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MG MGB GT V8 Factory Originals Technical - Advice on brake servos

This is an issue which is really confusing me.

If I have an empty CB shell for a conversion, plus a RB and another CB as donor cars, and I need a braking system and have the choice of using one from either of the donor cars (both need refurbished of course) - what should I do? particularly regarding the servo/master issue?

1. Use the RB combined servo/master cylinder.
2. Use the pedal cover plus a new remote servo from CB.

Particularly in the case of the CB, what bits do I need/need to add?

and if anyone has 'How to give your MGB V8 power' can they please tell me what I am looking at in photo 9/2 on page 89? It doesn't look like either the RB or CB master/servo set up's on the cars I have!

I suggest that it's not a rubber bumper versus chrome issue - its a dual circuit or space issue. If you have the option of dual circuits you should for obvious reasons consider it - against this you need a reasonable amount of space around the engine for all its ancilliaries - if you are going the fuel injection route space will be tighter - the GTV8 with a separate servo is a useful pointer.

Be careful with parts from wrecks.

From a performance/safety/effectiveness point of view - whch is better, the CB or RB set-up?

I have all options open to me, as I will be putting everything from scratch into a more or less empty shell.

The only thing I know for certain is that I will be using a webber carb set up not EFI so that gives me a little more space.

Is the recommendation that I should adopt the rubber bumper set up? It seems a bit easier to understand. I'm struggling to get my head around the CB set up.

Whichever route I go down I will be using the donor more as a donor for the set up dimensions etc. and trading in any parts for part-ex reconditioned ones or just buy new.
Liam H

Geoff King fitted the combined master cylinder / servo into his fuel injected V8 quite comfortably.
Mike Howlett

Would I also be correct in thinking that my choice of braking system would also dictate the pedal assembly and clutch master that I use?
Liam H

From a safety standpoint, the RB shell is stronger, the doors have burst bars and additional latch points to prevent them from coming open in a crash. There is considerable additional material in both the front & rear to support the 5 mph bumpers. With the rubber bumpers in place, I feel the car is significantly safer. That said, I used a RB shell & removed the rubber bumpers, but retained the rest.

Late model boosted brakes are my preferance, but only the pedal effort is changed, not the stopping distance.

The clutch master is the same for all MGB's, but the pedals ae determined y the servo/non-servo decision.

I have fuel injection & servo brakes with no problems on a left hand driver. Can't see why this would be a problem for RH drive, the RV8 had plenty of room.
Jim Stuart


The clutch master cylinder is the same but the pedal box and pedals are completely different between the single and twin circuit brakes. With Efi there is plenty of room for the twin circuit pedal box/servo/master cylinder assembly, if you post your e-mail address Iíll forward a pic of my car although from the engine bay shot here you can see that it fits without any difficulty.

Why are you using a carb when Efi is so much better? It certainly doesnít give you any more space.

Geoff King

Thanks Geoff, I have seen your car before on line, its very nice indeed. A roadster will be my next trip out, probs with EFI but for this one I'm sticking what what I know and already have - which is carbs.

If you want to email a pic it can go to my broadband account l.healy (at)

I would rather use the twin circuit set up, but have been concerned that space would be an issue, although I note your exhaust exits through the wings, mine won't be. A pic would be very useful indeed.

In your write up you said "The clutch master cylinder is a MGBGTV8 type with a metal reservoir because a new plastic reservoir type didn't fit as the cap fouled the bulkhead". Was that the RB one which didn't fit - or would neither CB nor RB fit?

Interestingly I will doing almost the same as you, Cb conversion (non-roadster though) with two more cars providing the spares. 3 in total, 4 including the SD1 !


The brake fluid reserve tank on the rangerovers from the mid '80s was almost identical to the dual circuit MG, except the cap is glued the other way around. I'm using one on my late '75 MGB master.
It could be that the master is the same as MG's which implies that it was used on many Leyland cars. Obviously cheaper than MG. Might be worth looking into.

somewhere in all my surfin/picture lookin/etc./etc. i seen somewhere??? a gm resevoir&booster[although the booster looked smaller] but as looks go it was the same as the one on my chevy truck,,anyone know of this??i definatly have brake problems myself, i think the master cyl. is shot [its the rubber bumper type] the rear drums are all rigged up by previous owner,, would love to do rear disks,, however not sure what rear i have,, was told[by previous owner] it was from an 85 post office jeep , cant find anyone to prove or disprove this.. i also have a proportioning valve i've turned it all over the place cant see where it does anything,,the gm set up i saw was on a B & was done very professional,,have any idea who is capable of this kinda work around s. central p.a.??? all the guys i seem to pick say they can do the work [NO PROBLEM..] it'll be a week,,, then 1 if i'm luckey but usually 2 months later there seems to be a problem,,,yep i can sure ...thanks...

Is this what you are looking for:
Tony Bates

Tony is right, that unit will bolt right onto the later pedal box. I used similar on my 1980 but went with a dual booster.

With their booster all you need to do is cut down the pushrod about 1".

If you do not want the booster you can use the later pedal box but with a $29 adapter use a GM MC.

I have yet to drive my car with the dual 7" booster so take this all with a grain of salt.



Why thank you Tony & Mike,,I especially like the stainless steel ones,, since I'm positive my master cyl. is shot this is the way i'm gonna go!! what about this proportening valve i've got?? why do i need that riggen?? especially since it seems to do nothing,,havent talked to anyone around here[scared to] my track record pickin mechanics is about 11 & 0, on the bad side,,since i also want to do rear disks the work is beyond me..thanks for your help..

This thread was discussed between 13/12/2005 and 22/12/2005

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