Front calipers centerd over disc

mauricejota7604

mauricejota7604

Hero member
Location
Victoria Australia
Hi I am in the process of fiiting up the front calipers on my 3C and finding the calpiers are sitting closer to the outer edge of the discs the spacers in the wheels all seem OK but is there an offset on the disc faces themselves the difference would be nearly 2mm, can someone tell me if I am missing something, I used to have an old SS Ducati that required shims between the fork leg and the caliper to center the calipers but this situation is the opposite any advice welcome.
thanks,
M.
 
Not an answer for you M, but made me wonder how important having the disc centered to the caliper is. If the pistons on both sides of the caliper are completely free in their action would they not both stop at the rotor when the system is being bled, ie the closest pad will hit the rotor 1st and stop on contact then the second pad will make contact with further pumping and also stop. That would then be their final positions when the bleed nipple is tightened and both should work equally when the brake lever is applied.

Not talking about huge asymmetry, but a couple of mmm maybe.

Or do I have it completely wrong ??

Awaiting the flames  :)
 
Thanks Davo yes I would assume it doesnt matter if the disc isn't perfectly centre but the outer face of the disc is nearly touching the inside of the caliper, but the plot thickens I have taken one of the discs off the carrier and found that one of the inner faces of the disc is slightly recessed hard to measure but would be about .8mm if I spin the disc over so the recess is against the carrier the disc will be more centred, has anyone else experienced this before.
Thanks,
M
 
Brembo does sell .5 mm caliper shims so obviously this is not a unique problem. I have also seen other references on this forum to discs being mounted backwards. OK, so how do you know what is the right way to mount a Brembo disc when you take it out of the box of rusty bits?

Ken
 
mcnicol said:
Brembo does sell .5 mm caliper shims so obviously this is not a unique problem. I have also seen other references on this forum to discs being mounted backwards. OK, so how do you know what is the right way to mount a Brembo disc when you take it out of the box of rusty bits?

Ken
Click to expand...

Surely you would have marked the faces of the rotor with felt pen indicating which side was which before you dismounted it from the carrier (says he who hasn't)
 
mcnicol said:
Brembo does sell .5 mm caliper shims so obviously this is not a unique problem. I have also seen other references on this forum to discs being mounted backwards.   OK, so how do you know what is the right way to mount a Brembo disc when you take it out of the box of rusty bits?

Ken
Click to expand...

Easy, Ken.

The stock discs are completely flat on their mounting side and have a little groove machined on the outside, a bit "outside" of the threaded mounting bores.

Mounting them "backwards" does not alter the spacing...

piet

Probably get another clever-bugger elephant stamp from Steve for that... :P
 
elephant_stamp.gif


Cheers
Steve B
 
Hi well believe it or not the discs I have are not completely flat there is a mounting face that is recessed out .5mm of the braking surface appears very original and yes there is a groove machined on the opposite face no idea why that is there??
But if you mount the disc with the groove to the inside it will fit very differently to the opposite way!
It is hard to tell which way discs go from a box of rusty bits.
M.
 
Maurice

The recessed surface you are reporting may just be due to wear. My Brembo discs also look like you report, with the friction surface ~.5mm below the more central area where the bolt holes are. Cast iron is relatively soft, when you haul on the brakes every 10-15 seconds, hour after hour, to slow from 150kph down to 80 kph in endurance races, that cast iron is going to wear away. Ask any car mechanic, they regularly see car discs that wear away so much that they fall apart into a hub and external remnant!
Or, somebody may have resurfaced your discs in the past. The cast iron discs aren't as prone to parallel circumferential grooves as stainless steel ones, but it's hard to pass up on the advice ""Ya needta get those discs resurfaced, ya'll stoppalot bedder" from your mates at the pub.

Ken
 
I was referring to new, unused discs!

Most discs that have seen any amount of use over the past 30-odd years will show some signs of wear.  As long as the caliper pistons have always been able to move freely and independantly, the wear will be as much as equal on both sides of the disc.  If at one stage one of the caliper pistons was siezed in its' bore, the other piston would have done the majority of the stopping work and one would find unequal wear at the disc.

The original Brembo drilling patern usually lets the discs wear smoothly, with no definite ridges/grooves showing.  Drilling patterns that don't have bores overlapping enough will result in grooved discs.

piet
 
Hate to harp on but this isn't wear it is a machined surface I have a couple of spare discs checked them and the same anyway blah blah, here's another question how many people have the little washer that "according to the drawings" sits on the axle between the speedo drive and the fork leg, that kicks the RHS caliper out more as well.
M
 
Maurice

I am missing that little spacer/washer (like most people), I keep meaning to see if Wolfgang can supply one. But I always fit a 2mm feeler inside the fork when I refit the front wheel ( ::) no I don't but I do check for a space and pump the fork a few times before tightening the axle clamps).
But my Brembo discs are definitely worn. I have a very small "lip", probably around 1mm high if I clean off the corrosion, right at the outside periphery on both faces of both discs, where the pads have not been bearing on the friction surface so have not worn the disc down. And I was talking about this with some local Italian bike riders and we all noticed the same thing had happened on Brembos with higher mileage bikes.

Ken
 
Hi M,
do you fit brand new calipers by any chance?
A while ago, I encountered the same problem fitting "Marzochi"-type (smooth mounting holes, only 1 bleeding nipple) calipers on a Ceriani fork. Closer inspection turned out, the casting paterns and machining is slightly different on both types. Means, the side that goes on the mounting lug on the sliders was not machined at all.
Solved the problem by milling off a bit to get a proper surface for a spacer that brought the caliper right in the middle of the disc. Secured them in place with some hi-temp epoxy and after a blast of dull black paint it looks like cast on.

Florian
 
I've never seen one of those washers fitted to any bike I've had Maurice. Regards Pat.

p.s. I've just totalled up what I've spent so far collecting bits for my incomplete 75 3C and it sure is a very expensive exercise even buying used parts wherever possible.
Still a fair way to go yet too.  :o
 
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