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Poor stability under braking

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by 87v30, May 14, 2003.

  1. 87v30

    87v30 Registered Member

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    I have had my near stock 87, 1 ton 4x4 pickup for close to two years and it has suffered from a tendency to wander during braking. This problem is more pronounced when the brakes are hot and when I am braking from high speed. Seventy percent of the time my truck pulls to the right, twenty-five percent of the time it stops straight, and the rest of the time it pulls to the left. The harder I press the brake pedal, the stronger the truck pulls. It can take as much as a quarter turn of the steering wheel to keep the truck pointing straight. When not braking, the truck tracks straight. Additionally the brake pedal can be depressed to the floor (this problem has persisted after three master cylinders, rebuilt brakes front and rear, rebuilt ps pump, and rebuilt booster) however the brakes are powerful. Here is a list of parts/labor I have thrown at my truck since I have had it in approximate chronological order. Not all of the items listed were replaced specifically to address my braking problem, but I thought that they were worth noting. No significant changes occurred after any of this work:

    1. New front rotors, performance friction pads, rebuilt calipers
    2. Rebuilt brake master cylinder
    3. Rebuilt hydro booster
    4. New proportioning valve (I did hold pin in during bleeding)
    5. New brake master cylinder
    6. New tires (and many subsequent rotations)
    7. New RS9000 shocks
    8. New Tie rod and pitman arm ends, steering damper, and alignment
    9. Measured pad thickness/wear side to side after 10k miles use. Difference of less than 0.010".
    10. Swapped pads side-to-side
    11. Had local shop measure line pressures at each front caliper. Measured same side to side (getting really pissed at truck by this point)
    12. Had local shop rebuild rear brakes. (Turned drums, new shoes, new wheel cylinders, new springs/hardware)
    13. Very careful inspection of hard lines, spring bushings, frame around steering box...
    14. New u-bolts and cleaning of area around axle/spring interface. Centering bolts and corresponding slots looked ok. (Note: Each of the four times I have torqued these nuts/bolts the suspension makes popping noises for a few hours under braking while driving. Two to three nuts went approx. 1/4 turn to reach spec each time )
    15. Begged to ColoradoK5 for help

    If anyone has any ideas or knows someone that might be able to help me, please let me know. I really want to like me rig, but she is being quite difficult.
     
  2. NITRO

    NITRO 1/2 ton status

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    did u replace the front calipers or just have the ones rebuilt?? sometimes its best if u just buy new calipers. how about the rubber lines?? those can expand unevenly and cause what u r explaining. and one more thing, put up the posts in the garage or the 73-91 forums.....they will get more views /forums/images/graemlins/grin.gif. other than that welcome to CK5

    NITRO
     
  3. 69K5

    69K5 1/2 ton status

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    nitro made me think of something. sometimes the inner core on the rubber brakelines will collapse or shrink. pressure might be the same but not getting there as quick?

    thats ny only .02

    nathan
     
  4. 87v30

    87v30 Registered Member

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    Thanks you two. Great idea but I wasn't thinking to straight on a couple of fronts when I asked for help. First I put it in the wrong place and second I did replace the front flex hoses with some stainless lines about six months ago. Aside from a slightly firmer brake pedal, I did not notice any difference.
     
  5. NITRO

    NITRO 1/2 ton status

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    did u rebuild the calipers yourself or buy them??

    NITRO
     
  6. 87v30

    87v30 Registered Member

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    Thanks to you two that help me out. Here is hopefully the end of the saga with my annoying brakes:

    16. Stopped the LIVING HELL out of my truck on the road and in a large parking lot. Measured temp of front rotors to be approx 490 deg F on Rt side, and 440 on left side. RF wheel would lock before LF wheel. Was unable to get rears to lock but they were generating heat. LR drum was about 60 deg F cooler than RR drum. Next I made a few low speed stops with the park brake and found that the truck pulled to the right. Pushing the park brake harder would lock the RR wheel, but not the LR wheel.
    17. Bled front brakes again and adjusted recently rebuilt rear brakes. Found fluid escaping from left-rear drum. NOT A GOOD DAY!
    18. Disassembled both rear drums and found that a lot grease that was used to lube the wheel bearings (14 bolt ff) got past the new seal, contaminating the new shoes. Differential breather tube is clear so I don’t have any idea how the grease got in there.
    19. Cleaned the LR shoes and drum the best I could with a steam cleaner and brake clean. Guessing that I will have to replace rear shoes again though...but maybe not /forums/images/graemlins/smile.gif . Reassembled and adjusted rear brakes.
    20. Purchased and installed a pair of Autospecialty rebuilt calipers with their 911 extreme performance pads.
    17. Disassembled old rebuilt calipers and found left caliper to have a slightly worn piston with numerous small pits in it. More importantly, the left caliper had a large amount of rust just outboard of the seal.
    18. Truck finally stops in a straight line!!! However brakes squeal in an unimaginably annoying way.
    19. After approx 300 miles (giving them a fair chance), got so sick of squeaking, smelly, poor stopping pads (would fade drastically when rotor temp got much over 400 deg F) I replaced them with the “old” performance friction pads. AHHHHH so much better. The autospecialty pads are the worst pads I have ever owned!!!!!!! Metal anti-squeal shims had come come lose on two of the pads, allowing them to rattle/resonate/piss me off. For what it is worth, the Autospecialty pads have a DOT rating of EE, while the Perf. Frictions have a rating of FF.

    After all of this work, it seems as if I have a truck that will stop in a straight line!! Now it is time for mods, hmmmmm. What to do first.... /forums/images/graemlins/truck.gif

    Thanks again
     
  7. Rusty68

    Rusty68 1/2 ton status

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    you can start by fixing the grease seals /forums/images/graemlins/thinking.gif
     
  8. 87v30

    87v30 Registered Member

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    Thanks for the insight Rusty. I thought that "fixing" the seal was a good idea too, that is why I had new seals installed when I had the brakes rubilt a few thousand miles ago and that is why I relpaced them when I discovered the contamination.
     

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