[Hatya]

Ok what is this part that attaches before the portioning valve, seems to be for the rear brakes prior to going into the portioning valve. Its the round part in the pic

[cdnpont]

It's a rear brake hold off valve. Delay's the application of the rears until a specified hydraulic pressure is reached. Lets the fronts set first. Reduces the chance of rear lockup.
Used on 67-70 GM cars with Disc/drum brakes.
71 and newer GM's used a Combination Valve.

[LCAC_Man]

Originally Posted by Hatya

Ok what is this part that attaches before the portioning valve, seems to be for the rear brakes prior to going into the portioning valve. Its the round part in the pic

I've seen it called "holding valve" and "control valve" it is the factory equivalent to a proportioning valve for a disc/drum system. Year One sells replacements, it's a pretty poor design, known to sieze and to leak. It plumbs to the distribution block (not a proptioning valve).

[funbnme]

Wild *** guess here......is it some type of sensor to activate the brake lights? Senses pressure and closes ground so your lights come on?

[Hatya]

Thanks guys,
Im having some serious brake bleeding issues, no matter what i do i get air out of the Left front wheel. I already changes the master 2 times, im going to remove this part and the distribution block, and replace it with real portioning valve out of my Disc brake kit for my 67.

The 67 is going a whole different direction anyhow, and my 69 needs this more atm LOL

Unfortunately I thought I had a brake line flare kit, seems someone at my old shop decided they needed it more, so since the brake line fitting is different on my portioning block this will have to wait till morning, GRRRRRRRRRRRRRRRRRRRRR

[joe69]

Originally Posted by LCAC_Man

I've seen it called "holding valve" and "control valve" it is the factory equivalent to a proportioning valve for a disc/drum system. Year One sells replacements, it's a pretty poor design, known to sieze and to leak. It plumbs to the distribution block (not a proptioning valve).

I tried 2 of the on my 69..both leaked...one actually blow the seals out..took the thing off and never tried another...was worried about the thing failing while driving....

[Hatya]

I cant tell if mine was leaking, since the guy who did the engine compartment prior to me was in love with high gloss black. I can almost guarantee the engine comes out this winter just to redo this, its ugly imho.

Ill save it in my pile of dont wanna throw out stuff..

Just gonna use a portionging valve to eliminate it. Its a mod not an original car anyhow.

Ive been finding some real kewl stuff on this car that makes me think it really is a low milage car. I beleive i just removed an original radiator, but im not sure gonna post pics elsewhere to see.

[Hatya]

Ok replaced both valves with a portioning valve, pedal is rock solid after bleeding. Thanks

[JohnZ]

Originally Posted by Hatya

Ok what is this part that attaches before the portioning valve, seems to be for the rear brakes prior to going into the portioning valve. Its the round part in the pic

There is no proportioning valve in the photo. The flat block with the electrical connection is just a distribution block, and its only purpose is to contain the differential pressure warning switch that lights the "Brake" warning light in the cluster if one side of the system has less pressure than the other.

The round valve on the right is the metering/hold-off/delay valve, which holds off pressure to the FRONT brakes until the system reaches 30-40 psi to allow the rear shoes to move out to the drum surface before the front calipers are energized, to avoid the disconcerting "dive" that results from "front brakes first" at low speed and light brake application.

The proportioning valve (if equipped) is mounted on the side of the subframe below the driver's door.

[RJBaileyrn]

Hello,
Question::
The brackets for the distribution block and the hold off valve mentioned above..were they cad plated or zinc plated on 69 coupes with front disc/rear drum applications?
Thanks as always.
RJ

[Fred Ficarra]

Originally Posted by RJBaileyrn

Hello,
Question::
The brackets for the distribution block and the hold off valve mentioned above..were they cad plated or zinc plated on 69 coupes with front disc/rear drum applications?
Thanks as always.
RJ

I'm trying to remember. OK, I'll take a couple pictures.
The brake system is original and untouched except for washing and touchup. Note the bracket holding the hold-off valve matches the booster. That would mean it was originally cad plated. 39 years of fade have taken their toll.


Next is the other side, of course. I think the bracket holding the light switch valve was natural. What do you think? Maybe zinc???


Oh, by the way, I've found that all of these parts are VERY dependable. Non has been serviced. Of course I can only speak for original factory equipment, in service for 39 years. Not reproduction or copy-stuff.

[68Lemans blue]

Originally Posted by Fred Ficarra

I'm trying to remember. OK, I'll take a couple pictures.
The brake system is original and untouched except for washing and touchup. Note the bracket holding the hold-off valve matches the booster. That would mean it was originally cad plated. 39 years of fade have taken their toll.


Next is the other side, of course. I think the bracket holding the light switch valve was natural. What do you think? Maybe zinc???


Oh, by the way, I've found that all of these parts are VERY dependable. Non has been serviced. Of course I can only speak for original factory equipment, in service for 39 years. Not reproduction or copy-stuff.

Fred,I was told Cad for the hold off ( prop valve)and booster and black for the dist block lite switch bracket at least for 68 anyway.do you think they changed it for 69??? Happy Motoring

[davidpozzi]

That booster matches a 69 setup I have in my shop. The silver cad is correct and when new. GM didn't have any gold colored boosters or brake brackets back then, but the booster does have just the slightest tinge of gold here and there. It's far from the gold you see on boosters now.
The booster on the right is an unused original.

[Hatya]

I saved all the bracketry when i swapped out to a portioning valve, PM me if you want any info or pics of them, They are painted but i can clean them off without messing up the coatings.