I need help w/a brake problem

[SCOTI]

I swapped discs on to my 68 beater over 2yrs ago & they worked great. For the swap I used a 71-2 pwr booster/mstr cyl combo & the lines, pro-portioning valve, & hardware are 73-up.

Ok, here's the problem . . ... last Sept, I was in a wreck while pulling my car trailer. Of course, during the wreck I panic stopped (the trailer brakes weren't hooked up) & locked up the brakes.

Since then, it's like I don't have rear brakes. At first, I thought the shoes were just worn down/out of adjustment so I replaced & adjusted them but that didn't fix the problem. Then someone said they had heard about panic stops causing the prop-valve to 'stick' & cause this dilemma on Chevy trucks so I got another prop-valve @ the wrecking yard & re-bled the brakes but the problem still exists.

I'm tired of my front brakes locking up whenever it rains because the backs aren't working. Any suggestions??

[cableguy0]

well u might wanna go get a new proportioning valve i dont trust any junk yard brake parts its not worth the chance. also pull off the drums and either pull off the dust boots or poke a hole in em the ones on the wheel cylinders if there is fluid there replace em they are no good theres not supposed to be any fluid in that boot also while u have the drums off have someone VERY lightly push the brake pedal and check the movemtn in the wheel cylinders wouldnt be a bad idea to hold the shoes on each side when u do this

[71Rat]

i dunno if this will help but it's free to do, my dad had a 65 chevy caprice and his front wheels kept locking up on him so when it happened we had to go in reverse quick and slam on the brakes, this set the rear brakes back to were they should be. i dunno if this will work for u but as i said it is free so there is nothing to lose. best of luck

[SCOTI]

Well, your right about the junkyard stuff being an unknown as far as quality, but since all the original swap stuff (p-valve, lines, & hardware) were from the junkyard I didn't think twice about it.

Ok, tonight I'll check the wheel cylinders for leakage (I haven't noticed any visible signs but I haven't inspected them closely) & carefully verify they're working w/o drums on.

71Rat, I actually thought about that but tried smacking the p-valve w/a big ol' wrench to 'unstick' it. I did brake hard a couple of times in reverse when adjusting after installing the new rear shoes, but when I switched out the p-valve, I thought that would take care of the prob.

Thanks.

[71Chev]

Have you reset the prop valve? There is a button under the rubber cap on the end. Use a clamp to hold it in then push your break pedal down hard and release the clamp. See if that did anything.

[SCOTI]

Ok, on my way home I was going over these suggestions & trying to think of everything that affects the brakes. I thought about what the symptoms are when each part actually fails & it dawned on me that lately when I hit the brake pedal I hear a funny noise. So I started pumping the brakes to see how they felt & then killed the motor & pumped them again . . .... guess what . . . ... no difference @ all! I checked & all vacuum lines are hooked up to the booster & in good shape so now @ least I know the booster is bad.

I guess between driving my 74 w/pwr steering & brakes I got into the 68 w/o pwr steering & it felt like it did before the brake upgrade so I didn't notice.

71Chev, no I didn't know they could be reset. I'll give that a try as well if the pwr booster doesn't fix it.

[Longhorn Man]

While you may have found the problem, look for sticking calipers too. jack it up and see if the front wheels will turn with minimal effort.

[Blue68]

Prop valves do stick. They are supposed to! If you loose the rear circuit, all pressure goes to the front, and the other way around, so the idea is you have some brakes at one end even if you have a catasrophic failure somewhere. Prop valves can also be un-stuck, but not always. If your prop valve has the brake light, and it still works, it should come on when this happens. In order to unstick (and this can occur when bleeding them) the valve, you open the circuit (bleeder) where you have pressure, the lack of pressure there will force the check valve the other way (toward the middle) and reset. Just don't try this with vacuum on the booster or the valve will flip the other way.

Good luck.