M201 Master Cylinder

[wc63-1944]

Hi Chaps, I wonder if someone out there can help please.

I was checking over the Hotchkiss today, oils, greasing, etc; On checking the brake fluid it was quite low. I topped it up to about 10mm -15mm bellow the top, replaced the cap and pushed down on the brake pedal and fluid leaked out of the breather. I took the cap off and lowered the level replaced the cap and tried again but the same thing happend. I then removed the cap and depressed the pedal again and a small fountain of fluid erupted from the cylinder.

Now the qestion is, is it normal for fluid to shoot up into the cylinder, I understand the fluid returns to the cylinder? and is the cap faulty, or is there a problem with the master cylinder? I took the jeep out about two weeks ago and the brakes were fine and there are no signs of any fluid leaks anywhere.

Any help/advice would be appreciated. Many thanks,

Chris.

[Jessie The Jeep]

Mine does exactly the same if that's any help! Just need to make sure you are slow on the pedal when bleeding the brakes and not to over fill it.

[Rangie]

Hi, so as you push down on the pedal, a fountain of fluid appears?

 

That sounds like the rear seal on the master cylinder piston has gone/is going. Typical system: a sprung-loaded plunger with a seal, running on/in the main piston (or a floating-sprung seal arrangement clipped onto the rear of the main piston plunger), that seals on the rear face of the M/C as the pedal is pressesed, locks a volume of fluid in the m/c chamber. This fluid is then pressed down the brake lines to actuate the brakes.

 

When the brake pedal is released, there is no force on the small rear seal, this allows the fluid to return to the reservoir of its own accord and under the small force of the brake pull-off springs at the wheel cylinders.

 

With fresh fluid in, gently/slowly pump the brake pedal. Have a look at the fluid, if there is black fluid appearing or a black swirl/trace of fluid from the intake hole in the bottom, the seal is disintegrating.

 

Worth a check, but thats what it sounds like to me.

 

Alec.

Edited June 8, 2010 by Rangie

[Jessie The Jeep]

Mine has done this since it was brand new if the pedal is released quickly. If the pedal is let out slowly, it doesn't blow back.

Edited June 8, 2010 by Jessie The Jeep

[wc63-1944]

Thanks for the replies chaps. Just noticed another thing, the fluid stops coming out the vent when the pedal is pessed a couple of times but then, when left for a minute and pressed again it bubbles out. Is this of any help? Thanks,

 

Chris.

[wc63-1944]

I have just been out to the garage again as I remembered buying a new master cylinder cap about 7 or 8 years ago. After rooting through several boxes I found it and fitted it, topped up the cylinder and there are no problems with fluid leaking out through the vent. I have looked at the vent on the old cap and wondered if it has been the problem, as the plasic cover seems quite loose, I wonder if the fluid has been getting round the back of the seal?

I shall of course keep an eye on things and see how it goes.

Thanks for all your help,

Chris.