Replacing Trek front suspension fork I have a Trek 26" Y-frame with beat-up, hardly functioning, yellow generic front fork. I'd like to replace the fork with a Rockshox Yellow Quadra or a Judy. Will they work on my bike? Thx
In short yes.  I had a Judy on a 1997 Trek Y Five-o many years back.  80mm version if I remember correct.  That frame and fork used a 1 1/8 headset steerer which I assume your frame will also have.

Just make sure the steerer tube on the fork is compatible and aim for form travel between 80-100mm

Specs on the bike I had are here:

http://www.bikepedia.com/QuickBike/BikeSpecs.aspx?year=1997&amp;brand=Trek&amp;model=Y+Five-0

I did not have the Manitou fork as indicated above I used a Judy