1981 GS850G rear brake master cylinder (I need help)

[bwringer]

Hmmm... I have no memory of which way that spring goes in.

And I don't feel like taking mine apart to check...

Someone? Anyone?

 

[Slowride]

Installed the master cylinder, bled the brakes, took it for a ride. It seemed OK (yes, just OK) but I think I'll take the calipers apart and check the pads. Any idea how often the pads should be changed? Although I don't have many miles on the bike, 14,300 (I'm ashamed) I'm guessing the pads should be changed since they are the original ones.

 

[bwringer]

You change the pads when they're worn out. Or if they get contaminated with oil for some reason; front pads, for example, must be replaced if they get fork oil on them.

If yours look good, then you can keep using them. However, there's also an argument for replacing them with modern pads so you can benefit from 40 years of advancements in brake pad compounds. This matters a lot more on front brakes, but the improvement from a fresh set of EBC red or black pads is downright astonishing compared to the 40 year old factory set.

 

[2BRacing]

So, does the tapered part of the spring go in first or does the larger diameter end go in first? I put the wider end in first, then the smaller diameter end seemed to fit into "cup" with the bottom of the cup coming in contact with the piston. It seems to move ok but I'll have to see what happens when I put it back onto the bike and connect the brake line. I may just end up buying the OEM parts.

Yes, the larger diameter end of the spring with the larger metal "cup" goes in first. That rubber cup that was at the right hand side of your photos of the repair kit in posts #15 and #16 goes between the smaller diameter end of the spring and the flat side of the piston as per the photo below. Looks like the rubber cup between the piston and the spring was missing in your original assembly (photo in post #14 and left hand side of post #16) - that was the cause of no pressure build-up and no fluid coming out!

 

[Slowride]

Thanks. I think I'll take your advise and get some new pads. It can't hurt.

 

[Slowride]

Thank you 2BRacing. That is how I ended up assembling it, I guess I got lucky. Yes, when I originally took the master cylinder apart, there was not a cup in there, just the piston and spring. I thought I remembered which direction the spring came out but, I forgot. (I'm blaming that on my age) Would you happen to know, when replacing the rear brake pads, if they are designed for placement in the calipers dependent on the direction the rear wheel turns?

 

[2BRacing]

.......when replacing the rear brake pads, if they are designed for placement in the calipers dependent on the direction the rear wheel turns?

If new pads are put in, direction will not matter. If you are putting used pads back, they may have worn according to the surface of the disc.

Place a piece of sandpaper on a smooth, flat surface (like a piece of glass) and sand away grooves in the pad surface.

 

[Slowride]

Thank you 2BRacing. Hopefully, I'll get to the calipers and pads today as long as my wife doesn't have too long of a list for me, of things to do.

 

[Slowride]

Thank you salty_monk for the tip on using air pressure to get the pistons out of the rear calipers. Took the calipers apart (yesterday) cleaned out all the gunk and sanded the pads, which were not too bad but I think I'll still order some new ones. To be safe, I used my little compressor (to get the Pistons out) outside on the lawn and the first piston only went about 3 feet, barely. So I figured I needed more pressure and sure enough, the other one went flying. If my neighbors were watching, I'm sure they got a good laugh. Anyway, put it all back together, put it back on the bike, bled the lines and went for a ride. Brakes work great (again).

Thank you all of you who gave me great info and tips.