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MG MGB Technical - Fitting Brake Servo to Older MGBs

Hello,

I have a 1971 mgb roadster (chrome Bumper) but want to fit a brake servo to assist in making it a easier drive. My year of MGB wasn't originally fitted with an MGB. A couple of questions:

1. Can the servo be fitted that was fitted to the newer models? If so is it possible copy the brake circuit (hydraulics) of a later mgb model?

2. Are the aftermarket conversion kits any good. If so please can someone recommend one?

Many thanks,

Alex Davies
Alex Davies

Alex

1 Yes. The servo fitted to later chrome bumper cars with single circuit hydraulics is a very simple install. It is possible to fit the system fitted to rubber bumper cars with twin circuit hydraulics, but it is much more complicated/expensive and in my humble opinion not worth the trouble.


2 Some of the cheaper after market servos are of questionable reliabiliy. Use either Girling or Lockheed, which ever you can find. The pedal pressure reduction is not dramatic but I think is worthwhile.


When you do fit ,take care with pipe runs, you will probably need to shorten the pipes in the kit, E mail if you need detail help. Regards Jim
jim soutar

Alex
Have a look at this site for some info

http://theautoist.com/convertingto-fromservoboostedbrakes.htm

Kent
DK McNeill

Alex, Its purely my opinion, but why fit a servo? It doesn't improve the braking, just requires less pedal effort (which may be exactly why you want it!)(Mine is a 69 roadster)FWIW there have been a couple of threads on the MGOC website where this was discussed (as a result of a brake fluid loss)Might be worth a look.
Michael Beswick

The remote servo only gives very light assistance (because it was initially an option and so the brakes without would have to be adequate at the very least), so light that after a tentative prod on the brakes when going from with to without I never noticed it. The later integral servo *does* give more assistance, but the master bore is also larger and the result is that overall pedal effort is also very similar. The difference is that when the integral servo fails you *do* notice it. Both can suffer seal failure which sucks fluid out of the reservoir - all of it in the case of single-circuit brakes leading to total loss of brakes, or the rear reservoir in the case of dual circuit which means the loss of the front brakes, which is almost as dramatic.

P Hunt

Thanks, from what your saying the remote servo is a bit pointless. Is it then possible to fit the braking system as per the later models (with servo and single line/circuit) but using the original master cylinder (and therfore bore size)? And would this help?

Many thanks for your assistance
Alex Davies

I had intended to fit a remote servo to my car but, by the sound of it, I'll be wasting my time and money.

Oh well, that's one less job to do before getting it back on the road.
Dave O'Neill 2

"Is it then possible to fit the braking system as per the later models (with servo and single line/circuit) but using the original master cylinder (and therefore bore size)?" says Alex.

I'm not sure what you mean. The discs, calipers and rear drum brakes were the same on all 1800cc MGBs, irrespective of age. So all 1800cc MGBs have the same basic brake components. All that changed on UK cars was firstly the addition of a remote servo to the single circuit, which as many people say really makes very little difference to pedal effort, and then in 1977 a new master cylinder with an in-line servo was fitted, and this gave the opportunity to use dual circuit brakes. It is not straightforward to fit this later set-up to an earlier car as the pedal box and pedals are quite different and bodywork needs to be altered to get them in.

Any MGB with or without servo should be able to stop very smartly on a dry road. If you can't, then adding a servo won't make any difference because the calipers aren't doing their job. Maybe a piston is stuck, or the pads and/or discs are worn or the wrong type. I drove a 1971 MGB for 12 years and getting into it from my modern car never gave me any cause for concern about the braking.
Mike Howlett

Ditto Mike, plus the later master and integral servo combined give much the same braking effort as the earlier system. I have known of people going to the trouble of fitting the later system to an earlier car, but that is to gain the split braking system, not servo assistance. Split-braking systems without a servo even as an option were used on export cars from 67 to 74.

