Caliper repair/replacement question

I have a 2007 Lexus 400h. I’ve replaced the rear brakes once myself under the guidance of my friend’s uncle. That was 4 years and 55k miles ago. I noticed a lot of rust on my rear rotors, and made no mind of it. Neither did Firestone when I got an awesome deal on new tires 4 months ago. Now, I just get back from an oil change, and the mechanic is telling me that my rear brakes aren’t working. He says that it is most likely a caliper issue, that is, it’s not sliding. He wants me to get new rear brake pads and rotors. If he can’t fix the calipers, then he wants to replace those too.

My questions are: if the brakes and rotors are not worn or warped, despite rust, aren’t they still good? I don’t mind replacing, but just curious. Why wouldn’t my calipers be sliding? Wouldn’t that be a master cylinder issue? I have had no warning lights. Is it an easy fix or is it worth it to replace completely? Thanks!

I looked up a FWD 400h; an AWD model might be different, but I doubt it.

The calipers are a single-piston design and thus must slide in their mounting to allow centering and self-adjusting. The slide pins are special bolts that hold the calipers in place yet slide in the caliper mounting bracket. If the caliper can’t slide, it will stop applying pressure to the outboard pad, and the inboard (piston side) pad will wear twice as fast. The problem and its repair have to do with the slide pins and caliper bracket, not the calipers themselves.

If the brakes aren’t applying at all, it’s most likely a faulty caliper with the piston seized in its bore. (It could also be a problem with the master cylinder or a brake hose, so it needs to be tested properly to be sure.) This, however, has nothing to do with the caliper sliding.

If the pads are worn fairly evenly but still have a good amount of lining left, there’s no need to replace them. However, the labor to replace them would be part of the work to fix the problem, so it would be cheaper to replace them now than to do it separately later.

If the rotors have a reasonably good surface, aren’t warped, and are thick enough, there’s no need to replace them. A little surface rust isn’t an issue, but if they are significantly rusted (e.g. have a “pebble grain” surface) then they should be resurfaced (if they’re thick enough to accomodate the amount of material that has to be ground away) or replaced.

You said you replaced rear brakes before (but not fronts? that’s odd) so you should be familiar with how it feels to retract the caliper pistons. First, remove the caliper and check the slide pins. They should be smooth and greased. If they have gunked up and the grease has run dry, this is probably your problem. Clean them up with brake cleaner and some very fine steel wool, then regrease with brake grease.

If they are fine and sliding nicely, then retract the caliper piston with a C-clamp. It usually takes a bit of force but should slide in smoothly. If it feels grimy and it takes excessive force to retract, then THIS is your problem.

With a sticking caliper piston, you have two options. Rebuild or replace. It is fairly easy (and CHEAP) to rebuild a caliper. The basic steps are to blow the piston out of the caliper with compressed air (an air chuck with rubber tip pressed into the brake line hole - put a rag in front of the piston to slow it down!), clean the piston walls and caliper inside with brake cleaner and fine steel wool, and reinstall everything in reverse order with new rubber seals (which you will get with your caliper rebuild kit). The seals are a square section “spring seal” that goes around the piston, and the “dust seal” goes on afterwards.

If that sounds like too much work, just buy a rebuilt caliper.

What Gary and Kazo said.

OTOH, how well do you trust this mechanic? Is he trying to generate revenue or do you have a problem? Have you noticed that the brakes are not as effective as they were after the new brakes? If it were my rig, I would get a 2nd opinion from another shop. This 2nd brake inspection should be relatively cheap or free.

Have you replaced the front brakes in between the rear brakes being replaced? How many times? Rear brakes should out last two to three front brake sets. 55K miles is about the right milage for new brakes if you drive in city traffic. Freeway driving it is a little early. Unless the rotors are warped, severely pitted, or too thin, reuse them. Some shops always relace rotors to " cover their a**".

IME some of the new rotors are made of softer material then the original ones. These new, softer, rotors wear fast and often only last for one brake job. Pay for, and get, the better quality rotors if they really need replacing.

IHTH, 48.

Note that on rear calipers that incorporate parking brake mechanisms, it’s necessary to simutaneously press the piston in AND screw the piston in.

This is correct; however, the RX400H does not have this type of parking brake mechanism.

Thanks for the replies. They are very insightful. My brother-in-law had the car for a month when I was overseas on business. He may have changed the front brakes. However, I’m amazed at how little wear there is on my brakes in general. I’m definitely going to get a second opinion. I may change them anyway as they look pretty rusty. I can’t believe how hard it is go get these rotors off.