Author Topic: Rear brake dragging  (Read 391 times)

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mr_diver

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Rear brake dragging
« on: July 10, 2018, 10:42:52 »
This one has got me stumped.
I'm no mechanical numpty -- I do all my own maintenace and know which end of the spanner to hold.

The bike is a XL1000v9 37k miles.
Still on the original front pads, rear was changed @ 21k miles. I've gone through 2 sets of rear pads since then and will need another set quite soon.

The Rear caliper is holding (dragging) the disk, but when moving. I can get both the other two pistons worked directly from the rear mast cylinder and the middle piston worked from the rear m/c and from the secondary m/c.
I have stripped all calipers, replaced the seals, greased the sliders, reassembled, bled (I know the correct process and pressurised the secondary m/c and bled the rear middle nipple with someone's help) 3 times!!!
I've replaced the Secondary m/c internals and rod.
I have stripped and cleaned the whole system, including the PCV. Everything seems to be functioning as designed.
I've replaced the rear disk as the old one was showing some scoring, but not warped.
I've checked front wheel alignment.
Rear wheel is aligned correctly.
Wheel bearings have been replaced.
I have checked if the bike has any outstanding recalls and it`s all clear.
Front left caliper is not dragging.

Still the rear brake drags and the disk gets quite hot and so does the caliper.
It happens whether or not I use the rear brake lever (not a suprise with linked system)

I'm stumped with this and it's starting to get to me.
I can't risk riding the bike incase it gets worse away from home. If I can't get it fixed the bike has to go, then there is nothing out there I can replace it with other than another Varadero.
I've found other threads for the Varadero, VFR800, ST1300 and CBR1100xx that has the same brake system with similar issues, but I've tried all the offered solutions but no one ever closes the thread with a conclution or solution of any help - Cheers everyone!!!  >:(

Hope someone can help.
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the prodded dog

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Re: Rear brake dragging
« Reply #1 on: July 10, 2018, 23:21:46 »
Only two thoughts spring to mind and it is a long time since I had a Vara.
Is there enough clearance between the pad backing and the caliper body?
Is the front caliper sticking on its pivot so that it activates the rear brake all the time?

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mr_diver

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Re: Rear brake dragging
« Reply #2 on: July 10, 2018, 23:48:08 »
Thanks for the input, but both of those have been checked and ruled out.

I'm in the middle of another full strip down, seals and pistons check out fine, slider pins are clean, pivots free.
I'm waiting on new rubber slider bushes to arrive. I'm changing them as they are 10 years old and it rules them out rather than they look suspect and I've run out of rubber safe grease.

I've also been told to release the rear caliper mount bolt and see if the angle of the caliper changes- maybe naffed mount.
 
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SB

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Re: Rear brake dragging
« Reply #3 on: July 13, 2018, 00:35:57 »
It would help if you could find a way of working out if its the middle piston or the two outer ones (or even all 3 ! ) that are dragging.

That would help to limit the number of components that could be causing the problem.

Problem is, other than putting a pressure gauge in the lines I cant think of any way of doing that !




mr_diver

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Re: Rear brake dragging
« Reply #4 on: July 14, 2018, 00:26:00 »
That's the problem.

I've run the bike on the centre stand in second gear at idle - holds around 20mph indicated and the disk doesn't even get warm.

Either it takes some heat from action at least once to start the issue or it, something to do with the secondary master cylinder, or the mount is bent and 20mph isn't enough speed.
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Jyrays

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Re: Rear brake dragging
« Reply #5 on: July 16, 2018, 19:40:03 »
As it is CBS you should check all front brake components too :)
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mr_diver

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Re: Rear brake dragging
« Reply #6 on: July 17, 2018, 10:52:34 »
ATM the whole brake system is on the work bench.

As it's all apart I'm going to change all the seals and rubber parts.
I've sourced an a new rear caliper mount from Ebay - a shocking total of 15 shipped to UK from Germany-
Possibly mine is out of alignment and for 15 it was worth a punt.

Thursday will be the rebuild day if I complete the modification to my new bicycle early enough
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Captain Scooby

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Re: Rear brake dragging
« Reply #7 on: July 19, 2018, 02:29:27 »
Fortunately I don't have this problem.
However, if the rear disc does not heat up whilst on the stand, would it not be logical to inspect the pivot master cyl on the fork as someone else suggested?
The centre piston on the rear is what, connected to the pivoting  fork master cylinder? That's the arrangement as I understand it.
Prove my theory is incorrect by removing the hose from the fork master cylinder that is cross linked to the rear. Block it with a bolt or something. . If the rear brake no longer drags when riding,  you have found the culprit - dragging front brake. It does not take much.
 I had a dragging caliper on one of my vans since new. 350,000 k later the caliper locked with sufficient force that the offending brake heated the wheel and I finally found the culprit. New calipers and now that van freewheels down hill which it never did. Turns out the piston was a bit scratchy.

mr_diver

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Re: Rear brake dragging
« Reply #8 on: August 23, 2018, 23:26:18 »
Ok so this is what I've done...
Replaced the Delay Valve rrp 190 (paid 20)
Replaced the PCV rrp 345 (paid 15)
Suprising what you can find online with the knowlage from working the parts desk in a Honda dealership for a couple of years. VCIF_ThumbUp
Replaced all pads (60 Ferodo Sintergrip)
Replaced all the rubber bushes on all 3 calipers
Stripped, cleaned and reassembled the rear caliper without new seals.

The result from a bench test is the rear brake releases quickly after a very short delay where before it would take a little time and be fairly gradual. This is giving the lever a firm press to activate the front system and get the PCV to kick in.
I'm yet to give it a full test ride as it was chucking it down and brand new rear tyre.
We'll find out tomorrow if it's truly worked as it's all loaded ready for the V-Strom forum meet this weekend.
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mr_diver

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Re: Rear brake dragging
« Reply #9 on: August 28, 2018, 16:07:45 »
Some decent riding and stopping on the Bank Holiday weekend has showed the rear no longer drags.  VCIF_a040hae VCIF_a040hae VCIF_a040hae
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zebulon

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Re: Rear brake dragging
« Reply #10 on: August 28, 2018, 18:13:12 »
 VCIF_ThumbUp
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