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MG MGB Technical - Brake Servo Mayem

hi everyone, i have a 68 GT with a brake servo. Lately the brake pedal had been pushing against me at times in traffic and figured the servo was on its way out. Today i had a load of white smoke coming from the back of the car with a horrid smell, then when i braked the pedal dropped to the floor. Thankfully i was just putting the car in the garage when it happened. Obviously i now need a new servo, but which do you fine folks recommend? there are the expensive genuine lockheed ones and the cheaper powertune ones. Anything wrong with the cheaper one? just im looking to do a lot of work on the car and need to save some pounds.


A P New

If you really want to save some money, bypass the servo.

They allegedly don't make that much difference and it's one less thing to go wrong.

I was thinking of adding a servo to mine, but I'm now reconsidering.
Dave O'Neill 2

i drove a triumph spitfire without a servo and it was horrendous! i much prefered the feel of confidence with the servo that my car has, and without a servo i dare say it'll be harder than the triumph what with being a heavier car. Im just concerned about the cheaper servo being a waste of time when compared to the lockheed type.
A P New

Adam, all the British MGBs up to about 1971 were built without a brake servo. Yours has obviously had one fitted by a previous owner. When MG put the servo on the car, they didn't alter the brakes at all. What I'm trying to say is that the MGB brakes were designed for non-servo operation. I used an MGB without servo brakes for 12 years and the brakes were fine. At best the servo only adds a very small assistance, not like a modern car at all where the servo gives loads of assistance. On the down side the servo makes the brake pedal more spongy with longer travel. Personally I would remove the servo and use the car without - that's how a 1968 MGB was meant to be. It will be fine and after a couple of miles you won't even notice the lack. Plus you will have a nice firm pedal. Don't take my word for it, read Paul's first paragraph here
Mike Howlett

when i fitted new copper brake lines to the car i did have left over the copper hose that bypasses the servo. Ill use that and give it a try this weekend without the servo and see what difference there is.
A P New

These are decelerations and pedal force required in road tests of MGB GTs.

1966 Autocar, 0.95g @ 125lb
1966 Motor, 0.98g @ 100lb
1971 Autocar, 1.04g @ 55lb
1977 Autocar, 0.98g @ 60lb

Whether any differences due to the servo can be described as only "slight assistance" I will leave you to judge.

Geoff E

now thats very interesting, pretty much half the force required. I'd say its a little bit more than a slight assistance, but quite a big one. But is there anything wrong with going down the powertune route as opposed to the lockheed?
A P New

I've been driving my '67, that has no servo, for almost 40 years and it has amazing brakes. I'm using stock brake linings, after experimenting with high performance materials. My other 2 vehicles have power assisted brakes, but the B stops with much more authority and the feeling is far more positive. The main reason that the booster was fitted to the B was that after the dual circuit master cylinder was introduced, for safety reasons, many people complained about a harder and less efficient brake pedal. Your car should still have the single circuit braking system, unless the PO converted the entire braking system over to the dual circuit system. Try bypassing the booster, with your spare line, and compare the results. I think that you will be pleased with the non assisted braking system. RAY
rjm RAY


For what its worth I have a Hyundai i30 as well as the B.

The B has no servo and the Hyundai has power assist, such that if you rest you foot on the brake pedal you go through the windscreen. When I drive one or the other I am not aware of any difference. I'm not saying that there isn't, but I guess I'm tuned into whichever car I'm driving, and subconciously adjust my foot pressure to accomodate the braking force required.

Herb Adler

Just bought my new remote servo from MG HIVE through ebay 74.90 delivered.
a goldup

One advantage of a servo is that the extra assistance allows the use of harder pad material which is more fade resistant. The down side is they do wear your discs a bit faster! I've had servo'd and non servo'd. I liked the feel of the non but my V8 has 4 pots, harder pads, servo, little fade and stops on a sixpence. I'll stick with that!
Allan Reeling

I have been servicing MGB's for 35 years & I have found that when I bleed a car with a booster I have the motor running which activates the booster properly and helps remove the air from the booster cyl. The booster is mounted with the cylinder on an uphill line but not enough for all the air to bled out. I always use air pressure to bleed the brakes.
I have a 66 GT with a lockheed 5/8 bore booster which gives a bit more boost than the 7/8 one & I also have a 70B that didn't have a booster and the brakes took more pressure. I have now fitted a 7/8 booster & they take more effort than the GT. I drove a GT the other day without a booster & noticed how much harder I had to push the pedal. Our race car had no booster but had an ex LHD tandem cylinder fitted for safety reasons. But never-the-less the brakes are perfectly adequate without a booster. The car will only stop as good as the tyre grip on the road.
Garth Bagnall

Years ago when my legs were stronger then they are now I removed the non-working boosters from my 69 C, I would not recomend this set up to anyone, the instalation of two new boosters gave me the brakes I needed.A different system to be sure but something to think about. Ric

It certainly is a different system. The MGB was designed as an un-servoed system, whereas the MGC wasn't.
Dave O'Neill 2

Something to consider, if you have a servo fitted to the vehicle then it will be checked at MOT time! so failing your car on MOT if it is non-working.
si robathan

To answer your question though (and I went to check ...! - well and cook dinner, and do various other things) - the Powertune one was bought for me so I'm assuming that they work just as well as the expensive ones.

I've not fitted it yet as I don't like to admit that I need assistance as I reckon that I can control 1/2 of single horsepower with a brain with my legs, then I can certainly do it in a car - but, the person who bought me it is a total fusspot, so, it probably works great :)

This thread was discussed between 14/04/2011 and 28/04/2011

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