Rear brake dragging

[mr_diver]

This one has got me stumped.
I've posted it on the Varadero forum but I expect feck all assistance there.
--------------------------
I'm no mechanical numpty -- I do all my own maintanace 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.

[tallpaul]

You say you have replaced the rear disc. Is the thickness of the new disc correct? If it was oversized on thickness it would cause the symptoms you describe.  It's about the only logical explanation I can think of.

[Gassoon]

Yes, you sure the rear brake setup is all original diver? previous owner might have changed caliper and disk, then you buy a new disk (or pads) which you think is correct? long shot, I know.

The other thing that springs to mind is the linked system - which are a bit of a mystery to me anyway.

[kwackboy]

I know the rear caliper floats but does it still drag when you undo the caliper mounting bolts .?
Obviously you can't ride it like this but put the bike on the centre stand and just loosen the bolts to see if it releases drag. 
Nipping up the bolts can sometimes pull the caliper hanger off centre (if hanger has an issue) causing slight drag .

Also,  just to add . Are the pads OEM ? And for your varadero ? I'm pretty sure that there are several different pad thicknesses for duel brake Honda's of that era .

[Gassoon]

feck - that sounds so likely! Takes a perfessional !

[hotbulb]

What are the hoses like? Sometimes the internal lining can start to break up and act as a sort of non-return valve, holding some residual pressure. I had a problem with the Land Rover's clutch because of this..... cured with a new hose.

[Mark Shelley]

Quote removed


This is really common on BMW bikes of a certain age, although you will usually see tiny pieces of the rubber lining in the fluid when you bleed the brakes as a tell tale.

[mr_diver]

Thanks for the replies. I've had more replies here, than people looking at the Varadero forum post!

Pads and Disks were all Honda Genuine (bought the bike with 9k on the clock)
I have changed to an EBC disk and Genuine pads after the original disk was scored badly. The Pads are for the Varadero - I took the part numbers from Honda EPC as I worked in a Honda dealer on the parts desk at the time.

Hoses are all good - I've been bleeding the buggery out of the system over the last few months and the fluid runs clear - no bits there is no restrictions I can find.

Kwackboy - I've not tried what you have said - maybe the mount it on the wonk - I'll give it a go when I put it all back together.
I've once again stripped all the calipers cleaned and checked/measured the piston seals.
I'm half way through re-assembling everything, but I ran out of rubber safe grease. 

Cheers  Chaps 

[kwackboy]

Linked brakes are a nightmare and if my GTR didn't have so many electronics I'd scrap the whole lot, and included and have old style brakes . Far simpler, more feedback and better in my opinion.

It sounds like you know what you are doing and I hope you find the issue .

[mr_diver]

I do know my way around a brake system...

that's what is so frustrating. 

I was hoping for someone to point out something I've not tried, which you did with the loosened bolt idea.
I'm souring ebay for caliper mounts. Found one but it's an ABS one and one in Germany for an 04.

[kwackboy]

Might not be the issue , try it first before buying a new one

[Gassoon]

Good luck with it diver - linked brakes (never had them) give me a headache just imagining how they work. Don't the front ones help operate the rear by the caliper moving slightly when the bike is moving and front brake operated? you mentioned it happens when moving. Maybe the problem is at the front....Meh...I'll shut up now mate, way out of my brake depth

[mr_diver]

You are exactly correct there Gassoon.

There is a secondary master cylinder on the front left caliper mount. As you brake with the front, the mount pivots, putting pressure on the master cylinder, through a delay valve, thought a proportional control valve to the middle piston on the rear.
Using the rear brake moves the outward two pistons on the rear, but also the middle pistons on both front calipers and in turn through a bypass of the secondary master cylinder the rear.
      

It takes 2 PHD's to understand it!

If I ever meet the sadist that designed it I'm going to put my size 11 up his Proportional Control valve! 

[tallpaul]

That sounds far too complicated for the British climate! Did Honda learn nothing from trac anti-dive or inboard brake discs?! Sometimes less is more...

[mr_diver]

My other Honda has TRAC forks 

[mr_diver]

And that bike is a CX500 renown for it's iffy cam chain tensioners in the 80's and so was the Varadero in the 00's 

Anyways... an update.
This is what I've done since last time...
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. 
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 Fat Rat's this weekend.

[Gassoon]

Wow! Best of luck with all that Diver...you probably have the only fully-functioning brake system on a vara in the country from the sounds of it!

[Fat Rat]

Nathan, we will line up the sandbags in readiness for your (speedy) approach into the Campsite 

[mr_diver]

Sandbags weren't needed.

Getting to the West Wales meet wasn't a good test... lets just say the bike was very water cooled by the time I got there.

But a long fast ride with some rapid stopping on the last few miles home on Monday did heat up the caliper - Luke warm... the front calipers were slightly warmer.