So I've been having some issues with my brakes ever since I changed the rubber lines 10 months or so back. Everytime time I would bleed then after I'd always get air at the front calipers and nothing was leaking and the truck would stop but not great so I just didn't drive it so much.
A few months back I decided to throw the hydroboost system in that I had kicking around with a new f450 master cylinder in and instant better brake peddle and stopping power, found out my old master was pitted to hell inside and that's probably why I had no luck bleeding the fronts never mind the ton of varnish in it.
So heading to a few weeks back I decided to do some front end work and found my driver side disc heat cracked bad... I don't tow anything so this raised questions. Well I found out today that brake calipers can actually get very sludge up! Now these are the old style with aluminum pistons that were pretty much seized in and where most likely dragging the front brakes causing the over heating of the one disc, I was going to reseal the calipers and used the phenomic(sp) pistons from some unknown condition calipers but scrapped that idea after every pair of calipers I have had extensive scoring on them. So new calipers and a good flush again and I should be good to go.

Moral of all this is change your brake fluid before it even has a chance to get black as 27 year old brake fluid turns into jello!

 

that was much worse than log trucks fluid when i got this truck.wasn't so far gone as that,but she sure was black!

Is brake flushing really necessary? - HowStuffWorks

so now your truck is going to stop like 50x better.good calipers,rotors and the almighty hydroboost upgrade.whole different truck now.

 

I didn't know brake fluid could sludge up like that, when I first got the truck 2 years ago I had to replace the rear wheel cylinders and everything else from the diff leaking and I bled all the nasty looking fluid out but the way the calipers are designed you only flush the top little bit of the caliper and all the old fluid stays in the bottom.

When I changed the rubber lines last year I pulled both calipers off and flipped them upside down to drain it all out and spraid brake cleaner in there to rinse them, clearly that didn't clean them out. At that time there was no cracks in the rotor and it looked alright otherwise I would of changed them.

The brakes were a heck of a lot better after I put the hydroboost in and then resealed it a bit later from a leak, the truck would lock all 4 tires and skid on pavement! and thats with the cracked rotor which I didnt even have a brake shimmy or pulsation. I only found it cause I was doing piviot bushings and radious arm bushings and rebuilding the rad support.

I'm curious how much it brakes better after I get it back together and clean out the RABS valve or replace it if it's rusted to crap.

 

or bypass it.

 

Trust me you don't want those phenolic pistons. The old ones are actually steel with a coating. At least GM had a lot of trouble with there's.

 

The pistons I pulled out of these calipers are anodized aluminum and ford had a service bulletin put out about these ones causing brake fade and boiled brake fluid. Every caliper now a days has the phenolic pistons in them (at least for these trucks) and I haven't heard any issues myself about problems with them on this era of trucks. I know on some gm vehicles they use aluminum calipers with phenolic pistons maybe those are the troubled ones? I know the phenolic pistons don't rust and they are pretty hard but can crack if abused.

 

The ones I changed on my 93 C2500 had phenolic pistons. They were swelled from heat I guess. I got new calipers from NAPA and they had both. I got the steel ones.

 

What I found with the 6 calipers I pulled apart to check out was they all rusted in the same place which score the pistons in the same place. These calipers are not designed well for keeping water out, what I found was the 1/8" or so thick part of the caliper/piston Boer that was on the outside of the piston seal rusted on all of them including the ones which had intact outer seals and this ares would rust and swell up and seize or score the piston badly. That's one of the reasons I didn't rebuild any of the calipers I had cause they all had the same issues.