Disco 1 Brake pressure valve testing

Hi first post here having found a lot of helpful information on various issues. I'm overhauling the brakes, with standard spec parts, in the hope of achieving adequate braking for road use. Its always passed its MoT but I've never had the feeling there is much in reserve. I've removed the pressure control release valve (NTC6868L) and wonder if and how I can test it. So far, I blew (by mouth not airline) into the device and air only came out of the front brake port. I put my thumb on the front port and gentle blowing resulted in air coming from the rear port. So it works after a fashion, but does anyone know how much pressure should be needed to overcome the spring? Might it be too weak if I can blow it open?

I have no idea on pressure. but it seems logical that the fronts do most of the braking as they will have the most grip.
EBC greenstuff brake pads are very good, bloody dear mind!

The best way to check if it’s working correctly is a brake tester roller, any MOT station could do it for a small fee,
It would tell you the percentage from to back and if you can lock each wheel independently,

Europa486 said:

The best way to check if it’s working correctly is a brake tester roller, any MOT station could do it for a small fee,
It would tell you the percentage from to back and if you can lock each wheel independently,

Click to expand...

Thanks I was hoping to find a way of testing it while I've got it all apart. Don't want to have to change it later and have to bleed the whole system again, but equally don't want to fit a new one now if it ain't broke. If I can blow it open the spring can't be that strong. I suppose I could buy a new one and if I can blow it open too I can send it back!

Ok the only way to test the brake pressure valve is to put a pressure gauge on both sides, then relate to the vehicle manufacturers spec. best of luck with that as u have the item apart.
All the valve does is balance the rear brake to the front under heavy ie emergency braking, therefore do your rear brakes lock up ? the abs won’t let that happen, but would always be kicking in...
For the D1 the thing to check if you feel there’s an issue with the braking although the fluid has been replaced, is calliper, pads, vacuum and the non return valve at the servo and plenum on a V8.

I think I'll re-use it, its not leaking and I'm hoping that changing the discs and hoses will make a big difference. Good tip to check the servo valve, I'll be doing that.

My thinking on this that all four brakes work in normal circumstances so the valve should allow this as it seems to do. Under heavy braking the rear should be restricted and I'm sure that would need specialist kit to measure. Some pressure valves operate on inertia, simple explation would be a ball valve, ball rolls forward under heavy braking and restricts flow (if you understand what I mean)

Yes the fact that I can blow it open doesn't mean it works on pressure, although my understanding is it is a simple bias valve that limits the pressure to the rear to 70-80%. I'll refit it and worst case if I experience rear lockup look at it again.