Rebuilding the front calipers on my 70! All good and cleaned up, but now I’m having a hell of a time getting lip of the boot that surrounds the piston to properly seat in the groove that’s inside the bore.
The boot goes over the piston just fine, and the piston can be pushed down into the bore…just not together, at once. Can someone please explain the trick to getting it back on. I’m sure it’s easy and I’m just being dense, but help is appreciated. TIA
Regulated low pressure air on a blow gun. . You will have installed the boot fully into the caliper with the piston out. Apply a little brake fluid to the boot edge. Slowly apply flow from a distance from the line inlet while pushing the piston into the boot to make the boot jump onto the piston. Release the air and push the piston in by hand
take out that old o-ring first.
Not everyone can rebuild a caliper. Sometimes it’s best to leave that to the professionals.
I can drop them off this afternoon. Will you be home?
I would probably buy calipers from NAPA. they are around $25 each and come with a guaranty. Hard to beat.
Here’s how I did mine a while back https://forum.classiccougarcommunity.com/t/brake-calipers-replace-vs-rebuild-etc/12224
Now that’s the response I was waiting for. Thanks so much!
While the air pressure thing is interesting, you can do this the other old way…
First, use brake snot/lube. Get a small bottle and it will last you a lifetime, it doesn’t go bad…
Second, as mentioned, put the new 0-ring (Retractor- cuz that is what is duz) seal in place and then seat the dust boot. This can be a little difficult as that slot is gnarly. Use a screwdriver handle or such to kinda roll it around to get good seating.
Third, lube it all up, rubber seal and just a tad around the side of the piston. Get your fingers inside the dust seal and slip the piston in one side. Use your remaining fingers to pull the rubber dust boot up and around the piston. Once on the piston, you can then push the piston into the bore and seat it…dust boot will slip into position around the dip in the piston. You will likely fail several times…! 
A substitute for meatball fingers would be softish plastic sticks or wood tongue style depressors… Butt my fingers are large and I can do it to these front pistons just fine. Smaller pistons require more finesse…enginuity… :)))) Good luck! Steve
Or brand new for $55
https://www.classicindustries.com/product/1970/ford/mustang/parts/2b120m.html
I have found that all the other gear heads on this community are correct with a little fluid and such. I would add that sometimes the rubber has other ideas…. I have found that dental tools have very small tines and sliding them Backwards with slight pressure on the rubber keeps it aligned…
