Disc rotors varying in thickness?

[Gremlin]

Anyone got any ideas how rotors end up varying in thickness? It's the official explanation for the poor man's ABS I'm experiencing, lurch - lurch etc.

BMW R1200 GS Adventure, I ended up with the problem around 40-50k on the OEM front rotors, tried for a goodwill warranty but declined. No guarantee I wouldn't have the exact same thing with another set and being BMW, the parts cost a fortune (I think it was around $600 for one disc, so probably no chance I'd get change from $1600). Eventually, around 80k I gave up living with it, tried Sweet Street discs from Napier way, they didn't fit. Shop offered Metal Gear, which I've run a rear on a CB919 for some time with no problem, so went with that - of course it's discs and pads thank you, recommended together.

90k service (10k and 6-8 months later) I get the shop to check as I could swear it's not smooth, sure enough, 0.01-0.02 variation in the thickness of the discs again. Naturally I'm telling the shop to start the process with supplier, as it's not satisfactory.

However, I'm after advice. Previous reading suggested stopping with brakes on, leaving spots on the discs, or pad material bonding to the disc as possible culprits. However, in 300k (90k on the BMW, so 200k on other bikes) I've never had this problem, and I'm even more cautious on the BMW. Anyone know how discs could be varying in thickness?

[Motu]

Previous reading suggested stopping with brakes on, leaving spots on the discs, or pad material bonding to the disc as possible culprits.

This is the official line from the experts ( brake manufacturers) and is possibly correct as some vehicles and owners are more prone to it than others. Although having machined many rotors, I've only removed metal. But pads these days are metallic, pad material transference is the most likely cause.

[Gremlin]

Ok, more details in that area, OEM rotors until 80k, front and rear. Metal Gear front rotors from 80k to 90k. Still OEM rotor rear.

Pads, OEM until about 30k, then worn out. I've have to check records for specifics, but second set of pads (replaced all round) was also OEM, I had a heart attack at the $660 charge for pads so third set was EBC, the second set being short lived, around 10-20k, possibly more on the rear. At 80k, Metal Gear pads fitted to front, along with discs.

I would have thought that using Metal Gear pads and discs, performance should be optimal, designed to work together etc. Metallic pads are the recommended fitment. I wonder if using organic once the discs are straight would yield better results...

[gijoe1313]

Nothing like throwing money at a problem that won't go away!

[Big Dog]

Metal gear brake pads are shite, or so their distributer advised when I was working in Red Baron and ordered some. On the road they get too hot and break down. Off road they become less functional in the wet, I assume due to lower temp.

Distributor also advised they only work 100% with sintered pads at touring speeds.
Are your pads pitted?

I found their rotors exceptional on dr.
Given distributors advice I have never installed the pads that came free with my rotor.

Stupid phone / Tapatalk, apologies in advance.

[nzspokes]

Anyone got any ideas how rotors end up varying in thickness? It's the official explanation for the poor man's ABS I'm experiencing, lurch - lurch etc.

BMW R1200 GS Adventure, I ended up with the problem around 40-50k on the OEM front rotors, tried for a goodwill warranty but declined. No guarantee I wouldn't have the exact same thing with another set and being BMW, the parts cost a fortune (I think it was around $600 for one disc, so probably no chance I'd get change from $1600). Eventually, around 80k I gave up living with it, tried Sweet Street discs from Napier way, they didn't fit. Shop offered Metal Gear, which I've run a rear on a CB919 for some time with no problem, so went with that - of course it's discs and pads thank you, recommended together.

90k service (10k and 6-8 months later) I get the shop to check as I could swear it's not smooth, sure enough, 0.01-0.02 variation in the thickness of the discs again. Naturally I'm telling the shop to start the process with supplier, as it's not satisfactory.

However, I'm after advice. Previous reading suggested stopping with brakes on, leaving spots on the discs, or pad material bonding to the disc as possible culprits. However, in 300k (90k on the BMW, so 200k on other bikes) I've never had this problem, and I'm even more cautious on the BMW. Anyone know how discs could be varying in thickness?

Unless your riding style has changed in the last 10k then the product is faulty. No question. If you got 50 to 80k out of the stock rotors then the new ones are not fit for purpose. Mention you are passing them on to Com Com for testing as you think they should have a nation wide recall.

Get your money back and get OEM ones.

