toyota brake proportioning valves

[rollaholic]

over the years i've heard many a story about rear brakes on various toys (mainly corolla variants it seems) with imbalances on the rear brakes, and all the usual solutions being fruitless. people start talking about proportioning valves, which i've always dismissed since they are typically so trouble free. have i been deluding myself?

today i worked on a car which had the above problem. a new (secondhand) proportioning valve fixed it immediately.

the interesting part is, it had been for a wof and failed on front pads low. the rear brakes read even at this stage. front pads were replaced, and the pistons pushed back without the bleed valve opened so fluid was returned to the MC. upon recheck, the rear brakes were found to be unbalanced as mentioned above.

i can only presume this was caused by the way the brake pistons were handled, the coincidence seems too great to me. has anyone else had any experience of this nature?

interested in peoples thoughts

[strx7]

over the past 12 months we have been selling quite a number of early to mid 90's brake prop valves from corolla's mainly

[Mr Revhead]

Yes they were a commonish thing to replace on 90ish onwards Toyotas.

[rollaholic]

yeah thats what im hearing from the wreckers too. im kind of interested to know WHY though

[Mr Revhead]

They get clogged and corroded due to lack of fluid changes.
It was most common on Corollas, coz you know you don't need to service Corollas

[iOnic]

Done a few on S engined cars (Coronas, Celicas, Caldinas, MR2's etc) for some reason. As they come up to 15-20 years old they seem to just randomly get unbalanced brakes - there's no real warning. It just fails a WOF and that's that. Regularly happens not long after a brake service.

[Mr Revhead]

Regularly happens not long after a brake service.

Pushing crap fluid back through the lines when squeezing the pistons in I bet

[iOnic]

I'd put money on it.

[YeMs]

they are actually realatively easy to clean out. i have done many of them. easy to see when its a prop valve when you have a set of rollers too. when you apply the brakes, 1 side reading will stop steady and the other will shoot up. and its generally the high side (stronger braking side) which is at fault. wat happens is the little spring gets stuck up and allows full pressure to go through to the brake. as mentioned its due to lack of fluid change and a build up of 'crap'.

if you pop the little steel caps off, you will find a little circlip underneath which hold in 2 little spring/piston type assemblys. remove the circlip (sometimes quite a bitch of a job, on the more difficult 1's iv drilled a little hole in slightly above the circlip so i can push it in so u can get a lil hook under it) once thats out (also, it pays to do them 1 at a time so as to not mix up parts) you then move onto pulling the little piston cap out which can require sum times abit of force via compressed air up its backside. give all the parts a clean up with brake clean. replace the little o-rins if need be. flush it out with brake fluid. re-assemble it remembering to lube the o-rings and pop the little circlips in and viola!.

99% of the time, honestly the blockage or build up will be so small, you will think 'shit im fixing the wrong thing', but it doesnt take much to mess it up.

[rollaholic]

interesting post yems! im kinda pissed i threw the old valve out already.

the brake fluid thing is what i was getting at with my original post, someone who shall remain nameless just pushed the fluid back through rather than letting it out via bleed nipples.

[YeMs]

haha yeh, gotta love that. bloody backyarders. you risk so much by pushing the fluid back through the system. and its so simple to open the nipple and force it out. im quite anal when servicing to check brake fluid levels and quality. even spent $150 on a electric hydrometre to keep in my tool box hehe.

[krock]

just gotta question, in regards to changing the prop valve and at the same time replacing the brake fluid, should i put the new valve in and then just bleed out all the old fluid until new stuff starts coming through?
or do new fluid then the valve?

[rollaholic]

unless you have the engine out, getting the valve out is a bit of a pain on most cars - and you lose alot of fluid doing so. i would change the valve first myself.

if you let the fluid drain completely out of the master you'll need to bleed it separately first

[krock]

if you let the fluid drain completely out of the master you'll need to bleed it separately first

sorry, just to check, does this mean the master cylinder in conjunction to the brakes? sorry bit of a newbie with brakes

[sergei]

if you let the fluid drain completely out of the master you'll need to bleed it separately first

sorry, just to check, does this mean the master cylinder in conjunction to the brakes? sorry bit of a newbie with brakes

master cylinder is the one you squeeze with the brake pedal.

[krock]

so, bleed the master separately from brakes?

[YeMs]

so, bleed the master separately from brakes?

asking questions like that, i would probly forward the job onto a mechanic if i were you. can get a little tricky bleeding a dry master cylinder if you dont know what your doin.

[krock]

yeah, i have bled brakes before-with my old man, so have a bit of an idea, but havent bled a master cylinder though.

i'm a student, so trying to do it as cheap as possible

[Dell'Orto]

While I'm all in favour of DIY, with stuff like brakes its really best to get someone who knows what they're doing to help out.

[rollaholic]

last time i changed a P valve, i went though most of a bottle of brake fluid keeping the res topped up while i changed the valve so i wouldnt have to bleed the master

if you do it this way you need to give each corner a good bleed too, especially the rears as there is a lot of fluid between them and the air you have introduced.