Brake residual pressure valves

[ampwhu]

subject of this has come up during conversation with some owners who have modified their braking systems. probably one for Phil's knowledge i guess

if you are fitting an alternative master cylinder to you car along with a remote fluid pot, if you fit a BRPV, it will keep a certain amount of fluid in the brake pipes for the next time you use the pedal. 2psi for disc brakes and 10psi for drum brakes.

question i ask is if you remove the very rear seal in the MC when you fit disc brakes, does this not get rid of the original BRPV from inside the MC? i vaguely remember that if you don't remove this seal, the brakes will stay locked on the discs. So fitting a BRPV would reverse this process surely? i could see the benefit of fitting a 10psi one for drums as the springs move the linings away from the drum after releasing the brake pedal.

so in theory the pedal travel would be less as there brake pipe is full of fluid always.

any comments?

[philthehill]

https://www.ebay.co.uk/itm/Wilwood-Resi ... SwX~BfevJA

Personally I consider that 10lb is too high. If I was to fit a valve and retain standard rear wheel cylinders I would fit a 2lb valve which returns the residual line pressure to near factory setting.
https://www.ebay.co.uk/itm/Wilwood-Resi ... OSwISBfevI~

As an aside:-
You do need to remove the BLRPV(1) to allow the calliper pistons to withdraw or be pressed away from the disc.

A BLPRV(2) was fitted to the Mini to alleviate the possibility of the rear wheels locking up under heavy brake pedal application.
A BLPRV(2) is a good idea but an adjustable pressure valve is preferred to a fixed pressure valve as not all cars have the same braking characteristics.

[ampwhu]

so lets say you had discs on the front and drums on the rear, would you only fit a valve to the rear brakes?

i thought it was something to do with the fluid resoviour being lower than the callipers?

[philthehill]

I would only fit the valve in the brake line to the rear brakes.

The requirement for line pressure in the Morris Minor rear wheel cylinders is to do with the style of cylinder seal fitted.

I have Wolseley 1500 brakes on the rear of my Minor which have a style of seal that does not require a residual line pressure.

I have the original Minor master cylinder and with Marina disc brakes on the front and never experienced drain back of brake fluid from the callipers which are on a slightly higher plane than the master cylinder.

[RobThomas]

FWIW, I'm 100% in agreement with Phil.

[kevin s]

I've got a beetle dual circuit cylinder with no pressure valves, standard rear brakes and a servo only on the front discs it works very well, though the remote reservoir must put a small residual pressure on the brakes.

[RobThomas]

2.31 feet of water exerts 1psi. Reservoir in the top od the dash?