Proportioning valve vs. load sensing valve

[ButchM]

Anyone have any document or exploded view on How the load sensing valve works inside?

Mats
These are out of the service manual for an 86. They may be of some help.
Butch

 

[Bear123]

Did you bench-bleed the MC? If you did not you will have that. I suggest perhaps re-bench bleeding it on the truck and then gravity bleed the the system test then maybe bleed normally.

 

[13matsc]

Just for closing this case for now, i bled the whole system again with approx 1,5 quarts of brake fluid. Also bench bled the MC again while it was in the truck. Problem seem to have vanished for now, but will keep an eye on it. If it happens again there must be a leak somewhere.

 

[Cyrillious]

this is my proportioning valve before I removed it. Yes I had to remove mine to move the spool/shuttle to centre it because it grounded out. Remarkably all the lines broke free without bending or cracking! The sensor connector on top you have to squeeze the sides to remove it from the sensor, leave that for last after you remove all the lines and the valve from the crossmember. Good luck getting the lines back on, that was a pain! LOL!

Been doing some brake work on my truck recently. Had some issues last season and recently replaced all the hardware, shoes and cylinders on the rear wheels. Also replaced the master cylinder and the two lines to each wheel since the old lines where so stuck in the cylinders I had to grind them off.

Bled all the brakes and everything seemed fine. Jacked up the rear end and pushed the brake pedal - no rear brakes at all. I can spin the wheels by hand. Front brakes work good and parking brake works. I adjusted the shoes outwards as much as i could, but that ended up with one rear wheel overheating, and still no braking power. Now im not sure if I ever had rear brakes the 3 years i`ve had the truck….

My suspision is towards the proportioning valve in the front or the load sensing valve in the rear.
Grounded out the cable on the proportioning valve and that gave me the brake warning light, so at least the wiring from there is good. If the valve has been out of position i should have got the warning light - if the valve is in good condiotion that is. How normal is it for these to go bad?
The placement is horrible and virtually impossible to inspect without removing it.

Too many chances of snapping a line, so not keen on removing it if one cannot with a fair amount of certainty say its defect. How is the little connector on top removed?

Disconnected the lever at the LSV and tried moving the little switch all different positions, but no changes. I can hear and feel some sort of piston inside moving when i spin it around.

Put wd-40 on all the connections but i can just feel everyone of them not coming easily off. Already startet rounding off one nut at the LSV.
Would like to snap as few as possible

Any tips for a poor guy?

 

[Ricko1966]

Thanks. My bad, but the pedal is not going to the floor, but as far as it normally do.

I did take notice, as there were a little sticker on it, but it seems like this spins freely with maybe two positions.

Plan was maybe to delete the whole load sensing valve.

If you remove it,replace it with an aftermarket adjustable proportioning valve. That way you can set rear brake bias to how the truck is used most often. Something like this.

 

[Grit dog]

for the GM reasons its more or less "if the truck is outside of factory specifications, remove the thing." and that could mean clapped suspension, lift blocks, wider tires, etc.

What it means is not “clapped suspension” etc, it’s no more or less than the name of the part applies. It’s load on the rear brakes. Or more accurately how much friction do you have on the road. A stock 3/4 ton with pizza cutter tires aired to 50-80 psi with an empty truck bed will probably lock up the wheels very easily with full rear braking force applied.
Increase the friction between the tires and the road in any way and they can handle more braking force.
Suspension and lift blocks have zero bearing on how much load or traction is on the rear tires.
There’s really only 2 things that do.
Weight over the axle
Tires (width, tread, pressure, traction)

 

[AuroraGirl]

What it means is not “clapped suspension” etc, it’s no more or less than the name of the part applies. It’s load on the rear brakes. Or more accurately how much friction do you have on the road. A stock 3/4 ton with pizza cutter tires aired to 50-80 psi with an empty truck bed will probably lock up the wheels very easily with full rear braking force applied.
Increase the friction between the tires and the road in any way and they can handle more braking force.
Suspension and lift blocks have zero bearing on how much load or traction is on the rear tires.
There’s really only 2 things that do.
Weight over the axle
Tires (width, tread, pressure, traction)

bad shocks will lift the tires off the road more than proper shocks. severely bent or worn leaf springs probably dont aid things either. that is what i meant. both of those translate to tire contacting the road. And one translates to side to side weight load (of the truck over the axle, the load in the truck is dependent on human loading it into the bed)