repair a 1967 brake proportioning valve?

[Donald O.]

On a 1967 without the J56 HD brakes, I know it is not a proportioning valve but rather a brake failure switch but is there a way to disassemble and repair? Is my only option to replace with new reproduction or find a NOS unit?
The GM p/n is 3904303, I think.

Don

[Joe L.]

Re: repair a 1967 brake proportioning valve?

On a 1967 without the J56 HD brakes, I know it is not a proportioning valve but rather a brake failure switch but is there a way to disassemble and repair? Is my only option to replace with new reproduction or find a NOS unit?
The GM p/n is 3904303, I think.

Don

Don------


I think they are serviceable but I don't know if they are field serviceable. Even if they are, you'll need a kit. I'd contact Lonestar. They'll be able to tell you if you can rebuild then and, if so, be able to sell you a kit.

Kits to service these valves were never available from GM. As far as GM was concerned they were serviced only as an assembly.

[Peter M.]

Re: repair a 1967 brake proportioning valve?

Don,
Rich Mozzetta has described his repair procedure as part of a post back on January 1/2015. It's covered in the restoration he preformed on a black 67 427 convertible.
It is a remarkable effort and we should all be glad he shared it here.
Kind regards

[Larry M.]

Re: repair a 1967 brake proportioning valve?

Lone Star can rebuild. Call Ken and talk with him. Cost is about same as current reproduction, but final product should be better than repo.

Larry

[Richard M.]

Re: repair a 1967 brake proportioning valve?

Don,
Rich Mozzetta has described his repair procedure as part of a post back on January 1/2015. It's covered in the restoration he preformed on a black 67 427 convertible.
It is a remarkable effort and we should all be glad he shared it here.
Kind regards

Thanks Peter, Here's the link....

https://www.forums.ncrs.org/showthre...lding&p=747936

Rich

[Steven B.]

Re: repair a 1967 brake proportioning valve?

I just recently finished up a complete brake overhaul on my '67 coupe. I replaced all brake lines, distribution blocks and rebuilt the calipers with new seals, and the master cylinder with a kit including new seals and springs. The master cylinder kit also included some new brass tube seats. I completely disassembled the master cylinder and at that time, decided I might as well replace the seats. I used a puller and a coarse threaded screw to get the seats out. They were subsequently destroyed but I had the replacements so I wasn't concerned about damage to the original seats. At the same time, I erroneously decided that I should rebuild the distribution switch while I had everything apart. It could have been left together as there was nothing wrong with it. When I unscrewed the switch from the block, it came out unexpectedly with spring force and I lost a small plastic part. At this point I decided to completely disassemble the block. I used the same puller to take one of the seats out and when I did, the valve also came out with force due to the springs that are against the valve. I almost lost the spring. I did not find the small plastic piece of the switch. I purchased a replacement block, disassembled it and did some research. The block is as advertised and previously mentioned, simply a distribution block. It does not function as a proportioning valve like some of the aftermarket systems provide. The springs hold the piston (which is sealed with O-rings as pictured in Richards link) centered in the block by spring pressure against each seat for the front and rear halves of the brake system. They are kept separate by the piston. There are numerous illustrations on the internet of the internal structure of the block as cutaways, although not all are identical to the one in question. If a failure on one half of the system occurs, when the brakes are applied, the pressure from the good half plus the spring pressure forces the piston against the switch contact where it grounds and indicates a brake issue by lighting the brake warning light.
If you really need to rebuild the distribution block and replace seats, I found a simple way to do this and potentially without destroying the seats. Simply tap the holes in the seats with a 6-32 tap. Use a 6-32 screw about 1-1/2" - 2" long (I recommend a stainless steel screw because they are a bit harder and are less likely to strip threads), a flat washer (which must be larger than the seat diameter), and a 6-32 nut. With the nut on the screw (run it up the screw about 1"), and the washer under the nut, thread the screw into the tapped hole in the seat. Thread it in as far as possible. Then simply run the nut down against the washer and tighten it. This will pull the seat out of the block. If it is necessary to replace the seats because they are not serviceable, you can get replacement seats. Either search for "brass tube seats" or you can go to a site I purchased from: https://www.musclecarresearch.com/gm...e-tube-seats-1
They also will sell you a seat removal kit.
You didn't mention why you felt it necessary to rebuild the switch. I would suggest that unless you have some evidence that it is necessary, that it be left alone. If you can push the piston by using a 1/8" piece of rod inserted through the seat (welding rod will work) while someone uses a multimeter to check for continuity, you should be able to see if the piston will ground the switch when it is forced to one side. If the piston will not move, you will then definitely need to rebuild or replace it. Good luck.

Steve