Front brake disks - should they get hot?

As said in your other thread, no.

 

When I switch from summer wheels to winter and vice versa I lubricate the brakes somewhat, they tend to freeze up, sounds like yours are frozen, as the brake shoes don't really stop the car unless it's a panic stop, this is a problem, another dealer may have the same opinion I do.

The rear drum brakes are adjustable, always worth while to jack up a rear wheel and check them for tightness, the gen 3 went to 4 wheel disks.

On my gen3 I lubricate both front and rear brake assemblies.

 

What is your MPG? I suspect your brakes are dragging as they should not be generating steam after a few miles.

If the dealer can't fix them then I suggest an independent brake shop.

 

That is what a Ford mechanic told me years ago too -- 6 TIMES -- before the brakes started smoking, as I mentioned in your previous thread. After that, I escalated and found a manager who knew what the real problem was. Yes, there was a very real misadjustment in the hydraulic system causing the pads to drag, and it worsened at high ambient temperature until the car couldn't maintain highway speed without downshifting.

A later car had this problem repeatedly with the rear brakes. Non-OEM calipers had a corrosion problem, causing pads to drag.

If this dealership can't even acknowledge the problem, then find another mechanic.

 

What's your mileage?
If you lift one of the front corners of your car, does your wheel spin freely?

What prompted you to touch your rotor after driving the car for 5 miles?

You may want to stick with the dealer.
Usually?
My problem with those guys is that they WANT to work on a car that doesn't need it....NOT that they won't work on a car that does need it.

Food for thought.

 

This is a continuation of his earlier thread: Fuel consumption increase after service and new brakes.

 

Oh OK.
Got it.

I see that the Dealers in other countries need to make house and boat payments too.

Normally when I see a car that needs brake service @ 70K miles it either means that the car was abused....the dealer's customer is BEING abused, or there is some environmental factor (driver delivers the morning paper) that's leading to premature repairs.

You're not the original owner, so it could be a combination of the three.
If your fuel efficiency decreased by 15MPG after a brake job, then I strongly "suspect" that the brake job was botched whether the miles in question are statute, Imperial, nautical, interstellar, or whatever.

First. Get the brakes fixed! ESPECIALLY if you're transporting children in the car.
If they're rubbing that badly, then you're damaging new pads and rotors that you've already paid too much for and may not have had to be replaced in the first place!!! There's also the possibility of brake failure induced by whatever is causing the brakes to rub.

THEN. Go after the repair shop. Depending on the laws over there, you're either better or worse off than we are, but there has to be some legal or financial recourse.

All of this started over a week ago???

Wow.

 

Some degree of rub or drag is acceptable, especially in the old days before efficiency mattered. But a Prius ought to minimize it, and it shouldn't get as hot as you found.

Under conditions similar to what you mention, I've been able to safely touch the brake discs of all my recent cars when they were working correctly.

 

If your brakes are getting too hot to touch without even using them, that is a safety issue. Unless you're racing or go down a big hill without using B, your brakes shouldn't get that hot. Noticeably warm is normal, but causing water to flash to steam is bad. When brakes overheat, they stop working.

Even with worn brakes, there is barely any gap because the piston doesn't really get retracted, it just isn't squeezing when you're not applying the brakes. Like ursle said, the slides may need lubricated. That would allow the brakes to stop squeezing easier.

 

In hindsite, whenever I'm coasting up to a stop and I just touch the brake pedal, getting ready to apply pressure I always feel the car surge forward, just a touch but it's always evident, I always assumed it was the stability control computer adjusting itself to travel(reading brake pedal pressure), so, if the plot thickens (symptoms come back) just something to ponder, I just can't imagine the obd2 port not throwing some sort of reading with the heat and problems happening.

 

Maybe, maybe not.

The problem on my old Ford stemmed from a simple unadjusted cap nut that set the pushrod length between the brake booster and master cylinder. The replacement booster was shared between several car models, and because it came with no adjustment guide for my particular model, the mechanic made no adjustment. As we figured out later, that left it too long and putting a bit of pressure on the brake pads. When everything was cold, no problem on my 25 mile commute. But as ambient and component temperatures rose, the brake fluid expanded slightly, causing more pressure, causing more fluid expansion and pressure, and essentially setting up a thermal runaway situation. On a 95F afternoon, this runaway lead to the very serious drag and heavy smoke event, providing the evidence I needed to rebute the mechanic's claim that the drag and heat I repeatedly complained about were 'normal'.

On the later car with the rear brake corrosion issue, the problem was infrequent, and depended on whether or no the rust could break loose. Twice it was still overheated as it rolled into the nearest shop. Once I got it cleared before getting to a shop ten miles away, and it stayed clear for the 400 miles home.

With the hydraulic problem on the first car (an early 80s model), both front discs got hot. The rear drums never seemed have a problem. With the corrosion problem on the later car, while it struck both rear discs, only one suffered it at any given time. The fronts never had parts from the same problematic supplier (which my mechanic quit using) and never overheated.

Don't take this as a full list of possible causes. I'm sure there are more.

 

The pads probably just need to bed in. I've previously had issues of a bit of excess drag after replacing my front pads. Took a week or two to bed in and then they were fine. That was on an older car though, so it didn't bother me too much. So far I haven't needed any brake work done on the Prius, but I've got to admit that the issue would annoy me more with the Prius than on the older car where this previously happened. The pads could potentially take a lot longer to bed in on a Prius too, since it uses so much regenerative braking.

Since it's bugging you and is gonna waste some fuel which ever way you go about it, why not take it for a drive in whatever large hills or mountains you have nearby and give those brake a nice little workout. If it's safe to do so you could put it in "N" to make sure it uses friction braking and give those pads a good workout on some downhill sections. This should help them bed in nicely.

 

Thanks for posting this personal experience. I'm facing a similar problem 2 days after new rotors and pads at 94K. Can't keep my finger on the disc for more than a half a second after a 5 mile mostly flat drive and weird noises coming from the front of the car, but only while in motion. I really appreciate the real world experience and comparison. Bringing it back to the dealer the day after tomorrow. Thanking my luck stars I'm working from home this week.

 

I had the same question when I had my Gen 1, and came up with my 15-minute brake drag test which worked on about the same principle. There was a road nearby where I could usually get in 15 minutes of cruising with no touch of the brakes, followed by a parking lot large and empty enough to turn into and stop with, again, no touch of the brake (B mode to get down under 7 mph or so, then R, which does no damage to the Pri transaxle, and brings it smartly to a stop). Stabbing the brake at the instant the car hits zero forward speed is fine, because that makes no heat.

My result was, once I had the caliper issues resolved, no detectable warmth at the rotors after that test, just stone cold metal, feeling the same as grabbing any other unrelated metal bits under the car. So that's clearly what the desirable and achievable baseline should be.

One thing I learned was that even the slightest use of the brake for stopping at the end of the test will leave the rotors warm to the touch, swamping what you really wanted to learn from the test. So that stop at the end really has to be with no braking at all.

In my case the caliper rebuild rubber kit was all I likely needed.

-Chap

 

My experience with serious brake drag on two previous cars was that my drag heating was easily separated from the warmth of a single ordinary light braking stop. My brakes were so hot that the lug nuts and center of the wheel rim were also hot. A few times, the heat radiating off the disk was very discernible without touching anything.

Those were older and less efficient cars than any Prius. Now that the efficiency bar has been raised, your test for truly cold rotors will pick up less serious drag cases that still deserve attention.