Mechanics

BRAKES

1998 Chevrolet Truck • V8 Automatic •

I have a Chevy K1500 4x4 pickup. When I step on the brake and turn to the right (only when I turn to the right) I loose pressure in my pedal and the vehical has a run away. The fluid is full and the pads and roders are good. I am not sure if it is pinching a line when I turn or what the problem is? Please help
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If you're not losing fluid, (which shouldn't happen only when turning anyway), raise the front wheels off the ground and check them for loose wheel bearings. I suspect your symptoms would be a little different, but if one is loose, the rotor will wobble and push the piston back into the caliper. The NEXT time you press the brake pedal, it will go down too far since more fluid is needed to push the piston back out.

Also check that both front calipers are mounted solidly and the slide bolts aren't loose or missing. If you can duplicate the problem while the truck is not moving, have a helper press the pedal while you are underneath and watching for movement in one of the calipers.

For the pedal to go further than normal when there's no fluid loss, a caliper piston has to be coming out too far, a rubber flex hose is expanding, or the rear shoes are out of adjustment. A hose or shoe adjustment problem will not be related to turning; it will be there all the time.

Something weird you might consider, if the problem does not occur when the truck is standing still, is to check if your truck has a height-sensing proportioning valve attached to the rear axle. Most trucks and minivans have them to set how much brake fluid pressure goes to the rear wheels compared to the front. That valve is designed to be non-adjustable for passenger cars, but for trucks and minivans there can be such a wide variation in how heavily the rear is loaded. Since we're looking for something unusual, during right turns that valve might let more brake fluid go to the rear brakes, and if they're out of adjustment, that would let the pedal go down too far.

Does this problem occur when turning just a little to the right or do you have to turn fully sharp right? Does the truck have to be moving?

Caradiodoc
Jul 7, 2011.
The problem occurs even when turning a little to the right. However, if im driving up hill it won't do it. It mainly happens when im driving on a downward slope where there is a little force behind the vehicle. The truck always has to be moving for this to happen.

It's going to look like I'm ignoring you, and I'm sorry for that, but I'm thinking. I'll be out of town for the next few days but I'll be checking in occasionally.

This is something I really hate to suggest, and I never let my students do it, but you might consider lightly clamping off one front hose, then driving in a safe area to see if the problem still occurs. If it doesn't, that might help determine which brake is the culprit. Don't squeeze the hose too tight that it ruptures. A vise-grip pliers should do the trick.

Caradiodoc
Jul 7, 2011.
If I clamp the right side and I have a run away it waould mean the problem is on my left side correct? Do you think it could be my one of my lower ball joints thats bad? Thanks for the help
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I've never heard of a ball joint causing your symptom. When the problem is intermittent, there are only two things that can cause the pedal to go too far. Either there is internal leakage inside the master cylinder or a piston got pushed back into the caliper and has to be pushed back out. I doubt leakage in the master cylinder would be affected by turning. If the piston is the problem, you should get a good pedal if you release it and press it again, or pump it a few times.

Another clue that a piston is being pushed back in is the low pedal will occur AFTER you turn right and straighten back out. If a rotor is wobbling and pushes the piston in, the piston won't magically come back out when you're driving straight.

Caradiodoc
Jul 11, 2011.
Let me know what you find.


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