Disc brakes


Old 06-10-03, 07:22 PM
J A Boggan
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Disc brakes

I am in the process of changing front and rear disc brakes on a 95 buick regal. I ran into a problem with the rear brakes. When I removed the old pads, I put a C-clamp across the piston to press it back in. It would not move, on either rear wheel. I wound up draining all the fluid out and putting it in a vise in the shop. The piston was probably sticking out 3/4" to 1". What I wound up doing was while putting some pressure on it with the C-clamp, I grabbed the piston with a pair of channel-locks and rotated the piston back and forth and finally the piston started to move back in. When it finally did start to move, it wasn't any problem to push back in. Has anyone ever run into this before...could anyone explain just what happened? Thanks in advance.
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Old 06-10-03, 07:48 PM
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There is a special tool to rotate the caliper piston into the bore again. Autozone will rent you the tool for free or various parts store have the tool. It doesn't push in like the fronts!

Get the tool and you'll be good to go.
Old 06-10-03, 08:34 PM
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Location: Kansas City, Missouri.
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Joe is quite right, (again ). J A Boggan, you have stumbled upon a widespread change in brake piston design that thousands upon thousands of do-it-yourselfers will encounter exactly as you have.

The new design pistons have a spiral groove on the outer side of the piston, causing it to rotate slightly as it moves in and out. You can't see this groove unless the piston is extruded from the caliper quite a bit. One tip off to this style of piston is that the piston cup has a (more or less) solid surface. Remember the older style pistons had cups that were hollow, thus forming a true cup.

Although this is a minor design change, it will have widespread consequences for years to come as millions of people learn about it. It's kind cool to think about, huh!
Old 06-11-03, 05:30 PM
J A Boggan
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I'm not trying to be hard headed...I simply don't understand. I've even tried to find a cut-away picture of it...no luck. Are there actual threads in the piston. I guess I need to take one apart so that I can see whats going on. What bothers me, is the fact that you screw it all the way in...and you just "let it go" right? Are the front pads the same way. If I can understand something I feel much better about it.
Old 06-11-03, 07:46 PM
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Location: Arkansas
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The read caliper acts as in a duel manner...1 for normal braking action, 1 for parking brake action. The reason it's threaded is so that as the pads wear down, the parking brake action (theortically LOL!) will stay in adjustment. So when you screw the piston back into the housing, it (piston) is actually moving back onto a threaded bolt..
Because it does duel duty as brake and parking brake, it is definately different than the front calipers. Another thing to watch for is on the driver's side rear caliper, the piston screws in "backwards" compared to the passanger side..Not all cars, but some..
A thing to watch for when doing these rear brakes, is to make sure the slots on the piston face line up properly so that the nub on the inner pad will lay in the slot once the caliper is placed back on. If the nub on the pad doesn't fit into the slot, it usually cause the pad to "**** off" crooked, and wear 1 end of the pad off, with the other remaining almost brand new..
Old 06-12-03, 09:16 AM
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MsArgent is correct.

Coming from a guy that owns two WS6 2nd generation Trans Ams with rear disc, indeed in "theory" the parking brake should stay adjusted and give you a firm pedal, but ummm, we know how thag goes. LOL

Bottom line: You need the special tool to rotate the caliper piston inward.

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