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Spongy Brakes

Discussion in 'Chevy Trucks' started by crossboneracing, Apr 14, 2009.

  1. crossboneracing

    crossboneracing Senior Member
    Messages: 137

    Hi Guys, This may be a question for B&B but I have a 2000 K3500 Chevy Pickup. 454 4x4, anyway the brakes are spongy. I have put all new front calipers, rotors, pads, and in the back I have put all new wheel cylinders, shoes and hardware (rears are adjusted correctly). My question is the brakes are still as spongy as they were before and dont feel like they have the stopping power they should. I have bled them all several times and no air comes out. I know this body style had problems with the abs modulator so....but looking on several sites, it seems to be that it could also be the master cylinder. Truck has about 109k miles on it. Any thoughs or suggestions would be great!
     
  2. mayhem

    mayhem PlowSite.com Addict
    from Peru MA
    Messages: 1,016

    Worn rubber lines expanding under pressure maybe?
     
  3. mcwlandscaping

    mcwlandscaping 2000 Club Member
    Messages: 2,557

    I was going to suggest unplugging your ABS fuse and seeing if that improves anything....easy way to find out! I had a lot of trouble with mine and ive unplugged mine!
     
  4. the new boss 92

    the new boss 92 2000 Club Member
    Messages: 2,989

    i have also unglued my abs box under the hood cause it caused my breaks to give out while i was towing a bob cat on day, and almost got bad!
     
  5. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    The ABS unit may have a bleeding procedure too. If you loose enough fluid changing the calipers this may be an issue. You did have a helper and used tubing on the bleeder screw when you bled it? CLOSE the bleeder before pedal let up? I always tap the calipers with a small ball-peen when I bleed them too. It gets every little bit of air out. All four wheels may need bled too. The new brakes may of just pointed out you still have air in the back circuit. Try not to unplug the ABS, it may save you a crash some day.
    The Wife and 3 Kids are trained brake bleed helpers at my house.The Dog never caught on!
     
  6. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Micki hit the nail on the head. To do a proper bleed procedure on it you need a Tech ll scanner to activate the solenoids/reservoir chambers in the ABS module or else you can not remove all the air from the system. Without the solenoids opened up the air is trapped in the chambers. So you can manually bleed it until you've gone through a barrel of brake fluid and you won't remove all the air. I've fixed many "un-fixable" spongy brake issues on those trucks by using this procedure.

    Even the newer trucks are the same way, even from the factory. Many times the brake pedal feel isn't what the customer feels it should be and a proper bleeding with the Tech ll connected fixes 90% of them.
     
  7. crossboneracing

    crossboneracing Senior Member
    Messages: 137

    Thanks B&B but is there any way that the actual modulator can be bad and the diaphram inside causing air to get in the line? I dont understand how air could have worked its way in there. I bought the truck from a GM mechanic who I assume had access to a Tech II, brakes felt like this since I bought it. I just dont wanna spend a boatload of money on a new module and pump setup.
     
  8. lilweeds

    lilweeds PlowSite.com Addict
    Messages: 1,178

    Hey B&B, I've had mine done with the Tech 2 twice now, and there are good till the ABS kicks on a couple times (which seems to happen at low speeds turning when coming to a stop or at least that's what it feels like) then the pedal just sucks. Anything else you can do with these things. I thought it had something to do with the Hydro Boast but what do I know. It's been 10+ years since I worked at a Chevy Dealer!
     
  9. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    The air could have been in there for a long time, from either a previous repair or ever since the truck was built (happens more than you'd think). Wouldn't normally be somehow ingested directly into the system by a failing component, especially in the ABS unit itself but the rear seal at the rear of the master cylinders will allow air into the the master cylinder when they go bad. Normally they'll also leak slightly and you'll find small traces of brake fluid leaking from between the master cylinder and the booster assembly but I have found a few in the past that were in fact allowing air in there, but never left a trace of fluid.

    And also, don't automatically assume that since the previous owner was a GM tech that he used a Tech ll and performed the required bleed procedure as you usually find technician's personal vehicles are the worse ones as far as maintenance. :nod:

    Before I replaced anything I'd be bleeding the system with a Tech ll connected.
     
  10. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    The fact that you lose the pedal after an ABS event after bleeding it with a Tech ll would indicate an internal leak in the ABS module. Possibly a damaged O-ring on one of the three internal dump valves. Only way to repair that is to replace the ABS module.

    The ABS activation during slow speed cornering probably isn't imaginary, they often do that when they're picking up an erroneous signal from one of the front wheel speed sensors. Either from a problem with one of the sensors themselves or a bad wheel bearing.
     
  11. lilweeds

    lilweeds PlowSite.com Addict
    Messages: 1,178

    Should have asked this 6 months ago before the warranty was up!
     
  12. Charles

    Charles Moderator Staff Member
    Messages: 256

    I am going to write all this down for the dummies who put my brakes on. I went back up there and they still couldn't figure out why the brake pedal had so much play in it:realmad:
     
  13. Bajak

    Bajak Senior Member
    Messages: 999

    rsvees. I had a similar problem with my truck too. Last fall my abs would activate at low speed. I took it in and there was a problem with the wheel speed sensor on the left side. The dealership repaired both front sensors for free. The truck is an 01 and was out of warranty but there was a bulletin pertaining too the sensors on some GM models. Maybe worth asking about.
     
  14. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    You have to be careful around the speed sensors if you do your own brakes. They are fragile and cost a bit to replace. Any dent or crease in the little can they are done. While your down there carefully separate the wire connector's to it and Dielectric grease the connection. This may save you from ever having a problem.