Grimeca Disc brake Adaptor
I have a Grimeca Disc brake caliper that I am attaching to a Marzocchi Bomber DJ3 fork. The adaptor bolts straight down into the fork and the holes are 74mm center to center on the fork. The Grimeca brake caliper bolts on to the adaptor sideways and they are about 48 or 49mm center to center. The rotor is 185mm. Can anyone tell me how to measure for the adaptor? I an not sure what to buy.
I have a similar setup on my bike, in my case the old M755 XT calipers on a Manitou fork with a 180mm rotor. I use the Hope adaptor linked below. Since your rotor is slightly larger, you'll likely have to put a couple washers between the adaptor and the fork to move the brake caliper outwards a bit.
Hope Mount Adaptor Front IS to Post +20mm | Buy Online | ChainReactionCycles.com
Thanks! How do bike shops measure to figure out what size is needed?
Adapters are sized for a few things: brand, location, mount type, and rotor size. Say...Shimano, rear IS mount, 180mm rotor.
That's really all there is to it. You can often kludge one brand's adapter to the other with the use of spacers.
Your fork is what is known as post mount "PM" with a 74mm spacing (as you found) as developed by Manitou and your brake is what is known as International Standard "IS" with a 51mm spacing.
You need the brand (though some brands are compatible, I guess Grimeca 4 piston caliper is exactly the same as a Shimano XT 4 calipers), type of both mounts and if it's for the front or the rear and diameter of rotor.
Sounds confusing but it ends up in something like "PM to IS - 185F, Shimano"
Other brands like to use designations as in +20mm to indicate how much the adapter puts out the caliper. This is important, the same adapter used in the front, will fit a 20mm smaller diameter rotor in the rear.
Say, the same 180mm rotor adapter on the front will fit a 160mm rotor on the rear.
Post a photo of the brake caliper you have.
Not all "IS" brake calipers are spaced at 160mm, some "IS" brake calipers are spaced at 180mm or 200mm.
A 180mm brake caliper with that Hope adapter that was previously linked will mean that you'll need to use a 200mm rotor on a fork that has 6" post mounts.
Look at these threads to see what I'm talking about.
Magura Marta 2006 IS front adapter
Magura Louise FR Front Brake Path Issues