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 - Which brake master cylinder?

Hi there,

Haven't posted on here in a while (no major probs with the BGT). I'm havings brake probs now. Pedal travelling right to the floor. Have bled the system a couple of times, but problem comes back after a few weeks/couple of months.

I'm not very technical, but my mechanic reckons I need a new brake master cylinder which are about euro150 to buy.

There appear to be 2 types - single & dual system. How do I know which one I need - my car is a 73 B GT, std UK spec.

Thanks
Mark 73BGT

If you have the dual system the master cylinder will have a large white cap and the reservoir will have a divider in it. You will also have two seperate brake lines leaving the master form two different ports.
John H

Mark,

the Leyland MGB parts manual (up to September 1976) states the following numbers:
GMC 122 -> G-HN3, G-HD3 101 to 138400 and V8
GMC 150 -> G-HN5, G-HD5 (+) to 410350

Both versions are fitted with an internal angular reservoir, a small filler plug and are single curcit cylinders.
They only have ONE line connected!

For cars with dual line system, another master cylinder was used:
37H 2780 -> most common on LHD cars up to the introduction of the 1974 1/2 modell.

This master cylinder is fitted with a large filler cap and a transparent plastic reservoir.
They have two lines fitted.

Cars with dual line servo assited brakes did make use of another mc.
37H 8093 -> GMC 149 -> G-HN5 386601 to 410000

This system is directed to the front of the car and has the mc fixed to the break servo.

Hope this helps

Ralph
Ralph

Ralph/John,

Thanks for the feedback. I checked the engine bay & there's just one resevoir/outlet, so it's the single system.

I double checked with the supplier - she also thought that the dual system was only post 76.

At least I know I ordered the right one... and it was only half the price I expected!

I had originally priced that dual master cylinder, thinking (on the law of averages & knowing my luck) my car would have the more expensive system.

Happily, I was wrong... turns out the single is a lot less expensive.


Thanks again
Mark 73BGT

A UK 73 should have a single braking system with a square metal reservoir, the UK dual is only 77 and later as you say. However the square ones had become almost unobtainable and very expensive when I bought one several years ago, the replacement is a large (larger than the clutch) round one. I've had to replace both the metal masters on the V8 in the past, the brake because the can had rotted through. Before I fitted them I sprayed them with clear laquer.
Paul Hunt 2


Even if the single-circuit system is "original", it might be worthwhile to have your car upgraded to a dual-circuit system at some point.

If you're interested in the theory-of-operation, this is one place to start:
http://www.britishv8.org/Articles/Tandem-Master-Cylinders.htm
Curtis

I've never really seen the point of the MGB dual system with both front brakes on one circuit and the rears on the other.
Paul Hunt 2

Paul,

there is one point... THE MOST IMPORTANT THING IS MARKETING...

As with many other mods of the B this system was asked for from people that tried to prevent the customers for these cars from theiselfs. Think of the three whiper layout, break failiure warning light, electrical oil presure gauge, all kind of buzzers and flickering warning lights and even the information printed on to the mirrors that things seen there might be larger as thought on first glance, all the funny warning decales on later MGB's that were exported to the USA and a lot of other strange nonsense.

'Keep it simple' was not a part of their vocblery, i think

Ralph

Ralph

Electric oil pressure gauge? Don't tell me that was to prevent hot oil being sprayed on the occupants!
Paul Hunt 2

This thread was discussed between 07/08/2007 and 12/08/2007

MG MGB Technical index

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