ABS Bypassing

Dejon Nell

Member
Joined
Sep 10, 2020
Messages
24
Location
Cape Town / South Africa
I have been having recent issues with my rear brake (like many in the forum have experienced). Rear brakes have been bled and the ABS pump cycled (multiple x10 times) only to be good for a day or two then it goes right back to being spongy and soft having to pump the rear brake to get pressure and feel any sort of braking power. The option to have the ABS bypassed is on the table now as the cost of a new ABS unit is pretty high especially for a 2011 Gen 1 S10. I would like to find out from those who have bypassed the ABS if there is any real big changes to the bikes braking ? Does the TCS still work? The unified front and rear braking i take it will no longer work? And then lastly what is required to bypass the ABS?
Looking forward to your responses. TIA
 

Jlq1969

Well-Known Member
Joined
May 5, 2018
Messages
1,749
Location
Argentina
I see that you have read post referring to the issue of rear brake failure. You cannot "remove" the module and bypass both brake lines because the abs control unit is the one that receives the signals from the wheel sensors and it passes the signals to the motorcycle ecu for the odometer, speedometer and TCS. You can simply make a bypass between the rear brake pump and the rear caliper, you will have a good rear braking but without rear abs, and the tcs will continue to work (which does not act on the brakes but rather acts on the handle throttle)…. .all this until you either get an abs module or repair the one you have. I have not read anything referring to "another" solution. The issue is based on "assumptions"...the truth is that air enters the rear circuit, the truth is that the air is introduced by the abs module...but from then on there are only assumptions, 1) maybe a seal? but the strange thing is that there are no fluid leaks along with the air intake… 2) there are “several” ones that started with this problem “after” changing the brake fluid of the circuit (in this forum and in others too) , that could be a sign that there is air "inside" the module, but since the problem persists after several purges, it gives the sensation that the air "enters" the module, now well... where does it enter?, no one clarified /solved. In any case, the problem is "according to my opinion", more related to the brake combining than to the abs. The combined brake is another system within the same abs module. The abs interrupts the braking pressure, and if this pressure exceeds certain parameters, it "returns" said pressure to the brake circuit (that is why a pumping is felt in the brake lever but also a rebound)... but in the actuation of the combined brake (rear only), there is only "push" on the rear line, no rebound on the brake pedal, only push on the rear caliper. This "push" is carried out by "the same" cam that returns pressure to the brake circuit when the abs works and causes the return/rebound in the brake lever/pedal. The problem with the operation of the combined brake is that to "push" liquid, you need liquid... when the combined brake works, the rear brake pedal of the S10 does not descend, so... where does the abs module get liquid from to "push" , well, that liquid is inside, and it is not part of the circuits, it is in a separate reservoir, which is the one used when the braking overpressure exceeds the abs valve, then that overpressure returns to the main circuit (rebound in the lever/brake pedal)……that is why it is important when cycling the abs, to keep the lever and the brake pedal “squeezed/exerting pressure), so that excess pressure releases the valve, and forces the abs to “return ” the liquid to the circuit…..but WHERE DOES IT RETURN IT?……there is no return circuit to the brake reservoir…..it returns it “Inside” the same pump, if there is air inside the abs moduke, it is trapped in the abs
 

2daMax

Active Member
Joined
Jun 3, 2015
Messages
675
Location
Penang, Malaysia
Air in the rear ABS system has been a mystery as there are no external leaks. The spongy rear pedal is a sign that air is a factor. Assumptions for presence of air would be the byproducts of corrosion from worn out brake fluids. Particularly for DOT4, it is more hygroscopic than DOT3 and has a 2 year or 24k km change interval. A worn out fluid would not provide the proper corrosion protection, particularly to copper ions that floats around. Copper ions comes from brake lines. The corrosion accelerates pretty fast once the inhibitors are gone. Some of the valves are coated or plated with Copper and causes sticky valves.

If u have access to the Service Guide, the rear ABS has 4 Solenoid valves are shown. The regular In and Out and 2 more that is part of the UBS. I believe these 2 are the ones that are trapping air. Also, the pump that is driven by the ABS motor may also hold air in the rear ABS system as there are 'dampers' in the hydraulic circuit. When the UBS is activated, the pressure comes from the pump, since it is not from the pedal.

I discovered something yesterday as I was cycling the pump to try to cure the hard rear pedal issue (not spongy). While in ABS diagnostic mode where the ABS can by cycled, while the key is ON, I rotated the rear wheel and press the front brake, and I could hear some liquid moving in the ABS. It was pretty obvious. When I off and on again to perform the cycling, I found that the rear pedal has less spongy feeling. I repeat this another 2X and found that the rear pedal is firmer as if any trapped air has been removed. I think what I did has somewhat activated the UBS valve systems. And if there are trapped air or vapors, it will get released when the UBS valves are actuated. Just sharing if you wanna try getting rid of the trapped air this way, plus multiple ABS pump cycling.
 

cadcamkenny

Climbing the cc ladder since 1979
2012 Site Supporter
Joined
Apr 26, 2012
Messages
121
Location
Merritt Island
Hello all, I'm looking for help and hope the folks with brake experience can help. I've tried everything I know and have performed several brake bleeds on other vehicles in my life. Any help is appreciated! Here are the clues:
1) The front brake lever goes all the way to the bars before I get some braking. feels like air in the lines.
2) The rear works as it always did and will engage the abs when pushed hard.
3) I've bled the brakes and cycled the ABS pump repeatedly. No bubbles, I used a mighty vac and sucked two pints of fluid through. also tried traditional bleeding methods outlined in the forum.
4) The brake lever will get rock hard when the pump is running but goes back to the bars with limited braking.
5) I can pump the front lever up and it will get somewhat hard but returns to soft and to the bar on the next squeeze.
6) I've looked at the abs pump and the vents are squeaky clean with no fluid leaks anywhere visible.
7) Its a 2012 XT1200 with 21,000 miles.

I am prepared to do the following next steps.
1) What would happen if I opened the nipple on the left front caliper while abs is cycling? I need a sanity check before I do this.
Maybe there is air in the line from the abs to the manifold? Those u shaped brake lines seem like a good place for air to remain trapped.
2) I ordered a replacement master cylinder off eBay and am waiting on delivery.
3) I have all the tools are parts to bypass the abs as a last resort.

Thanks for all who reply and sorry if this is off the topic thread but you guys seem like the best source for brake info!
 

EricV

Riding, farkling, riding...
2011 Site Supporter
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Joined
May 22, 2011
Messages
8,227
Location
Tupelo, MS
There is also a possibility of warped front rotors or bad wheel bearings. If the wheel moves around a lot or the rotors are warped it forces the brake pads back out more than normal, so when you squeeze the brake lever the next time it will go all the way to the bars. No air in the system, just more travel needed to get the pads to the rotors.

I have experienced this first hand with front wheel bearing failure.
 
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