Help me understand my brake problem

1989 Saab 900S. Right rear brake caliper was binding earlier this year, so I rebuilt it: seals, pins, bushings. Piston and bore looked OK, at least for a 30-year-old caliper. Handbrake adjuster is not stripped and adjusted normally. Haven't driven the car much, but a recent drive showed that it was still binding. I pulled it off this morning, cleaned the exterior, knocked loose rust out of the pad slide areas, chucked the pins in a drill and cleaned them up with a Scotchbrite pad. Put it back together and test drove it: it's still binding (as evidenced by the fact that it was notably warmer than the other side). Pulled the wheel again and - out of frustration, mostly - hit it with a hammer. Lo and behold, it freed up. I applied pedal pressure, and it was bound up again. A few shots with the hammer and it was free.

Obviously, something's binding. I greased the pad ends, but kept the pins dry - should I grease them with caliper grease? If it's not that, what else could be sticking? I don't know how it could be the piston, since it was just rebuilt and seemed fine when I reassembled it. I considered the soft line failing internally, but that's only a couple years old (I did them all when I got the car) and brake fluid seems to flow freely when I open the bleeder. Any ideas?

Could it be your rubber line collapsing?

EDIT - see that's newer.  Crud?

In reply to Stampie :

It's pretty clean at this point. Not saying it's impossible, but if it's causing it, it's hiding itself well.

Careful inspection for ridges anywhere? Something that'll give that ratchet effect without grime?

Percussive investigation? I just wanted to say that phrase, but what I mean is can you get it stuck and be scientific with hammer-taps to get some notion of where and what direction you need to move things to unstick it? If so, you might get some good info about where the bind is. Maybe?

I have it in my head that the pins should be greased, but this feels like one of those things that might not be a blanket statement across applications? It would mean cleanup, but is it worth greasing them just to see if it helps, even if in this application you'd need to clean it away afterward? I guess if that helped but wasn't supposed to be there, then doing something to smooth the bores might be the other half now that you've shined up the pins? Are there replaceable bushings (IIRC BMW E30s have an aftermarket bushing upgrade; again, case by case sort of thing... Looking up one of the options, it refers to replacement of rubber bushings... Rubber!? That makes me wonder whether you've got something so shot it's just allowing excessive movement and the caliper "cocking" and sticking in place.)

Sorry, that was a ton of verbiage with little of concrete value, but maybe a couple of loose threads to tug on?

Bentley says to grease the pins.

Did you pull the piston?  Happened on my R-90.  When the brake fluid is black, that's moisture (condensation?) mixed in, water rusts.  I bought  the same car new  in 1987, they advised flushing the entire system every two years.

My newish CRV told me to do the same, the stealership says the ABS fluid doesn't get moved around unless you use the ABS, now the stuff is just sitting and rotting its surroundings.  Pull the piston.

The piston was out when I rebuilt it. Fluid was changed when I got the car a few years ago, and it's clean and clear. No ABS on this car. The pins ride in rubber bushings, which I replaced when I rebuilt the caliper. Basically, everything except the caliper body and the piston was replaced, and the caliper was fully disassembled. I'm going to pull the pins and grease them (I have caliper grease, but it seems too thick and sticky for this application - use it anyway, or try something else?) and see what happens.

I'd use some silglyde on those pins and see if it helps

My Ford van was doing this; it was the caliper the bore was shot on the piston would stick.

procainestart said:

Bentley says to grease the pins.

Definitive!

I don't see thick and sticky being a problem here. It's a small amount of motion under a lot of pressure. I think this still falls into the category of what that stuff is for, unless there's some sort of compatibility issue with the rubber bushings. Certainly I get twitchier about a possibly-not-thick-enough grease moving around and making it onto a friction surface.

Sil-glyde on caliper pins

Do the pads actually move freely?

Pete. (l33t FS) said:

Do the pads actually move freely?

That is a really good point. I've had to dress down the overall backing plate length on a lot of aftermarket pads so they would slide properly in the bracket.

Finally had a chance to dig back into this. The pads do move freely. I got a tube of Silglyde and applied it to the pins (I did both sides, as it seemed like the right thing to do). They definitely moved more freely in the bushings with the grease, so I was hopeful. Unfortunately, a quick test drive proved that - once again - my hope was misplaced. Still sticking, even though it seemed to roll fairly freely when I declutched on a long downhill stretch. I'm at a bit of a loss. I guess I'm going to have to pull the caliper off again and get the piston out to see what's going on. And I'm going to have to put new pads in, because the pressure and heat build-up has taken these right down.

Ignoring future canoe above, I suggest you get in the car and give the pedal a good hard push and release, then crack the bleeder and see if fluid squirts out or just dribbles out. If it squirts, your new-ish rubber hose is under suspicion.