[Gremlin]

Unless your riding style has changed in the last 10k then the product is faulty. No question. If you got 50 to 80k out of the stock rotors then the new ones are not fit for purpose. Mention you are passing them on to Com Com for testing as you think they should have a nation wide recall.

Get your money back and get OEM ones.

Riding style hasn't changed, not actually that hard on the brakes as I'm not often exceeding 110kph, which means I don't have to brake much either. Stock rotors still serviceable thickness, just varying thickness which made them unusable.

Only problem with OEM ones, when I enquired last year, rotors were a touch under $600... each.

Thanks Big Dog... wonder if some sort of blend of other pads and MG rotors might work... will see what shop says, and if disti has any recommendation.

[Big Dog]

Premier sintered work real well with metal gear rotors. Take a lot of heat so not much use on the 350. Went back to standard. Freaking Awsome. A little noisy bit that is because of the thin profile of the rotor. Suzuki rotor was chewed at 8k. I have done 35+ on metal gears.

I put some ceramic ones in once. They certainly made the rotor shinier but opening my mouth in a full face helmet would slow me quicker in the wet before the rotor gets hot.

Simple fix, drag the brake for first 20 meters or so.


Stupid phone / Tapatalk, apologies in advance.

[TLJimmy]

Premier sintered work real well with metal gear rotors. .........Suzuki rotor was chewed at 8k. I have done 35+ on metal gears. ........

My fat old girl's pretty hard on brakes... my Suzooki discs lasted about 15k

I have had Metal Gear rotors for 35+k, with no problems - I used the pads supplied for 1000k's to bed them in, then changed to premier sintered pads and have had no issues - that includes 5 years of Cliffhanger Hillclimb (finally into the 2min 20's), and lots of pretty hard riding in all weather.

Cleaning the bobbins regularly is essential - otherwise you can get a slight runout, which could give you uneven wear.

Soapy warm water, and blow them out with a compressor - Ocassionally I put a bolt through the bobbins, tighten a nut until the bobbin spins, then spray with brake cleaner - you'd be amazed at the brake dust and crap that comes out.

Cleaning frees the bobbins, allowing the disc to float properly and deal with heat fluctuations. I also strip and clean my calipers every spring - this also will extend disc life.

[Gremlin]

Not sure where I heard/read this but its claimed using non BMW disc pads will wear out the discs quicker.

Essentially, it's a trade off between discs and pads. Sintered will eat discs faster than organic pads for example, but usually perform better. You're either buying more pads or more discs, just that discs are more expensive. The annoyance for me... I'm not wearing them out, it's the thickness varying that's ruining their life.

Thanks TLJimmy, some useful info...

[Big Dog]

Now that I think about it. With my busa I used to get the slight throb going on about every 20k. Solution was some brake clean and a Allen key the same size as the rotor perforations. Spray the whole rotor, give it a couple of mins. Poke the Allen key through each perforation and rotate. If it is sticky spot spray and repeat.
Don't forget to rotate your wheel to get the ones behind the calliper.

When finished doing each one spray on both sides lightly. You should see something similar to Mascara on a hot girl in the rain. Wipe from the centre out. The. Take it out like you are trying to bed in new pads. Speed up to 40 slow to 20 quickly, speed up to 60 and slow to 20 quickly, repeat until you experience brake fade or you are braking from 100.

Your pads should stink.

Would not account for uneven wear if you are able to say for certain that they a variable thickness but might account for the sensation.


Stupid phone / Tapatalk, apologies in advance.

[Gremlin]

Would not account for uneven wear if you are able to say for certain that they a variable thickness but might account for the sensation.

Shop measured the discs both times (OEM and MG), so yes, can say for certain the discs vary in thickness.

[Big Dog]

Shop measured the discs both times (OEM and MG), so yes, can say for certain the discs vary in thickness.

Was there any variance when they first went on?
Are the variances evenly spaced?
Have you pissed off any gremlins?


Stupid phone / Tapatalk, apologies in advance.

[FJRider]

Essentially, it's a trade off between discs and pads. Sintered will eat discs faster than organic pads for example, but usually perform better. You're either buying more pads or more discs, just that discs are more expensive. The annoyance for me... I'm not wearing them out, it's the thickness varying that's ruining their life.

Thanks TLJimmy, some useful info...

A competent engineering workshop will true them up. As per the removing of a warp in the rotor. It shouldn't take them below minimum specs in thickness .... if so little has to come off.

Setting the machines up for the process is time consuming ... and usually need to be bolted to a backing plate during the process.