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Replacing Brake pads

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J

jackathy

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I'm in the middle of replacing the disc brake pads on the front of a mark II Sprite. The old pads are out and the pistons are immoveable. How can I push them back so I can fit the new pads in?
 
There are a couple doffrent ways of compressing the pistons, but first you have to come to grips with the fact that if the pistons won't move fairly easily they may be siezed, in which case you may need to do a bit more than just break them loose and replace the pads because thay'll probably not function satisfactorily being partially gummed up - Brakes are something that have to be at the top of their form.

That said, try this:
open the bleed nipple on the caliper - If you want to do this neatly push a length of winshield washer tubing onto the nipple and place the other end in a small jar with enough fresh brake fluid in it to cover the end of the hose (This will not only catch the expelled fluid, but prevent air from invading the system.
Put the old pads back into place temporarily and
with a small piece of hardwood or a flat piece of barstock (steel) gently jack against the friction pad side if the brake pad - Don't use a lot of force - If the piston is going to move at all it will do so with medium force.

If this doesn;t work try plan B: Place a piece of sheet plastic over the mouth of the master cylinder reservoir and screw the cap on ( To prevent wholesale fluid loss and mess)Remove the flexible brake hose from the caliper, undo and remove the two large caliper retaining bolts from the backing plate and remove the caliper. Once off the car open the bleeder screw and try using a small to medium size C-clamp to compress the piston - place the screw end of the clamp against the back of the caliper in the hooked frame end agaist the inside of the piston - A word of caution - if the piston doesn't move with moderate attempts, don't force it - you could punch a hole in the face piston. If they still fail to move try

Plan C: Go to Advance Auto. Pep Boys or someone similar and obtain replacement calipers - They're relatively inexpensive and will save you time and aggevation and give you peace of mind. Also, while you're this far you may consider replacing the flexible brake hoses. Also determine that the rotors are serviceable as they are and don't need replacement or turning.- Cheap insurance.

When you've arrived at the point where you have working calipers reinstall them, add pads, spring clips, anti-squeal shims and cotterpins, bleed system and road test.

As I said before, if the pistons are siezed it's better to go further than breaking them loose and compressing them, even if you choose just to dissassemble them and put a rebuild kit in.

Best of luck -

Bob M.
 
Thanks for the detailed reply. The piston moved a little after I opened the bleed nipple and before I posted, but I didn't apply a great deal of force. Let me go and replace the old pads and try moving the piston. Thanks again!
 
Back in business and stopping without metal scraping. "B" worked for the outside piston and the inner piston I was able to press back in applying pressure between the pad and the metal plate that is next to it. There was no pad left on the old pads! Thanks again.
 
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