GM Proportioning Valves investigation for compatibility

[Specky]

How does the Nova item compare Bob?

I bet it has less corrosion than the Elan one you managed to pry from my fingers at Malvern...

would there be a pottential "group buy" on the horizon.....

TTFN

[scottswatches]

is the Nova part a like for like replacement? If so i will be trotting off to the vauxhall dealer tomorrow

All this good weather and the car on blocks is ruining my mood!

[saska]

I bet it has less corrosion than the Elan one you managed to pry from my fingers at Malvern... :-D
would there be a pottential "group buy" on the horizon.....

I'd be up for a group buy. I've been looking at replacing the 2 O-rings and seal as described HERE
Doesn't look very hard to do. Note, in the article Mark is aware that Lotus advises there are no serviceable parts & also notes that he is surprised by the amount of gunge he found in the valve.
Would think EPDM would work well. Don't have a later 0.2 valve to measure without disabling a car and don't fancy paying £88 just to measure the O-rings and seal.
Prefer to replace with a new part at a reasonable cost but if that doesn't work out then, if someone has a later bias valve they'd lend me to measure the 3 parts required for rebuilding, I'd investigate further with the O-ring/seal companies.

[Specky]

is the Nova part a like for like replacement?

Bad news I'm affraid...

I've only chatted to Bob...So I've not seen one, but the answer is No...

Long story short....

Ours are mounted at the back, there's are attached to the servo.... or something like that

Hence Bob is gonna try and marry the two up....


TTFN

[Specky]

saska

It could be a harder task than it appears...

I trashed a serviceable valve by just removing it (stripped the thread at one end) in addition the dissimilar metal corrosion was quite bad where the support mount attaches.

If you need any measurements doing I can measure my other one.... just give me the word...

TTFN

[saska]

It could be a harder task than it appears...

You might be correct and I'd prefer a new replacement to factory spec. BobB's stuff is always well thought out but if that can't be done then rebuilding may be an option.
I rather suspect from Mark Hooper's report that the proportioning valves collect gunge and messes up the rear balance causing weird brake behaviour under hard braking as noted by coupeboy (resolved by replacing one proportioning valve) and others. Since most cars are 15-20 years old these valves may well be full of muck.

If you need any measurements doing I can measure my other one.... just give me the word...

The O-rings are measured by Internal Diameter (ID) and cross-section size.
The seal will be measured by ID, cross-section size and thickness.
If you're so disposed then it might be an idea to get the measurements and add them to the Wiki whether BobB succeeds or not.
Posterity can be a lovely thing. Someone may make use of it one day

[addict]

im sure mk 3 golfs have inline brake valves.
or fit another mc with built in valves

[Specky]

I'll do it within the week, if no one else is all over it...

TTFN

[bobbrown]

IF I have this correct the Nova ones are attached directly to the master cylinder with a M12 x 1 thread (its the thread I am uncertain of) and ours have an adapter screwed on the end to adapt the M12 x 1 male thread to a M10 x 1 female to take a fixed brake line fitting, My hope is that you do not destroy the threads when taking the valve off the car and you can then split the adaptor off the original and screw it on to a Nova one.
Well that’s the theory and the Nova valve should be here tomorrow so I will soon find out, if the adaptor end is not the same or there is a need to replace that end as specky damaged the thread in his, I can alway make up an adaptor to suit.

Bob

BTW that's Vauxhall Nova for our american friends

[Specky]

Fingers crossed...

let's hope we get a result.

TTFN

[bobbrown]

Fingers crossed...

let's hope we get a result.

TTFN

So do I, more jobs to do.
At least the one I managed to pry from your hand, should be a good starting point as I needed one that I could take apart.
If I get a chance tomorrow I will take a look at the "O" rings as well as it is better to risk a damaged one than a good one.

[Specky]

Is this what you got?

http://cgi.ebay.co.uk/Vauxhall-Nova-Bra ... 27ad5bdc59

TTFN

[bobbrown]

Specky

No, just the part that fits in to the master cylinder as it was only £4.45 delivered new result, the item you are looking at has two of them screwed into the master cylinder.

proportioning valve.jpg

[Specky]

That's good...

