Rear disc lock up issues

[Zonka]

Howdy all,

Before I begin let me just say 'I searched' but I couldn't find any info that..... I could understand.

I've had rear discs on my SWB sierra for some time now but hate the fact the rears are doing most of the work ie rears lock up way before the front. In total I've changed 2 sets of pads on the rear & my fronts are still going strong (at this rate the fronts will never wear!!!). At first I thought the master cylinder was stuffed so that has changed & the rear calipers re-built but to no avail. I was considered putting in a manual proportioning valve but there has to be something I’m over looking. I know there’s a residual valve somewhere to hold the pressure for rear drums but where is it & how do you modify it? The only thing I could trace the problem to is this (see below):





Thanks heaps in advance for your advice!

[lay80n]

If you are still using the origional master cylinder, what you are overlooking is that drum brakes require much greater fluid volume than discs to opperate, therefore when you use the brakes, much more fluid is going to the rear, causing more pressure at the rear brake pistons than the front ones. . You need to either alter the master cylinder, or fit an aftermarket proportioning valve. Basically you need to make the pressure at the rear brakes slightly less than the front brakes so you have a good even and safe braking effect.

Layto....

[nicbeer]

ditto, same problem here, i have a manual valve here but not installed it yet. little bit scary in the wet with the back coming round to scare ya.

i beleive ca18escort i think it was did a mod with the original valve spring side of things.

[Zonka]

I saw that post as well but have no idea what spring has to be modified etc. Might just bite the bullet and get myself a manual proportioning valve...... what a pain!

[christover1]

Mine has no issues with rear lock up, brakes straight, but does use pads faster than the front. I have no special proportioning valves fitted.
Mine is a 1.0 litre brake system, which is different to some 1.3 NT and all 1.3 WT.

In mine, the spring to be removed was at the master cylinder behind the brake line fitting.
On 1.3's this can be at another point, tho.

hth
christover

[built4thrashing]

ive read somewhere a forested master cly can be used but not sure.


If the stock master pushes more fluid to the rears then could you just swap the lines over at the master clynder????

[MightyMouse]

Not a wonderful solution - but if you reduce the pad area on the rear brakes then this will change the overall balance.

You can grind away some of the friction material in increments till it feels "right"

However if its really out of wack then its not the way to go.

[christover1]

I must note, my rear disc calipers are from the rear of a Pintara, so were designed to be at the rear. This could make all the difference?

I have heard that some use softer pads up front and harder at rear to help with bias..and some turn down the rear disc to create less braking area..I don't like either of those options, tho.

christover

[Zonka]

Cant really see how that would make a difference considering both lines from the master cylinder make there way to the back anyway (both connect to that block just in front of the fuel filter) & from there goes off as one line to the rear diff (see pic)..... ahhhhh.... if only it were that simple!

[christover1]

Cant really see how that would make a difference considering both lines from the master cylinder make there way to the back anyway (both connect to that block just in front of the fuel filter) & from there goes off as one line to the rear diff (see pic)..... ahhhhh.... if only it were that simple!

Mine dont do that.
My line from rear of m/c goes to a splitter to both fronts.
The other is straight thru to the back end. Originally into one wheel, then across to the other. Now has a splitter on diff with a line out to each.

Later models have a 3 way splitter thing, so if one wheel/brake fails, the other 3 still werk.
Tho I don't understand how.

just realised who you are, g'day mate

[Zonka]

G'day!!! (not many bright yellow zooks out there!)

Been fixing little issue which I've lived with until now but I want a car which I can drive and not be a hindrance to myself & more importantly other drivers.
It seem as though I have no choice but to install the manual valve.... bugger... (I don't want to be grinding pads etc). Lets just hope it solves the problem!

[nicbeer]

post up pics once u done it as i am still looking at doing mine

[tanshi]

my calipers are from a ford corsair and i also have no issues with rear lockup. thought the actual pads a re smaller that the sierra fronts. Leyland Mini proportioning valves are the way to go so i have heard.

[MightyMouse]

my calipers are from a ford corsair and i also have no issues with rear lockup. thought the actual pads a re smaller that the sierra fronts. Leyland Mini proportioning valves are the way to go so i have heard.

Now that's interesting - anyone got any experiences with this ?

[Bazooka]

Just get yourself one of these;



Thats what I have for my rear brake setup. Although I havent put it in the system just yet it should do the job. Yes I do have the trouble of having the rear wheels lock up under hard braking.

[sic_zook]

bypass the proportioning valve the one in the photo n use a widetrack mastercyliner whichu should be already using

[nicbeer]

bypass the proportioning valve the one in the photo n use a widetrack mastercyliner whichu should be already using

WT ones do it also as i have one in mine.

[MightyMouse]

Always interested in a recycled solution - spending $$ is the last option

Anyone heard of the mini solution ?

[want33s]

Has anyone tried removing the bleed back/restrictor collet from the rear line outlet of the master cylinder?
It works in Falcons & old holdens when going to disc rears.

[christover1]

Has anyone tried removing the bleed back/restrictor collet from the rear line outlet of the master cylinder?
It works in Falcons & old holdens when going to disc rears.

I have, I think that is what they meant, maybe?

[mugginsmoo]

Always interested in a recycled solution - spending $$ is the last option

Anyone heard of the mini solution ?

the BMC mini prop. valves, lock when you "jump" on the breaks, this was to stop the rear breaks from locking up, under HARD breaking. because there is no weight in the rear of a mini. you can hear them working, if you "jam" your foot on the peddle you'll hear a "CLICK" in the rear of the car. the valve is found on the front of the rear sub-frame.

they are real simple as well, only a piston and a spring, so they would be easy to tune.

here is a link, look about half way down for MINI REAR SUBFRAME BREAK BIAS (RECONDITIONED) http://www.minisport.com.au/category9_4.htm

[tanshi]

the mini valve was advised by Graham from suzisport in springwood QLD so i would say it will work. It is supposed to be adjustable

[Zonka]

MINI REAR SUBFRAME BREAK BIAS (RECONDITIONED) http://www.minisport.com.au/category9_4.htm[/quote]

not debating that this wouldn't be a novel idea HOWEVER $175 is a little steep! I think the manual prop valve would be the go ($90 cheaper).
Although, if you could pick one up from a wrecker then you may be in business.

[mugginsmoo]

everything on that site is over-priced.

the prop. valves on a mini last for ever, so the only logical way to go is to get one from a wrecker.

[MightyMouse]

Thanks - mugginsmoo, I would guess its a $5 bit from a help yourself wrecker, and whilst I can't see it all, I suspect its adjustable as well.

Have a set of 180SX rears so this could be the answer if the bias is all over the place and with Murphy living at my place.......

[christover1]

May or may not be relevant.
Most of the minis and mokes I've had were metric in the brake lines, even if the car wasn't.
But some earlier types may be imperial.
Worth checking.

[MightyMouse]

Thanks Chris - will just cut the lines to get the flare nuts.

Although it goes against the grain to add any BMC to the mouse.

[oozuk]

I'm using vitara vented rotors and larger vitara calipers on the front with sierra front rotors and calipers now on the rear and works really well, pulls up nicely with 33's under hard lock up or smooth braking, rear's rearly lock first on mine