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MG Midget and Sprite Technical - dual type M/C use for twin circuit brakes ?

This idea may be a bit off the wall....

My 64 sprite has some other master cylinder installed, and a brake booster.
Master cyl looks to have had better days, ive not had a good look yet.

Originally the car had single circuit brake system with the cast iron dual M/C feeding brakes and clutch.

My engine has a cable clutch (Datsun A14 engine)...
.
If i got an original type M/C (available from rimmer bros https://rimmerbros.com/Item--i-GMC112 )

Could i use the brake M/C for the front brakes and the clutch M/C for the back ones ?.

Car would then look quite original but have the safety of a dual circuit system.

Would need to modify the pedal to push both clevises obviously....

And also if i did this i couldnt use the brake booster.
Has anyone managed some work around to use the brake boosters on a twin circuit system ?

Just musings at the moment.
A Phillips

MGCs for the US market had dual circuit brakes, but they had to fit a second servo.

Later MGBs had dual circuit brakes, but the servo was integrated with the master cylinder.

Using both bores of a dual-cylinder would be tricky to set up. You would need to check that the clutch part would work as a brake cylinder. You would also need a pivot on the joining linkage, so that both sides would actually pressurise the two circuits and it would probably need to be adjustable, in order to set the front to rear balance.
Dave O'Neill 2

From what i read, the difference between a brake MC and a Clutch MC, given the same bore diameter, is that on a drum brake car a valve is fitted to retain pressure in the circuit to stop the springs on the shoes pushing all the fluid back every time.(residual pressure valve).

I cant see a residual pressure valve in the hydraulic circuits for these cars, maybe thats why its so important to have your rear brakes well adjusted ?.

The exploded diagram of the dual MC on Moss seems to show the two cylinders as the same.
If they are both the same diameter, then that should be the same as just using one MC on a single circuit.
Pedal travel would be reduced of course ...

again, just musings at the moment, looking at original looking, but with better safety.


A Phillips

The cylinders are the same so no probs there. Also you have the choice of 3/4 and 7/8 depending on what you want. I'm guessing 3/4 will be the best.

I was advised by the BBS not get a TRW one like Rimmers and Moss etc sell, the original spec AP Caparo ones are still available. I got mine from David Manners Spares:

http://www.jagspares.co.uk/Abingdon/partdetail.asp?partno=GMC112
John Payne

It's actually quite a good idea thinking about out it. Obviously having a cable clutch means it's possible.

You could just make a full width tube for the brake pedal and weld on the clevis pin arm off an old clutch pedal. Then using the adjustable push rod arrangement you would also have the benefit of adjustable bias.

The only thing that might make it pointless is if the reservoir part of the M/C doesn't offer any redundancy. In that I mean is there a separate chamber for each side? If not then a leak in one would still mean no fluid!
John Payne

Carbuilder solutions has a twin circuit brake booster on its books.
M J Pearson

These are light cars they don't need servos (if you want or need them that's a different matter), IIRC (UK) B roadsters didn't have or need them and they're bigger and heavier than Spridgets.

The servo makes no odds to the braking (other than when the servo leaks fluid).

With front and rear m/cs you'd want to keep the designed balance of front to rear braking.

I was going to say the same as John, to research the m/cs for quality, quite a bit on this subject in the B section here.
Nigel Atkins

MGBs had optional servos, although they were standardised later in production.

Although they are bigger and heavier than Spridgets, they also have larger discs and drums.

I did consider fitting a servo to my B, but opted for simplicity.
Dave O'Neill 2

Yes, no servo on my frog, and no need in my opinion.
But some people do like them
I remember a BBS member several years ago being anti-booster then changing his mind after driving a car with one ?

If each cylinder only serves two brakes rather than 4 then maybe the smaller 3/4 bore would be better.

On my frog i made a similar arrangement using two MC's i got from my local parts store and a bias bar i got from car builder solutions.
It works very well. also what i did was lengthen the pedal and move the pivot point upwards into the engine bay by an inch so that gives more leverage.

TRW is quite big over here, advertising signs in all the parts shops so would be easy and cheap for me to get rather than having to ship something around the world.

Of course, i could just use the original type MC and keep the single circuit brakes and not use the cyl for the clutch.

A Phillips

Interesting project
You would need a pivot (balance bar)to adjust for differing m/cyl travels front-rear
You would need two boosters if boosting but,
with twice the amount of fluid being moved an adjustment to pedal leverage would be the best option in my opinion
compared to a small master cyl with normal leverage points, a larger cyl. combo and higher leverage gives a better more solid feeling pedal and the ability to pump heaps of fluid if needed
I like the idea you have and no booster
willy
William Revit

I done a back to back test between two Bs one with and one without servo both stopped the same just difference in pedal feel.

Having driven classics as 'dailies' for two decades plus I'd say it's fine to just use the original type MC and keep the single circuit brakes and not use the cyl for the clutch.
Nigel Atkins

best brake feel I ever had on a B was a 1" master cylinder with the pushrod moved 3/8" down the pedal - good solid pedal and amazing stopping power----no booster - don't really like the unreliable varied feel of a booster for competition use
William Revit

I had a Mk1 midget (disc brake car) with a servo that had been fitted by the previous owner and to be honest it was quite good. You don't need one and I'd never do the mod myself but it felt fine and worked well.

For some people they don't like the hard pedal when going from a modern to a classic so I suppose that's why they fit them. Where does it end though - power steering etc?!
John Payne

We used one of these cylinders in another car (Singer) when other changes to the brakes triggered a demand (by the certification system we have for modded cars) to install dual circuit brakes.
There was insufficient width for a conventional dual circuit pedal box, and a tandem cylinder was not an option either in case we needed to adjust front/rear bias.
It worked out well.
As per Willy's post above you need to have a balance bar,
Paul Walbran

This thread was discussed between 25/05/2019 and 27/05/2019

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