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MG MGB Technical - Brake slave cylinder empty

The slave cylinder on my 74 MGB is nearly empty but the master is full. What do I put into it?
John Nephew

John,
are you sure you mean the slave cylinder to the brake master cylinder, and why's it empty, do you have a leak.

Or do you mean a brake servo or clutch slave cylinder or which brake fluid to use.

You're not limited on space here for text so you can give more info which will help to give better and more relevant advice.
Nigel Atkins

Yes, I agree with Nigel that John is probably confused about terminology. I don't see how you can tell if the slave cylinder is empty since it is under the car, but under the bonnet (hood) you have both the brake and clutch master cylinders, sitting over their respective pedals. I reckon John has a full brake master cylinder and an empty clutch slave cylinder.

Let us know if that's right John.
Mike Howlett

Or as John is apparently in the USA maybe one section of the dual brake master is full and the other is empty.

On this type the section for the front circuit is furthest from the driver.

If there is a leak the brake balance warning light should have come on. If the front circuit has failed you would certainly know about it, less so if it's the rear circuit that has failed. But it may just need topping-up and keeping an eye on in case there is a leak that hasn't affected the brakes yet.



paulh4

I've never seen one, is the plastic reservoir pot divided into two then?
Nigel Atkins

Yes, it is. It’s similar to the late 1500 Midget.
Dave O'Neill 2

Thanks Dave, I've a couple of thoughts on the post but will hold off to allow time.
Nigel Atkins

John, if you are losing fluid and there is NO VISIBLE SIGN OF LEAKAGE, your brake fluid is being sucked out via the vacuum booster and consumed by the engine.

B.T.D.T. The master cylinder O-ring to the booster has failed. Replace the master cylinder.

This happened on my 79-B.

Cheers,

Gary
79 MGB
Gary Hansen

The early split circuit brakes didn’t have a booster/ servo, as they would have needed one for each circuit.
Dave O'Neill 2

Correct. If it's the front chamber losing fluid (i.e. the one nearest the pedal) then it could be the secondary seal failed and fluid is running down the pedal, not easy to see only feel.
paulh4

This thread was discussed between 14/05/2021 and 16/05/2021

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