04/05 Flange defect, take note

  • Thread starter Thread starter michnus
  • Start date Start date
Having read this thread I went out to check the "flange" on my 2004 12GS... thankfully no probs... but in the process I noticed that the rear pads are completely worn..... can anyone recommend a replacement set. Thanks in advance
 
You can pay top dollar for genuine BMW badged (Brembo) ones at your dealer, or buy aftermarket ones such as the EBC brand, Ferodo etc from places like Nippy Normans or a local brake suppliers.

Be aware that if your bike is under warranty you will invalidate it by using non-BMW items.

They take about 20 minutes to strip out, clean the caliper and fit new pads, hardly rocket science. Be sure to check the caliper slides freely once the pads are out.

Or you could pay your dealer to do the job.
 
I reckon the failures are simply caused by the stress generated in the lug areas by the disc bolts. The fact that the disc cyclically expands and contracts due to heating and cooling further loading and unloading the bolts won't help. I suspect if the bolts were shouldered and the disc floating we would not see this failure mode.

BMW have obviously got something slightly wrong, material, heat treat whatever. The problem facing the designers is the constant push to lightweight everything vs. longevity of the component. No amount of F.I. analysis and prototype testing substitutes years of field service. But to be fair they did take a lot of weight out of the 1200, the 1150s were stupid heavy.

I think the main thing is not to panic; whilst I would not suggest for one minute riding a bike with a cracked hub the failure rate seems low and no one is reporting catastropic failures. Regular inspection is the order of the day. Looking at the cracking I would suggest the lugs are unlikely to snap off but it is likely that the disc bolts could come loose.
 
Martin, the disks are held in by loctite as standard.

When I get the new flange I'll compare it with the older style part on the bike and if obviously different I'll get my head around the photobucket thing and do a write up.

BMW have obviously changed the part for some reason unless they just change part numbers due to a difference in their suppliers.Maybe they have done a design improvement along the way ??:nenau
 
Pukmeister said:
Martin, the disks are held in by loctite as standard.
Click to expand...

I know they're Loctited, I didn't mean the bolts might come loose and cause the failure, rather cracking will allow the threads to relax around the bolt and that may cause loosening

Pukmeister said:
When I get the new flange I'll compare it with the older style part on the bike and if obviously different I'll get my head around the photobucket thing and do a write up.
Click to expand...

From the photo it looks just like the one on my current '08 machine but as ever the devil may be in the detail, it could just be a different material or a subtle change in the rads.

Pukmeister said:
BMW have obviously changed the part for some reason unless they just change part numbers due to a difference in their suppliers.Maybe they have done a design improvement along the way ??:nenau
Click to expand...

Who knows? One hopes it's a more robust part.

When you mentioned Loctite I did have another thought re. the failure: Was the old hard Loctite cleaned out with a tap prior to rebuiding? If not winding the bolts into partially clogged threads may overstress the wall of the lug? Part of my job is supervising the maintenance and repair of high precision power presses where Loctite is used everywhere to stop things vibrating apart. We always, always tap out holes and run a die down male threads prior to rebuilding even on heavy castings and forged parts.

Cheers,

Martin
 
Yes, the old threads were 'chased' through with a tap to clean out the loctite before reassembly. A medium strength threadlocker was used and the bolts were torqued to the correct stages as per the RepRom.

I suspect this may be due to cyclical stressing/unstressing of the failed areas through repeated use of the rear brake over time. The wall thickness of the alloy component is fairly thin at the failed sections. I did supect some form of metallurgical fault eg brittle fracture over the recent cold winter whilst riding but now doubt that. I suspect it should be made from some form of precipitation-hardened alloy as standard (solute copper atoms to reduce dislocations).

Either way, a new (improved?) flange should sort it for £133 and I'm care-free once more.
 
Ravenbyrne said:
Having read this thread I went out to check the "flange" on my 2004 12GS... thankfully no probs... but in the process I noticed that the rear pads are completely worn..... can anyone recommend a replacement set. Thanks in advance
Click to expand...



