How to test calipers?

[TubeTruck]

I'm rebuilding the 8 lug 10 bolt I got and looking to save a little cash. The wife will be happier and I will be able to get more parts

I pulled the hubs apart and it looks like brakes were new when it was removed. The bearings are shot but the pads are still thick, the rotor is rusty but smooth and I have access to a lathe (also, what's the min/max thickness?). My curiosity lies with the calipers. They look decent but rusty and the piston is all the way in, probably because of the new pads. The hoses were left on the calipers and it doesn't look like they were contaminated, I get brake fluid when I turn the caliper upside down.

Is there a way to test them off the truck to see if they move out? If I can get them to move in and out freely I'm just going to blast them and paint them and put them back on.

 

[1987 GMC Jimmy]

Just surface rust on the caliper? Based on your appraisal of the situation, I’d be pretty optimistic about the caliper pistons if the seal is good. JMO, I think calipers are hardier than people who indiscriminately replace them would think, and I think hoses are oft overlooked as a failure component or even a maintenance item. Those hoses may look good on the outside, but they could be wrecked on the inside. I’d always replace them before calipers. You’ll definitely need to flush everything out. Rotor discard thickness is <0.966”. Besides hooking them up to a working brake circuit and pumping them up, I don’t know of a bench test procedure.

 

[Keith Seymore]

Yes. You can apply some compressed air at the inlet and it should blow the pistons out.

You will want a block of wood in there so the piston does not come all the way out, and keep your hand and feet clear.

K