13 replies to this topic

[fuzzypumper]

Well if you're looking to keep your engine bay as 1975 as possible and wish to keep the original big booster there is only one way to go really, original.

The standard factory LX PBR P7369 Disc/drum Master cyl has a 1"bore and should be used in conjunction with the original
Proportioning valve(bolted to the inner right hand guard).
For Disc/Disc models, I think the P7470 master cyl was used, well at least on kinkys anyway, but it was essentually the same as P7369 Disc/drum with out the check valve installed behind the brass connector in the rear outlet of Mcyl.
So you can convert one into disc/disc easily.
While the Proportioning valve was also different on Disc/Disc models, the original dics/drum one you probably have with markings "C150" will probably work just fine.

[76lxhatch]

I've run mine with the original master (with residual pressure valve removed) and no proportioning (disable valve or replace with drum brake thingo), no hassles whatsoever, doesn't lock rears.

[fuzzypumper]

I've run mine with the original master (with residual pressure valve removed) and no proportioning (disable valve or replace with drum brake thingo), no hassles whatsoever, doesn't lock rears.

Thats good to know, I suppose you tested that in the dry, but what does it do in the wet?
Its all about the size of rear brakes and weight in the back.
A heavy old 4WDisc Statesman has a a lot less proportioning to the rear with a higher 450 crack point prop valve but a standard Torana & Kinky
with Drums and a light rear end required more proportioning( less braking presure to rear to stop lockup of rear wheels before front).

I dont know but a Hatchback may be heavier over the rear wheels and add a drop tank worth of fuel and you might be able to squeeze more
braking pressure to the rear brakes.

[76lxhatch]

I have twin piston 290mm fronts and standard R31 Skyline 260mm rears, both slotted rotors. The rear tyres are 265s, front are 225s with a V8 over them. The drop tank is only a recent addition and I haven't been able to afford to fill it yet!

Ditching the proportioning was suggested by Hoppers so I tried it first and it has worked for me. No problems in the wet.

You could possibly be right about the hatch being different, with the stock brakes I found I lost a lot of braking power when the rear drums slackened off, I had to find some self-adjusters to keep them up for best braking.

Remember that unless you're running identical brakes front and rear, disc brakes will naturally have different braking abilities regardless of the line pressure. The fact that the Skyline discs are slightly smaller diameter may also help in my case.

Edit: my old HZ ute was a real hassle with wanting to swap ends due to rears locking up first, I know how dodgy it is and believe me if the Torana was to give any indication of doing so I'd fix it!

Edited by 76lxhatch, 16 June 2009 - 08:03 AM.

[dattoman]

HZ had 1 15/16" pistons but commy has 1.5" so force is less

And utes never had rear discs so chances are the setup was a dodge anyway hence it trying to swap ends with no weight in the back

[76lxhatch]

The ute had drums, just saying that I hated it, no way I'd put up with it on the Torana

[76lxhatch]

Yes with no proportioning I would expect front/rear balance would be fine with that setup. The proportioning valve can be disabled by disassembling and removing the plastic/nylon (whatever it is) piece, or just replace it with the drum/drum version which has no proportioning valve in it.

It won't lock the rears if you keep the proportioning valve as standard (disc/drum setup). Exactly the opposite, you will have very little rear brakes - don't do that.

[76lxhatch]

You can use the LC/LJ and probably other early Holden units where drums were fitted all round.

I have found that in some cases self adjusters on drum brakes can cause lock up problems. Also I mentioned the big rear tyres just in case that makes a difference.

[fuzzypumper]

Ok cool, I'll try disabling the disc/drum proportion valve as finding a drum brake one will be hard I imagine. I'm curious to figure out though why two Toranas I owned in the past, both with standard disc/drum brakes suffered rear wheel lock up. Emergency braking would lock the rears up & throw both cars sideways. One was a 4.2 V8 auto & the other was a 3.3 6cyl manual but both cars seemed to suffer this problem for some reason which lead me to believe a rear disc setup would be more prone to lock up with the proportion valve in place than a drum rear.

My brothers old LH Torana locked up the rear wheels too, many years ago. Being an LH it didnt have auto adjusters on the drums.
Unfortunately we never ended up fixing it because he sold it. Now that we are more knowledgable and look back, I can speculate the
problem was a seized proportioning valve as it was only thing we didnt change. It wasnt proportioning down the rears and applying full
pressure to rear I suspect.

[76lxhatch]

^^ could be, it wouldn't be hard to affect the valve operation with crud built up in the wrong place