Thank you one and all:thumb2

Picked up a set of EBC sintered this morning

Jobs a good one:thumb2
 
Got the new flange, slight design change to the rear face of it, it has less metal and has a fibre thrower ring bonded to it instead (?).

Halfway through the job, as already said the flange has to be heated then it comes off easily, it's an interference fit on the splined drive spindle.

Fun using a three-legged puller on a five-armed hub with a hollow centre.;)

New part now heating in the oven, will post some pics once the jobs finished if I can work out where/how to host them.
 
Job now done, took me an hour and a half due to making too many brews.

Pics below show my jury-rig of a cheapo 3 leg puller with an old metal test piece from my apprenticeship days as a plug in the hollow spindle to give it something to pull on. Note that it has to be pulled off-centre to get the 3 legs around the 5 armed flange. I heated the flange with my Turbotorch taking care to avoid the ABS sensor and wiring. Once hot enough to expand the flange, it easily slid off the splined rear drive hub with little effort. Without the application of heat it would never have come off as it is an interference fit.

GSFlange1small.jpg


Second picture below shows the naked splined drive hub once the flange is removed. The yellow spots next to the rear bearing seal is granular rock salt thrown up from the roads. How did that manage to get in there ?? A scrub with some WD40 and an old toothbrush was in order.

GSFlange2small.jpg


Heres the new versus old flanges shown in the pics below. Note the new item has a fibre thrower ring bonded to the flange, whereas the old part is simply a large diameter section of the flange metal. That appears to be the only difference, the brake disk mounting lugs are the same thickness.

GSFlange3small.jpg


GSFlange4small.jpg


The final two pics below show the cracks in the arms of the flange where the rear brake disk mounts. The first pic isn't too obvious but the crack is directly above the shadows edge. The second pic of the other lug is obvious.

GSFlange5small.jpg


GSFlange6small.jpg


Fitting the new flange is easy enough, just heat in a domestic oven to over 100 degrees centigrade then slide it onto the splined hub and refit the circlip to keep in place. As it cools and shrinks onto the hub it stays put. You can just hear the lip of the fibre thrower ring rubbing slightly against the final drive casing recess as the wheel is turned by hand, so presumably that will now prevent the rock salt getting in past the flange unlike the previous design.

Hope this helps anyone else with the same problem.
 
Also forgot, a new set of five brake disk mounting screws costs £4 inc Vat (and they are supplied with a dry film of loctite pre-applied) so not worth re-using the old screws.
 
I reckon those fractures were caused by the expansion of the disc with the heat generated from brakeing. The expansion of the disk has pulled on the bolts and the bolts have caused those fractures. Heat values are incompatable. Just my humble opinion.
 
You're probably right Billy, I rode on a warped rear disk for over a year as it had warped whilst outside warranty and as a disk is a consumable item I didn't persue a goodwill gesture. I then fitted a Galfer Wavy disk because:

a) They're cheaper than the stock item
b) They're meant to be better at avoiding distortion and cool better
c) They are thicker than the stock item
d) The stock item wears down quickly
e) I prefer the look

Maybe the old disk had warped and caused the cracking and I just didn't notice when I changed the disks? Maybe the cracking happened first and allowed the disk to warp? All speculation I'm afraid with no evidence to hand.

The disk screws are shouldered and fit into a recess in the disk mounting face, once tightened the disk is rigidly mounted but the disk and flange are of different materials with different expansion rates.
 
I took Ugly Betty for her MOT this morning but didn't mention anything.

Only after it passed I pointed out I have a crack on one hole on my disc carrier.

My man Roy Gardner has ordered the bits in: new carrier & disc bolts, £186 replaced.

He's told me stories of some carriers taking ages to get off - I'll be watching him take mine off! :)
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
You must log in or register to reply here.


Back
Top Bottom