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MG MGB Technical - Upgrade to tandam brakes

Hi,
I have just tucked my car up for the winter and am thinking of upgrades to do during the winter. I am thinking of changing from a standard brake master cylinder to a tandam one. I understand there can be problems bleeding the rear brakes with out some kind of valve.
Your thoughts please.
Thanks
s page

What age is your car? When I rebuilt my 1969 I decided to fit the later dual-circuit master cylinder with in-line servo. It isn't a straight forward swap as the hole in the shelf that the pedals go through needs to be bigger and some of the mounting holes are different too. I had to do some surgery in that area to make it fit. As well as that I had to knock a depression in the inner wing to accommodate the servo body. Just thought you should be aware. On the plus side, I had no problems bleeding the brakes once finished.



Mike Howlett

Anything can be done, if you are prepared to spend enough time and money.

Servo or non-servo?

The non-servo i.e North American system used two types of master one with a remote balance switch manifold, but the pedal arrangement was basically the same.

The servoed dual system used on all MGBs eventually uses a very different pedal arrangement as the master piston is pushed away from the driver whereas it it pushed towards the driver in the earlier masters. That also needs a repositioned brake light switch, on a bracket by the pedal in the cabin on UK cars.

Bleeding is a matter of recentralising the balance switch afterwards on the earlier dual master, but just partially unscrewing it during bleeding on the final master. Pedal bleeding isn't straight-forwards on any dual master as the circuit not being bled restricts pedal movement, making a gadget such as an EeziBleed preferable.

Even after all that it only splits the system front and rear, but 80% of the braking effort comes from the front. If that fails then you have little more braking effort than is applied by the handbrake - measure your stopping-distance from 30mph on handbrake only ... on a straight clear road when there is no-one around you.
Paul Hunt

I've owned my US spec single circuit braking system B since '72 and have never had a fault with the system. On the other hand, I've worked on numerous cars, equipped with the dual stage master cylinders, that are much more prone to failure.In my experience, when one half of the master cylinder loses pressure, the other half isn't far behind and often fails at the same time or shortly after. Single circuit systems were the norm for well over half a century and only the "safety police" and their "enlightened" ideas led to the changes that we are all stuck with today. I'd leave your braking system as it is. Just my humble opinion. RAY
rjm RAY

Hi All, I am an interloper as the car in question is a 1960 MGA 1600. I dont like the combined brake and clutch master cylinder so am going to fit a MGB pedal box and thought that a tandam brake cylinder was a good idea. Back to the bleeding problem, isnt there some valve or switch that comes into play if a line fails and this is what causes the rear bleeding issues in none standard applications.
Thanks for the responses so far.
s page

As I say the switch that detects pressure imbalance on a dual system (which is operated by a shuttle valve) doesn't impact bleeding apart from having to recentralise it afterwards on the early system, or partially unscrew it beforehand and retighten it afterwards on the later.

Irrespective of the imbalance switch dual systems are more difficult to pedal bleed as the circuit not being bled (assuming that has already been bled) prevents full pedal travel.

I don't see how 'non-standard' by which I assume you mean retrofitting to an earlier car changes that, if it is installed the same as they were by the factory.
Paul Hunt

When bleeding the tandem master cylinder, the brake low pressure warning switch should be unscrewed 1 1/2 turns. This will allow fluid to flow after the internal shuttle valve has moved due to the drop in pressure in one half of the system. When bleeding is finished, the switch must be re-tightened. If it refuses to go back in, slight bleeding of the front or rear brakes may be required to centralize the space where the switch resides. RAY
rjm RAY

This thread was discussed between 05/12/2015 and 06/12/2015

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