Brakes making noise

Is this true? I am surprised that it works this way. I would expect the control system to react to that input by doing the following, stepping through as additional braking was needed:

1) Reduce power.

2) Engage regenerative braking.

3) Engage friction brakes.

Tom

 

Hi Tom!
Good question. I don't know exactly at what point the friction braking begins, because I always brake firmly to achieve the desired effect. It is indeed possible that it first goes through power reduction and regenerative braking steps first before friction braking as you noted. Although the way it sounds to me when I do it, the regen' might come before the power reduction.
I will listen more carefully next time, with the window open, to see if I can hear exactly what's happening. But the next opportunity I have is late tonight.
Fred

 

I suppose almost anything is possible, since this is not exactly a normal control input.

Tom

 

Simultaneously applying power and brakes activates friction braking

Executive summary:
Simultaneously applying power and braking activates the friction braking mode, and if brake force is increased beyond a certain threshold engine power is reduced abruptly.
During braking, the braking mode can be switched from regenerative to friction braking by simultaneously pressing the accelerator pedal briefly.
The friction braking mode is deactivated when the brake pedal is released (except below 8 mph).


Last night I listened more carefully while simultaneously applying power and braking, and I also found that I could hear the brakes much better with the windows closed.

At first only the friction brakes are used during simultaneous braking, and engine power is not reduced and regenerative braking is not engaged. This was also confirmed by the fuel consumption screen, which showed instantaneous mpg responding normally to accelerator pedal input, and by the energy flow screen, which showed the usual fluctuations between battery charge and discharge.

When the brake pedal is pressed beyond a certain point during simultaneous braking, then engine power is abruptly reduced, resulting in sudden deceleration (watch out for tailgaters). I was not able to determine if regenerative braking was then also engaged, because it happened too quickly to get a reliable indication on the energy flow screen. (I have no special instrumentation)

Then something else interesting happened. There was a construction site, and I had to take a detour over a hill instead of my usual flat route just before arriving home. I continued to test the simultaneous braking while driving down the hill, but instead of releasing the brake pedal while continuing to press the accelerator enough to maintain speed on level ground as I usually do, I released the accelerator first because I had to keep braking in order to limit my speed going downhill. But the friction brakes continued to be used even though I was not simultaneously pressing the accelerator any more!

When I briefly released and reapplied the brakes, regenerative braking was reengaged as usual. Then I tried briefly pressing the accelerator while I was already braking, and braking was switched from regen to friction braking!

Fred

 

Squealing is probably merely rust. Shaking, that calls for a trip to a dealer.

 

OK, so what if your friction brakes make a HORRENDOUS high pitch squealing noise? I had the driver side front bearing replaced last week. After that (and never before) I have a very loud squeal when the friction brakes start to catch, all the way to a full stop. I took it back Monday (needed an alignment anyway). They said they cleaned some dirt and rust. It still does it and the rotor is as smooth as a baby's behind - shiny too.

So WHY do I all of a sudden have this LOUD squeal? I am going to try the 'drop to neutral and use the brakes' thing. I wasn't aware N forced friction braking. Can't do a lot in D since it doesn't get to the friction brakes until 8 MPH and if you push at all hard, you are very soon going zero MPH, defeating the purpose.

 

Could be some dirt/grease got on the pads or rotor after the bearing was replaced. It's easy to check on the rotor surface of the outward facing side. The dust shield on the inner side makes that pretty hard

 

If you want to isolate and test hydraulic braking by itself,
put the car in Neutral. That completely disables regen without
having to play hazardous both-pedal games.
.
_H*

 

Hi Bruce, some squealing at some times is usually considered normal. It sometimes happens after new pads or rotors have been installed, or after the brakes have been taken apart or worked on. Then the pads sometimes make uneven contact with the rotor. Often it goes away by itself when the brakes wear in.

It can also happen if the pads or rotors are damaged or worn out, or if the brakes are assembled improperly or missing parts. In your case that shouldn't be, but you might want to double check to make sure.

And sometimes the brakes squeal for no obvious reason. Then it sometimes helps to coat the brake pad backing with a new coat of anti-squeal compound.

 

Like he said about the missing parts. Look through your wheels at your brake pads. There are anti-squeal shims that are supposed to be on each pad. You are also supposed to put an anti-squeal compound (looks like silver grease) between the pad shims and the pad. It is possible that they either lost one or both shim on either pad or just did not re-apply any of the anti-squeal grease when they re-assembled them

 

Thanks, I'll have to look into the anti squeal parts.

New confusion:

When I put it in N coming to a stop the squeal does NOT happen!!??

When in D, I don't get the noise if I take my foot off the accelerator (coasting regen) and it doesn't happen if I press on the brake pedal at higher speeds for normal slowing to a light. I only hear it as I come closer to stopping, even above the 8 MPH regen cutout (maybe starting friction brake contact early? I don't push hard ) and as I come to a stop. If I modulate to a VERY slow stop, I don't hear much noise. A more normal stop results in more noise.

 

OK. I took the front wheel off today, the outside shim is there. I crawled under far enough to see the inside and there is no shim but that is OK because:

THERE IS NO F-ING INSIDE BRAKE PAD!!!!

How in h3ll do you forget to put in BOTH pads when you put the brakes back together????????

I hope the piston has not been damaged. Good thing I am gentle on the brakes, even more gentle now!!

