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MG MGB Technical - New Brake System Won't Bleed

Hi everyone,

A few weeks back while driving my 69gt I detected some difference in my brake performance. This was followed shortly thereafter with the brake warning light coming on (and staying on even when the car was off!).

Anyway, I knew I was due for new brakes, and after a quick survey, I decided to replace the calipers (rebuilds from Apple Hydraulics), rotors, wheel cylinders, shoes, and new hoses.

I replaced the MC about 6 months ago so it was left in situ.

After getting everything installed, the system won't bleed at all. More specifically, the right rear hardly has fluid emitted when the pedal is pressed. The other thing I noticed is that the MC reservor always empties from the rear chamber (the front maintains its level).
Is this normal.

One last fact, I have the rear still jacked up (from the installation work). Could this present problems?

Did I get a bad MC? Given that my problems seems to be one sided I'd guess not. How do I determine for sure? What else can I try to resolve this?

Thanks in advance for your replys.

Bill
Bill Schoolfield

Have you checked the valve that controls the brake pressure warning light? There is a "shuttle" inside that moves when the pressure is low that trips the light. From what I remember it will need to be reset so that may be what's keeping the front from bleeding. Unscrew the piece the wires connect to and step on the brake pedal. I think that's how it gets reset. If that doesnt help then I'd look at the master cylinder. Disconnect the brake lines coming out and see if you get any better fluid from straight out of it. If so then work your way out from there.
william fox

Bill; The reservior chamber associated with front/rear should empty when bleeding it's associated brakes. As I recall the rear chamber is for the rear brakes. If it isn't bleeding do you know where the fluid is going when the chamber empties? On my cars I need to open the rear bleeder screws more than is required for the front brake bleeders. It can take a little time to get the rear brakes to bleed. I use a Mity Vac, it saves me from having to ask my wife to help. One other question, did the brakes ever work since the master cylinder was replaced? I would jack up the front to keep the car level but having one end jacked up should not prevent the brakes from bleeding. Good luck, Clifton
Clifton Gordon

Bill; The brake pressure failure switch on chrome bumper cars does not block fluid flow when the shuttle moves. It's sole purpose is to turn on the light to warn you of a brake problem. The divided reservior will keep the master cylinder from leaking from the good circuit. FWIW, Clifton
Clifton Gordon


Bill,

I haven't done anything with the switch yet. I assumed that I might have to do something with it to get the light to turn off. I read several places in the archives that say to do what you mention, but elsewhere (including Clifton remarks) indicate otherwise. I do have fluid going out the other fittings so the MC is doing something.

Clifton,

The MC worked before, that is why I feel (maybe hope)it isn't the culprit. After years of frustration doing this job, I bought a mity vac. Imagine my dismay when the darn thing (as well as the jar method) didn't work.

I don't see any leaks. The fluid run thru the system to date has been mostly thru the left rear (and the the fronts to a lesser extent).

Bill
Bill Schoolfield

Bill, here's something you might want to try,
I once had great difficulty getting air out of the rear brakelines (it turned out the brakes had been fitted upside down!)
I placed a bundle of rags under the master cylinder then I unscrewed the rear brake line from the master and using a large plastic 50ml syringe and a small connecting peice of tubing, injected the brake fluid into the line. I then topped up the reserviour, removed the syringe and conected the line again. Any air was exclueded because the master and brake lines were full /over flowing. It took about 10 minute all up. Once the lines were full I has able to do a few traditional style pumps which infact turned out to be unnecessary. This proceedure worked so well that I used it again when I had to swap those upside down brakes around.
(Do wear safety glasses if you try this)
Peter

If the right rear is the only nipple open and the pedal is hard when little fluid comes out, but the left flows and has a soft pedal, then maybe the pipe to the right side has been pinched.
Paul Hunt

I had the same problem using my Mity Vac after changing the master cylinder. Never had a problem with any other car I've ever worked on except for the 67 B. I have a 'powerbleeder' and I will use that when I restore my car.
Mike MaGee

Bill,

Probably an obvious question, but have you checked the brake line for the right side to see if it has been pinched? My left rear line got pinched when I towed the car and tied the rear akle down to the trailer

Cris
Cris

This thread was discussed on 20/10/2003

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