12 replies to this topic

[nerodino]

Hi to all,
Restoring a 1989 Mini for my son and i want to fit a brake bias on as he has Metro 4 pot calipers/discs up front with standard drums fitted with fins at the rear........Minispares have been out of stock for ages for this unit (around £60-70 i think) Does any one know where i can get one from?
Also can some one post a diagram for the pipework layout?
I bought the car as an unfinished project and am not that up on Minis so any help appreciated Gents
Regards
Graham

[bmcecosse]

Can't suggest where to buy one - but the pipe from the master cylinder goes in the front - and a pipe to the rear brakes goes in one side. Just block the other with a handy bleed nipple. I mounted mine just below the master cylinder, where it was handy to open it up and change the spring till the balance was 'just right'.

[nerodino]

Thanks guys and yes i did ring them ,morew than once and they just keep stalling for time!

[R1minimagic]

Did you mean the pressure reducing valve? (4 way)

[nerodino]

Did you mean the pressure reducing valve? (4 way)

No, I was told to throw that away and fit a minispares bias...............or do you know something i dont?
I am ready to learn!!!!!

[R1minimagic]

I don't know why, who said to throw it away?!

[nerodino]

I was told just to come off the master and straight to front discs with one pipe and thru bias to rears and ditch the 4 way.......forget where i got that info but please tell if this is wrong!

[bmcecosse]

It was probably my advice - I certainly have said that a few times - and indeed did that. You need the 3 port limiting valve - not the ghastly 4 port 'reducing' valve. I had a few - but all gone now. I believe relatively expensive adjustable ones are available from specialist suppliers. The original Mini one works well if you can find one. Slightly larger (but exactly same mode of operation) valve was fitted on the 1100/1300 range - and that is equally suitable since you will be fine tuning the spring anyway!

[nerodino]

It was probably my advice - I certainly have said that a few times - and indeed did that. You need the 3 port limiting valve - not the ghastly 4 port 'reducing' valve. I had a few - but all gone now. I believe relatively expensive adjustable ones are available from specialist suppliers. The original Mini one works well if you can find one. Slightly larger (but exactly same mode of operation) valve was fitted on the 1100/1300 range - and that is equally suitable since you will be fine tuning the spring anyway!

Is it OK to fit an adjustable bias on a road going car?

[MiniLuke]

I have one on mine. If you have an old 3 port limiting valve you can make it adjustable yourself quite easily, google it there is a guide somewhere. I think I changed the spring too though.

[MiniLuke]

http://www.colinushe... Hood/mini.html

[tiger99]

This is a limiting valve, not a proportioning valve, and as such its setting will always be a compromise. If it is set too low, to prevent rear wheel locking when there is no load in the back and the road is slippery, it will deprive you of some braking effort when you have a load in the back, and/or the roads are dry. It you set the pressure higher, it will give you adequate braking on the rear wheels on adry road, but they will lock on a wet road.

That is a fundamental limitation of all such valves, including those with a knob or lever which fit in line and are sold as proportioning valves. Many of them are not, and a true hydraulic proportioning valve is rather more complex. The Willwood 260-11179 is a good approximation to a proper proportioning valve.

A balance bar is a true proportionming mechanism. It does allow correct front to rear proportioning on both wet and dry roads, since all 4 wheels will have their coefficient of friction equally affected. However, it does not compensate for having a heavy load in the boot.

A stepped bore master cylinder, sometimes used on Minis, is in effect a fixed balance bar. The larger end of the cylinder provides lower pressure for the rear brakes.

A device known as a load sensing pressure reducing valve, not used on Minis (maybe someone out there has?) is another kind of pressure limiting valve which sets the maximum pressure according to suspension height. That compensates for load changes, but again is not a proportioning valve, and will allow wheel locking under slippery conditions with a heavy load as it can't reduce the pressure accordingly.

ABS, not a standard fitting on Minis, will sort out all the wheel locking problems, while it works, but is prone to sudden electronic failure, and when that happens, some badly designed systems leave you with no brakes. And, you need to get the basic balance nearly right before fitting ABS, so that the hydraulic unit does not have to work all the time, which would wear it out quickly.

