About 10 years go, one of the first items I did was switched to 69 Front disks brakes, used all the components from the 69 out side what was the "available " cure for new rotors, not long after that switched to tach dash with ALL new harnesses from AAW. Since I have had this issue w/the car where the brake light would not come on when I used the parking brake, which was not a big deal until I switched from automatic to 4 speed. Then last year I took a trip from Phoenix to Pomona swap meet, and the light started to flicker, then out of nowhere, the light started to work when I used the parking brake, and when I was not using parking brake, it at times it would flicker, long story short, it works real bright using parking brake, and now it is on full time but not bright. So last weekend I put in a new master cylinder and "hold off valve" (not sure what that valve is), but replaced it since I was going to be there, found an issue with my booster, fixed it, bench bled the master cylinder before install, bled all brakes, light went out woo hoo I thought, last night, I start the car up and the red light is on dim again after releasing the parking brake, good pedal, no leaks.
I am planning a 1100 mile (one way trip !) to Spearfish SD next week (leaving Friday or Saturday) will be going through some mountains so brakes is something I don't want to scrimp on!
Going back to the "hold off valve" is there something I should know about this thing? Looking for some guidance, brakes seem to work good ideas?
I am not a mechanic, hate grease but can do most work myself outside a motor rebuild or trans rebuild, body was my field of choice, and in the 11-12 years or so I have owned it, the only thing I have done "body" on this car is paint the black on the rear body panel and the front argent filler. The rest is for future Clone car, Paint & Body then.
I suspect that your light coming on has nothing to do with the pressure sensor. Especially if it only comes on dimly. This light is activated when it gets a ground. The ground can come from either the parking brake pedal or from the pressure sensor. I suspect that it is getting grounded somewhere else. I would chase the wires coming from the light to these two places and see if a wire is chafed or damaged where it could be getting grounded. To narrow your search, try ungplugging one at a time to see if the light goes out, if it does not then unplug both of them, if the light still does not go out then you know for sure that there is a ground connection somewhere in the wires that is not supposed to be there. Hope that helps.
Thanks Pat, Since I have gotten back from Spearfish the car was put Dads garage, since then I really have not looked at even my garage, I am sure you are on target, usually, during the drive up to SD and back, when I started the day there was no light and it would start to come on dim, then by the end of 8,9 or 10 hours of driving the light would her brighter and brighter, then be on bright red like the park brake was on most of the time, the 3 in my groups concensus was it was a ground issue as well, it was just funny after several years of having no light on as all. I now have a light with a mind of it's own the brakes all work fine, so it is an issue that will be checked in the near future, I hope ... there always seems to be that 1 item that needs tweaking on these 50 year old cars! I guess that is what keeps us going I'll chime in when it works or does not work.
Ok, loose pressure, is that in the brake fluid, or vacuum pressure? On the road, got about 2 hours in, and the light starts to flicker, further I get brighter the light gets, have full fluid, not using the brakes, cause I am highway, factory cruise is working.... Could it be the vacuum release valve at the booster? The car stops ok when I do have to stop. Anybody run into this before? Suggestions?
check the switch at the parking brake assembly. It's triggered from the lever you push down with your foot. The switch at the booster only senses loss of hydraulic pressure. The same dash light serves 2 purposes, loss of pressure and a warning that you have the e-brake engaged.
When the light would not work at all, I did the brake switch replacement and "bending of the prongs" to make contact, it would not come on when you used the parking brake. Then one day, it started working like 5-9+ years later.... but about the same time the light started flickering, it stops well, and the flickering light went off last week when I put the master cylinder on, but now it is back on, don't see loss of fluid, but I guess I'll pull the wheels back off, and look closer as I cleaned everything when I had the rear drums off and the calipers when I greased the bearings.
So what does the "hold off" valve do? it's purpose
The hold off valve provides a brief delay for rear brake actuation. It holds off full pressure to the rears so they won't lock up when the brakes are hit hard. Modern disc/drum proportioning valves eliminate the need for one.
Great to hear a fellow '67 guy is attending the NIA this year. I have the gold '67 4-door hardtop with the plate 67MPALA. Hope to see you there. I am planning to bring my '67 display items and other goodies.
on 7/8/2017, 8:25 am
the brakes all work fine, so it is an issue that will be checked in the near future, I hope ... there always seems to be that 1 item that needs tweaking on these 50 year old cars! I guess that is what keeps us going 