"Any MGB with or without servo should be able to stop very smartly on a dry road" Quite so, you should be able to lock the front wheels on dry tarmac with *progressive* pressure on the pedal, and it's easier to lock them if you bang them on suddenly. If you can't then there is something dangerously wrong with your brakes ... or maybe your leg.
P Hunt

Sorry I was under the impression that the master cylinder changed when the remote servo was first fitted to mgbs.

Thanks for all your help I don't think its worth fitting a servo based on your comments, and that the difference will be negligable.

Thanks again.

Alex Davies

I've always wondered what the big deal was with the need to add a servo. My '67 has the single circuit braking system and stops on a dime, at any speed, with very little pedal pressure. RAY
rjm RAY

I fitted a Hillman Hunter servo to my 66 GT & it made a big difference. The reason for that is because the Hunter servo has a 5/8" bore not 7/8" as the B had so you get moore assistance but not as much as most modern cars or to make the brakes over sensitive. If you have a 7/8 bore servo you can fit a new cylinder or have the old one sleeved down & buy a hunter rebuild kit.
Garth
Garth Bagnall

Hi Garth

An interesting idea to fit a smaller cylinder.
My concern would be the greater length of travel required of the piston, roughly 30% more, which could conceivably cause the piston to hit the end of the cylinder before fully braking.

Herb
H J Adler

Hi again,

I've just had a rethink, and the above 30% quoted was based on diameter, not area as it should be. On area this would be about 50% greater movement.

Herb
H J Adler

My 66 GT brake pedal feels no different to my 70 B Rdstr which has a 7/8 bore cyl so that is not an issue. The governing factor is the master cyl hot the booster.
Garth
Garth Bagnall

That was my thought at first, but then it seemed to me that a smaller bore in the servo would allow a given vacuum pressure from the diaphragm to apply more pressure to the fluid (same pounds, less square inches, hence higher psi) to the brakes, with the trade-off of a longer travel. I.e. just like reducing the bore of a master with no servo assistance.
P Hunt

I don't agree that there is not much assistance from the remote servo. Brake pedal effort is reduced. Better brakes? No. Easier brakes? Definitely. Is it worth it? Hmmmmmm.

I thought about a dual circuit set-up, but it would involve moving all of the wiring on a chrome bumper car. Has to be safer, though.

N

Neil22

well if anyone is interested i have almost new remote servo and all brakes pipes ready to fit in fact everything required to fit, i bought it of a full restored car that had less than 1000 miles on the clock before it was written off
s truman

I put the servo from a '76 into my '71 several years ago. I don't remember all the work I had to do. I do recall I had to modify the firewall opening and I belive I had to use the pedals from the '76.

I like the power assist much better. I think it is a noticable difference. However, maybe I just have weak legs!

John in Music City
John Lifsey

I bought a Servo from MG BEEHIVE and the ratio was 1.9:1. The original ratio on factory options was 1.6:1
This 1.9 ratio means that only half as much effort is required for my ancient leg. Fitting was no problem, but I did make the two pipes required myself.

In fact I liked the action so much that I Fitted one to my 65 SPRITE. Whilst doing this I found that the fulcrum pin on the brake and clutch was so corroded that it had seriously affected the brakes and the clutch actions. Cleaning up the pedal bushes and fitting new clevis pins and fulcrum pin would have cleared the heavy brakes problem, but I,ve left the servo in. For the record it's fitted over the left front wheel arch and tucked under the wing.
AG Martin

I have been considering disabling the servo on my '79 B. I don't like the spongy feel you get for the first 1" or so of pedal travel.
Carl Floyd

I have a 69 Gt with dual circuit brakes no booster;
77 Roadster dual circuit brakes with booster.
Both cars stop very well, but there is very noticeable less pedal effort on the 77 Roadster.

Hart
Hartley Mayers

This thread was discussed between 26/12/2009 and 06/02/2010

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