RustyShackle

I'm thinking of doing my rear brake pads and rotors on my 2005 EL and wondering if there is a procedure to correctly align the rear disc piston (+) with the dimple on the inboard brake pad.

I've been watching all kinds of videos on replacing the rear disc brakes but everyone seems to ignore the significance of aligning the piston with the dimple on the inboard pad.

Also, is it necessary to do a brake fluid flush after retracting the piston to accommodate the thickness of the new pads?

Can I simply open the bleeder nipple - attach a bleed hose filled and submersed in new brake fluid - then retract the piston to avoid air being introduced?

I can't find a definitive answer on this - some claim it is absolutely necessary and others claim to have never had a problem.

ezone

You need to use a tool to screw the piston into the body of the caliper (clockwise).
Pay careful attention to align the slots in the piston to the correct orientation to go over the pin on the back of the pad.

A parts store "brake cube" may be sufficient if the piston isn't really stuck,



or a larger specialized setup may be available for rent at the parts store, this allows not only rotating the piston but also applying pressure to push it in at the same time







I usually give a small squirt of spray silicone lube around the piston boot so the boot can slide instead of trying to twist itself and tear as you attempt to spin the piston in.

I personally may go about fluid either way, keep in mind having the bleeder open just allows more chances for unwanted air to enter the caliper.... or with bleeder closed and then recommend a full fluid flush (3 year intervals on brake fluid anyway).. and if it's old/rusty enough you might just snap the bleeder valve right off.

RustyShackle

OK I will definitely just leave the bleeder closed and do a flush since it probably needs one anyways. I'm not overly worried about rust and seizing since the vehicle is only exposed to salty roads a few weeks of the year.


Any advice on aligning the piston (+) with the dimple on the inboard pad?

I hear you will get uneven pad wear and braking force if that dimple is not perfectly lined up with the rear piston?

ezone

Correct. If you don't get the slot over the pin, you'll end up with problems that won't be real evident until later on.
(I can usually see this misalignment using a mirror and flashlight when I'm doing a basic checkover, I love to point out this particular error on cars that had brake jobs elsewhere.)


Just screw the piston all the way in....At the end, it won't go any deeper but you will be able to keep rotating it until it is in the desired position.

I center a slot of the piston with the inspection opening in the top of the caliper.....then install, and after pumping the pedal up double check it really seated correctly before installing the wheels.


HTH

RustyShackle

This may be a stupid or irrelevant question but I have to ask as it may help my understanding -

Is there any particular reason that the rear brake pistons are slotted with a guide dimple on the inboard pad while the front pistons are not?

ezone

Because the rears contain the parking brake mechanism....


The pin/slot prevents the caliper piston from rotating when you pull the handbrake.

When the manual lever on the caliper moves, it rotates a big threaded screw inside (the same reason you have to screw the piston inward).