I have replaced the caliper and the proportional valve. After applying the brakes several times the rt front locks up. I have bled all 4 and the only way to release the front rt is to open the bleed valve on the caliper. Could it be a brake line or master cylinder? All other brakes seem OK.
Check brake lines they may have gotten pinched very commonok new c/k trucks when you crank the torsion bars up to far you may have hit something and pinched the brake line check those before messing with the master cylinder those are a real pain
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proportional valves are designed to give the right amount of hydraulic pressure to the back brake to prevent them locking up with a resultant loss of control of the vehicle
replacement of calipers would only be need once to fix jammed or leaking pistons but the pads may have to be replaced more often.
if it only the front brakes that is the problem ,I suspect that the fault will be in the compensating ports of the master cylinder that is not releasing the fluid back into the reservoir and the resultant heat build up from the pads still in contact with the discs is building up brake pressure and so keeping the pads on the discs to the point where lock up is evident
failed proportioning valves will result in no brake action to the rear wheels or rear wheel lock up
If parts are not available from the manufacturer spares department, they should be still be available from reputable brake shops as car manufacturers do not make brake parts as such but rely on brake manufacturers to supply items to specifications
the unit will be repairable by an accredited shop and failing that would be available from the wreckers.
A stuck proportioning valve will only prevent either the front or rear or corner / corner from working, it wont make them stick. More likely its one or more frozen brake caliper/s or a bad rubber brake hose/s or frozen brake cables etc.. Is it only front, rear, or both, one left, one right one side or all 4 ? You're gonna have to get the wheels off the ground even if only one at a time to check them. To determine if it is a bad rubber brake hose Crack open a bleeder screw. If the wheel then spins freely replace the hose. If it is still stuck then it is a stuck / frozen caliper, replace the caliper. In the case of rear drum brakes, you can checck the hose in the same way or if it's stuck cables you can try tugging hard on the cables to free them up some but otherwise you'll probably have to pull them apart and do a complete brake job including wheel cylinders.
if the proportioning clogs or damaged it can cause brake problems such as yours take pressure readings on all 4 calipers the proportioning valve is just as it says differentiates the pressure front to back also the abs unit itself can cause the same problem also
did you check the brake booster ? how long you use the brake booster? may be have no enough pressure in vacuum brake booster. get more details here for help : http://www.fiverhope.com/ http://www.fiverhope.com/category-67-b0-Brake-booster.html
You need to replace the rubber hose going to the brake caliper from the metal line. The inside of the hose is breaking down inside keeping the caliper from releasing. Hope this helps please leave comment.
check for front brake calipersdragging, if the are replace calipers and front brake hoses, if calipers ok replace master cylinder, This is how to check calipers, jack up front of truck have some one apply brakes and release as soon as they release the brake peddle the wheels should spin freely if not brake the brake line lose at master cylinder if wheels spin free with line loose replace master cylinder, if not replace calipers and hoses.....HOPE THIS HELPS
Did you replace your front brake lines as these are rubber and after time collapse causing the truck to pull in the opposite direction! In your case I'd say left front is crimped and blocks fluid and makes right front pull to the right. This is a common problem and one of the first items to replace on these trucks and at $30 cheap insurance.(REPLACE BOTH).