light brake pedal pulse - Toyota FJ Cruiser Forum
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post #1 of 48 (permalink) Old 10-29-2018, 08:05 AM Thread Starter
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Question light brake pedal pulse

I've been chasing down some strange feedback at the brake pedal for a few weeks. All started after returning from a trip to Colorado, it rained epic amounts on the way there and back but they symptoms only surfaced after I made it home. Feels is very similar to ABS or when ATRAC activates but not nearly as aggressive. It mostly occurs with light breaking at 20 MPH or lower but can not be produced consistently. My first thought was a rotor with some run-out so I swapped all of the brake wear components, sadly no change. The speedometer also has occasional irregular behavior mostly above 60 MPH where the needle jumps around +/- 3 MPH. When this occurs cruise control is still available but no fun to use.

Dash Lights - None of the typical trio lights are lit up. No ABS or a check engine either.

Codes - Had the truck scanned at O'Reilly's a couple times and it showed faults with both rear wheel speed sensors. All have been cleared with the reader but I suspect they will be back.

Parts Changed
4 new rotors
4 new pads
4 brake sensors not new but from a working vehicle. Thanks @RichJacot

Service - Cleaned sensors at all 4 corners and removed the grease from their mounting holes. Disconnected, cleaned and inspected wheel speed connectors and where the 2 rear meets the harness above the passenger spring. All were cleaned with QD contact cleaner spray. No breaks or obvious damage to the wires or connectors. Cleaned/Polished the plunger assembly in the brake accumulator.

Here is what we have done to "fix" it and where it gets weird.
***incorrect***Unplugged the black connector at the hydraulic brake booster and all symptoms are gone but at the cost of no ATRAC (possibly more) and the brake indicator light is on. I believe this is the Skid Control Unit that is integrated? into the brake booster.


Has anyone seen this and know a solution? If it turns out to be the brake booster how difficult is the swap?

Thanks,
J
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post #2 of 48 (permalink) Old 10-29-2018, 10:14 AM Thread Starter
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Re: light brake pedal pulse

Forgot to mention there were a few times in there where traction control lit up while driving on straight and dry ground but I haven't seen it since.
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post #3 of 48 (permalink) Old 10-30-2018, 04:58 AM
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Re: light brake pedal pulse

This may sound crazy at first read but I have experienced it first hand. A wheel bearing starting to go out will start to shed very fine metal "dust". That metal will work its way into the wheel sensor area and cause false readings. Obviously that may not be your problem but it is a place to checkout. You won't be able to simply pull the sensor and wipe off and say your done. Pull the wheel and inspect the wheel bearing with your eyes and feel it by spinning with your fingers.


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post #4 of 48 (permalink) Old 10-30-2018, 07:18 AM Thread Starter
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Re: light brake pedal pulse

Quote:
Sparky of SoCal previously said: View Post
This may sound crazy at first read but I have experienced it first hand. A wheel bearing starting to go out will start to shed very fine metal "dust". That metal will work its way into the wheel sensor area and cause false readings. Obviously that may not be your problem but it is a place to checkout. You won't be able to simply pull the sensor and wipe off and say your done. Pull the wheel and inspect the wheel bearing with your eyes and feel it by spinning with your fingers.


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Funny you should say that, I have two front bearings due for delivery today. One side has obvious play the other will get swapped regardless. There is no noticeable play at the rear on either side, fingers crossed the front is the culprit despite the codes pointing to the rear.
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post #5 of 48 (permalink) Old 10-30-2018, 10:12 AM
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light brake pedal pulse

I understand your codes pointed to the rears. Still a factor tor consider. I simply donít trust the primitive code structure with the FJ so I also factor that in. I wonít rule something out just because of what codes may or may not show up.


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post #6 of 48 (permalink) Old 10-30-2018, 10:35 AM Thread Starter
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Re: light brake pedal pulse

Quote:
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I understand your codes pointed to the rears. Still a factor tor consider. I simply donít trust the primitive code structure with the FJ so I also factor that in. I wonít rule something out just because of what codes may or may not show up.


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Codes were for the rear but the bearings are relatively fresh as its a replacement axle form Currie. I suppose they could have been from a bad lot or damaged when pressed on.
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post #7 of 48 (permalink) Old 10-30-2018, 10:36 AM Thread Starter
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Re: light brake pedal pulse

Quote:
Sparky of SoCal previously said: View Post
I understand your codes pointed to the rears. Still a factor tor consider. I simply donít trust the primitive code structure with the FJ so I also factor that in. I wonít rule something out just because of what codes may or may not show up.


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Correct the codes were for the rear but the bearings are presumed to be relatively fresh as its a replacement axle from Currie. I suppose they could have been from a bad lot or damaged when pressed on.

Is there a more scientific way of testing the rear bearings beyond rocking the wheels or spinning it and checking for odd sounds? I'm not opposed to swapping the rear too but the parts cost is adding up and the job isn't quick.

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post #8 of 48 (permalink) Old 10-31-2018, 07:41 AM Thread Starter
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Re: light brake pedal pulse

Significant improvement after last night's swap but still not 100%. At least I'm back to having all electrical components connected. Hope to change the other in a couple days then if need be I'll move to the rear.

Anyone know how long the codes remain after clearing them? Zapped them on Sunday but have only logged about 30 miles since then.
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post #9 of 48 (permalink) Old 10-31-2018, 08:26 AM
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Re: light brake pedal pulse

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istambull previously said: View Post
Correct the codes were for the rear but the bearings are relatively fresh as its a replacement axle form Currie. I suppose they could have been from a bad lot or damaged when pressed on.

Is there a more scientific way of testing the rear bearings beyond rocking the wheels or spinning it and checking for odd sounds? I'm not opposed to swapping the rear too but the parts cost is adding up and the job isn't quick.


The key to my suggesting to check the front bearings is the metallic dust that a worn bearing may produce. That metallic compound is conductive and will at times lead to false readings issued by the wheel sensor. The rears are built a little different. You have new parts back there.
Your codes suggest a problem originated in the back. That is important and needs to be considered.
Because I donít believe the software that is used to monitor data and produce the codes is not foolproof and when you are trouble shooting that needs to be considered when the errors can not be isolated.


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post #10 of 48 (permalink) Old 10-31-2018, 10:31 AM Thread Starter
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Re: light brake pedal pulse

Quote:
Sparky of SoCal previously said: View Post
Your codes suggest a problem originated in the back. That is important and needs to be considered.
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