rehabilitating rusty brake discs?

Difference between a Volvo and a porcupine?

The porcupine has the pricks on the outside  :LOL:

After refurbing the rotor hubs, nice chemical clean and re-anodised I took the rotors in to get skimmed as they had quite deep corrosion where the pads had been sitting (for a long long time). The workshop guys checked them out and informed me that 1mm would need to be taken off each rotor - would take them below minimum rated thickness.

So, rusty rotors sitting in 1 box, brand new looking hubs sitting in another, and EBC floates sitting on the bike.
 
I stopped about 8ft behind some kind of behemoth combine harvester in Kerry Ireland. He was signalling to turn right. A car pulled up behind me. Time and space froze as the aggro crunched into gear...In the time I was thinking " oh shute" the car driver read to a T  what was going on and hit his horn.

The combine had gone into reverse to re-align with the corner and shot back a foot and was on a collision course with my old Beemer...I do believe there would not have been much more than an oily smudge if it had hit me.

Now that was a good car driver.

joe

ps it was an Alfa Romeo  ;)
 
sfcpiet said:
I'm with Keith, use 'em... if they turn out to shudder once they've cleaned themselves up, you can have them skimmed then.  Absolutely no point in unnecessary metal removing.  They'll get too thin soon enough.

Haven't had much luck with skimmed discs myself.  

Beemer discs wear grooves because of crap bore spacing, no hole overlap, so there's always a "ring" that gets less/more pad pressure resulting in uneven disc wear.  Then there's the issue of cracking from the holes to the rivet bores... crap material as well.

Used to swear by the cast iron discs compared to early jap stainless in terms of outright performance, but wet-weather braking was never really what I expected/wanted.  The stainless Suzuki discs I now use, in conjunction with ceramic/kevlar race pads, are far better than I could ever imagine, wet or dry!

piet
Click to expand...

Piet,

"langsames ?berschleifen" does the trick, and you can check progress easily while the metal is skimmed down. Dunno what that's in English, but a friend at a large company with CNC machinery did it for me.

HTH
Gerald
 
Try a 3M roloc disc-great for steel/aluminum mating surface cleaning. Roloc discs come in various styles and grits-I would recommend a softer blue or gray to clean the rotor and give the mating surface a "tooth" for the new pads to bed into.

 
Gerald,

As a trained engineer, I'm fully aware how brake discs can/should be skimmed. :D  But, as Keith has already mentioned, due to metalurgical changes this isn't always successfull and trued discs can in some cases quickly warp again.

piet
 
Gerald said:
"langsames ?berschleifen" does the trick, and you can check progress easily while the metal is skimmed down.
Gerald
Click to expand...

I put it into Google Translate and it came up with 'slowly blending'.


sfcpiet said:
Gerald,

As a trained engineer, I'm fully aware how brake discs can/should be skimmed. :D  But, as Keith has already mentioned, due to metalurgical changes this isn't always successfull and trued discs can in some cases quickly warp again.

piet
Click to expand...

As a trained clanky fitter, I believe you should also ask yourself how the discs got warped in the first place!!!!!!!
 
SimonR501 said:
I put it into Google Translate and it came up with 'slowly blending'.


As a trained clanky fitter, I believe you should also ask yourself how the discs got warped in the first place!!!!!!!
Click to expand...

It's actually "gentle grinding" that's meant, Simon.

Uncontrolled heat does strange things to metals, and does it over and over again sometimes.  If internal stresses are still present, truing a brake disc can become very temporary.

Often worth a try to true a warped disc, sometimes easier to chuck it straight in the scrap bin.

piet
 
The bloke who did my wonky disks uses a process he calls "feather freeze grinding". It's a wet grinding process using some kind of chilled liquid (water/glycol?) as a cooling medium. He said it keeps the disks at a constant 0?C during the process. I think the "feather" bit refers to very light grinding passes, only taking off a gnat's whisker at a time. From the spiral cross-hatch pattern on the finished disks, I'm guessing he does it on some kind of rotary table or lathe.
 
Cam described the process that was used when my disk was skimmed, but it was done without the chilling.
Disk had the cross-hatch pattern as well. Perhaps I was just lucky......
 
I currently have my front brakes disassembled and had the same questions about cleaning up the front discs.  I did a bit
of searching on the internet and came upon this site.  I know it is in regards to automobiles, but motorcycles are given some
thought.

http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths

It suggests one way to clean up cast iron discs is with Garnet paper.  Note it warns to stay away with any sandpaper
or emery cloth containing aluminum oxides for abrasives as they will permeate the cast iron.  I have also read elsewhere
to "lightly sand" discs when renewing just pads to break the glaze that can accumulate on used discs.

I did use Garnet paper on my discs with a sanding block to keep the sanding surface flat.  After a few minutes of light
sanding the discs looked considerably improved.

I have a question about the Shnorr washers....I have looked in all the local hardware stores and I have not been able to
find new ones.  I still have the old washers (a bit rusty after 30 years, but all in still in one piece).  Is it O.K. to reuse
them? Should I try to source new ones?  Or has anyone just substituted split-ring lock washers? 

Thanks!

 
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