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MG MGB Technical - POWER BRAKE BOOSTER

Went to replace the vacuum hose to the power brake booster as it is looking and feeling rather flimsy.

Just wondering, do you really need to have the vacuum
booster hooked up?? It does require a bit of pressure applied to stop the car as it is. Having not driven any other MG but my own, there is nothing to compare it to but our other 21st century Hyundais.

Any thoughts??

Cheers

Gary
79 MGB
gary hansen

When the MGB was first produced it had no brake booster and the brakes were fine. The booster was added later but the brakes were not altered in any way, so if you take the booster out of circuit on your car the brakes will be exactly the same as the earlier cars. I had an earlier car with no brake servo and the brakes felt better to me. They were not unduly heavy to operate, although they will always seem weightier than a modern over-servoed system, but the pedal has a nice firm feel with less travel. I prefer them that way.

If you are going to do away with the servo don't leave it in circuit with the vacuum hose disconnected. Take off the hydraulic lines and join them together. Of course that means you will have to bleed the system.
Mike Howlett

"Take off the hydraulic lines and join them together"

As Gary has a '79 car, I'm assuming that it has the m/c with integral servo - although I'm not familiar with the North American spec cars.
Dave O'Neill 2

Thanks guys. The car has the dual chamber M/C that attaches to the vacuum servo. I guess I'm missing the point of

"Take off the hydraulic lines and join them together. Of course that means you will have to bleed the system."

as in Mike's post.

Not having worked on a UK MGB I'm not sure I follow what Mike is saying

Cheers

Gary
79 MGB
gary hansen

The early single-circuit cars had an optional remote servo. This could just be removed, if not wanted. Not so easy with the integral servo of later cars.
Dave O'Neill 2

Sorry, I was thinking of the remote servo, not the in-line dual circuit type. Ignore my post! Actually it would be a good idea to ignore most of my posts!!!
Mike Howlett

What Mike says is correct for the remote single-circuit servo, which adds very little assistance (unoticeable i my experience), but I've read that the later dual-circuit integral servo is very different and makes the brakes extremely 'heavy' if not working. The end result is much the same, which is noticeably heavier than a typical modern car.

Just replace the hose, and you may like to tentatively try it without vacuum and let us know what it's like :o)
paulh4

Mike, don't beat yourself up. I've looked at some of my own posts and think "Did I really post that?...oops"

Any and all info is gladly received here.

Cheers,

Gary
79 MGB
gary hansen

Paul, My thought process exactly! - heh heh :>{D



"Just replace the hose, and you may like to tentatively try it without vacuum and let us know what it's like :o)"

Cheers,

Gary
79 MGB
gary hansen

The integral m/c/servo is a different animal and was always designed to run with assistance. Not sure why you would want to experiment without servo, except out of pure academic, interest. Keeping the servo active also gives you some scope for using slightly "harder", more fade resistant, pads.
Allan Reeling

Allan: The idea to run without the vacuum booster is purely academic. It was an item one does not pay much attention to unless something appears off. In my case the hose from the servo to the intake manifold was quite flimsy and getting soft. So a replacement hose was imminent.

Cheers

Gary
79 MGB
gary hansen

Gary, Not sure if the tandem servo works in exactly the same way as the remote set up, would would assume so, as this gives progressive braking.
Light brake pressure; i.e., mild retardation, drifting up to a junction etc, doesn't put enough pressure in the system to open the air valve, whereas some heavy braking does. Hence you will only realise the lack of assistance under heavy braking.
Also rather than just condemning the hose, put a vacuum pump on the manifold end of the hose and check that it is holding a vacuum. If it doesn't put a sound piece of hose on to the servo and check again. The diaphragm can develop a leak itself and there can be a leak between the two halves of the unit or where the non return valve seals into the casing.
Allan Reeling

OK. Paul and Allan. Disconnected the vacuum line to the vacuum booster and went for a short drive. The brake pedal is significantly higher and much heavy pressure is required to stop the car.

So now we all know what happens when the vacuum brake servo is bypassed in a 79 North American spec 79 MGB.

Cheers

Gary
79 MGB
gary hansen

Thanks Gary, good to have it confirmed.
paulh4

This thread was discussed between 01/07/2017 and 05/07/2017

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