Just thought that I should explain all the options, before suggesting that the best course of action in most cases is to fit the 3 port pressure limiter valve, with spring chosen so that the rear wheels do not quite lock on a wet road with only the driver on board. There will then not be as much rear wheel braking as theoretically possible on a dry road, or carrying a full load, but in a Mini it is better to lose some slight braking efficiency than to lock the rear wheels, which is likely to result in a spin. The standard Mini valve, without adjustment facility, is correct, provided that the rear wheel cylinder bores are the same as when that valve was fitted as standard. Different wheel cylinder bores need a different valve setting, and a valve from other models is almost certain to need adjustment. The Somerford Mini site will tell you which wheel cylinders go with the pressure limiter.

Or, you could fit a Willwood 260-11179 . US price $83.94, which compares favourably with some UK products which are only limiting valves. But you will need to rearrange your plumbing to incorporate it. If you are handy with a flaring tool, and have a roll of cunifer, that should not be too difficult. The 260-10922 is simpler, just fitting into the rear line, and only $45.30, but is more of a limiter, less of a true proportioning valve. In either case I think you would need to find a way of locking the knob, once set, to keep it legal for the MOT. A simple cover bolted over it would probably suffice.

[nerodino]

This is a limiting valve, not a proportioning valve, and as such its setting will always be a compromise. If it is set too low, to prevent rear wheel locking when there is no load in the back and the road is slippery, it will deprive you of some braking effort when you have a load in the back, and/or the roads are dry. It you set the pressure higher, it will give you adequate braking on the rear wheels on adry road, but they will lock on a wet road.

That is a fundamental limitation of all such valves, including those with a knob or lever which fit in line and are sold as proportioning valves. Many of them are not, and a true hydraulic proportioning valve is rather more complex. The Willwood 260-11179 is a good approximation to a proper proportioning valve.

A balance bar is a true proportionming mechanism. It does allow correct front to rear proportioning on both wet and dry roads, since all 4 wheels will have their coefficient of friction equally affected. However, it does not compensate for having a heavy load in the boot.

A stepped bore master cylinder, sometimes used on Minis, is in effect a fixed balance bar. The larger end of the cylinder provides lower pressure for the rear brakes.

A device known as a load sensing pressure reducing valve, not used on Minis (maybe someone out there has?) is another kind of pressure limiting valve which sets the maximum pressure according to suspension height. That compensates for load changes, but again is not a proportioning valve, and will allow wheel locking under slippery conditions with a heavy load as it can't reduce the pressure accordingly.

ABS, not a standard fitting on Minis, will sort out all the wheel locking problems, while it works, but is prone to sudden electronic failure, and when that happens, some badly designed systems leave you with no brakes. And, you need to get the basic balance nearly right before fitting ABS, so that the hydraulic unit does not have to work all the time, which would wear it out quickly.

Just thought that I should explain all the options, before suggesting that the best course of action in most cases is to fit the 3 port pressure limiter valve, with spring chosen so that the rear wheels do not quite lock on a wet road with only the driver on board. There will then not be as much rear wheel braking as theoretically possible on a dry road, or carrying a full load, but in a Mini it is better to lose some slight braking efficiency than to lock the rear wheels, which is likely to result in a spin. The standard Mini valve, without adjustment facility, is correct, provided that the rear wheel cylinder bores are the same as when that valve was fitted as standard. Different wheel cylinder bores need a different valve setting, and a valve from other models is almost certain to need adjustment. The Somerford Mini site will tell you which wheel cylinders go with the pressure limiter.

Or, you could fit a Willwood 260-11179 . US price $83.94, which compares favourably with some UK products which are only limiting valves. But you will need to rearrange your plumbing to incorporate it. If you are handy with a flaring tool, and have a roll of cunifer, that should not be too difficult. The 260-10922 is simpler, just fitting into the rear line, and only $45.30, but is more of a limiter, less of a true proportioning valve. In either case I think you would need to find a way of locking the knob, once set, to keep it legal for the MOT. A simple cover bolted over it would probably suffice.

That is excellent information and thank you very much.......off to search willwood in the uk!