Warped rear disc??

[Francis]

I already posted this on another forum, but I thought you may find it useful:
On my recent MOT, I got an advisory for a slight warp on the rear disc on my R1150GS Adventure. This is what I did to get it sorted and what I discovered:
Removed rear wheel, removed disc and checked for "straightness", using a steel rule all over and placing on a bit of handy plate glass. It was pretty well spot on, and certainly nothing to worry about. Then I cleaned it up with a "flat wheel" on the drill and also ran a drill bit thru each hole for good measure. Put it back on again and reloctited the bolts.
Turned my attention to the caliper. Took out the pads. These are nearly new Ferodo sintered. One was slightly grooved at the bottom edge. On further investigation the pad material had unstuck itself from the metal back plate and was only held in by some of the material having been stuck in one of the two backplate holes. When I fiddled with it the final bit of glue gave way and I was left with a metal back plate. This was obviously giving the symptoms of a warped disc, grabbing it as and when it could and as it got hotter and expanded.
I'm really unimpressed with the Ferodo manufacturing quality and am grateful that it wasn't on the front, where it could have done (fatal) damage. Needless to say, I won't be buying Ferodo again.
Replaced defective pads with BMW OEM ones (UK£28.00 - how the f*** do they justify that??!!) cleaned the inside of the caliper out. Cleaned around the pistons and made sure they moved OK. Cleaned and greased the pin. Reassembled it all, bled the brakes and everything back to normal and as it should be.

So a final question - where's the best (cheapest) place to buy BMW spec pads, presumably they are made for them by Brembo anyway??
BTW I've also used EBC before with no ill effects.
I hope this helps someone else!!

 

[Decster]

Were you advised at the MOT to replace said disc?

if so, did you re do the MOT with the same disc and pass?

As Den of this parish had a disc fail his MOT.

 

[Francis]

I was advised at the MOT that it was a potential problem, but not bad enough to warrant a failure. I was aware of some slight binding and had ridden in such a way as to avoid heating the disc and making it worse
There is nothing worse than having the pressure of an MOT failure on the daily rider, as it has to be fixed immediately
Having got the MOT under my belt I then set too to discover the source of the problem, at my own pace, results as explained above...

 

[Steptoe]

Could a sticking caliper have caused the pad to overheat and the friciton material to come away Seen it many times on BMW pads over the years but never had it happen on ferodo pads before.

Once caused a customer to crash outside the firestation on roseberry avenue in london.

BMW pads are prone to corrosion between pad and backing pad plate, especially if washed and garaged over a period of time, but as i've said, i've never seen it any other make of pad EBC, ferodo or Dunlopillo.

 

[Francis]

Well the caliper seems OK, but I've only been riding it for 4 days since doing the job (about 176 miles) and no repetition of the problem so far. When I cleaned it out it was for peace of mind really and to eliminate the possibility, rather than because it needed it. The pistons seemed to be moving OK and there was no obvious crud around them. When the disc was binding, on stopping it was possible to hold it with the naked hand, so I'm not certain it got hot enough to cause the pad material to come away. Obviously if it happens again, then I'm going to have to try swapping the caliper to see if that makes a difference - quicker and simpler than messing around with a rebuild kit and as cheap if I can get a reasonable one from the dreaded E Bay... Can't think it can be anything else, unless you know better - you probably do a few more of these than me Steptoe!!

 

[Steptoe]

It's not so much the pistons that stick, but the sliding pins on the caliper.

If everything is free and moving can't explain hope it doesn't happen again.

 

[Francis]

OK, I failed to mention that as I'm fairly paranoid I also peeled the rubber boots back and checked the caliper pins for any corrosion. Couldn't see any, so re-located the rubber seals. They could have been a bit dry though - what should be in there? Some silicon grease? Other than that, I'm exhausting possibilities myself. I agree with you though - don't fancy it happening again

 

[Francis]

OK, typical. Just as I thought I'd got it cracked it started binding slightly again this morning.
Anyone got a decent cheap secondhand rear caliper going spare? I will check E Bay anyway and see what's there...
Unless you've any bright ideas Steptoe? (The one on the front discs worked a treat!)

 

[Stewart H]

OK, I failed to mention that as I'm fairly paranoid I also peeled the rubber boots back and checked the caliper pins for any corrosion. Couldn't see any, so re-located the rubber seals. They could have been a bit dry though - what should be in there? Some silicon grease? Other than that, I'm exhausting possibilities myself. I agree with you though - don't fancy it happening again

I just clean them and use ordinary grease, no issues so far.
Stewart

 

[MattW]

A couple of weeks ago I noticed my rear caliper was binding slightly. I stripped it, cleaned / greased everything and fitted the BMW 'rebuild kit' (actually just a pad retaining pin, circlip and anti squeal shim - not much of a 'kit' ).

When I took it apart the sliding pins were dry but not cruddy so I cleaned them and greased with red rubber grease (which is silicon I think?). The pistons were pretty crud free but I pumped them out a bit and cleaned them up.

It seems to have cured the binding (although I find it hard to tell due to the drag of the final drive and gearbox output shaft ) - time will tell - MOT next month

 

[Francis]

OK, so I've been and raided the stores at work and I've got a syringe full of high load silicon waterproof grease. I've glued a bit of heat shrink, shrunk to size over the end of the syringe, so make it easier to apply. That's going to get squeezed past the little rubber boot/s. Let's see if that solves it!

