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i believe a have the wrong master cylinder for disc/drum


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#1 Alistair

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Posted 01 April 2020 - 08:12 PM

Hi All

My Torries brakes were ungraded before my ownership, it now has UC (metric) alloy front calipers and the the all in one proportion valve/master cylinder pictured.

With the slightest bit of moisture on the road it locks the rears, and through forum searches, leads me to believe it may be a disc/disc master - would that be right?

 

my questions are - 

if I dismantle the prop valve what should or shouldn't i find for disc/drum set up?

I've read - to upgrade to rear discs you can remove bits from the prop valve. can you puts bits back in make it disc/drum?

if I have to replace, which master would suit?

 

I would go back to original set up but there doesn't seem to be an abundance of prop valves available (and I'm in the UK)

 

thanks guys

 

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#2 yel327

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Posted 01 April 2020 - 08:40 PM

Just a replacement late UC disc/drum one should do. Should be able to get one posted from Australia. I think they are basically the same as VB-VH, possibly P10220. Someone here with a PBR book might know.

#3 S pack

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Posted 01 April 2020 - 11:16 PM

Have you checked the rear drum brakes to ensure you don't have brake fluid soaked linings from a leaking wheel cylinder?



#4 Alistair

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Posted 02 April 2020 - 01:20 AM

yep, i have completely rebuilt the brakes, thats when I frustrating found out the calipers were metric.

The rear flexible pipe with T piece had collapsed and was blocked, the bleed nipples snapped off in the calipers 

and i refurbed the wheel cylinders......i was only trying to bleed the brakes.

 

I was going to make up a master cylinder pressure tester to see if it was proportioning correctly



#5 Dr Terry

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Posted 02 April 2020 - 07:29 AM

I think the simple fix would be to convert to the late UC type rear drum brakes. These are the Commodore style & are not duo-servo so will match the proportion valve in that master cyl.

 

There is no disc/drum version of the late UC m/cyl made.

 

Dr Terry



#6 caterham2

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Posted 02 April 2020 - 07:57 AM

You could use a proportioning valve off a Volvo car. From memory early 240 series I recall. Wrecking yards are full of them, easy to fit AND externally adjustable to get the balance right. I fitted one to a Austin Healey Sprite I had once after fitting a boosted disc set up to it. Worked well and you don't have to pay many $$ for them as no one wants them as a 2nd hand part from a wreckers.



#7 Alistair

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Posted 02 April 2020 - 08:30 AM

so Dr Terry, as I had no understanding of your post i did some study - duo servo shoes are floating and bottom and non are fixed? (with the adjuster just below the slave)?

and to stop my rear lock up problem would mean there are less effective?

 

please excuse my ignorance


Edited by Alistair, 02 April 2020 - 08:31 AM.


#8 Alistair

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Posted 02 April 2020 - 08:36 AM

caterham2, yeah as a last resort I thought off installing a brake bias adjuster, if i couldn't get the right bits for my existing setup 



#9 yel327

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Posted 02 April 2020 - 09:09 AM

Terry, what about a WB commercial cylinder? I know they are 1” but should work?

#10 dron

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Posted 02 April 2020 - 07:00 PM

Hi

   The best way to sort out brake balance on a disk drum set up on a Holden that I know of is to change the size of the rear wheel cylinders. I have hq rear drums on a uc with a 9" diff. 287mm front disks (upc kit) A9x booster and a wb commershal master.   I started with 9/16 rear wheel cylinders using ht disk front Rear brake shoes  (different to the 4 wheel drum set up on that model)  They were too small and the rear brakes were not good. Went up to 5/8 cylinders with hq linings  (with push rods unlike the ht version) and all was good   The front locks shortly before the rear and it passed brake test and inspection for rego.

 

If you have torana rear drums the 9/16 cylinder may not work as the shoe will suite a push rod type cylinder so I think 5/8 will be the smallest you can run.


Edited by dron, 02 April 2020 - 07:01 PM.


#11 dron

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Posted 02 April 2020 - 07:21 PM

I should have answered the original question 1st.

 

          The disk/ drum master has an extra valve in the outlet for the drum brakes. It retains a small pressor in the line when the brakes are released, Removing this valve in the outlet will convert the cylinder to a disk/ disk set up. If you do have a disk/ disk brake master the symptom should not be the rear locking up. If the peddle feels good and is not to low to the floor when braking the master cylinder may not be the problem. I would then look at wheel cylinder size on the rear to get a better balance. Messing around with valving will be a lot harder to get a good result.



