need pics of '75 proportioning valve

[GreenMystChevy]

I am looking for anyone with good pics of their proportioning valve on their '75 3/4 ton 4x4 with power brakes. They might all look alike, not real sure on that, I just know that is the one that I need a good look at. Need to see which lines and wires go where. Thanks for the help guys.

[Russell]

Where is the valve? I can take a picture of the one on my 80 3/4 ton 2wd if you want

[bigblock73]

Not sure if it is the same, but here is the one on my 73 1/2 ton 2wd..

[bigblock73]

2nd pic...

[GreenMystChevy]

Thanks for the replies guys but I am still not sure what it exactly looks like on a 4x4, I do believe it is diifferent than 2 wheel because of how the lines are plumbed (I've been wrong before). I am building up my '72 with '75 axles and they say to use the proportioning valve from a '75. Long story short, none of the lines are the same size, it looks to be in a different spot, I need to figure out the proper routing, etc. etc. etc.

So if anyone has a '75 4x4 3/4 ton, I would love to see your proportioning valve and what lines go where. Thanks!


bigblock73: nice looking frame. There's a lot of work in that thing and it shows.

Russell: thanks for askin but I am hoping for a 4x4 shot from the same year. Thanks though for the offer

[bigblock73]

I believe Mike Reeh has a 77 3/4 ton (maybe 1 ton now) 4x4...try contacting him maybe.

[GreenMystChevy]

Do you know how to get ahold of him? Thanks

[bigblock73]

Originally posted by GreenMystChevy
Do you know how to get ahold of him? Thanks

hit the "members" button on the top of the page, then go to page 11 of the "m"'s...mike reeh. From there you should be able to send him a PM.

[Grim Reaper]

75 looks the same. As it is mounted on bigBlock73's pictures is the same as it would be on a 2wd. All the valve look the same on the 73-91 body(87 on truck). Even the one on my 88 Burb look identical and it has a second proportioning valve that adjusts from weight. All mount in the same location.

Actually that's not a Proportioning Valve. It's a Combination valve. THe proportining valve is in the side going to the rear circuit and on the front circuit is a hold off valve. The whole assembly is a Combination valve.

As it is pictured above you have 5 lines and one electrical connection. The electrical is in the center of the top and is tripped by a Shuttle insde the valve that moves if either circuit looses pressure.

As mounted inthat picture, starting top left at a 45degree angle is the driverside front line 3/16 t. To the right of it is the front inlet for the forward section of the master. To the right of it on the other side of the electrical connection is the Rear inlet. It's 1/4 inch line. The rear outlet is on the very end and it is 1/4 inch line as well.

The front passenger oulet is on the bottom left .

Now here is the hang up. GM used some od sized fittings and they are not eay to find. Junkyard is the easiest and fastest. www.inlinetube.com can get you new ones.

Those are a pain to bleed from dry. I have some tips here.
http://coloradok5.com/atrondiskbrakes.shtml
What I neglected to mention in that write up is the front circuit has a plunger that you sometimes need to pull to get them bleed. There is a actual tool to do this but it can be done with a small pair of vice grips.

Pop the rubber boot off. under that poot you will dee small tip in the middle of a machined peice retained with a circle clip. Push down on the part retained with the circle clip and it will expose the pin. Grab the pin and pull out slightly to unseat the holdoff valve in the combintation valve. Now only puch in just enough to grab it and don't overdue it and flaten the pin out or it won't seat. when you let go of it.

What the hold off valve does is hold off pressure to the front calipers for just a second to let the drums catch up a little. This helps accout for excessive trave in the drums if the pads have worn faster then the adjuster kept up. This goes back to how the master is designed to operate.

If you were to look at how a mastercylinder works you will find that when the system is properly bleed the fluid in the rear brake part of the master is what moves the piston for the front brakes. If either system looses pressure there is enough travel to alow the master to bottom out and move the pisions mechanicly instead of hydraulicly.

Here is the gamble on a old CV. There is a O-Ring that might run over some cud and depositis in the CV when you push it in.Then it will start leaking.

[GreenMystChevy]

bigblock73: thanks for helping me out. I appreciate the effort.

Grim Reaper: Wow, that is exactly what I was looking for, that description with the picture from bigblock73, I should be ready to roll. This thing is in a completely different place then my '72 which has it right next to the master cylinder so I am going to have to pre-bend and run some new linies. PITA but I just gotta do it.
Thanks a lot for the help and if I run into a snag I'll give you a holler. You guys over here all almost as cool as the guys from the 67-72 forum, lol
you know I'm playin