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Old 01-04-2015, 08:11 PM   #1
viperh OP
viperh's Avatar
Joined: Jul 2010
Location: Raleigh, NC
Oddometer: 122
Need help with rear brake problem. 81 r100rt (Fixed)

EDIT-Found the issue.. Somehow debris found its way into the M/C. Was going to delete the thread but no delete button.

Long story short bought 81 r100rt in order to make a hack. I have everything but haven't attached the side car until I get the rear brakes sorted out.

I have done everything but replace the rear caliper.

First trip brakes locked up and wouldn't release. Lots of corrosion in the pressure relief hole on front brakes. Tow bike home. The rear brake seemed weak but it worked at least on that initial trip. Granted I couldn't lock the rear tire up no matter how hard I tried.

I order the whole she-bang front and rear rotor rebuild kits, front M/C, Rear M/C rebuild kit, all SS lines. Upon putting everything back together I stripped the rear M/C and the hardline . Now I have also replaced rear hard line and M/C.

I have everything put back together. Front brakes are solid. The rear not so much. I used the mityvac method to get the air bubbles out but the rear doesn't seems to be putting much pressure on the pads. I hit the rear brake lever I watch the pads press against the rotor then when I release they back off to their starting position.

I'm also putting the rear brake at its absolute max before the pads make contact with the rotor. In other words by the time the rear M/C articulates through the motion pretty much when I hit the point where it can't articulate anymore is right about when the brakes touch the rotor and put the pressure on the rotors.

There are two problems with this.
1. I don't think I'll be able to lock up the rear wheel at all. (granted no test ride).
2. I wouldn't be able to articulate my ankle that far with my motorcycle boots to make the brakes effective in the event of an oh shit moment.

I haven't taken it for a test ride yet but this doesn't seem right. So a couple of questions.

Can an '81 r100rt lock the rear tire up when you hit the rear brake?
Are those '81 r100rt's such a bitch to bleed the lines and rotors properly that not even the mightyvac method works?
If so? What is a better method than the Mightyvac method?
Is there a newer brake system that I can just bolt on to a stock bike '81 r100rt?
Is this a symptom of a bad caliper?

I rebuilt the calipers, there was a lot of gunk in there. I verified that the orings are in the correct spots and there is no fluid leaking. Did I ef something up when I put the caliper back together? It's a really simple process. Maybe too much grease around the piston.

I figured the stopping distance of this bike wouldn't be as good as my 2010 r1200GSA. But the rear brake doesn't seem to be pulling its weight. Even on the initial test ride I tried like hell to lock up the back tire and it just wasn't locking up. With the additional weight of a hack and the extra gear I would like to have working brakes.

I'm only being extra cautious on this because on my '10 the brakes have saved my ass so many times on my commute to and from work that I'd hate play with fire.

viperh screwed with this post 01-04-2015 at 09:13 PM Reason: editing speelling and proper use of terms.
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