ABS Failure!

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Sep 16, 2009 | 08:51 PM

#31

mrglide

6th Gear

Joined: May 2009

Posts: 14

Likes: 0

From: Florida

This may not be an ABS problem at all. As suggested earlier, my money says the dealer misdiagnosed the problem or is only trying to cover up that your new 2010 was delivered to you without enough brake fluid in it.

Sep 16, 2009 | 09:01 PM

#32

nocarb

Road Master

Joined: Jul 2008

Posts: 868

Likes: 51

From: Illinois

Quote:

Originally Posted by mccollde

I am hoping someone out there understands how HD's ABS braking system works so you can tell me what just happened. Was driving my 2010 FLTRX to work Monday and was running about 45 mph. Came upon a red light and begin to apply front and rear brakes as always to stop..... The brake pedal for the rear brake went to the floor! No rear brake at all. Spooked me a bit but I came to a normal stop using the front brake. Thank god this didnt happen in a emergency situation. Anyway I take the bike to my dealer to find out what happened. They tell me today the ABS modulator that controls the rear brake failed and they have me another one on order. Done some Q & A with the service guy but i am still not clear as to what happened.

Questions? What if the front had failed also? Does this mean I have no brakes? Is this possible that HD would design a braking system that has the ability to completely fail and leave me with no brakes? Shouldnt my ABS light have come on and warned me of a problem during the start up diagnostics check? If the ABS system failed shouldnt the braking system default into a manual (normal) braking system?

Sorry to be long winded but this has me a bit spooked. If anyone can explain or answer any of these questions it will sure make me feel better.

You are assuming the tech guy is compatent. He may not be.

Sep 16, 2009 | 09:15 PM

#33

wingman05

Road Captain

Joined: Aug 2007

Posts: 642

Likes: 3

From: Bellmawr, New Jersey

If the ABS fails, your normal brakes will still be effective. The ABS light cycles and goes out after starting when you start to move. Did your ABS cycle when starting? Even if the ABS was faulty, the rear brake should not have reacted as you described. I think your issue goes beyond the ABS system.

Sep 16, 2009 | 10:14 PM

#34

CarbideDude

Tourer

Joined: May 2006

Posts: 449

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From: Helena, AL

2009 FLHX w/ ABS - occasionally rear brakes just don't work, but the pedal doesn't go any further down. First couple of times I thought, hmmm, could the rear tire be starting to slide and they released? But they didn't re-activate. Like the original poster, I was able to brake sufficiently with the front.

Been out of pocket with surgery lately and just now starting to ride again, so this post is motivating me to check with my dealer.

Sep 17, 2009 | 12:12 AM

#35

RexBuck

Road Master

Joined: Sep 2007

Posts: 899

Likes: 2

From:

Quote:

Originally Posted by mrglide

This may not be an ABS problem at all. As suggested earlier, my money says the dealer misdiagnosed the problem or is only trying to cover up that your new 2010 was delivered to you without enough brake fluid in it.

Bingo!

Sep 17, 2009 | 01:40 AM

#36

Potato_Potato

Outstanding HDF Member

Joined: Sep 2005

Posts: 2,600

Likes: 7

From: Minnesota

I think your title should be brake failure rather than ABS failure.

Sep 17, 2009 | 03:15 AM

#37

Rugar

Tourer

Joined: Apr 2008

Posts: 356

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From: Berdoo, So Cal

subscribed

Sep 17, 2009 | 03:42 AM

#38

sgdiesel

Road Warrior

Joined: Nov 2008

Posts: 1,296

Likes: 3

From: Cheltenham, UK

The modulating valve, which is at the heart of an ABS system, will modulate between the pressure supply line and a return line to tank, the output going to the brake caliper - i.e. it is a 3 port valve.

It will modulate the output pressure based an a feedback device being compared to a set criteria. This means that in principle there is a possibility that the valve could modulate the output brake pressure to zero under some circumstance (when working correctly when the wheel is locked up - or fractionally just before), so in principle the system could fail in the mode described, but I do not no any of the specifics of what measures are taken to prevent this happening although I suspect there are numerous robust back up systems in place, including reverting to "normal brakes".

I am not speculating that this is what happened, nor am I disagreeing with the theory concerning a MC failure. If the brake pedal is depressed, incompressible fluid (assuming correctly bled) should be displaced. That fluid will take the path of least resistance back to the reservior (or leak externally of course but that appears to have been ruled out) if there is a breakdown in the integrity of the system (i.e. broken seals or faulty modulator valve). If the integrity of the system is sound then pressure will build up when the pads make contact with the disks and braking will take place.

So, in summary, if the brake pedal has moved and there is no brake effect then either no fluid was displaced or the integrity of the system is in question. That is as far as we can go at this stage.