Weird problem with rear brakes, no pad/disk contact - Acura MDX Forum : Acura MDX SUV Forums
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post #1 of 17 (permalink) Old 4 Weeks Ago Thread Starter
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Weird problem with rear brakes, no pad/disk contact

So for the longest time I've had weird issues with the rear brakes. While the fronts were wearing nicely and evenly, disk surface was always nice and shiny until the breaks were gone, the rear would always rust in the middle of the rotor and it always seemed that braking is only done on the outer 50% of the rotor's surface (farther from the hub's center). I've cleaned and reinstalled many times hoping for an improvement. No go. So I've finally decided it must be shot calipers and bought all new parts: calipers, rotors and pads. To my shock, 3 months later, yet again I am getting no contact between the pad and disk on the inside rings, ie. closer to the hub and good wear on the outside (recall I am not talking about inner and outer pads, but rather distance from the hub center to the outer edge of the disk.

WHAT GIVES????

Is it that rear brakes get a very light pressure on them compared to the fronts, AND, perhaps, this causes insufficient force to use push the entire pad onto the disk??

I've also bled my system about 5 times since the issue emerged many years ago.

The brakes look like **** basically... And they are 3 months old! Any ideas??

This is not my picture, but roughly what i am talking about. nasty! And all the parts are new!



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post #2 of 17 (permalink) Old 4 Weeks Ago Thread Starter
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And to make it even more weird and harder to troubleshoot... BOTH rear sides show the same symptom!!!

One small EDIT: my contact area is closer to the center, outer 50% makes no contact.
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post #3 of 17 (permalink) Old 4 Weeks Ago
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Try braking hard a few times from about 60MPH. They may need to be seated.

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post #4 of 17 (permalink) Old 4 Weeks Ago Thread Starter
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Tried many times. Makes no difference.
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post #5 of 17 (permalink) Old 4 Weeks Ago
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Do you have the springs. shims, and shim grease installed?

Pads are not flipped, correct? - meaning pad arc is aligned with disk arc (they’re almost rectangular but have some arc).

Not backwards, as in pad backing is against the rotor? - only asking because the back of the pad is not flat.

Curious to see what the back side of the rotor looks like - same or are they worn opposite indicating a tilted caliper.

You’d think even if high or tilted, the pad would eventually wear down to make full contact. An end view inspection of the pad should tell you if it’s tilted.
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post #6 of 17 (permalink) Old 4 Weeks Ago
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Wonder if possibly due to worn slider pins or grooves on caliper holders. Caliper squeezes and rocks not putting equal pressure on pads?

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post #7 of 17 (permalink) Old 4 Weeks Ago
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Looks like your pistons are not pushing your pads firmly against the rotors.

Possibly due to seized caliper pins.

Could be bad pistons, too.

Course of actions I suggest:

1) Check the brake fluid level and fluid condition (even if you don't have a tester, just see if it's contaminated badly in the reservoir or not).
2) Take off one wheel on either side and unclamp the caliper.
3) Check the caliper piston rubber boot for cracks, tears and leaks.
4) Try moving the piston with a screw driver using a pivot action leveraging it against the caliper itself and see if the piston moves back freely (it should with minimal force). Be careful not to damage the boot with the screwdriver.
5) Take the upper pin bolt off and take the pin out. See if it's lubricated with silicone based grease at all and see if you can take it out and put back all the way in easily (you should).
6) Take out the pads one by one and check their condition.
7) See if you can spot if the back pad is doing the same as the outer one.
8) Take the caliper off completely leaving only the bracket and carefully place it so the brake line is not bent or stressed (I would use a small rope or something like that to secure it as well).
9) Repeat step 5 for the lower pin.

Unless you are using incorrect or incorrectly installed pads and non-compatible caliper, by now you should have all information to determine the cause.

Good luck!


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post #8 of 17 (permalink) Old 4 Weeks Ago Thread Starter
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Yeah.. but if you recall that ALL PARTS ARE BRAND NEW... ie. rotors, pads AND calipers with all the hardware in them..., sliders, pistons, gaskets... That is exactly why got them new because I've had this weird problems 5+ years prior (slight edit here: the stores sells them as new (and they look new) but they are re-manufactured, they took my calipers as core too).

Yes, grease was installed. Could you even possibly install pads wrong? Meaning wrong arc? I doubt they would fit (and I've been doing brakes for 20 years so unlikely I'd screw up that bad, would have to be drunk i think LOL)

Thank you very much guys. Yeah, sounds like I may need to disassemble the system again and you are correct : it would be interesting to see what the inner side of the rotor looks like.

What puzzles the crap out of me though is that BOTH sides are doing the same: suggesting that it is NONE of the hardware listed here in my post, but smthg else: I am really tempted to think there is insufficient power pushing on the rear brakes. Does that sound legit? The car is 15 yrs old and perhaps something in the brake lines going from the master cylinder is acting up? As in both rear wheels are not getting the braking power they need hence there is only light contact of the rear brakes (distance much greater and if the master cylinder/lines are junk?)? The car is driven very sporadically these days... not sure if that makes any difference. Less than 5k miles a year.
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post #9 of 17 (permalink) Old 4 Weeks Ago
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Re hydraulic power to the rear, you mentioned multiple flushes so I take it you have no air in your system and reservoir is full. Are the lines linked or pinched in any way?

Did you try hard braking like Bluepill suggested?

Not saying you did but the pads can be installed with the arc incorrect. They will fit in that position.

If it’s not the caliper, it seems the rotor is tilted relative to the pad. Not sure how that could be possible. You’ll know more when you look at the back surface.

