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Getting to the bottom of the brake issues!

jimmy4xjimmy4x Posts: 7
edited October 2016 in Chevrolet
03, 1500, z71. I've had a soft peddle ever since I did my first brake job using 3rd party parts. Over the years tried everything, every solution I could find on forums. Finally got new everything directly from GM parts (except for rotors and calipers). Lines, MC, hoses, pads. I always used Bosch rotors and have tried four different calipers from two different stores (their top of the line). I've had them bled over 6 times. Three by professional mechanics. NO IMPROVEMENT at all. However...

The reason for the post is to point out something I did to troubleshoot the issue and want to know if the results can help anyone understand what the problem may be. When I clamp off the two front brake hoses (from line to caliper), I get a really hard, and high, peddle. It's exactly how it is supposed to be, how it was when I fist bought the truck. When I remove the clamps the peddle returns to soft and low. My understanding of this method is that it's telling me, then, that there's nothing wrong with the system "before" the clamps. Something between the clamp and the caliper piston is causing this. If it's in fact due to non-OEM calipers I would like someone to explain how third party parts are causing this.

Other Notes: Brakes do not leak. Three bleed methods have been tried (push, pull and gravity). I even did a "bench bleed" just so i could turn the caliper in positions that ensured the pin was definitely at the top and air couldn't be trapped anyplace else. Rotors and pads are wearing evenly, although my impression is that the rear brakes are working harder than the fronts. I base this on it feels when stopping, and physically touching the wheel rim and noticing that the backs are hotter than the fronts. I can do long four hours rides and the heat remains the same. The peddle is soft, but the stranger issue is that peddle goes about halfway down before it even begins to brake.

Odd side note: Once in a great while, like one drive out of 30, the brakes perform much better. Much higher and harder. But, only first drive of the day. It returns to crap after about 10 stop signs.

Hoping for help.

Thank you!

Jim

Comments

  • thecardoc3thecardoc3 Posts: 5,117
    With the engine off. Hit the pedal one time and using "normal" braking effort try to judge just how far the pedal traveled. This first application of the pedal is a subjective opinion of the travel based on the booster having retained vacuum and actually assisting in the application of the brakes.

    Now hit the pedal several times bleeding off any assist, then leave the pedal unapplied for about ten seconds.

    Hit the pedal one time with a reasonable, repeatable amount of pressure and memorize how far the pedal has traveled. Now pump the pedal about five times, somewhere between two to three times a second stopping with the pedal applied with the same force as the previous step. Answer this question.

    Is the pedal travel the same, higher or lower than the previous application after you bled off the assist?

    Now release the pedal and count to ten and then push the pedal one time with that same force as before and evaluate the pedal height once again. Is it the same, higher, or lower than the previous check when you pumped the pedal?

    Next, without releasing the pedal or changing the pressure against it after the last check start the engine, what did the pedal do?
  • I have done the typical booster and vacuum tests, but nothing this elaborate. I will do what you suggest this morning and post results. Thanks, thecardoc3!
  • With the engine off. Hit the pedal one time and using "normal" braking effort try to judge just how far the pedal traveled. This first application of the pedal is a subjective opinion of the travel based on the booster having retained vacuum and actually assisting in the application of the brakes.

    :::: Peddle goes down about 2 inches.

    Now hit the pedal several times bleeding off any assist, then leave the pedal unapplied for about ten seconds.

    ::::: Same as above

    Hit the pedal one time with a reasonable, repeatable amount of pressure and memorize how far the pedal has traveled. Now pump the pedal about five times, somewhere between two to three times a second stopping with the pedal applied with the same force as the previous step. Answer this question.

    :::::: Goes down maybe an extra inch (so 3 inches).

    Is the pedal travel the same, higher or lower than the previous application after you bled off the assist?

    Now release the pedal and count to ten and then push the pedal one time with that same force as before and evaluate the pedal height once again. Is it the same, higher, or lower than the previous check when you pumped the pedal?

    ::::: This test is about the same as the first - 2 inches.

    Next, without releasing the pedal or changing the pressure against it after the last check start the engine, what did the pedal do?

    ::::: Peddle drops to half way. I'm guessing 4 inches. Which is where it usually operates.

