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Stumped, lose power brakes /hard pedal after prolonged application?


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Brake system on my 02 4x4 was not opened up, problem started a few weeks ago after replacing both front hub assemblies. Just pressed brake pistons in and left them hang. Before starting it I pumped the brakes a few times to get the pistons filled and pushed back out. now ever since I loose my power brakeing after about 2-3 applications or prolonged applications like rolling to a stop sign ect. The pedal gets rock hard and there is a grinding noise almost like air in the system and a pump is cavitating sort of like the abs pump is acting funny. I have bled the brakes and get no air and the power steering is operating well and level is good. Brakes work excellent otherwise, not week or spongy ect but only does this after what I describe above. What am I missing. No brake light or abs lights on. I replaced the right hand abs brake cable as that one was ground up when the bearing failed but I reused the left one and shimmed it as it came on the new bearing, it was getting loose but hadn't failed yet. Don't think this is the issue as I would have an abs light I would suspect if it wasn't reading wheel speed correctly. Short stops or 1-2 short applications there are no issues everything works perfect. Anymore use then it acts up. No leaks anywhere either. I have had many issues over the years but this one has me stumped. Anyone ever run into this?

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Is the pedal fighting you back? Like the ABS pump is runnig but like fighting to keep you from stopping? What I found out in my case was the 2 front sensor didn't match quite right and so the ABS pump was trying to keep the wheels from locking even though they were not locked. So if the wheel sensors are functional and showing speed but there is a mild offset to it it will treat it like there is excessive brake pressure on on side at this point you'd have a hard pedal. But since both sensor are functional its not going to throw the ABS light. You might consider replacing the other side so the are both matching... :shrug:

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Yep Mike thats exactly what it feels like. I will put the cable on that came with the hub then. Makes sense as it only does it at really slow speeds like less then 10 mph or even slower right up to the stop. I got pretty much the same response on midwest also. Hopefully it takes care of it even though both unit hubs are different brands.

So much for trying to save a part and a few minutes of labor.:doh:

--- Update to the previous post...

Well I just got done replacing the abs sensor cable on the driver side with the one that came with the hub assembly. All works perfectly now after a test drive.

I micrometered the distance to the tone ring and the oem sensor was the exact distance as the replacement with shims so there must be a difference in the sensors and are matched to the tone rings inside the hubs.

Such a simple fix to a problem that wouldn't have been if I wouldn't have cut a corner and tried to reuse the oem sensor cable.

Thanks for the input guys.

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are you sying that the sensors are matched to the tone ring? one of mine got rubbed by the tire and i figure it is only a matter of time before i have to replace it. the only replacement i have is off of a new bearing i have.

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I know you didnt push the fluid back up the line did you? :nono: I know you didnt, just thought I would throw that in for some who may.

Actually I did, I have done it for 25+ years and have never had an issue but I do realize it could on a contaminated system.

are you sying that the sensors are matched to the tone ring? one of mine got rubbed by the tire and i figure it is only a matter of time before i have to replace it. the only replacement i have is off of a new bearing i have.

It would appear so. The sensor that came in the replacement hub was a bit longer than the oem sensor but it had 2 different thickness shims under it which brought it out to the same length dimension as the oem and the oem didn't have any shims.:shrug:
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Only time you don't want to push the caliper piston back in is when you know you have a bound up piston. So like my truck right now the front caliper is binding up from debris most likely. So if you push it back in you take the risk of tearing chunks out of the seals. If you brakes are working fine then I've push the pistons back in as well. No issues here...

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