Hey Everyone,

I was at the Supercar Reunion on Saturday (awesome vehicles there!) and was looking at the routing of the brake lines from the master cylinder. The big block cars have a distribution block and a proportioning valve and the routing of the tubing on the cars seemed a little different. The took the outlet of the master cyl to the proportioning valve (see pic) then out of the proportioning valve to the FRONT of the distribution block. Well, last night I was installing my brake lines from Ground Up and, according to the bends of the lines and fitting sizes, the proportioning line runs into the SIDE of the distribution block. I thought this was wierd so I looked in the assembly manual and sure enough, the Ground Up routing is what GM reccommends.

Does anyone know why these guys would want to take the prop valve lines to the front? Is the distribution block simply as it is named - distribution for the fluid without regards for what is screwed in where? Every Yenko at the show was plumbed the same way so I am perplexed.

Thanks for any info,

Bill

http://dive-ids.com/yenko/images/smDSC_0096.JPG

Bill, the pic you posted is exactly how my 69 Z is plumbed.

That's consistent with the cars at the show. I am wondering what the impact is (if any) of using the GM routing...? The piping that I got is certainly meant to have the prop valve go to the front side hole rather than the front. Do you know if these distributiong bloack have differing pressures for each of those holes?

Bill

Bill - what were the years of the cars you looked at, and were they "correct"?

I checked my AIM for 69, and RPO J52 (front power disk brakes) shows the lines routed as shown in the photo.

I checked the AIM for 68, and J52 shows the lines routed as you describe, with the line from the holdoff valve entering the distribution block on the front driver side corner, rather than into the front as used in 69.

So, adding to the list of things I never noticed, it looks like the routing for 67 and 68 with J52 was one way, and 69 was different.

And, if the cars you noted this on were 69s, then they were correct. If they were 67s and 68s, it's possible that they were converted to front discs using a 69 style kit (single piston calipers, 69 style hardlines, etc.).

Either way, it doesn't matter. The orifices inside the distribution block/low pressure warning switch assembly are the same in all directions, so it doesn't care which way fluid is passing through.

It sounds like you have the correct lines for 67.

Up until recently you couldn't get a repro acorn so I think they were plumbing the front MC bowl straight to the dist block. I think this may have been factory on a 2nd gen but not 100%.

Here is a 68 manual brake system.

Please don't call the round valve a proportioning valve, it is a Metering, or Hold Back Valve. It holds back pressure from reaching the front until the rear drum shoes have made contact. It helps all four brakes begin operating at the same time. This is only an issue on slippery surfaces at light brake applications.
David

Okay - the "Metering, or Hold Back Valve" :thumbsup:

Eric - I think you are right! All of the cars that I could see the "Metering, or Hold Back Valves" on were '69s.

Thanks - this solves the mystery!

Bill