30 replies to this topic

[MFM]

I seem to have a dicky proportional valve (safety valve?) in my car as the brake warning light comes on every month or so irrespective of the handbrake position. The light is brighter when the handbrake is activated and duller when you disengage it. I was told to re-set the safety switch attached to the top of this valve which sometimes extinguishes the brake light but sometimes not and this week is a 'not'.

 

The history of this car I believe might be relevant to the diagnosis as the car sat for near 20 years up till 3 years ago so I went through and reconditioned the master cylinder, put a kit through the front calipers and new wheel cylinders on the rear, bled the whole system, and replaced all the original rubber brake hoses. The original master cylinder reservoir was like a cesspit of dried and crusty brake fluid. It was an all aluminium one so I assume it wasn't original to this car, so I replaced it with a big nut cast iron one. I never did think to clean the proportional valve which must have consumed some of that crud (I assume).

 

I went to a brake shop today and all they said was that it was unusual that the safety switch was being activated and to look for a problem elsewhere? Apparently the internal component is just a springloaded rod with grooves that the switch pin drops into if there is a drop in brake fluid pressure from front or back brakes.

 

This has been an intermittent issue with this car for 3 years. Does anyone have any idea;s?

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Edited by MFM, 24 January 2022 - 05:28 PM.

[S pack]

If you disconnect the wiring bullet connector from the brake fail switch does the warning light go out?

[MFM]

Yes it does Dave

[S pack]

Sounds like the switch is faulty.

[Indy Orange]

Pic of the internals for you.

Attached Files

•  364F5158-0546-44F7-A71D-948C16223C6E.jpeg   19.54K   11 downloads

[S pack]

Sounds like the switch is faulty.

Remove the switch and test it to ensure it is functioning correctly. If in doubt take it to your auto sparky to test.
 

[RallyRed]

Is it  just the picture?  or is that switch always going to report a fault, as it has both the output pipes are on the same side of the internal shuttle valve? i.e. there will always be a percieved pressure issue/ imbalance?

[Dr Terry]

This is often incorrectly referred to as a 'proportioning valve'. It isn't !!

 

It is just a junction block incorporating a pressure differential switch. As you can see the rear half has one 'in' & one 'out' going to the rear brakes. The front half has one 'in' & two 'outs' each one supplying pressure to the two front brakes.

 

In normal operation the same pressure will be in both halves of the system, so the 'shuttle' which operates the switch will remain central. If either the front or rear brakes lose pressure (i.e. fail) the shuttle will be forced towards the half with the lower pressure & the switch will close to put the light on.

 

If the switch is on (or partially on) either the shuttle is jammed off centre or the switch is faulty.

 

Dr Terry

[MFM]

I suspect my shuttle is jammed full of crud or corrosion (from the master cylinder reservoir)  as its never ever been apart that I know of. Just another job to do. Thanks for the responses

[meanmachine72]

When i did my brakes/booster.my valve was also got a reco..cost 140 for kit ect.
For some reason my ex brake shop sent stuff to brisbane to get done

[MFM]

I should have done it when I did the master cylinder as the master cylinder had terrible crud inside it and the brake lines run from it straight down to this shuttle so stands to reason its probably full of crap.

[S pack]

I doubt it will be full of crud. If it were you would have experienced difficulty in bleeding the brakes. The shuttle/piston will probably be gummed and sticking in it's bore.

[RallyRed]

Is it  just the picture?  or is that switch always going to report a fault, as it has both the output pipes are on the same side of the internal shuttle valve? i.e. there will always be a percieved pressure issue/ imbalance?

No??

[S pack]

No??

No Col, it's just a dodgy drawing.

[RallyRed]

no....the photo 

[S pack]

The front circuit of the switch block acts as a tee junction to split off to each front brake.

 LJ Brake fail switch label pipes.jpg   162.32K   8 downloads

[jd lj]

Since you're going to have to take it off anyway, pull it apart give it a good clean, lubricant the internals with brake fluid, put some thread seal on the rear plug and test it again. There's not much to them from what I saw.

My disclaimer is that I'm not a mechanic or brake professional so take all the necessary precautions when working on your brakes.

[RallyRed]

ta Dave...buggered if I can see the "rear out"...but there you go

[grumpy xu1]

Since you're going to have to take it off anyway, pull it apart give it a good clean, lubricant the internals with brake fluid, put some thread seal on the rear plug and test it again. There's not much to them from what I saw.

My disclaimer is that I'm not a mechanic or brake professional so take all the necessary precautions when working on your brakes.

Did i hydroblast yours James ? I can't remember if we did that. I have bought kits for them, they're not cheap for o-rings !

[jd lj]

Yes, it was blasted. I was glad that I opened it up after that because water had made it's way inside and it was a bit gummed up from that. It was in good working previously fortunately.

[grumpy xu1]

Wow, i haven't had that before & try to seal them completely water tight.

[dattoman]

Its 2 o-rings

pull it apart . clean it out and replace orings

[MFM]

So sounds like its either the switch or mine is gummed up and to restore it I need to chase up the O Rings before I start the job. Doesn't appear to be a common issue as the brake joint acted like they had never reconditioned one ever. Not even sure where you would buy a switch to try. The switch is clean enough and if the O Rings were rooted wouldn't the fluid bypass the O rings into where the switch operates?

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[dattoman]

Switches are long gone

You won't buy a new one

But while out you should be able to test it

 

Long ago when I worked for the brake shops - 15 yrs ago

We got our o-rings from bearing services and their part # was BS010

[grumpy xu1]

I should be able to get a chance to go to the shed tomorrow & look at the o-rings in the kits Mark fingers crossed.