Bleeding ABS Brakes

I'm in the middle of the dreaded 'Bleeding Brakes Problem'.

I have the front sorted out pretty well, but the rear is giving me trouble.

I can't seem to get it firm before the lever hits the handlebar grip. At that point it seems to have the rear wheel braked but it's certainly not the way it was before I started.

I'm noticing a difference in the bottom of the two master cylinders.

The front has a little round 'upstand' to the right of and beside the 'sump' hole in the bottom. The left (rear) has a little hole (no upstand over it) and it appears to blowback (not air) some fluid when you briskly pump the lever.

Can any kind 'Swinger' throw some light on this for me?

I've been reverse bleeding the system since the conventional method was showing poor results on the front brake previously.

Sorry Donie, no help here from me.

Tim

Although most of my experience is in the auto industry,it is important to start from the beginning. Did this start out as a maintenance project or some other concern. Disk brake master cylinders have no check valve in the master cylinder so it is important to operate the lever (or pedal) slowly,they can draw air back to the master cylinder.Are you doing this by yourself or is someone helping? Do the closest caliper first this would be the front on the Silverwing.Be careful and do not let the master run low on fluid. If you are doing this by yourself you can run a piece of tubing from the caliper to a container making sure the tubing in submerged in fluid. Always take your time. If you are planing to do your own maintenance a power bleeder is not that expensive.  Please let us know.  Howard

It started out with a dragging front brake, and even before I got that sorted the back brake was also dragging,

So I removed both calipers and took out the pistons to remove all brake dust, and give the piston a good cleaning with emery paper.

When I began bleeding the system I had difficulty getting any sort of pressure with the conventional bleed procedure, until I decided to reverse bleed from the bleeder up through the master cylinder with a syringe.

Now the front brake is fine but the back one is not improving, and I notice a squirt of fluid, when I use the lever, coming up from the small hole to the right of the sump feeder hold in the bottom of the master cylinder.

Hmm...In rereading your posts I suspect that you've still got air in the rear brake system. When you were reverse bleeding the rear system you may have introduced more air into the system.

At this point I would suggest that you top off the left master cylinder and bleed the system convertionally. Start with the bleeder valve on the front caliper for the small front piston. Top off the master cylinder again --make sure that it never runs out of fluid though. Then move to the rear caliper bleeder. Bleed that caliper conventionally.

After you are satisfied that you done the best you can with that rear brake bleed then you might want to try this trick an 'old timer' taught me: top off the master cylinder, apply the rear brake and zip tie the lever ON and leave it there for a couple of days --the longer the better. Don't "check on it" in the mean time. Somehow that encourages the air bubbles hiding in the system to rise to the top (i.e. the master cylinder) and become displaced with brake fluid.

Dunno if that trick will work with an ABS system, but it worked for me with my spongier-than-normal rear brake lever. Hey, at this point it's gotta be worth a try. HTH

Tim

I don't know how many I've done over the years but I like my Mighty Vac and one word SLOW, you're bleeding not hemorrhaging, on my GW I did the clutch by gravity the secret as said keep the reservoir topped up.

Hopefully we are not beating a dead horse here but from what has been stated It should be noted you should limit the amount of air into the system when ever possible.First only one caliper should be removed at a time. Find a short piece of rubber tubing that will slip over the line to the caliper and install a snug bolt in the other end of the hose to limit fluid loss. I used to make steel lines to do this but the hose works just fine. When you re-install the caliper open the bleed fitting and wait for fluid to start running out. After that you can apply pressure but make sure you close the bleeder valve before the brake lever runs the full distance. As stated earlier disk brakes have no check valve in the master cylinder. Slow steady pulls of the lever work the best. Depending where the bleeder valve is located some times a gentle tap with a soft mallet will send air trapped in the caliper out. This holds true for most disk brake vehicles.
p.s. That small squirt of fluid you saw in the master cylinder is normal.  Howard