[catc]

looking to see if anybody has any thoughts on what might cause the brake light to remain on...i started a thread a couple years ago on the brake distribution block..never got anywhere on the problem ,so recently replaced every line and soaked all 3 valves in a cleaner for 2 weeks ,blew them out with compressed air ,bled the system last weekend and the light remains on...if you pull the plug off the distribution block the lamp goes off..it appears to me that it is just a pressure switch..and was wondering if the hold off valve could be causing it to grd out or could the pressure switch in the distribution block be stuck?...the only available valve is the hold off valve..so ,does anybody have any advice on how to repair this or had this experience and solved it?.should i remove the pressure switch on the distribution block and see what's going on, or purchase a new hold off valve? .thanks for any possible solutions

[West Coast GTO]

I hope this doesn't sound like a stupid question but have you looked at the brake light switch under the dash?
I only ask because my 71 switch backed itself off and the brake lights stayed lit.

[catc]

sorry..i need to calarify...the brake light ..on the dash stays on..nothing to do with the rear Brake lamps or the E-Brake...

[Aus78Formula]

If the proportioning valve has a fault that light will stay on, if the e-brake is still applied, that light will stay on. If the switch or wire to it are split or grounding it will also stay on. It's an easy start, wiggle the wire around, make sure it isn't touching anything and depress the spring on the switch a few times to see it isn't stuck. Even unplug it if not sure, then you know to look elsewhere. You could try unplugging the prop valve pressure switch but I think it may be wired to show a fault if not plugged in too, easy to test.

[catc]

i've eliminated the ebrake..in the equation...already checked everything i can with it and it works as it should...it's definitely in the combination ,hold off or proportioning valve..i've tested the combination valve with a test light and it comes on, which it should have seeing how the light on the dash is on...from what i can find in the service manual that indicates a pressure differential,.... the switch has been grounded causing the lamp to power on, but is it the hold off valve causing the pressure differential???..or??i don't see in the service manual where it states if the button on the hold off valve needs to be depressed while bleeding by the foot method.????? any thoughts.....or possibly a stuck valve in the combination ???.no parts are available except for the hold off valve, so can the combination valve be taken apart?

[Judge273]

I got my proportioning valve rebuilt at White Post restoration. Very reasonable and quick turnaround.

[Pepi]

Sounds like it is definitely in the proportioning valve or the switch mounted to it. Since you can unplug it and the light goes out, that eliminates the e-brake. At least that is what it sounds like to me. I always thought inside the proportioning valve looked like an hour glass on it's side and the switch had a pin that ultimately sat in the indent. If the hour glass shaped piston moved too far one way or the other, the pin for the switch got pushed in making the ground for the wire. I'd say take the switch out and ground the body and see if the light is still on, and if it is a pin, can you push it in and out freely, if not then the proportioning valve to me would be the culprit.

[Pepi]

Here is a cutaway picture of a proportioning valve showing what I was trying to explain.

[johnta1]

See if these help:

[catc]

thanks for the photo of the proportioning valve,Pepi, That appears to me a 71 and later style,,mine is a 70 with the hold off valve..i don't believe mine has that button on it..i believe the button is on the hold off valve..that's why to me it's somewhat confusing..would be simpler if it just had the proportioning valve and that's all....i totally understand what you are saying about the piston moving forward or rearward inside, but here's a thought....there were no issues bleeding all four corners...good fluid,firm pedal and on jack stands appear to be holding good, so wouldn't one assume that the piston in the proportioning valve has NOT moved forward or rearward as wouldn't that cause bleeding issues in the frt .or rear????..could the hold off valve be causing a pressure differential??,....i will remove the switch in the combination valve and see what i find..really appreciate any thoughts or experiences on this..thank you..

[catc]

Thank you JohnTA1..i appreciate that info...will look into that..,so i should have depressed that switch on the hold off valve when bleeding?

[johnta1]

If it has the button.

Basically it keeps that valve centered while bleeding.
(needs to be centered when no pressure in lines)

[johnta1]

could the hold off valve be causing a pressure differential??

Shouldn't?

The proportioning valve part should do that.
(because disc brakes need that)

The differential valve is for showing loss of pressure in one side basically.
It should be before the proportioning valve so it 'reads' the same pressure for front/back from the master cylinder.



Have you tried the brakes with the engine running?

[catc]

yes, there is a button on the rear of the hold off valve, facing the booster, none anywhere else that i can see... i will give that a try..thank you...

[catc]

[Attachment 453784 here's a photo to show the setup on a 1970 only, the hold off valve on the rt. has the button on the rear of it facing the brake booster...the only button i can see that one would press...

[tdavidl]

i just had the same issue, we went over all the brakes...problem was the switch on the valve....we found out as I had a spare valve (71, i know) and switched them out & tested & it worked as it should....so I had a bad switch which I think they sell separately now

[catc]

just in case tdavidl....do you have a link to who might have the switch ?

[tdavidl]

here's one from our host:

https://secure.amesperf.com/qilan/De...A&web_access=Y

[FrankieT/A]

We used to run into this all the time. Here's what works....remove the switch from the proportioning valve. Lay a rag over the hole. From in the car stomp the brake pedal hard. Replace the switch and flush the area around the p valve with water to prevent brake fluid from marring painted surfaces. You may have to bleed after that. This will reset valve.

[catc]

Thanks for the tip, FrankieT/A,...just got done bleeding them a little while ago and all seems good...brakes are firm and NO LIGHT!!!!