Good luck!
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post #10 of 17 (permalink) Old 4 Weeks Ago
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Just out of curiosity which calipers. pads, rotors did you purchase and from whom? It is odd that it is happening on both the rears? Who installed the pads.rotors calipers?


First thought is that the piston is at fault and it might be but not because the piston or its bore are out of wack. Instead it is the Pins that are installed incorrectly not on their flats in their slot on the caliper? This is sometimes over looked as when one tightens them they too turn and do not locate on their flats and flats on the caliper. This will cause the whole caliper to twist and cause uneven wear like you are experiencing here! Make sure the pins are located properly and ensure that they are properly lubed from manufacturer.



The other possibility is that your rear brake hoses need to be replaced as they maybe collapsing causing uneven pressure on the piston due to lack of pressure! This is plausible due to the fact that both rear wheels have the same issue. No mention of ever having replaced and seeing that you have replaced everything else has me suspect that this is a real possibility.



It takes 10 minutes to pull a wheel and put a square on the rotor in various places to verify any irregularities, check the pin's are lubed and install them correctly and recheck that the piston moves freely in its bore. Check too that the pads move freely in the caliper prior to tightening caliper bolts. Honda has had issues with rear pads "ears" not fitting properly and taking a little bit off may be required or they can "bind" causing improper contact.



When was the brake fluid changed out fully? If it has not then do so as it will have broken down and will not perform properly and make sure you use the appropriate brake fluid.
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Yes, tried hard braking. Very hard braking. I replace them myself, after having it done about 50 times on many other cars (20 years). All other cars are fine. Brake fluid was changed a couple times in the last 4 years.

"The other possibility is that your rear brake hoses need to be replaced as they maybe collapsing causing uneven pressure on the piston due to lack of pressure!"

I am really thinking that might be the issue. So you suggest (after verifying everything else I have installed, ie. pads, rotors and calipers/cylinder, pins, etc) maybe replace both rear brake lines, only the part that is rubber right? Can you verify for me? Please see the pictures below.

One is the OLD brakes showing the same symptom.

The other one is my brand spanking new set.

Let me know if the suggested brake line hose replacement is the piece circled in the pic.





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post #12 of 17 (permalink) Old 4 Weeks Ago
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yes , that is the hose but look it over and inspect it for cracks, blisters , bulges. I would grab a second person and have them start the car and pump the brakes while you watch the brake line for any movement, swelling, movement or other defects. I state this step i mentioned as it will allow you to see the pressure and how the hose reacts. Some hoses have small grooves that allow you to see if hoses are twisting when pressure is applied in which case they can be replaced.



There is a lot you can;t see from the outside which the pressure test can tell you. This being said and after viewing your under carriage i notice a great deal of rust and not being there i would recommend that you follow both rear brake lines all the way up to the master cylinder under the hood! There could be a damaged rear metal line or fitting and the only way to rule it out is to trace both rear brake lines and connections looking for any damage, leaks etc. How did the rear brake bleeding go previously? Did you notice any reduced pressure, harder to push brake pedal, fluid flowed out bleeder valve without obstruction? if so i will leave it there for now.
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post #13 of 17 (permalink) Old 4 Weeks Ago Thread Starter
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Well, with regards to bleeding, yeah, it went well BUT I was very perplexed by something...

Even after bleeding many times (and doing it correctly, with the bottle to trap air and not to suck it back in etc), I have NOT been satisfied with the result AND now i wonder if this is related to my rear brake issues.

Basically when I brake, the pedal goes to the middle and when i pump it again (just ONE extra pump, total of 2), it catches nice and high. Seems like there is some air in there right? Wrong!!! Bled many times and no air is coming out.... (and do know that I've bled many other cars before and all is well, i am not sucking any air back in)

So... maybe it is some deteriorated hardware on the way as you have suggested... I really wonder...
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That is frankly why i was asking the questions and having you do a pressure test on the hoses prior to replacing them as i am not totally convinced that is the issue! The dealership would say they needed replacement and just replace them however if they pass the pressure test i would not bother yet. I would run through the rear brake lines as stated and fittings looking for anything out of place.

The fact that the pedal requires a 2nd pump abd that you were concerned when pumping the brakes that something felt off has me thinking that the brake master is not building sufficient pressure to the rear brakes? A bad brake master cylinder may result in a pedal that feels mushy, spongy, or slowly sinks to the floor when depressed. It isn't sinking to the floor but it is mushy and spongy you say requiring a 2nd pump! The internals wear out causing internal leaks and a new master is required! I say this as you state that you have bled the brakes umpteen times and still have a spongy pedal and you swear no air!!! so good news its not a $500.00 part but only a $60.00 -100.00 part.

This would make sense especially if brake hoses,fittings, lines are fine and no leaks or kinks of any kind are found and pressure test successful on hoses.
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post #15 of 17 (permalink) Old 4 Weeks Ago Thread Starter
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Yes, I was afraid that was coming. The mushy pedal, still doing the job and stopping the car fine, but nevertheless really weird 50% travel down on freshly bled system had me wondering ...

If this explains why pressure may be decent in the front (not prefect by any means, the car does not stop as well as new, but it does the job...) but very weak in the back, then I am happy and I will look into master cyl replacement after quick visual on the brake lines.

Appreciate the time and guidance bud. Thanks everyone else as well, you guys are awesome (this forum has helped me countless times before, I have paid back a bit myself with some DIYs on here). But Arrgh.. another job..... and this is now my spare car that does few k per year only... Though my kids are growing up and the usage will pick up soon probably...
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