Bicycle Mechanics - Brake Caliper loose on new fork

I just completed an upgrade from factory aluminum fork to Easton EC90 (This is on a 91' model Trek 2300). Thing is the brake caliper is loose on the new fork. I have tightened it as much as I am willing to and the whole caliper is rattling around (has play up and down). This is a shimano 600 (ultegra-6400) caliper.

Can I add some washers to take up the slack, or is there another way? I read the brake info on Park's website, but I just saw how to correct centering.

Pictures would help.

I'm very familiar with the Treks of that generation having had a 2000 (still great riding bikes, IMHO, and classier than a welded frame). It depends on the caliper, but I would first recommend checking the length of the hex nut. The Trek aluminum forks back then (made by Kinesis, I believe) had a very short spacing between the brake mounting holes, so often the hex nut would bottom out on the end of the caliper's threaded section before it could properly secure the brake on the fork. If the new fork is similar, an easy solution is to get a shorter hex nut. You could get a spacer to place between the caliper and the fork, but why bother? Hope this helps. Luck.

P.S. Please tell me you don't have one of the lime green and yellow ones.

Easton carbon forks have a recessed pocket at the back of the "crown" so they can use a "standard" length recessed hex nut. Most carbon forks require an extra length nut so, if your bike has one of the longer nuts by mistake, it would also bottom out and leave the brake loose.

Easton carbon forks have a recessed pocket at the back of the "crown" so they can use a "standard" length recessed hex nut. Most carbon forks require an extra length nut so, if your bike has one of the longer nuts by mistake, it would also bottom out and leave the brake loose.

I bought a 105 brake caliper a couple years ago that came with (I think) FOUR different length hex nuts.

Now here's the good news. Generally the people who post need a longer hex nut to fit a carbon fork. That leads me to believe that many bike shops will have an excess supply of short ones. If they like you that might even be a "gimmy".

$2 short recessed nut, problem solved.

Yep lime green and yellow. Actually the green wasn't so bad, but the yellow had to go. About a week of wet sanding and panting and now it's silver! I had the factory colors for 6 years and it always drove me nuts.

I had a bunch of washers that fit, so I put them there to take up the slack for now, but I plan on visiting the lbs for a proper length nut.

Thanks everyone!

I bought a 105 brake caliper a couple years ago that came with (I think) FOUR different length hex nuts.
I have Kestrel EMS Pro carbon forks on a couple of bikes and they came with the much longer brake nuts needed to compensate for their wider crown. The directions with these forks were very explicit that you must use the supplied nut.

I guess this was before carbon forks were so common and so variable that the brake manufacturers supplied the variety of nuts to fit all of the different possibilities.