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    Results 1 to 5 of 5
    1. #1
      Join Date
      Feb 2019
      Posts
      12

      Wilwood 4-Wheel Disc Kit Having Trouble Locking Rear Wheels While Truck Is In the Air

      Hey guys I have an issue that is just really stumping me, which is no matter what I do I can't get the brakes to bring the rear wheels to a stop when the truck is in the air. So I obviously can't drive it lol. I’m using a 4-wheel Wilwood kit spec’d by them for 15” wheels for my 1977 Chevrolet C10 pro touring/ retromod build (D52 front calipers, Dynapro rear calipers). I plumbed the whole truck with 3/16” line and there are no leaks or air bubbles coming from any of the fittings or bleeder screws anywhere in the system. The master(s) I’ve tried have been bench bled correctly and fluid volume is a nice clear stream without bubbles.



      I’m running a Wilwood “combo” splitter/ adjustable proportioning valve and I’ve tried adjusting the bias every which way... makes no difference to the rear lockup problem. With the rear axle lifted, and the truck in drive or reverse, I can slow the rear wheels a little but I can’t bring them to a complete stop. I haven’t driven it yet because I’m sure the truck would lurch forward and might be unstoppable given the inability of the rear brakes to stop the truck.

      I’ve tried both a stock replacement 1.125” master as well as a C3 Corvette disc/disc 1.125” master (the bore size that Wilwood recommends for my calipers). Both had identical results. At this point, I don’t think the master itself nor bleeding is the issue because two new masters had identical results.

      Could the problem be that I’m using 3/16” lines with these two OEM masters? Obviously the C10s had 1/4” rear lines but I’m not sure what C3 Corvettes had. I’d like to avoid spending $300 on a Wilwood master if it’s unnecessary. They’re gawdy and stick out in the engine bay.


    2. #2
      Join Date
      Apr 2009
      Location
      Michigan
      Posts
      322
      Country Flag: United States
      Do the fronts work if you spin the wheels while up in the air? My next step would be to bypass the proportioning valve and see if the problem persists. You should be able to use a typical brake line union in place of the proportioning valve so you don't have to make new lines.

      3/16 lines are not the problem. If anything, the rubber line to the rear axle could be swollen shut if it's super old, but that's unlikely.
      - Ryan

    3. #3
      Join Date
      Feb 2019
      Posts
      12
      Quote Originally Posted by stab6902 View Post
      Do the fronts work if you spin the wheels while up in the air? My next step would be to bypass the proportioning valve and see if the problem persists. You should be able to use a typical brake line union in place of the proportioning valve so you don't have to make new lines.

      3/16 lines are not the problem. If anything, the rubber line to the rear axle could be swollen shut if it's super old, but that's unlikely.
      Thanks for the post. Yes fronts do work. I will bypass the prop valve next. That's a messy affair but needs to be done. I was advised on the Pro Touring facebook group that the rear soft line (in this case braided stainless) can become blocked which causes this same issue. That's an easier thing to try so I'll start there first. I think before I bypass the prop valve I'll put gauges on the caliper fittings to see what sort of pressures I'm getting.

    4. #4
      Join Date
      Mar 2005
      Posts
      345
      Need to bed the pads before testing the brake system.

      Bob.

    5. #5
      Join Date
      Sep 2010
      Location
      Orange County, CA
      Posts
      665
      I would confirm adequate pedal travel, and also confirm that you have the correct front/rear lines going into the master. Sorry if that seems so basic, but when trouble shooting start with the basic and easy stuff





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