19 replies to this topic

[GreaseMonkey]

Hi,

My mini was born in 1994, so it has a Servo which I'm removing for space. I'm going to replace it with the pre servo yellow tag master.

I'm after the thread sizes so I can have some brake lines made up

This is the master



I need the sizes for the top and bottom, from the instructions that came with it the top thread is smaller than the bottom?

This is the limiter valve fitted



I need the thread sizes for the top two and bottom two.

Just want to be sure as I've heard mixed answers from searches on forums saying metric/imperial

Cheers

[Dan]

The yellow tag master and FAM7821 valve should both be all metric. Just trying to remember if the yellow tag master is smooth bore or stepped though. I seem to remember it's stepped while the master you are replacing is smooth, if so it will alter your brake ballance.

[bmcecosse]

I would (and did) get rid of the ghastly taper nose 'pressure regulator' valve - it's not a limiter. It's threads are m10X1 and I believe the smaller thread on the master is also m10X1 and the other one m12 - but sorry don't know the number. Possibly 1.25.

[GreaseMonkey]

Dan, the master is a stepped bore from memory. It said on the instructions that came with it, I'll confirm. I've seen people running this type of master with the brake regulator valve? Didn't minis from '78 on use the same regulator valve on the bulkhead and yellow tag master?

Cheers

Edited by GreaseMonkey, 18 February 2011 - 04:56 PM.

[Ethel]

Yellow band cylinder is 10x1 top & 12x1 on the bottom. you will most likely have to swap the connections over on the FAM thingy - the bottom (12x1) outlet should supply the rear brakes. Minispares have a pipe conversion kit.

[bmcecosse]

When I got my last Mini the (no servo) brakes were connected wrongly at the regulator. It would lock the rears in an instant - as a high speed spin revealed on the run home. I got rid of the regulator - swapped the pipes around, and fitted a pressure regulator in the run to the rear brakes. MUCH better - no more heart-stopping spins!

[GreaseMonkey]

Aha I'm glad someone mentioned swapping the pipes around, it says so in the instructions too!

So 10x1 and 12x1 for the Master. Are all the threads on the FAM/limiter/balance valve 12x1?

Thanks

[1984mini25]

This is how the yellow tag masters connected up an an 84, so as fitted from new.

[attachment=108088:DSC_00592.jpg]

Ps. I’m also after a fully working type 4 green tag master cylinder.

[Dan]

Didn't minis from '78 on use the same regulator valve on the bulkhead and yellow tag master?

They did but the issue is the size of the rear cylinders, the regulator has nothing to do with it. Just now I can't remember if the size of the rear cylinders changed when the servo was added but the braking effort at each wheel is largely a function of the difference in size between the piston in the M/C and those in the slaves.

I too have had the displeasure of driving a Mini with the regulator fitted backwards, it's very scary. We have tested this regulator on the forum and cut one apart (they are not serviceable) to find out what it does because nobody seems exactly sure. It seems to be a delay valve that slows the application of pressure to the rear wheels, but does not limit the pressure at all. It only limits the rate at which the pressure can rise.

[1984mini25]

Just found this while searching for something else.

[MRA]

It is a proportional valve, and as such the internal pressure is divided between front and rear in a % proportion, due toi the action of the spring the percentage split can change, ie. if yo uhit the brakes real hard it can apply a lower percentage to the rear.

I was sure I saw rebuild kits for these recently ??

[Ethel]

I don't see how it can proportion, i.e. create different line pressures. Surely the pressures would also be fed back to the master where they'd equalise across the pistons?

My speculative guess would be that it closes the rear brake circuit at a certain pressure (set by the spring) in a similar way to the old valve on the rear frame. Also, thinking of what it replaced, it might incorporate a shuttle valve so it can close the front circuit if it loses pressure. It'd explain why getting the plumbing arse about face with the stepped master is such a disaster.


Al the connections are M10x1, apart from one the lower outlet on the master cylinder.

[Dan]

It's built to open the shuttle as pressure is applied though, not close it. It doesn't have any sort of burst valve function.

[Ethel]

I've never had one in bits, so I'm purely guessing. That doesn't sound incompatible though: no pressure = a leak, so you'd want the shuttle to be shut. The puzzler is why the front circuit connections are offset, there must be a purpose in only blocking off one port - maybe to allow the brakes to release?

The main function has to be to limit rear brake effort, I can't see that anything else would help.

More line pressure = more braking = more weight transfer to the front = less tyre grip on the rear = locked rear wheels at lower & lower brake effort.

Ideally, you'd want it to reduce the rear line pressure as the front line pressure increases, but I can't see how you could do that without isolating half the master cylinder, or it would just rebalance the pressure across the upper piston. Also, an inertia valve would be more effective and cheaper.

[GreaseMonkey]

Great thanks, one other question, what thread is at the end of the metal pipe which goes into the hose for the brake caliper?

Thanks