ill have another look at the master today, dont think ill be ble to tell if the springs are different tension, but ill have a closer look

i dont think i spun the wheels to check if the pressure was that great, but pushing it around the shed got annouying so i disconnected the front brakes and it suddenly became easier to push

but now i will have to wait till i put the new brakes on to test it again

daveman what rear brakes are you running in the sedan ?? and how close is it to seeing the road ?? i'm looking forward to hearing about it

when i had the brakelines done for my front brakes i asked the guy doing the work his thoughts and experiences ..... based on the front discs holding 2psi in the lines there should be very little drag on the rotor, to test he suggested have the front wheel off the ground apply the brake and release, spin the wheel by hand to feel the drag. then quickly crack the bleed nipple to release pressure in the caliper re spin the wheel by hand and feel the drag, if it's noticibly less then the pressure valve thing is holding too much pressure in the line. the wheel should spin relatively free from drag when the brake is released. unfortunately he didn't really have any suggestion in regards to rectifying it
as for the rear he suggested to replace the drum brake valve with a disc brake valve in the master cylinder, if this wasn't possible due to the size of the valve then run with out it but look at installing a bias valve to get the required brake pressure to the rear brakes .....

daveman was talking about drilling the rubber valve. Not the master cylinder.

I don't think it's a good idea to play around with the master cylinder too much.

you know I just had a thought but it probably not worth much investigation. What if there is enough room in the master cylinder assembly to drill out that hole large enough and plug it up with a carby jet. That way you can change the pressure with the jetsize?Quote:

What do all the kids with 1600's do when they upgrade to R31 rear discs?

For my rear discs I drilled a very small hole in the original valve to relieve residual pressure. As per what Dattodude said, perhaps this was the wrong things to do. Maybe I'll also find the rear brakes not doing much?

I didn't look that close, but the springs might be different tensions, or the hole into the master cylinder might be smaller. While you have it apart (if the beer is not affecting you too much) have a look at that.

I know of loads of people who didn't do anything about these things, and didn't have any problems.

well the thinkg that has confused me is that the front and rear pressure doovy are both the same in my 1200 coupe master, disc drum
and i also pulled apart a 120y master and they were both the same in that as well

thats the thing that has stumped me. why are they the same if one is for disc and one for drum

PS really hard to type when drunk

yes. All master cylinders have some form of residual pressure valve integrated.

But they are specific to discs or drums. I once recommended removing the residual pressure valve, I'm less likely to recommend that today. Getting another spring rubber valve thing from another master cylinder's front circuit would be the best advice.

My rear brakes hardly worked at all, Not that the car has been driven much. I haven't even bedded in the full width of the brake pads yet.

kinda makes sense, but realistically wouldn't all master cylinders that are designed for a disc/drum application have valves internal designed to hold the correct psi in the line regardless of the caliper on the end ?? or does the actual caliper have some influence in the amount of psi the master cylinder will hold/release ?

I can answer this.

Discs use 2 psi residual pressure.
Drums use 10psi residual pressure.

Now this is why there are drum master cylinders and disc master cylinders. Or more commonly a mix of disc/drum master cylinders.

You can buy the expensive wilwood in-line residual pressure valves, and remove the ones in the master cylinder, or you can use a factory one that's appropriate for your disc/drums disc/disc configuration.

So when you do a 120Y brake upgrade from a 4 wheel drum setup, you should use the 120y master cylinder (Preferably from the earlier non-boosted 120Ys).