WILLYumD

Started doing my brakes today and I'm stumped as to why the new rotors and pads will not fit.

For the rears, I ordered the Centric 12044085 "Premium Daily Driver" rotor and Akebono ACT325 pads.
The piston was compressed all the way but the lower caliper guide boot(?) still would not slide into place.
It was a few millimeters too much for it.

What are some possible culprits for my issue?

The upper caliper guide pin is not stuck, the surfaces were cleaned as much as I could.

I read a lot of people for many different cars were shipped the wrong part. I've given up and gone back to my dorm for the time being, but I will double check the part numbers on the actual parts themselves tomorrow. (The boxes all check out.)

808mcv20l

I've rebuilt the rear calipers on my mom's 99 Camry LE V6, they are the exact same brakes on the ES300.

I rebuilt the pistons using the centric kit, and recall that the slide pins were stuck when trying to reassemble everything.

My best advice to you is to recheck the slide pins to ensure that they are extended fully, I vaguely recall some kind of sleeve on one side.

Other option, take some sand paper and sand down the pad down a little on both sides until they fit.

I doubt it's the wrong part if the pads fit in the caliper brackets properly. Aftermarket parts sometimes need a little work to "make them fit".

But I've used Akebono pads before and never had a problem with fitment, although ymmv.

WILLYumD

For the slide pin, does the lower "boot" move?
I know the upper pin that is attached to the caliper bracket freely slides so I can take the caliper off. The lower one has a double-sided boot that I thought would move, but my attempts to try and budge it failed.
Not sure how to word it, but I'll try again tomorrow, thanks.

808mcv20l

Does the caliper clear the pads?

The piston should retract nearly flush, if the piston does not retract flush it's not fully retracted.

Look at the sliding bushing below, on my car this was stuck and preventing me from putting the caliper on.

I suspect you have the same issue, took a few light whacks with the hammer to free up.
Make sure you lubricate it as well as the sliding pins, make sure you use silicone grease or brake lube, no petroleum stuff.

WILLYumD

That's the part I was suspecting to be the issue. Thanks!