MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - MGB Brake Servo

Can anyone provide me with some advice on fitting a brake servo and split circut (Fr/Bk) to my 69 MGB?? The standard brakes are fine, however, the wife would prefer power assistance.

Regards,
Ken
KM PHILLIPS

PBR in Australia make a huge range of original and replacement brake equiptment.

Go to your nearest PBR supplier (Repco?) and look for the replacement parts for the later MGB's and fit those.

You will need a dual circuit master cylinder with vacuum assist as a unit, or a separate dual circuit master cylinder and remote servo, plus pipes and fittings.

Cheers
Ian F



Ian Fraser

Talking about servo's

My 78 GT 1800 has a duel circuit brake system with servo. But not sure its working. I get a peddle movement after starting the engine.(having pressed them a few times with the engine off and held them on) However if whilst driving I stop the engine and de-clutch and use the brakes they feel exactly the same as they do with the engine running.
Any Idea's ?
Rgds Bob
R. C. Elwell

Bob,
sounds like that the one-way valve is leaking. I am no RB expert, but guess there should be one on the manifold where the hose from the servo attaches.
Rufus
Rufus Pool

Bob,

I agree with Rufus. Either the valve is leaking or not working. When I put in my supercharger Moss supplied a one way valve that went next to the carb. After a couple runs I also noticed my brakes seemed no different. I didn't know what was wrong either until I took off that valve and blew into it. Yes, the heat actual melted the valve inside enough to stop the servo from working.

Luckily I left the one on the servo and after conecting the lines back up minus the other valve I was back in business. Works like it should. So again, check your valve and see that it is working.

Regards, Ray 1977mgb
Ray 1977mgb

Hadn't thought of that will look.
thanks guys rgds Bob
R. C. Elwell

Gooday mr phillips.

I have a 69 roadster and fitted a vh44 brake booster to it. you dont need a duel braking curcuit. It is plumbed in at the 4 way junction box for your brake lines opposite the distributor . you take the line from your master cylinder and run that to the booster then return from the booster to where you removed the master cylinder line. All you need then is a hose from the booster to the inlet manifold for vacuum. I fitted the booster to the passenger side on the flat tray (part of the firewall) as there is plenty of room there and the new brake lines are easy to run across the firewall. Not sure about nsw, but in victoria you cannot use copper brake lines. they must be steel. No big problem. You can also use the vh40 booster. difference is in the braking pressure. 44 has a large diaphram inside and requires less pressure on the brake pedal to stop the car. there were laots of cars fitted with these boosters as option accessories throughout the 60s and 70s so sourcing one from a wreckers shouldnt be a problem. You can still buy them new from most auto acc shops and i believe they are around 300 dollars. Any further questions, dont hesitate to ask and i hope this is of help. BTW, they do help the foot pressure but do not increase the braking efficency of the car.
Cactus

Replaced both one way valves. Servo one was a little sticky. But still the same. I am wondering if the servo rebuild itself is a fault with the adjustment to the mastercylinder correct. My Workshop Manual does not show the servo that goes with the dual brake master cylinder but the old one. Any more ideas
rgds Bob
R. C. Elwell

Ken,I agree entirely with what Cactus says. I converted my '71 rdstr this way. The VH44 is larger than the in line split system servo & replacement or reconditioned exchange units are available in OZ. Not so with the split system MC/servo unit. If you live in Sydney, give me a call ( 9525 7031 )or email me if you want to see such a conversion. I also have a '78 GT so you can compare the 2 systems. If you choose the VH44 servo, I have a spare mounting bracket you're welcome to. Barrie E
Barrie Egerton

Bob-
" I get a peddle movement after starting the engine.(having pressed them a few times with the engine off and held them on)"-- This means it's working. "However if whilst driving I stop the engine and de-clutch and use the brakes they feel exactly the same as they do with the engine running." This means it's STILL working; the booster holds enough vacuum for several applications of the brakes AFTER the vacuum source aka engine is shut off. That's the point of the check valve. How many applications is a function of how much travel it takes to apply the brakes; for a well adjusted system it's likely good for 4 or 5, for a loose system 2 or 3. The "boost" comes not from applying vacuum to the booster, but from letting air on to one side of the diaphragm which normally has vacuum on BOTH sides. This gives much better and faster response than applying vacuum would, since the atmosphere can push air in faster than the engine can pull it out.
FRM
FR Millmore

Thanks FRM,
Maybe I,m expecting more from the servo than it is capable of giving. I'll try blanking it off and see how much pressure is needed.(carefully)
rgds Bob
R. C. Elwell

I'm not sure adding a servo will make that much difference anyway. The remote servo makes very little difference whether it is present or not, and whilst with the integral servo there is a much more noticeable difference between having the servo operational and not, I didn't think there was that much difference between the two systems with servo operational, i.e. if the integral servo fails it becomes very much more pedal pressure to stop the car. If you added the later servo to the earlier master, if that is possible, I *would* expect to get a noticeable difference.
Paul Hunt 2

Gooday Paul.. Re your comment

I would have to disagree with the thought that a servo,(remote at least) as this is what i fitted to my car, makes little difference. I would estimate that the pedal pressure required to lock the brakes from around 50mph, would be halved.(estmate only)and with vh44 booster. As i stated in earlier post, the braking efficency is no different with or without a booster but the required pedal effort is much less with a booster. It gives you the feeling that your brakes are much better but that is not the case. Just easier on the foot. the duel line braking circuit also makes no difference to effincency. It is used as a safety device incase a leak occured in either the front or rear brake cylinders. you could lose rear brakes for instance, but the front brakes,because it runs through a different line, would still opperate sufficiently to stop the vehicle.(that bit for referance to ken)
Perhaps the smaller booster ( vh40) would make little difference given it;s smaller diamater diaphram, but the 44 does work well. I am not sure if these pbr boosters are australian supply only or worldwide but for kens purpose, they are avaliable here in aus land.

only personal opinion

cheers
Cactus

Hi Cactus - I've driven cars both with and without the remote servo connected, back to back, and the difference in pedal pressure *is* marginal, after the first tentative push at the pedal to see what difference it made I simply didn't notice the difference. This servo was only an option originally. The stated experience of others is that the attached servo *does* result in a significant difference to pedal pressure. I have taken this at face value, and it implies that the greater boost is combined with a changed ratio of master to slave bore to give shorter pedal travel for the same braking pedal pressure and stopping distance As I understand the dual system it splits fronts from rears, therefore if the rear circuit should suffer a puncture the effect on pedal pressure vs stopping distance is relatively marginal. However if a front circuit pipe should fail the efect is still pretty catastrophic.
Paul Hunt 2

The time you notice the difference between assisted & unassisted brakes the most, is when the servo fails for first time & you use the car in front to stop. Don't ask me how I know ! Barrie E
Barrie Egerton

This thread was discussed between 02/05/2006 and 13/05/2006

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.