Brake problem?

In this post you will find how to do a sensitive test that I use for brake drag. The ideal result from that test is for all four rotors to be stone cold to the touch.

Key to the test is coming to a stop with absolutely no use of the brakes (other than stabbing them right at 0 mph to keep the car stopped). Even a little braking to bring the car to a stop will make a difference you can feel, reducing the usefulness of the test.

 

Periodic brake service done?

Toyota USA's vague, but a close look at the schedule, you'll see the "visual" brake inspection that's noted every 5k (or 6 mo) is replaced by a more serious sounding (but vague) mention of checking rotors, etcetera, at 30k mile intervals (or tri-yearly).

A 2010 with 226k miles and no oil consumption, you must be doing something right. EGR ever cleaned? See you were asking about the latter, back a few years.

 

Efficency drop's more likely due to dragging brake.

With 226k it's somewhat amazing the engine's still running. No coolant loss, cold-start shaking? C'mon, I don't want to be eating crow for lunch.

 

When disc brakes drag, the cause is as likely to be some little thing, or combination of little things, as it is to be some big thing. So it's worthwhile to check (and fix, as needed) all the little things, before jumping into some ambitious replacement hoping that will fix the problem.

The ears of the brake pads slide in notches of the caliper mounting bracket, and those notches have shiny, springy clips fitted into them (Toyota calls the set of those clips the "fitting kit"). In fact new ones from Toyota aren't shiny, because they have a factory-applied Teflon-like dry lube coating. (Grease there would just collect road dust and be worse.) Eventually, the dry lube coating wears off and the pads don't slide as easily, and not long after that, the clips start to show rust, and the pads really don't slide as easily.

When I've done routine inspections of Prius brakes, my most common findings are (a) no issues, or (b) need a fitting kit. It's rare as heck for me to find any other problem (other than pads worn to min thickness and time to replace them after a good long life).

Another thing that can happen is the mounting-bracket notches (where the fitting-kit clips go) can develop some rust, and that makes them effectively narrower. It's like they are squeezing the fitting-kit clips down onto the pad ears, and then the pads won't slide easily even with a brand-new fitting kit. That can be fixed by taking a file to the bracket notches.

It's worth making sure the slide pins can be pushed and pulled smoothly in the bracket. It's normal for your first push/pull to feel as if they are peanut-buttered inside instead of greased, but then the grease remembers it's grease and they move smoothly. If they do that, and you see no nicks or tears in a careful inspection of their rubber boots, I'd see no need to harass them further. If they have any rubber boot damage, or do not move smoothly after the first push/pull, then they can be taken out and cleaned and inspected and regreased with the proper glycol-and-lithium-soap red grease.

Also a careful inspection of the rubber boot around the caliper piston is in order. If it has any damage, a caliper rebuild is indicated.

All of those inspections can be done without opening the hydraulic system and therefore with no need for bleeding. (If you end up rebuilding or replacing a caliper, naturally you'll have to bleed after that.)

It is also worth testing that the caliper piston returns by an appropriate amount after being applied. That test can be done with a block about the thickness of the rotor/pads and a dial indicator (cheap at places like Harbor Freight), as described further in this post.



On the bench with the caliper removed, that test can be done with gentle puffs of compressed air. It may also be testable on the car without removing the caliper (so, without any need for bleeding later), if you've got a buddy on the brake pedal, but only if the buddy applies the brakes extremely gently. You only want to see the piston extend and just touch the block, then watch the dial indicator for how far it returns. But the brake system can develop such high pressures (without your buddy even pressing the pedal very hard) that the dial indicator reading will overstate the piston return, because of your block compressing and caliper stretching.

If the piston does not have a good return, caliper rebuilding is indicated.

I would normally prefer to rebuild an original Toyota caliper, using the Toyota rubber kit, over throwing on some aftermarket reman. At the aftermarket reman shops, generally, even when they start with an original Toyota core in good condition, it isn't, after they're done sandblasting it half to Hades and spraying it with their rust-in-weeks shiny coating. Now, a Toyota reman—look for the caliper part number with -84 on the end—I would use any day, when possible. Those are sometimes available and sometimes not.

There can be a reason to bleed the brakes even if you do not rebuild or replace a caliper. Prius brake systems can slowly accumulate nitrogen bubbles over time, even if the system has never been opened and no air ever let in. If you slow the car gently in a quiet area and you hear a 'whoosh' sound just as the regen braking to friction braking change occurs, or you hear a honk/bark/quack noise when releasing the pedal, you can go through the long-form bleed routine to get those bubbles out.

 

Eric O (South Main Auto YouTube) likes to clean up those notches, then butter them with anti-seize.

 

IMHO; if your not experienced enough in doing brakes and need to consult YouTube to do the job - you probably shouldn't do it. Take it to a 'Professional mechanic', that knows what they are looking for and can perform the task correctly.
Chapman's test is a 'down-n-dirty' and if your not experienced enough to interpretate the results. What's 'normal' what's not - no offense Chapman..... Heat is a by-product of drag and there's more weight on that side of the car, so being a little bit warmer on the driver's side isn't abnormal, since we don't know how big you are and actual measured temperature differential. FWIW; the drivers side front pads always wears down faster than the rest - in a fully normally operating brake system.

Hope this helps.....