Spongy Rear Brakes After Bleeding - CBR250ABS

[Generalchaos]

I have renewed the brake fluid on my old Honda CBR250R ABS and have managed to get the front brake rock solid a vicious again, however, this is a split system (combined - I don't think it is TRUE ABS) with ABS and try as I might, I just cannot seem to get the rear brake to be anything other than mediocre.

When I bought the bike the rear brake was rock solid, but over the years the fluid has turned brown and needed replacing.

After following the service manual and bleeding each caliper separately, I still cannot get the rear brake to stiffen out.

I saw some video on YouTube where they mentioned that if the bike has combined or ABS brakes that you should take it to the dealer as the ABS pump needs a special program to be run in order to successfully bleed the ABS side.

 

The Honda manual says nothing about this at all.

 

I have bled the front without a problem, then followed the instructions to bleed the rear, i.e. first bleed the front nipple furthest from the rear master then finish by bleeding the rear caliper. No matter what I do it is still soft.

 

Would it be worth retrying this process with the engine running after the ABS light has gone out or am I flogging a dead horse?

 

I don't have any fancy kit, just pumping the brakes into a jar of fluid via a hose. I am beginning to wonder if maybe the nipple on the combined brake or the rear brake may be letting in air when loosening the nipple, however, there is no signs of any bubbles?

 

Cheers!

 

[Strange]

How many times did you try it? I would bleed, then test ride, then bleed again, then assess. 

 

Even with ABS it should still purge the air. 

 

You held the brake lever down somehow when you cracked open the bleeder nipple right? And when the brake lever started to move down, you immediately closed the bleeder nipple before lifting off the brake lever right? You don't want to lift before the bleeder is closed.

 

Are there any places on the bike where the brake lines are not steel? IE Flexible tubing of some sort? They can age and flex and take firmness out of the pedal. 

[Strange]

26 minutes ago, Generalchaos said:

Would it be worth retrying this process with the engine running after the ABS light has gone out or am I flogging a dead horse?

 

Its worth trying of course. I don't think it would make a difference but its nothing to try. 

[Generalchaos]

Strange - Yes, closing the nipple before bottoming out the lever,  there is no sign of air, no bubbles nothing! that is what makes me think there may be air trapped at an angle, the nipples are at about 30 degrees off to the left of vertical.

 

Yes, I did everything I normally do bleeding hydraulics, I have bled brakes on cars for more than 30 years. The only other thing I can think of is to remove the calipers and try to get the bleed nipple in a straight up position.

Understand what you are saying about the rubber hoses flexing, that is worth looking at! But the front and rear use the same tubes yet one is fine and the other is like granny's sponge cake!

The combined brakes are working, if I stamp on the rear brake hard, you can feel the front brake biting as well, they just seem horribly soft.

Maybe I am expecting too much, but to be honest, they did feel a lot more responsive before I changed the fluid.

I asked my son to give the bike a go and he said the same thing, back brake is crap!

Edited December 11, 2016 by Generalchaos

[Generalchaos]

4 minutes ago, Strange said:

 

Its worth trying of course. I don't think it would make a difference but its nothing to try. 

Been through almost a litre of DOT 4 already! Maybe I will wrap some of that white PTFE tape around the nipple threads and give it another go. Something is definitely different between the front and rear.

Thanks for your response! Any suggestions are appreciated.

[Strange]

13 minutes ago, Generalchaos said:

The combined brakes are working, if I stamp on the rear brake hard, you can feel the front brake biting as well, they just seem horribly soft.

 

Im not mega bike techie but I thought it was a split system? Master cylinder on the handlebar and another on the foot brake? Or am I confusing something? You mean the dual rear caliper or the front wheel caliper is biting as well when you stand on the rear brake?

 

If you have 2 master cylinders, you checked the level in both right? with the cover off and all that? 

 

I know you know how to do it, just asking. 

 

11 minutes ago, Generalchaos said:

Maybe I will wrap some of that white PTFE tape around the nipple threads and give it another go.

 

The threads are not tapered and it shouldn't matter they don't seal that way. You could easily pull one off and hijack a replacement from anywhere really though. Car shop, motorbike shop, scooter shop. Any auto shop probably has tons lying around they will give you free if its a concern thats what I would try. 

Edited December 11, 2016 by Strange

[Generalchaos]

Just now, Strange said:

 

Im not mega bike techie but I thought it was a split system? Master cylinder on the handlebar and another on the foot brake? Or am I confusing something? You mean the dual rear caliper or the front wheel caliper? 

