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Rear brake line

Discussion in 'Chevy Trucks' started by 400hp408sb, May 19, 2004.

  1. 400hp408sb

    400hp408sb Junior Member
    from Maine
    Messages: 25

    I have an '87 3/4 ton chevy. There are a couple brake lines that are getting pretty rusty and need replacing. There is a gadget that my truck has that most don't. I attached a picture of it, hopefully it works. My plan is to take it out and run my new brake line directly to the rear. My question is has anyone had any issues as far as safety or working properly afterwards. My understanding of the device is that it detects the amount of weight in the bed and pushes harder on the rear brakes with more load. Now I could be completely wrong. It's always nice to get a second opinion before I do something stupid :)
     
  2. wfd44

    wfd44 Senior Member
    from Maine
    Messages: 369

    This sounds like a weight sensing proportioning valve. Does it have a lever connecting it to the rear axle and brake lines going to it?

    If so it is a weight (height) sensing proportioning valve. In a truck like this one (I think) without rear wheel ABS (introduced on the 1988 C+K series I think) this proportioning valve essentially limits the ammount of pressure applied to the rear brakes proportionally to the ammount of load on the rear wheels. In a lightly loaded pickup truck without ABS this is a pretty important piece of equipment. Without it the rear wheels can lock easily under braking throwing you into a skid. Remember a locked or spinning axle will try to lead the vehicle. Hence the sensation of the rear axle trying to pass the front one.

    Also be sure to alway replace brake line with seamless steel or stainless tubing and only double flare fittings. Absolutely do not use copper line and/or compression fittings on hydraulic barke systems.
     
  3. 400hp408sb

    400hp408sb Junior Member
    from Maine
    Messages: 25

    Yes, it does have a bracket that is mounted to the rear axle, with an arm that is able to move/rotate at the point where the brake line comes in and goes out. It already has a compression fitting in the line that's another reason why I want to replace the lines. And I already have a double flare tool. I just don't see why this item is even there since none of the other 80s trucks had them with the same rear drum brakes. And I currently run 36's with ideas of going to 38.5 - 39s. So a little extra braking power wouldnt be bad.
     
  4. wfd44

    wfd44 Senior Member
    from Maine
    Messages: 369

    39's on a plow truck??? Isn't that a bit tall?

    I still stand by my recommendation to leave the weight sensing prportioning valve as is. An empty pickup is heavily weight biased towards the front and so should your braking force. Regardless of tire size (from 215/85R16 all the way up to ?) brake bias should be towards the front when unloaded. Weight sensitive proportioning is an improvement that came along before ABS.

    As an example of a similar situation. Just because my '66 has the fuel tank inside the cab and your '87 has it outside the frame rail doesn't mean I would recommend relocating the tank on my '96 to either of those locations.
     
  5. Rick Loncosky

    Rick Loncosky Senior Member
    from 17557
    Messages: 102

    I seen that on a C 30 4 door single rear wheel I just junked. I was wondering what the heck that thing is doing on the rear brakes. I thought it was related to the Hydo-Boost type brakes.
     
  6. 400hp408sb

    400hp408sb Junior Member
    from Maine
    Messages: 25

    my bad guys. I guess I should have been more specific. This is a mud truck not a plow truck, the plow would never reach the ground :).Thanks for the input