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MG MGB Technical - Caliper Bleed Screws Clogged?

Tried to drain the brake master cylinder today on a 69 B and could not get fluid out of either front caliper bleed screw. The rear was no problem. I was using a mity-vac as I had already disconnected the pedals. I assume that they are somehow clogged so my question is how to unclog so that I can bleed when a new mc is installed?

Could this blockage have somehow caused a brand new mc to leak from the main seal? This will be the third new mc put in this car in 4 years. The first was rebuilt and the second was new.

Advice and opinions appreciated.
Warren
wwp

Warren,

I have had this problem on many types of cars. These all incorporate a small ball bearing in the bleeder. Some systems do not, but just have a tapered bleeder screw. Where this ball bearing is used, it sticks in position when the bleeder screw is loosened.
I always loosen one bleeder and then give the brakes full load, then close off and do another one.
As you have removed your pedals, can you apply high pressure air to the brake line?
The bleeder screw should be fitted loosely in case a ball bearing comes out at high speed.
A blocked brake bleeder should not affect the master cylinder in any way.

Mick
M F Anderson

Warren. I just checked the size for another post. The bleed screw is a 3/8"-24 UNF thread. It has a tapered end which seals the hole in the caliper, hence, no ball bearings or other interface. The bleed screw can be removed, in your situation, and a fine wire inserted to clean out the hole. Also check the two holes in the side of the bleed screw and above the tapered area. They are what allows the brake fluid to vent through the hollow stem of the upper part of the bleed nipple. It would require a great deal of pressure on the brake pedal to cause a problem with the seals in the master cylinder. On a properly set up car, you can lock the brakes without damage to the MC. Hence, for a blocked nipple to cause damage would require a great deal of force to be applied to the brake pedal. Les
Les Bengtson

Just to add a thought to those of Les and Mick - is yours a dual circuit system - if so, you will probably need actual movement of the shuttle in the m/c to uncover the front port and apply pressure to the front system - this wd explain why you have rear pressure but no front pressure from your bleeding system

Chris
Chris

Thank you all very much for the replies. I will pull the bleeder screws out today and see if I can clean them out.

I do have a compressor and can add air to the line and may give that a go, but now that I think about it, I still have a front brake line full of fluid. Could get messy.

Thanks again,
Warren
wwp

Warren,
Pull the bleeders and clean out the debris. I have had use a drill on some because the debris had setup so hard.
Leland Bradley

This thread was discussed on 16/02/2003

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