Brakes

[ants]

After some advice from the knowledge base please.
Having trouble with rear brakes locking up if I have to brake hard.
I know the cause (7/8" wheel cylinders).
From previous discussions on here having the wheel cylinders sleeved down to 5/8" is the fix.
My questions are -

Is 5/8 a good option or being a GT Falcon spec, is it more a race option and not have enough rear braking for regular driving? Maybe go 11/16 or 3/4?

Would I just be better off fitting an adjustable proportioning valve and tune the brakes with that?

Current setup is....'70 Mach 1, standard booster that was recoed 4 years ago, XA master cylinder, XF alloy calipers, 7/8" wheel cylinders and no proportioning valve.

Interested to hear your opinions

[Shaunp]

5/8 is what they need or a willwood proportioning valve in the rear, which is cheaper than the cylinder.

[ants]

Thanks for the reply Shaun.
Which option would you choose?
Wheel cylinders are dearer but easy to fit and possibly give a slightly higher pedal.
Proportioning valve cheaper but a bit messing around to mount and modify the pipes.

[Shaunp]

So in my 67 which currently has XF fronts but will end up with either a dual piston PBR or a set of lager Willwoods that came of one of Fataz racing Trans-am cars both of which I have in the cupboard , I have fitted a valve and some off the shelf 13/16 XY cylinders. Ray at Knights in Brisbane charges 200+ to make the 5/8 ones. On Astroboys 65 I did the same Valve ,13/16 and it has original 4 spot KH front brakes stops fine,

[ozbilt]

The adj prop valve goes in the rear line easily.

65-7 goes in the back where the original was fitted. 68-70 in the front where the original one was fitted.

Just need the adapter fittings, no big deal.

[smh00n]

Put in the proportioning valve. I spent a lot of time and money chasing rear brakes locking.
I now have a valve, wind it off, no more rear brake locking. Probably feck all rear brakes but enough was enough.

It's got me beat why these things lock rear brakes, surely they didn't do it from new.

[Shaunp]

Put in the proportioning valve. I spent a lot of time and money chasing rear brakes locking.
I now have a valve, wind it off, no more rear brake locking. Probably feck all rear brakes but enough was enough.

It's got me beat why these things lock rear brakes, surely they didn't do it from new.

They would have, my v8 torana was bad. Ive also watch some old episodes or Peter Wherette on Torque . He was test driving a brand new HZ Premier, and he demonstrated how it locked the rears and would spin in an emergency stop