Strange brake behaviour

[georgesgiralt]

Hi !
My '82 R65 had Brembo caliper.  Quite a long time ago, I put  brake rotors made of plain  steel (I do not know the exact composition).
When I restarted the bike in 2012~13, I completely overhauled the master cylinder, calipers and put braided stainless brake lines. Of course I  installed new brake pads.
On dry roads the braking is very good even if I need  high hand effort   because of the 16 mm  dia master cylinder.
The braking  on wet  roads is  terrible. IMHO  it is a consequence  of the rotor material. But the main  problem  I've  found is that only the center part of the pads  are braking.  There  are  two portions  on the rotor which  seem not to be touched by the pad. It is obvious on wet  weather because there  are two concentric  wet bands, one near the wheel axle, the other  near the exterior of the rotor.
Question  :  What  is the cause of this ?
How could I  improve the area of contact   f the  pads  ?
Will it  improve wet braking ?  
Thanks for your wisdom !

[Barry]

Do the replacement discs have holes ?   If not that might be the reason why water is not being displaced across the whole width of the pad.

You could drill holes but even drilled discs are relatively poor when wet.  I think only cast iron discs are good.

[georgesgiralt]

Yes they are drilled and look like the OEM discs on that respect.

[mrclubike]

Do you have 1 rotor or 2 rotors
36 or 38 mm caliper pistons
A 16 mm MC is way to big for a single rotor system

The pads should seat  in after a while

I am running 12mm MC with single 38mm Brembo caliper

[georgesgiralt]

Dual brakes.
I bet it is the 36 mm Brembo as they are the exact ATE replacement.
The pads have around 35 000 km ...
I agree, 16 mm is *also* too big for dual rotor brakes...

[Bob_Roller]

If the pads are only contacting a portion of the rotor, the rotors may not be true, or there is a problem with the pads .

I've got steel rotors on my '81 R65 and EBC organic pads (FA57)and the wet braking is great .

[Tony Smith]

George

I'd be inclined to do the following:-

1/ spread Talcum powder all over both sides of the disk and then use the brakes whilst travellign at a moderate speed and then go back home asap and look very carefully at what the talcum powder tells you about the contact (yes I know you have sort of done this with water but bear with me, water is insidious stuff, heat makes it go away and surface tension makes it go places which means that the "watermarks" may not be truly accurate as far as your "contact strip" goes).

2/ fit new pads - don't flinch at this because either way this goes you will be fitting new pads, and then repeat the talcum powder application - do you now have a "normal" contract strip or is it still much less than the full width of the pads?


If you do now have a normal contact, your problem is solved.


If you do not, dismount your disks and take them somewhere to be properly ground flat - they will be fine after that.

It is a bit of a worry not knowning what sort of steel the discs were made from

for example - sintered metal pads work brilliantly on cast iron, may work OK on bright mild steel, but will tear most low grade stainless steels to pieces (counterintuitively low grade stainless is softer than bright mild).
 
Organic pads work well on steel, less well on cast iron.

Asbestos pads, if your country still allows their use, work well on just about anything, but apparently give you cancer.



PS the talcum powder test is well know to those unfortunate to have ATE "swinging" calipers on older/larger airheads.

[montmil]

... PS the talcum powder test is well know to those unfortunate to have ATE "swinging" calipers on older/larger airheads.

I have dual 40mm ATE "swingers"on the R100S. That are not difficult to adjust... once you learn the proper drill. Another way to check pad-to-disc contact is to mark the discs with a dark-color permanent marker.

[Tony Smith]

I have dual 40mm ATE "swingers"on the R100S. That are not difficult to adjust... once you learn the proper drill. Another way to check pad-to-disc contact is to mark the discs with a dark-color permanent marker.

Monte I never suggested that they were difficult.
I will state categorically that they are just about the worst disc brakes ever fitted to a  motorcycle, and frankly the sheer volume of words written about them, in the fettling, diagnosing and improving arenas is proof of that.

Even BMW realized they had made an error when they discovered that the single ATE they "blessed" the R75 with in fact did not work as well as the drum brake it replaced - BMW quickly fitted two discs. And for all the fiddling about with piston bore size, mastercylinder bore etc. If you swap between a ATE brakes R100 and a brembo braked on, the difference is kind of obvious

[georgesgiralt]

Yes, but ATE was a German brand, Brembo nor Grimeca where not.... This is IMHO  90% of the reason this choice was made.
I'll play with chalk, talcum and my marker to see what's going on... Thanks.

[nhmaf]

As a swinging ATE owner also - I can say that even when they are adjusted OK, they don't work nearly as well as the Brembos - I only have 1 ATE on my1977  R100/7 and keep an eye open for a post-1980 front end with dual Brembos... someday.

[Tony Smith]

As a swinging ATE owner also - I can say that even when they are adjusted OK, they don't work nearly as well as the Brembos - I only have 1 ATE on my1977  R100/7 and keep an eye open for a post-1980 front end with dual Brembos... someday.

In another forum I inhabit someone has made an adapter kit to allow 'radial" Brembos to be mounted on ATE swinging caliper forks. Not a bad idea as the early model forks are in my less than humble opinion superior to anything up to 1985, its just those blasted ATE brakes that are a bit of a worry - personally I have done what everyone else does - fettle them to get the best possible braking (which truthfully isn't bad, just not as good as it could be) and grizzled a lot. like you i have half had my eye out for a Brembo front end - just never quite got around to it and now the R100RS is mroe attractive 100% original.