    Note: I'm determining my measurements from the very bottom edge of the rubber part of the peddle.
  • thecardoc3thecardoc3 Posts: 5,117
    Everything makes sense except for "Goes down maybe an extra inch (so 3 inches)" when you pumped the pedal. It is a bit subjective how you are trying to judge how far the pedal went and it does take a learned feel to do this but based on everything else there is no air in the system. After the pause with the pedal released when you hit the pedal one time, the pedal would travel four to six inches, and when you hit the pedal fast (pumping it) if there was air the pedal height would have increased. Then releasing it which would allow the pressure you created by pumping the pedal to bleed off, the next single application would have seen the pedal travel increase to the six inch or so distance.

    The pedal dropping off when you start the engine is normal since the booster charges and multiplies your apply force. At this point I suspect you probably have a different car that has a pedal feel that is higher and firmer than this truck which is why you think there is something wrong but based on what you wrote here the travel is normal.
  • Thank you for your help. I appreciate your time in helping me. I do want to make sure I explain this correctly. When I bought the truck the peddle was high and hard. Only after I did my first brake job on the truck did this all begin. Since then my peddle always travels half way before pressure is felt and it's soft, meaning soft as if there was a tiny bit of air somewhere in the system. And as I stated, when I clamp both front brake hoses the peddle becomes hard immediately - no travel at all. This tells me that my issue is somewhere in the system AFTER the clamps - between the clamp on the hose and the caliper. I even had an assistant remove the clamps while I was applying the brake and as each clamp was removed the peddle dropped a little for each clamp removed where it went back to half way and soft again. While we were both still in position (the brake still applied) I had my assistant reclamp the hoses. I then release the brake and reapplied. The peddle was again firm and would not travel. He released the clamps again and the peddle went right back to half way and soft.

    To me the only thing that would be considered "normal" is having the brakes perform the same or better than they were before I did the first brake job.

    Thanks again. I really hope to figure this out.
  • thecardoc3thecardoc3 Posts: 5,117
    The first thing that I am going to point out is that clamping brake hoses is a mistake. You can damage the nylon central liner as well as the steel braiding which can result in fluid leaking into the inner layers of the hose assembly. Read further for what could happen if that was the case beyond ending up with an external fluid leak.

    The second thing is with the routine that I gave you, I had you bleed off the assist so that you could actually feel just the pad and caliper movement and you came back with only about two inches of pedal travel which would be well within normal expectations. Then by having you pump the pedal and hold it again you were checking for air which if air in the system was a possibility, you would have gotten an increase in pedal height. However again with only about two inches pedal travel on the first application, there really could not have been any air anyway because it would have been compressing and allowing for greater pedal travel. (Rem fluids are not compressible for this exercise)

    So if this isn't air and the pedal travel really is too far and soft then something is flexing and allowing for greater than normal fluid movement. Hoses can do this if they are weak, they essentially balloon under pressure and then recover. FWIW Clamping a hose can cause this failure. A brake pad that has been bent could be springing and pressing the piston back further than it would retract on it's own. A brake pad mis-installed and hanging up on the knuckle could be bending on application and springing back when released. The trouble her is that each of these conditions would also give you a lower pedal on the first application with no assist that would pump up to a point and by what you wrote that isn't happening.

    Is this the only vehicle that you drive or do you usually drive a different one? You have not convinced me that there is a genuine issue at this point and it sounds like you are comparing this pedal travel to a different vehicle which happens to have a higher and firmer pedal.

    How far do you have to push the pedal to lock up the brakes and or get the ABS to activate such as in a panic stop? Can you in fact lock up the wheels?


  • Yeah, I'm aware of the concern with clamping hoses, which is why I performed that test on old hoses before I replaced them with new OEMs. I have only one vehicle - my truck, and drive nothing else. As I stated I'm comparing what's "normal" to how the brakes performed when I first bought the truck. New truck equaled hard high brake peddle. After first brake job brake peddle is now low and soft. So, there is an issue.