 

 

The threads are not tapered and it shouldn't matter they don't seal that way. You could easily pull one off and hijack a replacement from anywhere really though. Car shop, motorbike shop, scooter shop. Any auto shop probably has tons lying around they will give you free if its a concern thats what I would try. 

Yes, split system, but I don't think it is a true ABS, it is a Honda thing.

There is a MC on the front bars and a MC on the rear pedal, when you whack on the front brake you only get the front brake (dual caliper), when you whack on the rear brake pedal about 30% of the braking force is transferred to the front, it is not a true ABS system.

[Strange]

Just now, Generalchaos said:

Yes, split system, but I don't think it is a true ABS, it is a Honda thing.

There is a MC on the front bars and a MC on the rear pedal, when you whack on the front brake you only get the front brake (dual caliper), when you whack on the rear brake pedal about 30% of the braking force is transferred to the front, it is not a true ABS system.

 

Gotcha.

 

Did you do it exactly like this:

 

http://www.cbr250.net/forum/archive/t-54202.html

[Generalchaos]

16 minutes ago, Strange said:

 

Gotcha.

 

Did you do it exactly like this:

 

http://www.cbr250.net/forum/archive/t-54202.html

Exactly as mentioned in the link, it is exactly the same from the Honda manual. I still feel it might be worth pulling the rear caliper and getting the nipple up to the 12 o'çlock position.

Edited December 11, 2016 by Generalchaos

[Strange]

13 minutes ago, Generalchaos said:

Exactly as mentioned in the link, it is exactly the same from the Honda manual. I still feel it might be worth pulling the rear caliper and getting the nipple up to the 12 o'çlock position.

 

Here is something interesting to try. Makes sense too assuming you did everything right. 

 

http://www.cbr250.net/forum/cbr250-problems-issues/4330-abs-rear-brake-spongy-can-improved.html

[ktm jeff]

You are correct , in that this system is not a "true" ABS system. Honda calls it CBS - combined braking system - and it causes a few problems. Try removing the caliper to bleed with the nipple higher than the inlet hose from the rear MC( taking care to wedge the pads and possibly zip tying the front brake lever to activate the front brake ) and try this interesting "fuse" option.  Ive never heard of that one before. Keep us informed.

[surangw]

a clear hoze on the bleeder nipple into a small container of brake fluid  I how we use to do it, does that still work not to prevent air getting  back into the line?

[ktm jeff]

5 minutes ago, surangw said:

a clear hoze on the bleeder nipple into a small container of brake fluid  I how we use to do it, does that still work not to prevent air getting  back into the line?

Sounds like the OP is doing that. I think the problem is in that  CBS system , either caused by a bad hydro dynamic design or requiring "that" fuse removed.

[Strange]

19 minutes ago, ktm jeff said:

Sounds like the OP is doing that. I think the problem is in that  CBS system , either caused by a bad hydro dynamic design or requiring "that" fuse removed.

 

Hey now, Im not saying its "that" fuse. Im just trying to help. Im not a bike guy per se, but I'm pretty switched on and can knowledge battle pretty well. 

 

You are probably right with it being the "CBS" system, or bleeding sequence wrong, as it was better before OP started, and mechanically its more than likely sound.

 

This is how I problem solve. I do not think unbolting the caliper, wedging the pads, zip tying the brake, holding it at a certain angle, above the rear MC - Will resolve the issue. It won't. 

 

Its either a sequence issue, or a mechanical failure, or a stupid little trick. 

[ktm jeff]

I get what your saying , but that stupid little trick may involve bleeding out the trapped air by holding the caliper at different angles so the air - if any - can rise up , and out. The rear caliper on my Aprilia RSV is funny , like that !. Im still liking "that" fuse   LOL.

[Strange]

10 minutes ago, ktm jeff said:

I get what your saying , but that stupid little trick may involve bleeding out the trapped air by holding the caliper at different angles so the air - if any - can rise up , and out. The rear caliper on my Aprilia RSV is funny , like that !. Im still liking "that" fuse   LOL.

 

The stupid little trick I was referring to was the "Fuse" not the crazy-angle-caliper-ziptie-using-all-fingers-&-toes-deal. 

 

But hey maybe I'm wrong. I probably am. But Honda is pretty good & I highly doubt OP tipping his caliper at just the right moons alignment will resolve his issue. 

 

Its gonna be way more simple than that.