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MG MGB Technical - Remote Brake Servo

I am nearing completion of my '77 GT V8 conversion and wondering whether to install the remote brake servo.
I have read varied reports in the archives regarding it's effectiveness or otherwise.
Could I please have comments from those with recent experience so that I can make a decision.
Peter M
Peter M (Member)

I would recommend you fit a servo.Whilst it only reduces the effort required at the pedal it does make the car nicer to drive. I trust you have already upgraded the front brakes to at least factory V8 spec. Hi spec supply some rather nice alloy 4 pot princess calipers at sensible money that bolt straight on. Jim
jim soutar

I've driven V8s both with and without, and was amazed just how little difference it makes. It was only optional (4-cylinder anyway) at one point so the brakes would have to be effective on those cars without. Some people prefer the harder pedal of the non-servo arrangement.
Paul Hunt

I used a Hillman remote servo which has a 5/8" bore rather than 7/8". It makes the pedal much lighter. The 7/8 cylinder could be sleeved down to 5/8.
Garth
Garth Bagnall

Thanks Jim, Paul and Garth. I have decided to go with the booster if only for originality. I know that Paul is not an advocate and I respect his opinions greatly but others suggest that the servo does offer an advantage albeit slight.
Peter M (Member)
Peter M

I removed my servo and ran without it during a time when I was having it plated and quite frankly the difference was really minimal. If you intend to use silicone brake fluid don't fit the servo because it does not work properly with it or alternatively use normal fluid with the servo.
Iain MacKintosh

I wouldn't say I'm not an advocate, both my cars have them and I wouldn't remove them and I would replace them if they failed. But as Iain says if you are expecting a significant difference in pedal response you won't get it.
Paul Hunt

Iain,
Can you add some explanation to your statement recommending the none use of silicone brake fluid with the servo? I was planning to go this way.
Richard
Richard Coombs

Richard, I have two MGs a GT and a roadster. When I built the GT I used silicon brake fluid without a problem and so when I built the roadster went a similar route. However with the roadster I had numerous problems with the brakes sticking on and not releasing and in the end made up my mind that the problem must be due to the lack of lubricity of the silicon fluid. As a result I rebled the system using conventional mineral fluid and the problem immediately disappeared never to return. Now sometimes the GT also suffers the same problem but releases the brakes after about two seconds which is not really serious so I don't intend to change its fluid unless the problem worsens. Now both braking systems were completely new and the servos rebuilt. I also spoke to Norton Classic Servos who advised me that the problem could be with the reaction piston trapping an air bubble underneath it and to pack some silicon grease in the hole before installing the piston. Whilst this seemed to alleviate the problem for a while it did not effect the permanent cure that changing the fluid did.
Iain MacKintosh

I also had problems with servo (new) sticking with silicon fluid. Worked perfectly after a flush then dot 4.

Mark
Mark

Very interesting. Sometime ago I asked Automec why Lockheed do not recommend using silicone with their products. They have asked Lockheed but, up to January 2007, they had had no reply. Automec say that they have had no complaints from users due to the use of silicone.
Richard Coombs

I've only ever used non-silicone fluid, but get the servo sticking on in hot weather, usually able to release it with a couple of prods of the pedal. One cure was said to be a dab of silicone (interestingly) grease on the air-valve piston, but as mine was wet with fluid I didn't bother. Another cure is said to be to reorientate the servo so that the air-valve is lower than the slave cylinder, unstead of above as it is in the MGB. Other BL models do seem to have it below. The sticking-on was so bad on a friends V8 whilst touring Ireland we disconnected the vacuum hose and stuffed the ceramic end of a spare spark plug up it! That's when I discovered how little difference the servo made.
Paul Hunt

The fitting instructions for my LOckheed servo show the air control valve below the slave which I've never seen on a 'B'. Lockheed say this is to assist with bleeding the system but maybe there's more to it than than that. Attached are the key diagrams.


Richard Coombs

I *think* that is as much to do with the 'nose up' attitude of the servo allowing air bubbles to get to the outlet pipe instead of being trapped above it in the cylinder when it is horizontal like in the MGB. Air valve down *will* stop bubbles getting trapped in the bottom of the valve though. I've not had a problem bleeding the brakes, except that after using the gunsons EeziBleed to fill the system and get rid of most of the air it leaves it a bit spongy so I have to get someone to stand on the pedal while I rapidly open and close each caliper nipple in turn. That always blasts an extra bit of air out and after that the are fine. Roadster and V8.
Paul Hunt

Hi Iain - & others,
The air valve sticking is a problem I encountered many times. I remove the piston & lube it with rubber lube. One car had a repeat problem so I got a small piece of steel rod, cut a slit in it , wrapped a piece of 400 wet & dry around it until it was a tight fit & then polished the hole - no further problems.
Garth
Garth Bagnall

Hi Garth,
Would that be with silicone or standard brake fluid?
Richard
Richard Coombs

Just noticed something relevant in the Linsay Porter mgb restoration book (p 209). "MG originally fitted the remote servo with the air control valve uppermost. AP Lockheed now suggest turning it through 180 degrees." My copy has revisions up to 1994 and, though the words may have changed, the photos still show their servo air valve on top. The car rebuild in this book also goes for servo and silicone.
Richard Coombs

From the above you may have noticed that I was intending to follow the revised Lockheed servo fitting instructions. (see image at my post of May 8th)Unfortunately if you do this there are real problems with siting the unit in an MGB. For starters the 'standard' bracket requires redrilling to allow the rotation of the servo to put the air valve below the centre line; the requirement to tilt the servo at 25 to 45 degrees also means that the bracket mount requires bending; so far so easy.
However, a tilt of only 30 degrees obviously raises the servo outlet considerably, so much so that if fitted square (across the engine bay) onto the LH 'pedal box' shelf area, as is normal for a Lockheed unit, it is fouled by the bonnet hinge. Turning it forwards through 90 degrees means it fouls the bonnet. My current solution is to fit it across the shelf, angled at about 30 degrees to the rear bulkhead, taking the outlet forwards and away from the hinge. It's a bit tight but it doesn't look too ugly.
It's a shame but it is a matter of fact that all of the mounting kits that I've seen offered by UK suppliers do not allow the fitting of a Lockheed servo to these instructions. Now why would that be?
Given that there are thousands of servos fitted using the factory method I wonder at the need to alter things. Does anyone know why the changes occured? I wonder what the original instruction sheet was like? Have any of you fitted a servo as per the new instructions?
Richard Coombs

As I say I think it is just to do with bleeding. With the air-valve at the top there is a small cavity under that which can trap air, and with the cylinder horizontal or only slightly tilted more air can be trapped above the outlet port. But since many thousands of MGBs were made with the air valve at the top and the cylinder almost horizontal, which don't suffer from spongy brakes, I doubt it really matters, for the sake of having to do a high-pressure bleed after having worked on the hydraulics. Even though I clamped my hoses during a caliper change the other day and only released them when the EeziBleed was connected and the bleed nipple opened, I still found I had to do the high-pressure bleed i.e. my beautiful assistant pressing down as hard as she could on the pedal while I rapidly opened and closed each caliper nipple, probably because I had to slacken the hose to pipe connection both sides to prevent a twist in the hose because the thread in the new calipers didn't start in the same place as the old.

As I get the brakes sticking on in warm weather I may well try turning the air valve down as Chris Betson has recommended in the past, and fully expect to have to redrill the mounting bracket.
Paul Hunt

This thread was discussed between 22/04/2009 and 29/05/2009

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