I have the front caliper sitting on my workbench and just wanted to make
sure of the re-assembly procedure.
1- Piston get cleaned with denatured alcohol and dried off...can I use
brake parts cleaner instead. Piston wall looks pretty clean...is there any
need to polish ??? If it was dirty..what does one use to polish?? emery cloth
2- Piston seal is lubed with brake fluid and inserted. Or should it be
inserted dry and then lubed.
3. Piston boot goes into counterbore first and then piston is inserted
and then the boot seal is pressed into the bore.... is this the correct
4. Can I use an approriate size socket to press the piston back into
the bore. What tool should be used.
5. A tech tip suggested introducting air flow into the brake bleeder screw would
make piston insertion easier. Is this a good tip ??
6. Is there a way to test for leakage past piston, just to make sure that seal
was not twisted during piston insertion.
Thanks in advance for your help !!!
Peter (learning auto mechanics one step at a time).
I prefer to insert it dry and then lube the inner surface (surface that
will seal against the piston), but you could do it either way.
I find it easier to install the piston dust seal "onto" the piston
and then press the piston into place. Once you have the
piston close to the bottom of the bore, you can then press
the dust seal into it's bore. There are special tools to
press them into the bore, but you can get away with large
blunt ended blade screwdrivers. The only thing is that it
is extremely easy to poke a hole in the seal, then you are
screwed and need a new one.You can also use brake fluid
on the outside diameter of the dust boot, makes it easier to
install in "it's" bore.
I use a large enough C-clamp and line up the piston, apply a slight
amount of pressure with the clamp and then rock the piston as
you start to apply more pressure.
That doesn't make much sense for insertion, I will use compressed
air to blow the piston out of the bore. Again, some common sense
is required here....you want something to stop the pistons movement
as it comes out of the bore....piece of wood, a couple of rags bunched
up...etc. Just don't get your fingers in there...that would be regrettable.
If you are careful and apply small, smooth pressure to the piston
while rocking the piston (make sure you lubed the piston surface
with brake fluid), you should have no problems. I've never personally
rolled a seal over yet.
***Agree with Ian. But if you DO need to polish, dont use emery cloth. Use
****Nope. I have seen people put vacuum on the bleeder to help suck the
piston in, but have not needed it myself.
And they taught us---all too many years ago---never to use air pressure to
push the piston out. It works, but there is a safety hazard involved with
compressed air in this way. We used a liquid pump with brake fluid to pump
out the piston.
Thanks for the technical advice Ian .... everything went together
nice and smooth...operates flawlessly.
Thanks again for taking the time to explain the procedure. It's good to learn
repair things correctly the first time instead of through trial and error.
is a great help in learning the basics and moving on to new repair challenges !!
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