Sportster suddenly lost rear brake
Thread Starter
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Road Master
Joined: Mar 2020
Posts: 1,077
Likes: 267
From: New England
Sportster suddenly lost rear brake
2005 XL1200R
Rear brake pedal is going straight to the floor and not building any pressure whatsoever. Haven't worked on the brakes recently or anything like that. No obvious leaks, the fluid is full in the reservoir and looks very clean. The brake pads are nice & thick.
What should I try first? Changing the fluid (suck the old fluid out and refill with new)?
Rear brake pedal is going straight to the floor and not building any pressure whatsoever. Haven't worked on the brakes recently or anything like that. No obvious leaks, the fluid is full in the reservoir and looks very clean. The brake pads are nice & thick.
What should I try first? Changing the fluid (suck the old fluid out and refill with new)?
Seasoned HDF Member
Joined: May 2008
Posts: 21,095
Likes: 12,639
From: South Carolina
The machine is 20 years old...
I suggest rebuilding the master cylinder and caliper, and inspect the hoses for bulges, leaks etc.
New brake hoses would not be a bad idea also.
When still available, stick with OEM parts.
Disassemble the master cylinder and the caliper before you buy any parts, make sure they are in good condition and rebuildable.
Master Cyl. rebuild kit is item 20 in the illustration:
Rear Master Cylinder Illustration
Piston and seals for caliper, if the piston is good, just replace the seals.
Caliper Illustration
I suggest rebuilding the master cylinder and caliper, and inspect the hoses for bulges, leaks etc.
New brake hoses would not be a bad idea also.
When still available, stick with OEM parts.
Disassemble the master cylinder and the caliper before you buy any parts, make sure they are in good condition and rebuildable.
Master Cyl. rebuild kit is item 20 in the illustration:
Rear Master Cylinder Illustration
Piston and seals for caliper, if the piston is good, just replace the seals.
Caliper Illustration
Last edited by Dan89FLSTC; Feb 3, 2025 at 10:06 AM.
HDF Community Team
Joined: Dec 2011
Posts: 8,512
Likes: 3,924
From: San Diego, CA
Not an unusual problem. See this recent post.
https://www.hdforums.com/forum/sport...-cylinder.html
John
https://www.hdforums.com/forum/sport...-cylinder.html
John
Thread Starter
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Road Master
Joined: Mar 2020
Posts: 1,077
Likes: 267
From: New England
I should mention (if it matters or means anything) when I push on the brake arm there's no reaction in the fluid. Meaning, with the cap off and I'm looking into the reservoir at the fluid, nothing happens when I reach over and pump the brake lever - no air bubbles, nothing.
HDF Community Team
Joined: Aug 2019
Posts: 1,828
Likes: 1,920
From: Santa Ana, CA
Sounds like the master cylinder went south. It's cheap and easy to rebuild. While I agree with generally sticking with OEM parts if you are going to replace the brake lines I would suggest going with stainless.
Last edited by OCSpringer; Feb 3, 2025 at 10:27 AM.
Road Captain
Joined: Feb 2015
Posts: 586
Likes: 126
From: Boston
I too, have a 2005 1200R and haven't had this problem, but its been a while since i've re-flushed the fluid and to my knowledge the rear master cylinder has not been rebuilt. Is there a rebuild kit sold like there are for CV carbs? Of just take apart, inspect and order the individual parts from the HD parts diagram?
EDIT:
I see now there is a kit on that link posted above:
But aside from the lines, does that cover all the likely parts that could have went bad?
EDIT:
I see now there is a kit on that link posted above:
Ref:
22
42810-04B
KIT REBUILD,RR/MSTR CYL,XL
22
42810-04B
KIT REBUILD,RR/MSTR CYL,XL
Last edited by tvon; Feb 3, 2025 at 10:42 AM.
Thread Starter
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Road Master
Joined: Mar 2020
Posts: 1,077
Likes: 267
From: New England
Trending Topics
HDF Community Team
Joined: Dec 2011
Posts: 8,512
Likes: 3,924
From: San Diego, CA
If the caliper seals are bad, you'd have some pressure at the master cylinder, and brake fluid all over your brake rotor. There would at least be some backpressure in the system, you have none. If the brake line is bad, you'd still have pressure at the pedal, unless the line is completely severed. Your symptoms indicate no fluid is moving, so the master cylinder is suspect.
John
John
Last edited by John Harper; Feb 3, 2025 at 11:03 AM.
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Last edited by OCSpringer; Feb 3, 2025 at 12:13 PM.
Seasoned HDF Member
Joined: Aug 2006
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From: Pennsylvania
The machine is 20 years old...
I suggest rebuilding the master cylinder and caliper, and inspect the hoses for bulges, leaks etc.
New brake hoses would not be a bad idea also.
When still available, stick with OEM parts.
Disassemble the master cylinder and the caliper before you buy any parts, make sure they are in good condition and rebuildable.
Master Cyl. rebuild kit is item20 22 in the illustration:
Rear Master Cylinder Illustration
Piston and seals for caliper, if the piston is good, just replace the seals.
Caliper Illustration
I suggest rebuilding the master cylinder and caliper, and inspect the hoses for bulges, leaks etc.
New brake hoses would not be a bad idea also.
When still available, stick with OEM parts.
Disassemble the master cylinder and the caliper before you buy any parts, make sure they are in good condition and rebuildable.
Master Cyl. rebuild kit is item
Rear Master Cylinder Illustration
Piston and seals for caliper, if the piston is good, just replace the seals.
Caliper Illustration
All though $99 is not bad for a complete master cylinder.