Can Can
Pusher Man
Can anyone explain to me how the rear height-sensing proportioning valve works on my 89 V3500? Does it need any periodic maintenance or adjustment? 
CK5
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Need some schooling- rear height-sensing proportioning valve
- Thread starter Can Can
- Start date
My understanding is this...as you load weight onto the truck the arm lowers. That arm is like a flow control valve for the amount of rear braking you're going to get. More load, more rear braking. Light load, less braking in the rear. I don't think there is much you can do as far as maintenance on it. Maybe hit the pivot points with a bit of lube now and then...
Rene
Rene
Yep, what Rene said. 
neverendingproject
1/2 ton status
Yes.
When I did a 4" lift on my crew I ended up using a 2" block in the rear to level the truck out. I just removed mine because I was too lazy to "adjust" the arm longer 2 inches. I havent been able to tell a difference stopping from before and after it was removed. I would venture to say it probably was so old it didnt work but my crew cab is in really good condition.
The only time you would notice is in a full-on panic stop. The valve is supposed to prevent the rear wheels from locking up first. A truck with an empty bed needs way less braking out back than a fully loaded one needs. You won't notice a difference in normal braking.
sled_dog
1 ton status
it definetally does something too.... the previous owner of my Burb broke the fittings off in the valve so he bypassed it. That thing would lock up the rear tires in a heartbeat.
sled_dog
1 ton status
only on some vehicles. 3/4 and 1 tons. My Burb was a 2500, so it had it.
My k20 had it. it wasnt hooked up, just the arm off the diff. I have seen it on a few 3/4 and 1 tons since though. i never knew what it was and wound up just unbolting it. I had a few panic stops in that truck but the rear never really locked up (and the brakes were good too)sled_dog said:
I locked up my 37"s on the freeway doing about 55mph and the truck stopped great. 
Some dip lady pulled out in front of me on the freeway. It was a hard stop and started to go out of my lane but I was trying to steer away from her. It felt as though the front and rears locked at near the same time. Before I made any mods to the truck (lift, tires, and removal of valve) I also had another hard stop and the truck felt exactly the same. And that was with radial dually tires.
Im very impressed with the way the hydroboost stops the truck, in fact I cant believe how well the crew cabs take lifts and tires. Other than sitting a little higher there hasnt been a huge noticeable difference in ride, stopping, turning, performance, or anything thats usually associated with lift and tires. But I only did a 4" lift so that may have alot to do with it.
Some dip lady pulled out in front of me on the freeway. It was a hard stop and started to go out of my lane but I was trying to steer away from her. It felt as though the front and rears locked at near the same time. Before I made any mods to the truck (lift, tires, and removal of valve) I also had another hard stop and the truck felt exactly the same. And that was with radial dually tires.Im very impressed with the way the hydroboost stops the truck, in fact I cant believe how well the crew cabs take lifts and tires. Other than sitting a little higher there hasnt been a huge noticeable difference in ride, stopping, turning, performance, or anything thats usually associated with lift and tires. But I only did a 4" lift so that may have alot to do with it.
Goose
1/2 ton status
I bypassed mine when I put new rear brakes on.
Haven't had any problems with the rears locking first.
Testing on sand/gravel roads showed the front tires still locked first.
On a side note, just had to replace the passenger side rear brake line.
Good thing for dual resivoir master cyclinder. I was able to make to the parts store and back home without too much trouble.
It did take a lot more pedal travel to stop and I held my foot over the e-brake just in case. $7 for brake fluid and a line, not too bad.
Bent it myself, hooked up the mitivac and bled it. About 2 hours in all.
Haven't had any problems with the rears locking first.
Testing on sand/gravel roads showed the front tires still locked first.
On a side note, just had to replace the passenger side rear brake line.
Good thing for dual resivoir master cyclinder. I was able to make to the parts store and back home without too much trouble.
It did take a lot more pedal travel to stop and I held my foot over the e-brake just in case. $7 for brake fluid and a line, not too bad.
Bent it myself, hooked up the mitivac and bled it. About 2 hours in all.
