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MG MGB Technical - Servo assisted Brake Bleeding?

On a similar note to my namesake, I have a question about bleeding the system when it has a remote servo as part of it.

I've bleed our race midget numerous times, with a gunson system and without using the aid of a mate.

I've never done a system with a servo.

Simple question, can a Gunson be used on the system in the same way as a non servo assisted system could be done.

I don't want to risk damaging anything with my naivety.

TIA

Andrew
Andrew McGee

Andrew-
All the same, servo or no. The output end of the servo should ideally be pointed up, but level is OK.

FRM
FR Millmore

Thanks Fletcher.

A
Andrew McGee

I've always had to do it in two stages:

Using a Gunsons first (low pressure) for filling/replacing fluid and expelling as much of the air as it can always leaves a long pedal that 'pumps up' with a few quick pumps, then goes long again if left a few seconds.

The second stage is to get someone to press down hard on the brake pedal while I rapidly open and shut each caliper nipple in turn, and that always blasts another lump of air out of at least one. After that the pedal is fine.

This is on three cars, all with remote servos, and all as the factory fitted them i.e. outlet horizontal. It *may* not need this second stage if the servo is repositioned as per the after-market Powertune/Lockheed fitting instructions, which is outlet inclined upwards between 25 and 45 degrees. This also shows the air-valve pointing downwards, not upwards as fitted by the factory, which may also have an effect on bleeding. This part *may* also prevent the sticking-on that this servo seems to suffer from on quite a few cars, but I'm sure others have said turning theirs round made no difference, and there is talk of silicone grease on the air-valve, or relieving the piston to bore interface with fine emery or wet-and-dry.
PaulH Solihull

Never had a Gunson's or any other flim flammery. Used to use helpers but they are inconvenient and increasingly hard to lasso. I lock up all adjusters, pump up the pedal and jamb a fibreglass pole against the seat, such that it acts as a spring to push the pedal down; a large chunk of iron lying on the pedal works too. Then open a bleed screw. Repeat for all four. After you have some fluid in the system, open one bleed screw at a time and let it gravity bleed. Go get some tea while it drips. Repeat for all four. The advantage here is that you are not constantly aerating the fluid; probably excellent for silicone fluid, but I do not use it. Usually have a rock hard pedal, with no squish or travel. Back off the adjusters to correct point.

If you look at the servo, it has the output tube in the center of the end, clearly creating an air trap. That's why the later instructions say to point it up. We didn't get many B with remote servos, but I recall swearing at Healeys.

Don't think the control valve position has anything to do with the sticking; it might have the possibility of creating a very small bubble with the air valve facing up, but never seemed a problem. Sticking is a matter of lubricating the control piston, especially on cars that sit a lot.

FRM
FR Millmore

This thread was discussed on 05/02/2013

MG MGB Technical index

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