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My SMC started sticking a few days ago so I ordered one, but was worried whether or not I would get it time to make my trip this Thursday up to the BRP for UPs
STOC event.
Along comes Dave Duelin on his white horse and offers to loan me a rebuild kit
AND ride 2 hours to meet me halfway !
Thanks Dave.
So I pulled it off the bike and disassembled it.
During the dis-assembly, it was difficult to remove the piston assembly even using 125 lbs of air pressure to try to push out the piston assy'.
It took a few fairly hard taps to even push the piston assy' downward and then it would stick there.
Eventually , by shoving the piston down and popping it with air multiple times, it came out .
I cleaned out the bore, honed it with 320 grit sandpaper and checked for pits and ridges with a dental pick.
When I put in the new piston set, it would still stick in the bore .
I put the piston in upside down just to see if I could tell where the binding was occurring and found the metal end of the bore was too tight.
I measured it with some calipers and found it was out of round varying from around 13.96 to 14.20 mm. That was about the same as the old piston set.
I chucked the old piston into a drill and lightly held a file against the edge to hopefully make it rounder and a few thousandths smaller .
You can see in the picture that the right side of the piston is shiny where there was a high spot .
So it now freely moves in the bore and I hope it works ( and doesn't leak )for more than the 16K the last one did..
Picture 1 shows the piston seized in the bore.
Pic 2 and 3 shows it stuck lower in the bore after tapping it down a bit .
Pic's 4, 5 show how the piston is supposed to be when properly tensioned .
Pic 6 shows the new piston set still hanging up in the bore .
Pic 7 shows the metal end of the piston after "machining".
Note the shiny right side where the high spot was shaved off .
I don't think this was related to lack of brake bleeding or weather corroding anything.
If there was any type of wear, it would have been too loose rather than too tight.
I think the tolerances between the bore and the piston end were poorly designed or poorly matched .
STOC event.
Along comes Dave Duelin on his white horse and offers to loan me a rebuild kit
AND ride 2 hours to meet me halfway !
Thanks Dave.
So I pulled it off the bike and disassembled it.
During the dis-assembly, it was difficult to remove the piston assembly even using 125 lbs of air pressure to try to push out the piston assy'.
It took a few fairly hard taps to even push the piston assy' downward and then it would stick there.
Eventually , by shoving the piston down and popping it with air multiple times, it came out .
I cleaned out the bore, honed it with 320 grit sandpaper and checked for pits and ridges with a dental pick.
When I put in the new piston set, it would still stick in the bore .
I put the piston in upside down just to see if I could tell where the binding was occurring and found the metal end of the bore was too tight.
I measured it with some calipers and found it was out of round varying from around 13.96 to 14.20 mm. That was about the same as the old piston set.
I chucked the old piston into a drill and lightly held a file against the edge to hopefully make it rounder and a few thousandths smaller .
You can see in the picture that the right side of the piston is shiny where there was a high spot .
So it now freely moves in the bore and I hope it works ( and doesn't leak )for more than the 16K the last one did..
Picture 1 shows the piston seized in the bore.
Pic 2 and 3 shows it stuck lower in the bore after tapping it down a bit .
Pic's 4, 5 show how the piston is supposed to be when properly tensioned .
Pic 6 shows the new piston set still hanging up in the bore .
Pic 7 shows the metal end of the piston after "machining".
Note the shiny right side where the high spot was shaved off .
I don't think this was related to lack of brake bleeding or weather corroding anything.
If there was any type of wear, it would have been too loose rather than too tight.
I think the tolerances between the bore and the piston end were poorly designed or poorly matched .
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