Hi!
Got a problem I haven't seen before in my lengthy (joking) 2 year career as a mechanic, nor do I remember being directly addressed in my few classes at community college.
I'm looking at a 1994 Pontiac Bonneville, with front disc, rear drums. Err, I don't think it had abs. I can check, if that's important.
A coworker pulled it in and did the "brake eval." What he observed was that whereas you normally expect modulated, even, brake application; the lightest tap on the brakes causes the LR drum to seize up instantly, while the other 3 wheels get progressively firmer braking as expected. Naturally, the vehicle stops hard and pulls every time you even lightly apply the brakes. It's not very driveable, and the customer wants it fixed.
Once you let up on the brakes, the pressure releases, the shoes return normally, and it operates normally: so probably the spring hardware is functional, and pressure isn't being held by a bad rubber hose either, for example.
I just want to be sure about this.
My understanding is that there are two types of proportioning valves: one is for level sensors, to send more brake pressure to the rear first if you heavily load down your SUV, for example. Not all cars have this. Another, sends pressure to the drums first, because they have further to travel than the .010" of the front discs, and exists in all front disc/ rear drum systems.
Finally, being a 1994 and not a 1964, I expect it has a split system.
So I'm speculating... is it possible that there are two proportioning valves, one for each leg, and therefore, if just the one is sticking, it's sending much too much pressure to just the one drum first, before any other wheel gets pressure? And I should sell a proportioning valve?
Again: just want to be sure.
I've got coworkers presenting ideas like, "master cylinder" "the brake hose by that wheel cylinder" "new wheel cylinders," and well, we could do it all... but I want to be right the first time.
Let me know your expert opinion.
thanks!
-Bernard
Got a problem I haven't seen before in my lengthy (joking) 2 year career as a mechanic, nor do I remember being directly addressed in my few classes at community college.
I'm looking at a 1994 Pontiac Bonneville, with front disc, rear drums. Err, I don't think it had abs. I can check, if that's important.
A coworker pulled it in and did the "brake eval." What he observed was that whereas you normally expect modulated, even, brake application; the lightest tap on the brakes causes the LR drum to seize up instantly, while the other 3 wheels get progressively firmer braking as expected. Naturally, the vehicle stops hard and pulls every time you even lightly apply the brakes. It's not very driveable, and the customer wants it fixed.
Once you let up on the brakes, the pressure releases, the shoes return normally, and it operates normally: so probably the spring hardware is functional, and pressure isn't being held by a bad rubber hose either, for example.
I just want to be sure about this.
My understanding is that there are two types of proportioning valves: one is for level sensors, to send more brake pressure to the rear first if you heavily load down your SUV, for example. Not all cars have this. Another, sends pressure to the drums first, because they have further to travel than the .010" of the front discs, and exists in all front disc/ rear drum systems.
Finally, being a 1994 and not a 1964, I expect it has a split system.
So I'm speculating... is it possible that there are two proportioning valves, one for each leg, and therefore, if just the one is sticking, it's sending much too much pressure to just the one drum first, before any other wheel gets pressure? And I should sell a proportioning valve?
Again: just want to be sure.
I've got coworkers presenting ideas like, "master cylinder" "the brake hose by that wheel cylinder" "new wheel cylinders," and well, we could do it all... but I want to be right the first time.
Let me know your expert opinion.
thanks!
-Bernard