TTFN

[bobbrown]

Measured the two "O" rings and they are as follows

smaller one is 3.75 mm id and 1.8 mm cross section
larger one is 7.1 mm id and 1.8 mm cross section

This does assume my measurement are correct as O rings are tricky to measure.

It is very important to select the correct material as some materials are not compatable with brake fluid! so do not just pick them out of a box of standard O rings

proportioning valve.jpg

The two O rings form the seal between the piston and the outside so if they are worn or damaged it is these that cause the leakage and the spring needs to be in good condition as it is this that controls the valve

[bobbrown]

I like the positioning of these new valves - they're much less likely to get full of gunk and crud.

Lets not lose track of the fact the Wilwood valves are by no means ideal and I do not see how the internals of the current valves can get full of "gunk and crud" unless you are running contaminated brake fluid.
The one I opened up to get the O ring sizes was as clean as a whistle on the inside, dirty and a bit of corrosion on the out side but that is to be expected after the years it has been sitting exposed to the elements.

I have asked the question of a couple of O ring suppliers to quote for suitable O rings in a material suitable for the application should be cheap enough.

[Coupeboy]

I am watching this thread with a vested interest in a solution. Whilst I have swapped one of my valves for an unknown mileage/age unit, and got a positive result, my suspicion is that 15+ year old valves are suffering out there and I would like longer term comfort that I can leave it alone for a while yet. A solution that offers either a rebuild or a replacement of alternative origin is keenly sought. I would suggest a site 'recall' to make everyone aware if and when solutions are on the table. In other words, if a solution or two is offered then these should be publicised as a 'sticky' or whatever the web techo speak is. The thought of several of these cars zooming around (never mind in the wet) experiencing strange braking effects possibly attritributable to failing/failed valves is quite alarming. The MoT does and will pick up uneven rear pressure distribution (beyond an acceptable margin) but has a dormancy of a year for it to worsen and catch you out when you need the brakes (happened to me). As a matter of course, we should all check/clean/grease brake sliders annually (prior to the MoT) and note any rear lock-ups/yawing as an alarm bell to sort out potentially failing proportioning valve(s). On the solution of rebuilding these the Lotus Manual does not recommend this. In the absence of new (Lotus) units being available, there is no reason why a rebuild should not be persued so long as there are foolproof instructions for a rebuild (body torque values, o ring material spec etc) and you feel competent to trust your life to this (probably why Lotus does not recommend it). All power to Bob and others looking at this.

[scottswatches]

Like what Coupeby said!

All power to Bob for trying to find the right o-rings - i'll have a set!!!

In regards to the gunk, this could be from either contaminated brake fluid as mentioned or that the o rings were so badly worn that dirt was getting into the unit past them.

I don't see any reason why a semi decent mechanically minded person could not rebuild these units - they are not complex, and the chances of getting something really wrong is slight. Remember it was Lotus who recommended not to rebuild the units, and it was Lotus that designed calipers that seize to sliding pins annually ! (unless you have Bob's ali sliders!)

[bobbrown]

I think the main reason these are classed as non servicable items is not so much the O rings but more to do with the little shut off valve which closes the rear brakes off completley once a certain pressure is reached and the valve is retained by a very light spring and to remove the valve you would need to get the spring out which I do not think is possible with out damaging it.
As for crud the only way other than contaminated fluid is past the threads!
Do not for get brake fluid is hygroscopic hence the reason to change it every 2 years irispective of miles, wonder how many people do that.


Bob

[scottswatches]

if the valve was jammed closed, you would have little or no rear brakes, which is my current MOT failure.

It is soooooo tempting to give it a tap outside the MOT station to see if it frees it up to pass the test! At least i could then use the car while sourcing a replacement part.

Surely these things should be designed so that if they do fail they stay open, allowing too much braking pressure rather than too little? Or am i missing something?