    ABS testing shows they ABS is working as designed. Although braking hard on pavement (like changing your mind on racing through a yellow light) requires me to push the peddle near the floor to a point where I am seriously concerned the truck may not stop.
  • thecardoc3thecardoc3 Posts: 5,117
    edited October 2016
    jimmy4x said:

    As I stated I'm comparing what's "normal" to how the brakes performed when I first bought the truck. New truck equaled hard high brake peddle. After first brake job brake peddle is now low and soft. So, there is an issue.

    It would really help if I got to feel what the truck is doing first hand. When you went through the previous exercise after you bled off the assist you only had two inches of travel, that's not a low pedal but there are things that can go wrong that make that insufficient to result in stopping power.

    In this next paragraph you state:
    jimmy4x said:


    ABS testing shows they ABS is working as designed. Although braking hard on pavement (like changing your mind on racing through a yellow light) requires me to push the peddle near the floor to a point where I am seriously concerned the truck may not stop.

    The next question that I need to see answered is....
    How hard would you have to push on the brake pedal to get it to go that close to the floor if you didn't have the booster assisting you? With the engine off hit the brake pedal four to five times to bleed off all assist. Release the pedal and wait five to ten seconds. Now try to push the pedal all the way to the floor first with one foot, and then with both feet if necessary. Were you able to get it to go that far? If so how difficult was it?

    What I need to determine is if what you are really referring to is poor braking effort as compared to before the brakes were religned and if you are now just keying in on pedal travel that in fact might not have really changed but has your attention because of possible reduced effectiveness.

    A routine that we use to determine brake application is have the vehicle off the ground in neutral, transfer case in 2 High if 4WD. Have an assistant hit the pedal several times to bleed off any assist and release it. Now check to make sure that all of the wheels turn free.

    Then start turning one of the front wheels by hand as the assistant slowly applies the brake pedal with increasing pressure. The person applying the brakes needs to increase pedal pressure as the one turning the wheels asks for more and more pressure. Once the wheel being turned stops moving, not just a drag but stopped the person applying the pedal needs to memorize how much travel was required. Repeat this at the other three wheels. How much travel was required to stop the wheels? Were they all about the same or not?

  • I'll go try this now. Q: Transfer case in 2H, not in neutral as well?
  • thecardoc3thecardoc3 Posts: 5,117
    2 high is fine. You won't need the transfer case in neutral to do this.
  • How hard would you have to push on the brake pedal to get it to go that close to the floor if you didn't have the booster assisting you?

    :::: The peddle became solid as a rock. If it traveled at all it was maybe 1/4 inch. I couldn't push it further than that.

    With the engine off hit the brake pedal four to five times to bleed off all assist. Release the pedal and wait five to ten seconds. Now try to push the pedal all the way to the floor first with one foot, and then with both feet if necessary. Were you able to get it to go that far? If so how difficult was it?

    :::: I couldn't get the peddle to move more than that 1/4 inch. Even with a lot of pressure.

    Then start turning one of the front wheels by hand as the assistant slowly applies the brake pedal with increasing pressure. The person applying the brakes needs to increase pedal pressure as the one turning the wheels asks for more and more pressure. Once the wheel being turned stops moving, not just a drag but stopped the person applying the pedal needs to memorize how much travel was required. Repeat this at the other three wheels. How much travel was required to stop the wheels? Were they all about the same or not?

    :::: Each wheel stopped with just about the same amount of pressure on the peddle. There may have been a difference of an additional 1/4 to 1/2 inch between one or two of the wheels, but each still felt solid and the peddle didn't travel more than 1/2 inch max.

    I also did the same testing with the truck running. The peddle for each could stop the wheel with about 1 inch of travel, BUT each could still be forcibly turned by hand until about another inch of travel before it was too hard to turn by hand (close to halfway but not quite.).
  • thecardoc3thecardoc3 Posts: 5,117
    jimmy4x said:


    With the engine off hit the brake pedal four to five times to bleed off all assist. Release the pedal and wait five to ten seconds. Now try to push the pedal all the way to the floor first with one foot, and then with both feet if necessary. Were you able to get it to go that far? If so how difficult was it?

    :::: I couldn't get the peddle to move more than that 1/4 inch. Even with a lot of pressure.

    Then you don't have a soft/low pedal. This sounds a lot more like a brake pad performance issue where the coefficient of friction is too low between the pads and rotors.

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