tarzandaddyman

My 1975 Corvette appears to be leaking brake fluid from (and possibly sucking air in through) the small "crater" on the side of the proportioning nut on the proportioning valve. What is the purpose of this small "crater", and can I replace the nut or do I have to replace the entire valve? Andrew

Duke94

You will need to replace the valve. The hole in the side of the end plug is a vent between 2 o'rings inside the plug. There is a pressed in plug that holds it together. The one in the 2nd photo was machined to get it apart.

Gary

tarzandaddyman

Gary, Thank you for your reply. The photos are a great help. If I can get my hands on a plug that isn't leaking from the vent, can I not just swap it over rather than having to replace the whole unit? Andrew

Duke94

Yes, but it should be be from a Vette as some other GM cars and trucks had different proportioning valve performance specs. But it looks like one from any 75-80 GM 'A' body (Chevelle, Tempest, Cutlass, Century etc) will work. Note that there were 4 Suppliers for GM Proportioning valves back then (Delco, Kelsey Hayes, Bendix and Weatherhead). You need the Weatherhead which is the only one with a brass body. There should be a ton of them out there. Good luck

Gary

tarzandaddyman

Gary, The replacement valve that I'm looking at getting has the following number stamped on it:
366/810.3637963
WAG 6 139
7
GM part # 339780
Have I got the correct brass body Weatherhead unit?

Duke94

Andrew,
Yes, 339780 is the correct part number. If you are going to toss the old one, I'll take it for the cost of shipping. I want to try and figure out a way to get it apart to replace the O'rings and keep it useable.

Gary

tarzandaddyman

Gary, As soon as I've pulled it, it's yours! Could be a couple of weeks. Andrew

Steve COSD

I would check with MP Brakes for those parts. I believe recently the valve for the 75 is now being reproduced.

SAH62

Digging up an old post...

I've been talking to Duke94 about this valve since I first found this topic a few weeks ago. He found a way to remove the plug by inserting a piece of steel pin into the outer fluid port and tapping or pressing to force the plug off. I came up with another way using a spindle nut and a side-mount retaining ring:

Doug1

is this the same part that I have read somewhere else can be gotten rid of? judging from the posts so far, probably not. what part am i thinking of?