Author Topic: Rear disk brake lockup - '95 K75  (Read 5258 times)

Offline Motorhobo

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Rear disk brake lockup - '95 K75
« on: November 03, 2013, 07:16:05 AM »
Finally got the bike back together after finishing the rear end half of the resto on my 95 K75. It misses on one cylinder at low rpms but that's probably a bad spark plug wire so I thought I'd take it out and run through all the gears once before starting on the font end.

After about 3 miles at 60mph there's deceleration and I was able to get it to the shoulder. The brake pedal and wheel were completely locked up and the disk was hot. Within seconds, a Harley owner had stopped in his truck and offered to give me a lift back to my house to get my tools (HD owns the road in this neck of the woods). By the time I got back to my bike, the disk had cooled off and the brake was operational. So--

I put new Spiegler lines on and ran it 3k miles before starting the resto so the lines are fine.
I had the calipers apart and cleaned them up when I did the brake lines, also 3k miles with no issues prior to starting the resto.
I had the footpeg off and removed the break pedal during resto to clean it up, leaving the MC dangling there -- maybe I screwed something up on reassembly.
The line from the reservoir to the MC runs behind the footpeg plate...doesn't appear to be pinched anywhere.

Those are things I will check today. Did I miss anything? Do I need to crack the valve and release some fluid? I'm thinking maybe there's too much pressure and there's just enough friction between disk and pads to allow heat and ergo expansion to take place, resulting in the siezure. Maybe the brake/ABS assembly were repositioned on reassembly just enough to increase the pressure in the lines just enough to push the bore just enough to cause just enough friction to etc etc etc.

Any input appreciated...

Van
1994/1995 K75 ABS Frankenbike: original engine 136k miles, frame from Gary Weaver (RIP), 173k miles -- Current Odometer: 198k miles
1994 K75 since 2013, 82,000 mi (19k mine) w/California Sidecar Friendship II Sidecar & Black Lab 'Miss B' - RIP

Past: 1974 Honda 550/4 (first bike), 1994 K75 (sold), 1995 K75 ABS (parts bike), Sidecar Dog & Best Bud 'Bo' - RIP

Offline Inge K.

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Re: Rear disk brake lockup - '95 K75
« Reply #1 on: November 03, 2013, 08:07:58 AM »
Check that you got a small amount of play between the pedal/pushrod and the piston,
and that the piston returns fully.

If OK, check if both the intake and return port in the cylinder is open.
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Offline Motorhobo

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Re: Rear disk brake lockup - '95 K75
« Reply #2 on: November 04, 2013, 11:08:52 AM »
OK, thanks. BTW maybe it's a dumb question but that set screw,#12 in pic -- there's nowhere to put a wrench on that. Am I supposed to turn it with my fat fingers? I don't like putting wrenches on threads.




V
1994/1995 K75 ABS Frankenbike: original engine 136k miles, frame from Gary Weaver (RIP), 173k miles -- Current Odometer: 198k miles
1994 K75 since 2013, 82,000 mi (19k mine) w/California Sidecar Friendship II Sidecar & Black Lab 'Miss B' - RIP

Past: 1974 Honda 550/4 (first bike), 1994 K75 (sold), 1995 K75 ABS (parts bike), Sidecar Dog & Best Bud 'Bo' - RIP

Offline Inge K.

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Re: Rear disk brake lockup - '95 K75
« Reply #3 on: November 04, 2013, 06:54:29 PM »
that set screw,#12 in pic -- there's nowhere to put a wrench on that.

It's a inside hex at the brake pedal end.
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Offline Chaos

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Re: Rear disk brake lockup - '95 K75
« Reply #4 on: November 04, 2013, 09:31:04 PM »
a Harley owner had stopped in his truck

 :hehehe
  • sw ohio
1987 K75S    VIN 0231
Original owner, Original litter
200,000 miles (plus or minus) and 5 paint jobs
sold 6/23
2023 Ural 2WD sidecar (BMW's bastard step child)

Offline Motorhobo

  • +25 years of K75
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Re: Rear disk brake lockup - '95 K75
« Reply #5 on: November 05, 2013, 07:45:38 AM »
I've never seen an inside hex before -- never would have thought to look at the end of the screw. Thanks Inge!

Yeah, lots of Harley owners around here. They even ride them sometimes.

V
1994/1995 K75 ABS Frankenbike: original engine 136k miles, frame from Gary Weaver (RIP), 173k miles -- Current Odometer: 198k miles
1994 K75 since 2013, 82,000 mi (19k mine) w/California Sidecar Friendship II Sidecar & Black Lab 'Miss B' - RIP

Past: 1974 Honda 550/4 (first bike), 1994 K75 (sold), 1995 K75 ABS (parts bike), Sidecar Dog & Best Bud 'Bo' - RIP

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