ABS Bypassing

[Dejon Nell]

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]

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]

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]

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!

 

[scott123007]

I "think" you have a bad master cylinder, so I would wait until you install the one you ordered before I did anything else.

 

[EricV]

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.

 

[cadcamkenny]

Update on spongy front brakes. I replaced the front master cylinder with a factory new one ($110) but am still at a point where there appears to be air getting in the system.
I have bled and cycled abs at least 25 times and cant seem to remove all the air or new air is getting in. The front left caliper has an impossible amount of air in it. The front right comes out no bubbles, the rear no bubbles. no brake oil leaking anywhere. I can pump the lever up and get full brakes but that only lasts till the next time I pull the lever and it goes to the bars. The ABS works front (when I pump the lever) and rear on Grass at 20mph.

I have read that a bad abs pump manifests as a rear brake loss. has anyone had a problem where the front brake lever gets spongy, goes to the bars and it is a bad abs pump?
I've ordered a set of speed bleeders to try next. I also replaced the pads front and rear, I had about 60% left on old pads.
I have bled brakes on many bikes and cars in the past but have hit a wall with this situation.

 

[Jlq1969]

“Let's suppose”…that you have a valve stuck inside the ABS, but with a very small leak…”minimal”….if you want to pass a liquid under pressure through that minimum gap….the liquid (under pressure), will break its liquid structure and It will transform into gas (bubbles)...I think you should go in parts. put a direct line from the brake master cylinder to the front calipers...if everything worked well, you would have already ruled out that part
Perhaps the liquid is recirculating inside the module, instead of going directly to the front caliper, and this recirculation is being done through a stuck (closed) valve, but with minimal leakage, which causes the liquid that passes through there to bubble. and that you don't have all the pump pressure in the front calipers

 

[simmons1]

“Let's suppose”…that you have a valve stuck inside the ABS, but with a very small leak…”minimal”….if you want to pass a liquid under pressure through that minimum gap….the liquid (under pressure), will break its liquid structure and It will transform into gas (bubbles)...I think you should go in parts. put a direct line from the brake master cylinder to the front calipers...if everything worked well, you would have already ruled out that part

I agree, still sounds like bad pump to me until proven other wise. When/if mine ever quits I am going to bypass it and ride on.

 

[Jlq1969]

I agree, still sounds like bad pump to me until proven other wise. When/if mine ever quits I am going to bypass it and ride on.

You said that you had changed the master cylinder... rule this out, but if you have doubts you should test it isolated from the rest

 

[OldRider]

The front left caliper has an impossible amount of air in it. The front right comes out no bubbles, the rear no bubbles. no brake oil leaking anywhere. I can pump the lever up and get full brakes but that only lasts till the next time I pull the lever and it goes to the bars.

First off you can draw air into the system and not have a fluid leak. That doesn't make sense because if there is a hole for air to enter, there should be a hole for fluid to exit, but think of it as a self sealing one way valve. Happens a lot with master cylinders.

Now the part that sticks out to me is that you are getting a lot of air out the left caliper, but none out the right. I would think any air coming down from the master cylinder would go whichever way the fluid is flowing when it gets to the hose connections on the left caliper. I would expect the air to exit the right side same as the left side.

First thing I would do, requiring no parts, is put some pipe sealer tape on the bleeder screw to be sure it isn't leaking. Next replace all the sealing washers where the hoses come together and last would be to replace all the orings on the caliper pistons. It just looks to me like you're drawing in some air somewhere around that left caliper.

 

[patrickg450]

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.

I second this

 

[Jlq1969]

Maybe you have to cycle the abs...if you changed the master cylinder, the air before reaching the front calipers goes through the abs, and what happens inside there, I think even God knows

 

[OldRider]

A warped caliper would come in to play if the wheel was turning and pushing the pads/pistons back in a little farther than normal, but I don't think it would do anything sitting still. Also a warped caliper isn't going to cause air to continuously get into the system. You would also feel the warped caliper while riding and a warped caliper causing this much trouble would be very noticeable. JMO

 

[cadcamkenny]

Another update. I still had spongy front brake lever. never had a problem with the rear brake. I followed 2daMax procedure to rotate the rear wheel during the cycling of the abs pump. After the cycle, I heard a click from the abs pump and the front lever is now firm like new. That sounded like a stuck valve becoming freed up...
Just like that and out of no where, the front brake lever is acting normal and is very firm. The rear is firm as well. I am happy about this but WTH.
I've cycled the pump at least 30 times and bled 3 pints of fluid through the system.
Now, i notice while on the center stand, i can grab the front lever but the rear wheel can still rotate freely. Does that seem normal? i expected the unified braking system to grab the rear wheel as well.

 

[scott123007]

A warped caliper would come in to play if the wheel was turning and pushing the pads/pistons back in a little farther than normal, but I don't think it would do anything sitting still. Also a warped caliper isn't going to cause air to continuously get into the system. You would also feel the warped caliper while riding and a warped caliper causing this much trouble would be very noticeable. JMO

I think you meant to say "disk" every time you said caliper.

 

[scott123007]

First off you can draw air into the system and not have a fluid leak. That doesn't make sense because if there is a hole for air to enter, there should be a hole for fluid to exit, but think of it as a self sealing one way valve. Happens a lot with master cylinders.

Now the part that sticks out to me is that you are getting a lot of air out the left caliper, but none out the right. I would think any air coming down from the master cylinder would go whichever way the fluid is flowing when it gets to the hose connections on the left caliper. I would expect the air to exit the right side same as the left side.

First thing I would do, requiring no parts, is put some pipe sealer tape on the bleeder screw to be sure it isn't leaking. Next replace all the sealing washers where the hoses come together and last would be to replace all the orings on the caliper pistons. It just looks to me like you're drawing in some air somewhere around that left caliper.

I think you meant to say "can't" , not can.

Don't worry man, I got your back, LOL.

 

[Jlq1969]

Now, i notice while on the center stand, i can grab the front lever but the rear wheel can still rotate freely. Does that seem normal? i expected the unified braking system to grab the rear wheel as well.

The unified system, such as the abs system...should not be working because the abs ecu is detecting an error (only one wheel is spinning)...when you spin the rear wheel on the center stand, the abs light should be on ( the system is not working)

 

[OldRider]

I think you meant to say "can't" , not can.

Don't worry man, I got your back, LOL.

No, I said that you CAN draw air into a system and not have a leak and that's exactly what I meant. Master cylinders will let air be drawn in by the cup on the piston, but fluid pushing on the cup will seal it against the walls of the bore and not let fluid out. Works the same as a check valve.

 

[OldRider]

I think you meant to say "disk" every time you said caliper.

Yep, I did mean to say disc on this one, not caliper. Good Catch. I think you meant to say disc, not disk. I got your back too. !!!!