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ALL WHEEL DISC BRAKE MASTER CYLINDER

Started by _LH SLR 3300_ , Aug 29 2009 10:12 PM

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3 replies to this topic

#1 _LH SLR 3300_

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Posted 29 August 2009 - 10:12 PM

Hi all. Awhile back I posted a question regarding using the factory proportioning valve in LH LX Torana with rear disc brakes. Got some very helpful tips & advice off a few forum members, thanks heaps guys. I now have a much better understanding of how the braking system works in that the valve keeps regulated pressure to the rear drums, pressure not needed with rear disc brakes. In any case, following some of the advice i was given I modified the factory proportion valve that bolts to the engine bay skirt. Here is the valve & the parts i removed.
Posted Image

I thought this would be the only mod i needed until i went to buy a new master cylinder. I told my supplier that the Torana was going to have rear disc brakes & I wanted a master cylinder that would bolt up to the standard Torana brake booster. He said he could either supply a disc/drum or a disc/disc one as used in HX/HZ. Which one do I use? He told me the disc/drum master cylinder has a proportion valve in it where as the HX/HZ disc/disc one doesn't. So did Toranas have two proportion valves, one in the master cylinder & one that is part of the junction block that bolts to the engine bay skirt? I'm a little confused now & there is a price difference between the two master cylinders, $180 for the disc/drum & $240 for the disc/disc so I want to make sure I get the right one. Any advice would be very much appreciated. Thanks Matt

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#2 dattoman

Do I feel lucky? Well, do ya, punk?

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Posted 29 August 2009 - 10:36 PM

Either your supplier is a clown or you misheard him
The disc/drum one has a residual line pressure valve in it
Not a proportioning valve.
WB was the first bg Holden to have a prop valve built in
Also A9X and late UC which shared the VB Commodore master.

Now... if your car is an early car which by the pic of that single pole switch valve it is
Then there is no disc/disc master for it as there was no car used with that configuration master cylinder offered by Holden before 1977

So what you have to do is use the disc/drum master and remove the afor mentioned line pressure valve
That valve is a rubber duckbill looking thing underneath the brass olive that your pipe tightens up on in the master cylinder

Now... in a perfect world you would remove the drum brake valve... and refit a disc brake valve in its place
But if your just buying a cylinder from an auto parts store and not a brake specialist who can refit a disc valve... just remove the drum one and toss it over your shoulder
Then refit olive and plumb it up

The HX/Z cylinder although it looks the same has the pipe outlets swapped so you would need to repipe to the prop valve to make that work... but it could be done if you want to pay extra for the master then extra to have new pipes made

Personally I would use the early cylinder , original pipes , and do the valve mod

Rear brakes of course being the larger of the 2 threaded outlets

There was a link on the homepage that described how to do this but as our mainpage seems to have evaporated in the forum upgrade...you'll have to do it yourself without the pretty pictures.

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#3 76lxhatch

That was easy!

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Posted 29 August 2009 - 11:23 PM

Just to add to the above, your prop valve may leak having removed all those parts as the big rear seal isn't really designed to hold pressure. Refit everything except the plastic/nylon tapered bit that sits inside the spring and it should be good.

As above with the master cylinder, just use an original style 1" with the residual pressure valve removed.

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#4 _LH SLR 3300_

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Posted 30 August 2009 - 09:13 AM

Thanks, thanks heaps dattoman & 76lxhatch. My supplier is very good so it's more likely I miss heard him & he did mention that I would need to change one of the brake lines too. Dattoman, I think I will follow your advice regarding modifiying the disc/drum master cylinder, rather than muck around with custom made brake lines etc. My project is a budget build so I don't want to spend money where I don't have to. In saying that, I don't want to compromise safety & reliability either, which is why I'm doing as much research as I can before I attempt any mods etc so I don't have to learn the hard way. Thanks again, your advice is very much appreciated. 76lxhatch, you've helped me with advice before, for which I'm very grateful too. I noticed that you agree with dattoman regarding removing the residual pressure valve from the disc/drum master cylinder too, another reason I will choose this mod over using custom made lines & the HX/HZ master. I also believe you suggested the mod I did to the skirt mounted valve. Again, thanks for your input, & yes I've had these valves leak before from that same spot & these particular valves weren't modified either, just worn. I will refit the parts minus the nylon tapered part. Without your input, I would've learnt the hard way by finding the valve would no doubt leak all over the fresh paint in my engine bay as soon as I attempted to bleed the brakes, so many thanks again.

Cheers Matt