Bad Brake proportioning (combination) Valve

[DangerDan]

My brand new proportioning valve is leaking out the front around the valve stem. NAPA part number NMC M552 does not specify if it is for Disc Disc or Disc Drum. I need a good Part number for a Disc Disc proportioning valve. Preferably NAPA so I can get it today. None of the Auto Zones - O'Reily's or Advance Auto even carry them. I see them on Summit and EBay.

[GASoline71]

Power or manual brakes?

Gary

[RichardJ]

>>My brand new proportioning valve is leaking out the front around the valve stem.<<

You mean to say your Combination Valve is leaking from the Metering Valve stem.

NAPA NMC M552 is listed as used for '87-'93 and I don't know that any of those years had disc/disc brakes. Probably a disc/drum valve.

Is this a new rear disc installation that isn't yet operational? Before it leaked, did the combination valve work as needed?

CPP actually sells a Metering Valve replacement/repair part. Not sure it fits your NAPA valve. Yours might be loose, have dirt in it or need a new O-ring.

If this is a disc/disc setup of your own creation. you may want to use an adjustable Proportion Valve.
They sell stand-alone Prop Valves, but Wilwood, CPP and maybe others sell a switch/distribution block with adjustable Prop Valve build into it. Your Combination Valve is 3-in1. The Wiwood is 2-in-1

The Wilwood type unit will allow you to adjust for the needs of the disc/disc setup.

If you find that you need a Metering Valve, you can add a stand alone unit later.

You need a Metering Valve only if the brakes put your passenger through the windshield under low speed and light brake applications. Does the vehicle nose-dive while driving in a parking lot with relatively light brake application. A Metering Valve is sometimes called a Hold-Off Valve. It works only BELOW about 50 psi, which is little more than the weight of your foot will create.

[DangerDan]

I found the correct combination valve AC Delco 171 1361 it is a disc Disc valve the NAPA Number you mentioned I had called on. It is a disc / drum unit. My entire system is new and they are power brakes. I looked at the Wilwood unit too.
I used the brake tool to block the spool when I was bleeding the system. I just got this truck on the road 8/2/17 so I guess I am in a debugging phase. I really have not driven it enough before discovering the leak to really know how it is performing as far as you nose diving question. I'll change the valve and go from there.

Thanks for your help.

[mike16]

87-93? would that be metric?