Help, keep blowing out wheel cylinders

[Wolfj359]

I just blew out my third wheel cylinder on the drivers rear last night. This has all happened within the last 2 days after thorough examination of the brake system I think the problem lies in the proportioning valve giving too much pressure to the rear brakes. I noticed that the button on the end of the valve was stuck and not moving. Is the default position for this button in or out? I have heard that you need to hold the button in while bleeding the brakes and I did not do this, but I have before without any problems. Could the valve come open while bleeding the brakes? Also could pumping the pedal with the key off instead of on have anything to do with the problem I was having? This all started when I noticed that the brake line coming from the prop valve to the right front brake was leaking so I replaced it. I am out of ideas and tired of changing wheel cylinders and adding brake fluid to get the car home. Any help greatly appreciated.

 

[John Larkin]

The system should hold 1600psi stock and with Ron's custom auto jumper valve 3000psi. I don't think excess pressure is the problem; sounds like a mechanical problem. How much room is between the shoe notch and the wheel cylinder pushrod thingies (the pieces that go inbetween the ends of the wheel cylinder and the shoe)? Are they even in there or could they have fallen out? Shouldn't be much more than 1/4" of gap from memory (the pushrod thingies hydraulically take up the gap but you get my drift). You might even have the wrong shoes on there also and be leaving too much gap, giving the pucks room to "blow out". I wouldn't think that even having out-of-spec drums (too large I.D.) would allow for excess adjustment outward to create this situtation either. Good luck.

 

[UNGN]

If the system provided enough pressure to the rear to "blow out" the cylinder, you be locking up the rear and swapping ends at every stop sign. Sounds more like a piece or two was left out (or has fallen out)

Were the wheel cylinders changed to S10's? Was the clip properly put back on?

 

[boostedmaxPSI]

Can someone helpout with the correct part # for the S10 wheel cylinders upgrade? Or is it just as simple as going to my local Auto parts house and asking for S10 wheel cylinders. Does the year matter?

I can only hold about 1# of boost at the line. Finally need to upgrade.

Thanks,

 

[QuickWrench]

The wheel cylinders you need are 7/8" (vs. 3/4" stock) units from a 1985 Chebby S-10, with manual transmission.

 

[boostedmaxPSI]

Now that's specific! Thanks...

That's a pretty impresive time in the 1/4. What's your secret?

 

[QuickWrench]

Secret? None, really, just...

1. Excellent Norwalk track. 1.59 60' on Drag Radials.
2. 43 degree, cool air.
3. 27 pounds of boost.
4. Drove it home.