Rear brake issues, '13 796 ABS

[Charlie98]

Yea, yea, I know about the rear brake issues, and particularly the ABS model...

It used to be, if the bike sat for a while, and then I ride it, I could pump the rear brake a few times and get some pedal, and I could actually bleed the line, even though it would only last about 12 seconds or so (I'm exaggerating.  A little.)

I changed my front brake pads this weekend, so I figured while I'm at it, I'll bleed everything out.  At this point, I can't even bleed the rear... I have no pedal, and no amount of pumping will get me anything.  Pumping the brake, the master cylinder actually squeaks... like it's dry, even though there is fluid in the reservoir.  Is the master hosed... or is there just that much air in the system that it's sort of 'vapor locked?'

[koko64]

On top of all the usual tricks, e.g. removing and elevating the caliper, pumping fluid through, sucking fluid through, resonating micro bubbles out of the system with a device (I use a de-fanged shaver or hair clippers), there's other stuff to consider. Some are using DOT 5.1 (not DOT 5) fluid which handles heat better and there are low viscosity brake fluids on the market designed for the micro valves in abs systems.
I do all the above and also the equivalent of cable tying  brake levers. I wedge a block of wood between the brake pedal and clutch cover to have the pedal depressed overnight. I start with my compressor run vacuum bleeder and apply the other methods once I'm in the ball park. I have also heat wrapped the rear exhaust to protect the fuel pump, lines and nearby brake line. After a concerted effort the brake works well. I get about a year and a half out of 5.1 fluid before having to do it again.

Im going to try the low viscosity fluid next.

[Howie]

If koko's advice doesn't fix the problem bench test the master.  Remove it from the bike (carefully since brake fluid ruins paint).  Find a bolt that fits where the brake line was.  Bench bleed.  Now see if it holds pressure.

[koko64]

If koko's advice doesn't fix the problem bench test the master.  Remove it from the bike (carefully since brake fluid ruins paint).  Find a bolt that fits where the brake line was.  Bench bleed.  Now see if it holds pressure.

Yes that noise from the master is a concern.

[Blackout]

I just removed mine after a couple of unfortunate lock ups.

[Charlie98]

I just removed mine after a couple of unfortunate lock ups.

Well... I've gotten used to not having much of a rear, and 99% of the time it's not a problem.  I had to make a pretty hard stop last week... and it sure would have been nice to have even a little rear brake... I'm not much of a stoppie person.

A friend of mine gave me a vacuum pump... maybe I'll give it a go and see.  I'll try the depressed pedal, first, and see if anything comes of it.

The 796's master is buried behind the footpeg sub-frame... so it won't be an easy removal.

I'm still using DOT3 fluid... motorcycle shops here are not open on Sunday... that's all they had.

[koko64]

Make sure its the DOT 5.1 you get. DOT 5 is incompatible with DOT 3 & 4 fluid. I knew a bloke who used DOT 5 in a system that had DOT 4 and had brake failure. Brake lines were full of concealed silicone and he had to Fred Flintstone it at a red light.
I don't think the proximity of the rear brake line (and fuel system components for that matter) to the rear exhaust pipe on some models is helping at all.

[Charlie98]

Well... and that was one of the reasons I just stuck with DOT3 fluid.  I knew there was some difference with the 5's... and I don't like to take chances with my brakes.  Odd thing is...

The manual says DOT4.  The filler caps say... specifically... 'DOT 3+5' ... which makes no sense.  DOT3 is always a safe bet... so that's what I did.

[Charlie98]

As a follow up, holding the brake lever down for a few minutes seemed to work... you could actually see the fluid draining from the reservoir... so I finally got a little pedal.  This weekend I'll see if I can't bleed it out a bit and get a little more pedal back.

[koko64]

So Dot 3, 4 or 5.1m but not the Evil 5.
After about 18 months my bike rear brake is just starting to get squishy again.