but the fluid squirt is ok. You should replace the filler cap when pumping the brakes

Post by **PSL184** » Wed Nov 05, 2008 5:30 pm

M/C is shot and needs replacing I'm afraid.... Also, drums sound like they have been previously skimmed past their best so these may need replacing also. At least parts are cheap !!!!

Post by **alex_holden** » Wed Nov 05, 2008 5:55 pm

^^^ I agree with PSL184. Old master cylinders often fail when you try to bleed the system because you're pushing the piston further than it normally goes. Probably not worth trying to change the seals - just get a new Lockheed one.

Post by **bmcecosse** » Wed Nov 05, 2008 7:40 pm

Hmmm - I would try adjusting the snails right up so the drums don't turn -and then bleed again. Wee fountain is ok! Don't worry about that. Start bleeding at the back nearside, then offside, then front nearside and finally front offside.

Post by **MGFmad** » Wed Nov 05, 2008 10:48 pm

Interesting comment about the shoe adjusters being near max with new shoes, mine are exactly the same - there is no wear ridge on the drums so would not be surprised if mine have been machined in the past!

I had a similar problem to you when fitting a complete new braking system including the m/c, pumping the pedal would bring up the pressure. After reading the forum suggestions I removed the rear drums and pumped the brakes to try and get the air to the top of the rear cylinders, then bled the rear cylinders again. Repeated this a few times until I got a good pedal. I am planning the do this again in a few days, just to be sure all the air is out.

Post by **bmcecosse** » Wed Nov 05, 2008 10:54 pm

Some shoes seem to 'catch' the snails and stop them turning long before they are at 'max'. Try turning them with the drum off and see if that's the case. A rub with a file removes the edge from the shoe where it can catch. Note there are also different 'snails' for 7" drums and 8" drums. I've not had any problems bleeding rear cylinders - but it's worth trying as MGF suggests!

Post by **mof** » Thu Nov 06, 2008 6:17 pm

Thanks folks. Some useful stuff to ponder. The bit about excessive travel on the master cylinder strikes a chord, as the squishy noise suddenly appeared half way through one of my many bleeding sessions. I think I'll just go for a new M/C and then re-bleed using your many suggested techniques.

Post by **bmcecosse** » Thu Nov 06, 2008 9:02 pm

You may not need a new master - try the various ideas first!

Post by **Dominic** » Thu Nov 06, 2008 10:53 pm

the squishy noise suddenly appeared half way through one of my many bleeding sessions

When I was bleeding my brakes after re-piping and new cylinders all round, I had the same "problem". It turned out that I had inadvertantly spilt some fluid inside the chassis leg, and the rubber boot was sucking fluid inside via the breather hole. A very squishy sound ensued for a while.

Post by **bmcecosse** » Thu Nov 06, 2008 10:56 pm

Well diagnosed Dominic!!

Post by **mof** » Thu Nov 27, 2008 9:06 am

Sadly no evidence of excess fluid round the rubber boot.

New m/cyl fitted and we flew through the MOT first time! Thanks to all

Post by **PSL184** » Thu Nov 27, 2008 9:16 am

Congrats

Post by **alex_holden** » Thu Nov 27, 2008 9:55 am

Glad you got it sorted.

Post by **rayofleamington** » Thu Nov 27, 2008 12:47 pm

Glad you got it sorted.
Just for reference a squishy noise will be air coming out of the m/c boot - they make noises if the breather is slightly clogged (with dirt/rust/fluid).
It does not mean M/C is shot, however it could well be!

Post by **MGFmad** » Thu Nov 27, 2008 9:05 pm

Best thing to do was fit a new MC - you don't want to take chances with that.