Brake Proportioning Valve Question

[Toxic Orange]

I have disk brake front and drum rear. Does this proportioning valve look correct? If not what would be the best replacement? Seems like a later model master cylinder, so not sure on the bolt pattern with 67-72 brake lines. What would be a good replacement (model numbers etc)? I would say I don't have great braking... would a new valve help that? Thanks for your input.

[mgchevyparts]

That's a distribution block with low pressure warning switch. A prop valve is needed if your rear brakes lock up excessively before the front brakes, if the rears don't lock up first don't worry about it. Prop valve won't make any difference in your braking abilities other then the lock up issue.

[Don Quixote]

That distribution block was used for drum/drum applications. "For best results" you will want to invest in an actual proportioning valve designed for the GMs. They're actually not difficult to come by and they normally have the low pressure switch on them as well.

I had one from when I went to drums on the front. I know, crazy but with the loads I was pulling and the hills I was going over, I was warping rotors left and right. The rotors were not ready for me. :P

[Stocker]

Also, if your MC has equal-sized reservoirs, it's for drum/drum. MC for front discs will have a larger rear reservoir, which serves the calipers. The smaller front reservoir serves the rear drums. And IIRC, rear drums use a larger diameter brake line than the front brake lines (not sure but I think it's 1/4" rear and 3/16" front).

[Toxic Orange]

Stocker:

My MC has a big reservoir in front and a small one in rear. Brake lines seem to be the same size. Likely a power brake conversion but I am not sure.

Jocko:

Truck is 1970 1/2 ton. It is a single bail MC and it seems that would not be the original, but not sure.

Sounds like I for sure have a simple distribution block and likely need a proportioning valve.

[mgchevyparts]

Originally Posted by Toxic Orange

Stocker:

My MC has a big reservoir in front and a small one in rear. Brake lines seem to be the same size. Likely a power brake conversion but I am not sure.

Jocko:

Truck is 1970 1/2 ton. It is a single bail MC and it seems that would not be the original, but not sure.

Sounds like I for sure have a simple distribution block and likely need a proportioning valve.

Disc/drum master, do you have disc brakes? You need a prop valve if the rears lock up before the fronts with disc brakes, if not don't bother with one. If you have four wheel drums you do not use or need a prop valve what so ever. Line size means nothing, no differences with line size as the pressure equalizes.

[jocko]

Originally Posted by Toxic Orange

Stocker:

My MC has a big reservoir in front and a small one in rear. Brake lines seem to be the same size. Likely a power brake conversion but I am not sure.

Jocko:

Truck is 1970 1/2 ton. It is a single bail MC and it seems that would not be the original, but not sure.

Sounds like I for sure have a simple distribution block and likely need a proportioning valve.

Thanks t.o. - the number of bails/straps does not matter, it's just an indicator that it's probably a parts store replacement - which is fine - because you answered the critical question as to whether or not it's a drum/drum or disk/drum mc, and you have the correct type for your disk/drum setup - so, it sounds like the po got the mc selection correct.

It is correct that you probably have a drum/drum conversion since it's ALL 1/4" lines. Technically, you'd need 3/16" lines for the front disks (the line that comes from the REAR port on the MC).

You could buy a set of lines (front only, incl from prop valve to front junction block). And you need to have the proper distrib block/prob valve arrangement.

Here are part numbers for you, if you were to order from LMC, for example (just an example, you can get them many places - I've purchased two 72 prop valves/distrib blocks from LMC, and have had no problems).

Lines:
OEM (non stainless) #34-5412 (includes the forward 1/4" lines that go to the rear junction block, so you might be able to buy the 3/16" only lines separately - or bend em yourself)
http://www.lmctruck.com/icatalog/CB/full.aspx?Page=158

Prop Valve/Distrib block/pressure switch:
You could use an adjustable one - #37-8559
http://www.lmctruck.com/icatalog/CB/full.aspx?page=155
or
Factory-type 72 valve - #34-3200 http://www.lmctruck.com/icatalog/CB/full.aspx?Page=158
(and associated mounting hardware might be required)

[Toxic Orange]

Originally Posted by jocko

Thanks t.o. - the number of bails/straps does not matter, it's just an indicator that it's probably a parts store replacement - which is fine - because you answered the critical question as to whether or not it's a drum/drum or disk/drum mc, and you have the correct type for your disk/drum setup - so, it sounds like the po got the mc selection correct.

It is correct that you probably have a drum/drum conversion since it's ALL 1/4" lines. Technically, you'd need 3/16" lines for the front disks (the line that comes from the REAR port on the MC).

You could buy a set of lines (front only, incl from prop valve to front junction block). And you need to have the proper distrib block/prob valve arrangement.

Here are part numbers for you, if you were to order from LMC, for example (just an example, you can get them many places - I've purchased two 72 prop valves/distrib blocks from LMC, and have had no problems).

Lines:
OEM (non stainless) #34-5412 (includes the forward 1/4" lines that go to the rear junction block, so you might be able to buy the 3/16" only lines separately - or bend em yourself)
http://www.lmctruck.com/icatalog/CB/full.aspx?Page=158

Prop Valve/Distrib block/pressure switch:
You could use an adjustable one - #37-8559
http://www.lmctruck.com/icatalog/CB/full.aspx?page=155
or
Factory-type 72 valve - #34-3200 http://www.lmctruck.com/icatalog/CB/full.aspx?Page=158
(and associated mounting hardware might be required)

Jocko - Thanks for all the detialed info and the trouble getting part numbers, etc... Exactly what I was looking for! Sounds like I need just a few parts to get it set up right.

[jocko]

correct statement on the line size differences

toxic orange - just out of curiosity, is your truck 1/2 or 3/4 ton? Am assuming 1/2, but wanted to ask - MC line routing is different between a 1/2 and a 3/4 tonner. Yours is correct for a 1/2 ton truck, but Stocker is right - I'm not quite certain you have the correct master cyl. What year is your truck? As for what is correct? I'd go to Oreilly and ask for a 72 C10 (or 20 or whatever you have) MC and prop valve/distro block. Several vendors also sell the correct valve. Unfortunately, the correct stock part isn't cheap. Am sure CPP and a few other aftermarket vendors would offer a universal option, but I prefer stock personally (no real reason, just like a known quantity, I guess).