They cranked the bolts so tight I couldn't get the caliper off to look at the piston. In fact I was barely able to break the last lug nut off with an 18" wrench on that tire. I also took off the passenger side just to make sure I knew what I was looking at. One lug nut was so tight the socket cracked. I ended up using the car's lug nut wrench and a 3 foot breaker bar. They will hear about that early in the morning as well.

 

Golly. Uh, which shop did that fine work?

 

Bruce

You have GOT to be shi**ing me!

Looked at the photo, so no, I guess you're NOT shi**ing me

The piston is probably shot, it has been rubbing against the rotor. The rotor is probably shot too. Since you need the Toyota scantool (Handheld or the newer Panasonic ToughBook version) to properly bleed the brakes after replacing the caliper, this is a dealership repair

Unless it was the same dealership that conveniently forgot to put the pad back on!

I guess this is another reminder why it's always best to do these things yourself. Even if you manage to f*** something up, it was with good intentions. When a "pro" f***s something up as badly as this, I have to wonder if a) they were high as a kite that day at work, or b) did it on purpose?

Get this fixed ASAP

 

Funny, EVERYONE that I told the reason my brakes were making a horrendous noise said the same thing "How can you forget the pad??". Yeah, well it seemed pretty unlikely to me as well. I calculated it out - there are 7 parts and you can't put it back together without the caliper and the 2 bolts. That leaves 4 parts and he forgot half of them and didn't notice?? Even the next week when I mentioned the HORRIBLE squealing noise that had NEVER been there before the bearing replacement AND they checked and cleaned something (or so they say) and said they were fine? You couldn't even back the car out of the bay let alone test drive it and NOT hear that noise.

The rotor didn't look damaged from what I could see and the "deal with the customer" guy said the piston looked OK as well. But, just to be sure, they did a full replacement on the driver's side - caliper, pads and rotor AND all but the caliper on the passenger side. Not real sure why other than trying to make amends for the major screw up. VERY quiet now, just like it was before the bearing replacement So I used to have 60% front pads and 80-90% rear left at 94K miles, now I have 100% on the front and shiny rotors. A little time will fix that and they will look like proper Prius rotors again I think the only reason there wasn't a groove in the rotor and serious damage to the piston is that it IS a Prius and I always go for REALLY gentle braking, especially when it sounded so bad.

But, of course, now you have me worried they may not have bled them properly. They feel OK, is there some way to tell, other than the standard "sinks to the floor but hardens up if you pump them" method??

This was not at the dealer. I stopped having the dealer do the oil changes because they could never get it right unless I gave them the EXACT amount I wanted put in. They couldn't even remember to give me back an empty when I DID give them 3.5 quarts. Then one day a couple of years ago they didn't give me my 1/2 quart back. There was weird stuff happening with the credit card that day, I used it at the grocery store, then 1/2 hour later it was rejected at the Toyota dealer so I was distracted. Perhaps you heard in the news recently about the guy who stole tens of thousands of CC numbers from a few chains, one being Hannaford - the supermarket where we shop. Great timing, they apparently detected it in that 1/2 hour period! When I checked the level the next day I found out why I didn't get my 1/2 quart back, they had put in the full 4 quarts. I have a Fumoto drain valve now but at the time I went to the marine chandlery and got an electric oil change pump and sucked out the extra 14 oz.

So, I don't trust the dealer and now I don't trust the tire/automotive shop so much either. What to do??!! I mean if I HAD originally needed new pads, I would have done that myself but the bearing 1) wasn't a sure thing when I took it in, though I was pretty sure it was 2) from what I have seen on-line, the bearing replacement isn't really a "handy at a lot of things but master of none and probably don't have the right tools" kind of job. I kind of dread the 100K service, I didn't bother with the valve adjustment back at whatever time the service manual suggested since I have no problems but I suspect it should be done at 100K. Plus, I think the inverter fluid is supposed to be done at 100K as well.

 

Well, in theory the brake warning lamp will be on if there is a problem with the brakes. If you don't have access to the Toyota scantool, there is a complicated "dance" you can do with the brake pedal to cancel some error codes, such as for the brake warning

However, you can NOT properly bleed the brakes without the dealership scantool. I suspect this garage just put new pads in, without replacing the caliper or piston assembly.

I'd be surprised if they went through all that work, when they at first claimed they "inspected" the car, somehow not noticing major brake parts were missing

I'd take the car to an empty parking lot, get it up to about 30-40 mph, shift into N (So regenerative braking is out of the loop), then firmly apply the brakes. If the car veers to one side, that's a sure sign one of the front calipers isn't doing the job

Not sure what you can do at this point. Sounds like that independent shop can't be trusted. If I were you, go to the shop manual section I posted about how to bleed the Prius brakes, print it out, and show it to this character. Ask if they followed it to the letter, and ask to see their genuine Toyota scantool

TO answer another question: no, there is no other scantool that has the brake bleed procedure. You must use a Toyota dealership scantool, either the older THHT or the newer Panasonic ToughBook version

 

Definately a new caliper. It has a black cap sort of thing on the lower end. That was not on the original nor is there one on the passenger side. I haven't looked at it real closely but I will and I will try the brake while in Neutral test.

Thanks

 

Hmmmm. I posted the shop manual section on brake bleeding here

http://priuschat.com/forums/gen-ii-...em-rear-brakes-no-pressure-when-bleeding.html

I really don't see how this independent garage could have properly bled the brakes after putting in a new caliper, unless they have access to the Toyota scantool