Intruders-Alert

Locked the rear brake up for the second time in four years. Time to rebuild the rear master cylinder I guess. Parts on order.

Get the parts?
Things go well?

Did you have to pull that whole band with the pegs and kickstand on it to get your master cylinder off to work on it?
I like to do all that I can myself on my lil slice of heaven.

Was a bit surprised when I got my rear tire replaced they told me my rear master brake cylinder was shot.
I almost never use the rear brakes so god only knows how long it has been like that.
Rebuild kit was easy enough to find, went to pull that lil bugger and damned if I can see how to do it without pulling that and everything attached to it under there.

Would love to hear about your experience with yours.

I haven't done that work, but yeah it looks like the exhaust and foot-peg bracket has to be removed. I wonder if the shop was really talking about the caliper, which is easy to rebuild...and not the rear master cylinder.

When brakes need rebuilding, they usually go the other way and don't work.

How old is your tyre? Could it be hard and just not gripping anymore??

Calipers are good and I have had the bike so long I can do them in 5 minutes on a good day, 15 on a bad one.

Definitely (90% sure) master cylinder - all soft on the push, never gets pressured up, and we both (tire place and I) tried bleeding em.
Only mentioned tire replacement as that was who noticed - they got the tire on, took it out to make sure it was hunky with a side of dory, and when they went to hit the back brake, sponge city.

Never had it off - owned since mile 0, and we just passed 26,000 this year.
Guess I been lucky.

Saw the soft boot on the front of the master cylinder right under the pedal, and had hopes for a micro-second that the engineers may have made the ring accessible under a soft boot, but when it dinna want to come off, I was not interested in tearing it.
Hating the thought of pulling all that mess, but if that is what needs doing, incest lovie

Ah OK - when you said "locked the rear brake up for the second time in four years" I thought you meant it was braking too hard, not being spongy.

Could also be the rubber inside the MC cap - there should be a little notch in the cap which allows air to get in between the cap and the rubber. If it is blocked and not breathing it will hold the reservoir in a vacuum and this can cause the pedal to get spongy.

Sorry - that was OP who locked.
I am just the guy who asked after him and accidentally hijacked his thread.
Sorry OP. My bad.

If you still have the stock metal shims on the rear brake pads, pull them out and throw them away. The brake will work much better and you won't need to rebuild the master cylinder.

There are 2 problems with the shims, 1 is that the coating on them starts to bubble and pushes the pistons too far back into the caliper, 2 is that they will warp, probably from heat, and then they do the same thing as the bubbling paint. Both of these things cause a mushy pedal and no brake power unless you pump the brake pedal REALLY fast.

Great tip there, but mine are loooooooong gone.
Probly more than 20,000 miles ago.
Back brakes squealed non-stop when I bought it so those pads and shims didn't make it to the first oil change

Herb wrote:If you still have the stock metal shims on the rear brake pads, pull them out and throw them away. The brake will work much better and you won't need to rebuild the master cylinder.

There are 2 problems with the shims, 1 is that the coating on them starts to bubble and pushes the pistons too far back into the caliper, 2 is that they will warp, probably from heat, and then they do the same thing as the bubbling paint. Both of these things cause a mushy pedal and no brake power unless you pump the brake pedal REALLY fast.

Replace the shims with aftermarket, or do away with them altogether?

My face is red.
Got the bike up today, pulled all that comes with a VS1400 / S83 rear master brake cylinder rebuild.
If you have done it you know, if you haven't you don't want to.

Once I had the rear master cylinder off, I put my thumbs over where both lines attach and hit the plunger a few times, and there was pressure

Long story short, in my case, the reservoir was vacuum locked.
Dinna need to do any of that mess.
Bled em with the cap off, refilling as needed and my rear brakes are back to normal.

Never should have listened to that tire place in Reno.
Usually they are pretty sharp, but I guess this one got past us all.
Bugga

Long story short, in my case, the reservoir was vacuum locked.
Dinna need to do any of that mess.
Bled em with the cap off, refilling as needed and my rear brakes are back to normal.

There must be some dirt or corrosion that is blocking the air weep hole in the cap. The rubber boot seals the fluid in the reservoir, but the boot is expandable as the fluid drops and the weep hole allows it to expand and provide fluid. If you didn't fix the hole, when the pads wear and more fluid is required, you'll get the same vacuum problem again.

I was going to suggest removing the cap prior to pulling the rear cylinder...wish I had.

Still a great day working on the bike.
Love it.

Dead on about the expandable bit.
That thing was fully out