 

[fatnfast]

I think it would be worth your while taking the caliper off and cleaning the sliding pins that are covered by the boots, rather than inject some grease in there. Its an easy job to do with just the pad pin to remove (and the caliper mounting bolts of course). The pistons on mine push easily in with thumb pressure, do yours? I prefer to pump them out a little, clean the pistons with brake cleaner and an old toothbrush, wipe dry and leave them that way. You can use the 'red' rubber grease on the pistons, but this may just attract dirt in the future?
The pins are easy to get at, just slide the caliper body and mounting bracket apart, clean and use copper grease on the pins. The little rubber bellows will pop back into place, with a little help, on reassembly.
You will always have a little drag with these calipers which is made worse if the disc is not wearing evenly, got ridges etc.
Good luck

 

[Francis]

Hi Fatnfast. Doing it tomorrow morning - will report back...

 

[Francis]

OK. Here we go again.
Removed disc, noted there was a strange deposit on it, with a few high spots in places so something had got on to it (paint from the OEM pads?). This was having thoroughly cleaned the disc last time. Cleaned all this off again, this time using "production paper" (very corse sandpaper). Nice and shiny/scratchy and a good key for the pads. Refitted.

Removed caliper and disassembled. Noticed the small circlip had managed to ping off somewhere on my route to work (unimpressed). Pins were lovely and golden and well lubricated - no obvious sign of wear and free moving. The caliper lock pin is also fine. Took out the pads, rubbed the faces down using the same corse paper, to remove anything that might be on them and shamfered the edges for good measure. Checked the pistons, which are clean and move freely. Retracted them and refitted everything. Brake functioned OK and wheel ran freely.

Approximately 100 miles later the brakes are locking intermittently. Bizarrely, in a 22 mile run to work, they lock on for approximately 8 miles of the journey, making filtering a distinct challenge. Then, for no apparent reason, they free off again and are fine. Doesn't happen on the way home at all.
Any ideas gratefully received, because I'm getting close to total bafflement!!

Finally, anyone sourced a supplier for the circlip (for less than the 8 quid that buys the full kit), as BMW won't sell them by themself??

 

[Stewart H]

You do have a little free play between the pushrod and the master cylinder dont you?

Stewart

 

[Francis]

Normal freeplay... This morning it was cooler and no binding occured, but I reckon there is only an air gap the size of a gnat's. The inner pad seems butted right up against the disc. Any more ideas?

Also, anyone got any thoughts on an alternative supplier for the circlips - £8 for the kit seems a bit unnecessary when the pin is fine. Anyone know if Brembo do it as a separate item?

 

[MattW]

Normal freeplay... This morning it was cooler and no binding occured, but I reckon there is only an air gap the size of a gnat's. The inner pad seems butted right up against the disc. Any more ideas?

Also, anyone got any thoughts on an alternative supplier for the circlips - £8 for the kit seems a bit unnecessary when the pin is fine. Anyone know if Brembo do it as a separate item?

There will only ever be a tiny amount of clearance between pad and disc but tiny is enough.
When you checked the sliding pins, were they smooth and free from burrs?
When you checked the pad retaining pin, was it also smooth and free from burrs?
(either of these can prevent the inboard 'fixed' pad from fully retracting from the disc).

Failing this, if you're absolutely sure that the caliper is sliding freely on the pins, then it must either be sticking pistons (do you need huge pressure to push them back into the caliper?) or some sort of missassembly. I once bought a bike where the caliper carrier had been refitted with a washer between the carrier and the hub on one side - this caused the carrier (and hence caliper) to twist slightly and bind.

Regarding the circlip, it might be worth phoning Steptoe (or even a dealership) and see if they have a spare lying around. I kept my old one as a spare when I serviced my caliper last week and fitted the rebuild kit (but I'd like to keep hold of it just in case I have your problem one day ) If I was you, I'd just buy the kit and fit the new pin, circlip and anti-squeal shim - at least you're ruling these out of the equation then

 

[Steptoe]

Might be a long shot and only seen it a couple of times, but if any previous owner has ever had the brake caliper bolts stuck in place and has used an impact driver or hit a socket into the bolt to release it, it can cause the lugs on the final drive that the caliper mounts on to bend slightly, causing a misaligned caliper.

 

[Francis]

Q. When you checked the sliding pins, were they smooth and free from burrs?
A. Yes - almost perfect & no obvious wear at all.
Q. When you checked the pad retaining pin, was it also smooth and free from burrs?
A. Yes and I gave it a thorough clean for good measure.
Q. Do you need huge pressure to push them back into the caliper?
A. Not "huge" but some leverage was required - it was easier to slacken off the bleed nipple so they were nice and loose to move back when I fitted the new pads (and then rebled the system).

To be honest I suspect the caliper, but I can't put my finger on why - I prefer to have a logical reason than to rely on intuition.

Might be easiest to go back to plan a and get another caliper - at least doing the substitution method I can eliminate the caliper as a possible cause and look at the rest of the system.

 

[harry]

Strikes me it could be a master cylinder prob