#12 dattoman

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Posted 02 April 2020 - 09:09 PM

The master cylinder you have is correct for the car

Regardless of disc or drum rear

Its also got metric threads

Its the same master as used on the first Commodores too.. with either disc or drum rears... no difference.

P10220 as mentioned is the correct cylinder

You said you changed cylinders... but which ones did you fit ?

And which shoes did you fit ?

Maybe the issue is with the items you changed... not the master cylinder

Though it doesn't hurt to throw a kit thru that too while your at it if you are competent to do so



#13 Alistair

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Posted 03 April 2020 - 06:29 AM

good news about the master, thanks dattoman

I didn't change the wheel cylinders, just refurbished them(a good clean and new outer dust boots). did not change the shoes as still had plenty of meat

just new flexi brake pipes all round.

 

A little history - I test drove and bought the car in Sydney, it then sat in a shipping warehouse for 7 months waiting for its 6 week container ride to England

trailed it home, drove it off the trailer and the brakes were terrible.

Set about bleeding them - 

no fluid from the rear wheel cylinders and the bleed nipple, disconnected them.

no fluid from the pipe, disconnected pipes from T piece on diff

no fluid from T piece, disconnected flexi (with integral T piece) from hard line, finally fluid.

flexi and T piece replaced

moved to the front, snapped both bleed nipples in the calipers

I was having a lot of fun by this stage

 

i look after vintage and classic race cars but my main experience is with cable drum brakes,

I'm not totally out of my element but my 2 previous torries with the stock setup

where excellent on the brakes and i have to drive this one on tiptoes

so I want to blame the non stock parts

anything I can do to gain confidence on he brakes would be great



#14 yel327

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Posted 03 April 2020 - 07:20 AM

If you use this drilling down using Holden, Torana, 1979, 3.3, etc you’ll get to where it shows outlines of the 2 x different shoes for the different calipers.

https://www.dba.com....line-catalogue/

#15 Dr Terry

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Posted 03 April 2020 - 07:21 AM

I've had a car like this before.

 

A previous owner had fitted an early UC rear end to a late UC with the later m/cyl.

 

I tried several fixes, the most obvious was to fit the smaller 9-16" wheel cylinders & brake shoes to suit.

 

This worked OK, but we later fitted the later UC (Commodore) style brakes, this worked very well.

 

Dr Terry



#16 dattoman

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Posted 03 April 2020 - 08:30 AM

Would you be able to get a pic of the rear brakes with the drum off ?



#17 Alistair

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Posted 04 April 2020 - 04:07 AM

I did take pics when I stripped them down and I searched old phones and my pc for them last night, but no go

 

i'll whip of a wheel first thing tomorrow



#18 Alistair

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Posted 04 April 2020 - 05:06 AM

found em

 

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#19 claysummers

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Posted 04 April 2020 - 07:52 AM

Early type duo servo with self adjust


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#20 Alistair

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Posted 08 April 2020 - 05:22 AM

so - if the front calipers are UC, the master cylinder is UC and the rear brakes are also LX/UC - assuming there all working correctly, there should be no problem with the hydraulic system or the size of anything

 

with that said - its gonna be bad linings and/or oval drums......right?



#21 yel327

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Posted 08 April 2020 - 07:38 PM

I think what has happened is you have an earlier UC with the early type rear brakes but it’s been fitted with later UC front calipers and master cylinder. I think you need the later UC rear brakes.

#22 claysummers

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Posted 08 April 2020 - 07:44 PM

It’s either that or revert to the early the front brakes and master cylinder really.


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#23 Dr Terry

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Posted 08 April 2020 - 08:22 PM

Guys, you've got it all wrong.

 

The late UC master incorporates the proportioning valve.

 

The proportioning valve for the late brakes (inside the m/cyl) has a proportioning pressure way too high for (early) duo-servo brakes.

 

The only way to fix this is to fit the early m/cyl (& booster & prop valve) OR fit the late style rear brakes.

 

Changing the front callipers won't change things all that much.

 

Dr Terry



#24 claysummers

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Posted 08 April 2020 - 08:29 PM

We were half right...........
Change the master cylinder or the rear brakes.


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#25 Dr Terry

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Posted 08 April 2020 - 09:04 PM

We were half right...........
Change the master cylinder or the rear brakes.


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The old m/cyl won't fit the later booster.

 

You have to change both.

 

Dr Terry






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