R100RT front brake rebuild - HELP!

WU7X · 11-25-2012, 12:22 PM

The gaskets on my master cylinder piston assembly failed after only 30 years, 8-12 recent years of which were sitting idly in a garage. Imagine that.

While disassembling the unit to initially find out where the problem was, a small part fell out and I can't figure out where it goes. In the Clymers book, p. 624, figure 117, this piece is #11 "PAD". It's ~1.5 cm long, striated on one side; the other two sides are smooth. There is a small detent where the two smooth sides meet, about midway along that line. I'm guessing that detent matches something in the unit that holds this pad in place.

The diagram isn't doing me a bit of good trying to figure out where the h*ck the part needs to go when I reassemble the master cylinder. Can anyone give me a hand with this?

One more question; my rebuild kit has a brass colored washer as a part of the piston assembly #14 in figure 117. In the figure it appears to go to the right of the last rubber gasket. The circlip then holds the entire assembly in the body. the only problem is that the old piston assembly didn't have that washer, and the unit won't go back together properly if I try to put it together like that. I can mount it on the piston assembly AFTER the last rubber gasket and after snapping in the circlip to hold the assembly in place. What to do? Leave the washer off like the system originally was, or install it between the two large black body segments? Hope this is clear enough for you to understand.

Help!

WU7X · 11-25-2012, 05:56 PM

I think I've figured it out, finally. Think Dale, think! The pad is a shim in the accelerator handgrip mount.

I still don't know what to do with the extra washer.....

bmwrench · 11-25-2012, 07:11 PM

I think the part you describe is the control wedge. It goes in the perch. The "detent" is to alloy the 5mm clamp screw to pass through it.

The brass colored washer goes into the perch outside of a shouldered rubber washer, which should also be in your kit. This is supposed to keep dirt out of the master cylinder pushrod section.

WU7X · 11-25-2012, 07:31 PM

Quote:

Originally Posted by bmwrench

I think the part you describe is the control wedge. It goes in the perch. The "detent" is to alloy the 5mm clamp screw to pass through it.

The brass colored washer goes into the perch outside of a shouldered rubber washer, which should also be in your kit. This is supposed to keep dirt out of the master cylinder pushrod section.

Thanks for confirming the location for the wedge.

I kinda thought that the metal washer would go to the outside of that rubber washer. There wasn't one in there when I tore it apart. But when I was fiddling with the thing the location you confirmed made the most sense to me. thanks again! tomorrow I'll get everything put together. Then when SWMBO gets home from work, we'll add the brake fluid and get her up and running.

BTW, it's clear and cold here in Spokane tonight. Should be near 22 Deg. F by morning. Once I get the air out of the brake lines and everything set up, I should be able to drive it before it gets too cold tomorrow evening. Anything above 35 deg. and I'm good to go.

kbasa · 11-26-2012, 01:48 PM

Moved to Airheads. Please familiarize yourself with the posting rules here. Thanks.

11-25-2012, 05:56 PM	#2
WU7X ^OP The Old Fart Joined: Aug 2007 Location: Spoke Can, WA Oddometer: 1,619	Never mind... I think I've figured it out, finally. Think Dale, think! The pad is a shim in the accelerator handgrip mount. I still don't know what to do with the extra washer..... __________________ "Fiona" - 1982 R100RT - Hacked - EML suspension, Squire ST2 chair "You can tell a woman's mood by her hands. If she has a gun in one, she's probably mad."

11-26-2012, 01:48 PM	#5
kbasa Tinaversal Joined: May 2002 Location: Marin County, California Oddometer: 59,330	Moved to Airheads. Please familiarize yourself with the posting rules here. Thanks. __________________ IMHO. Fuck Cancer. Ride bikes. - dave + tina

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11-25-2012, 12:22 PM	#1
WU7X ^OP The Old Fart Joined: Aug 2007 Location: Spoke Can, WA Oddometer: 1,619	R100RT front brake rebuild - HELP! The gaskets on my master cylinder piston assembly failed after only 30 years, 8-12 recent years of which were sitting idly in a garage. Imagine that. While disassembling the unit to initially find out where the problem was, a small part fell out and I can't figure out where it goes. In the Clymers book, p. 624, figure 117, this piece is #11 "PAD". It's ~1.5 cm long, striated on one side; the other two sides are smooth. There is a small detent where the two smooth sides meet, about midway along that line. I'm guessing that detent matches something in the unit that holds this pad in place. The diagram isn't doing me a bit of good trying to figure out where the hck the part needs to go when I reassemble the master cylinder. Can anyone give me a hand with this? One more question; my rebuild kit has a brass colored washer as a part of the piston assembly #14 in figure 117. In the figure it appears to go to the right of the last rubber gasket. The circlip then holds the entire assembly in the body. the only problem is that the old piston assembly didn't have that washer, and the unit won't go back together properly if I try to put it together like that. I can mount it on the piston assembly AFTER the last rubber gasket and after snapping in the circlip to hold the assembly in place. What to do? Leave the washer off like the system originally was, or install it between the two large black body segments? Hope this is clear enough for you to understand. Help! __________________ "Fiona" -* 1982 R100RT - Hacked - EML suspension, Squire ST2 chair "You can tell a woman's mood by her hands. If she has a gun in one, she's probably mad."

11-25-2012, 07:11 PM	#3
bmwrench Beastly Adventurer Joined: Nov 2006 Oddometer: 1,465	I think the part you describe is the control wedge. It goes in the perch. The "detent" is to alloy the 5mm clamp screw to pass through it. The brass colored washer goes into the perch outside of a shouldered rubber washer, which should also be in your kit. This is supposed to keep dirt out of the master cylinder pushrod section.