Disc brakes

[dalekerr]

I had the front drum brakes replaced with disc today. After driving it a bit I noticed the back brakes are the only ones that are locking up when I try to stop quick. The master cylinder was replaced with the one for disc brakes. The brakes were bled properly.

Do I need to change the proportioning valve?
The mechanic who changed it only does brakes and is very knowledgeable, but not sure how to handle this?

Help please!

[GMAD_Van Nuys]

A Camaro that originally had drum brakes does not have a proportioning valve:

http://www.camaros.org/brakevalve.shtml

You need to ask your mechanic if the correct proportioning valve was installed on your Camaro.  You should also not attempt hard braking when you have installed new rotors and pads until they have been used for awhile.

[dalekerr]

I currently have the original proportioning valve on the car. My question is do I need to replace it. If so what valve, one made for front disc brakes?

[69Z28-RS]

Read this...         http://www.camaros.org/brakevalve.shtml

And then re-read response #2 ...   

[KevinW]

Dale, are you sure you are referencing the correct name?  Proportioning valves are brass, bolted to the drivers side subframe rail (2 piece brake lines). They came on 67 Camaros with Air Conditioning, but drum or disc was not a factor in their usage. 

Drum brakes usually only used the distribution block under the master cyl (with brake warning switch). This was also used with disc brakes. 

With factory disc systems, the metering valve was added to apply more force to front brakes before the rear wheels engaged.  Modern aftermarket brake valves are adjustable to serve the same purpose.   

[dalekerr]

You are correct, my car has a block under the master cylinder that is distribution block and not a proportioning valve as I stated.
Do I need to replace this or add a proportioning valve to get the front disc brakes to work properly?

Currently I cannot get the front brakes to lock up and the car is not stopping as good as the original drum brakes.

[GMAD_Van Nuys]

Camaro Central sells a proportioning valve for a 1967 Camaro that eliminates the distribution block:

https://www.camarocentral.com/1967_1969_Proportioning_Valve_and_Bracket_Set_p/brc-106.htm

I have no experience with this vendor, but know that you have to be careful whenever replacing a proportioning valve.  Good luck! - Mark

[KevinW]

Dale, I posted a rebuild thread of all 3 components here :  https://www.camaros.net/threads/1969-j52-power-disc-brake-valve-rebuild-tutorial-metering-proportioning-and-differential-valves.483596/#post-1783304849

This may help showing you what is inside each.

You probably need a factory metering valve (or an aftermarket adjustable one like what Mark posted) to make your front discs engage 1st before the rears come on. 

[Sauron327]

Kevin, You are mistaken. I have no interest in my front brakes locking up first. I have rebuilt all brake parts and own a resto shop. I don't think many in this hobby do this every day.

[jwbavalon]

I'm with Scott,  Metering Valve, "Its function is to hold off any fluid flow to the front disc calipers until the valve sees 30-40 psi of pressure; this ensures that the rear drum shoes have expanded into contact with the rear drums before the front disc calipers begin clamping on the rotors, balancing initial brake application to avoid the disconcerting front end "dive" associated with "front brakes first" under light brake application".

[KevinW]

OK, my bad.  Serves me right for relying on memory  

But OP still need the metering valve for front disc/rear drums, right?

[GMAD_Van Nuys]

I believe that the proportioning valve used in the kit I referenced earlier does not require a metering valve as described in the CRG reference material posted below:

Combination Valve
Although not used on any first-generation Camaro, all of the separate distribution/valving functions described above (distribution block and warning switch, metering/hold-off, and rear proportioning) were integrated in later second-generation disc/drum cars into what became known as the "combination valve". This valve, usually machined from brass, combined all those functions in one single device, which simplified packaging and plumbing. Multiple part numbers were required to accommodate calibrations for differing vehicle weights and configurations.

[David K]

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[David K]

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[David K]

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