Brakes grabbing

sounds like the abs control unit which includes the accumulator and the actuator

DH got one like this fresh off the truck. took him 30 seconds of driving to say "hey that's the abs actuator"

unbelievable pain in the butt to replace, but what has to be done has to be done.

 

My 06 is 2 weeks old and I noticed that the brakes at low speed behaved unlike any other car that I have driven (happened since leaving the dealership).
Applying a moderate and constant foot pressure the car slows down but when it is almost stopped (less that 8 km/h) the brakes suddenly grab. The stopping force is enough to throw me forward in my seat. The problem can be overcome by applying less foot pressure at the last minute.
I should not have to do that to have smooth braking and will bring it up when I take the car in for its first service.

 

<div class='quotetop'>QUOTE(Orf @ Apr 19 2006, 03:19 AM) [snapback]241979[/snapback]</div>

With the car that new, I think I would call the service department right away. Perhaps also talk to your sales person. My 2006 doesn't have that problem although it took a few weeks of driving to have completely smooth stops (the brakes did seem quite different than the Audi I had been driving beforehand). The sales person could let you compare yours with another vehicle. This is useful if you get the "they all do that". Why drive it for 5000 miles with screwed up brakes? Of course, I live 3 miles from my dealer and they have really good service hours so it is not that much of a hassle for me if I had to take it in.

- Tom

 

<div class='quotetop'>QUOTE(galaxee @ Apr 18 2006, 10:58 PM) [snapback]241886[/snapback]</div>

Galaxee: I've got just under 5k on my new car, and I'm still getting this grab. (worse in the morning and even more so with heavy humidity/dew). It's starting to bother me and I'm hoping you can ask DH if he tried to "clean the brakes" first by doing a hard brake stop or a neutral stop without regen before replacing the ABS stuff.
I wonder too how the car behaved after replacing the necessary components. If replacing those components did cure the problem, I guess it's time for all of us to make an appointment. Can I specify DH to work on my car? You're only about 3 hours from me.

 

<div class='quotetop'>QUOTE(unruhly @ Apr 19 2006, 08:31 AM) [snapback]242012[/snapback]</div>

in the case of the car he had, it was more than obvious what the defective part was. he didn't even bother with anything else, just went straight for the assembly. if the problem is in the assy, there's no point in dealing with cleaning anything anyway.
(and on a side note, the job is a real pain. he had to pass it off to another team member when he went to school that week, and said team member swore at him for about 3 hours when he got back :lol

i'll ask about that. i'm assuming it was okay because the team member who did the work is almost as thorough as DH.

he saw this thread and said "oh great, so we're going to be replacing a bunch of these aren't we?"- sounds like that's going to be the case.

and in all seriousness, you're welcome to make the drive but you'll probably go home in a loaner for a couple days.

 

<div class='quotetop'>QUOTE(galaxee @ Apr 18 2006, 10:58 PM) [snapback]241886[/snapback]</div>

Galaxee,

I am guessing DH is your significant other... the one you speak of in your signature? I'm sorry, I'm sort of new(er) to these forums. Either way, he sounds like he knows what he is talking about when it comes to Prii (and since he is working on the certs, he definitely knows more about them than anyone I know of). Hence I was wondering if you could forward my findings to him (or mention them) and ask him if these definitely look like signs of a bad "ABS Actuator".

Signs:
1) Brakes "grabbing" more pronounced in colder weather; early mornings usually (which in Pittsburgh means approx 43 degrees these days). It rarely/never happens on my way home.
2) Smooth stops (whether hard or light pressure on pedal) when applying brakes in Neutral.
3) NO "grabbing" when constant (harder) pressure applied on brakes when coming to a stop. It only happens when you ease off slightly on the pedal when coming to stop(when in Drive).

I just want to be sure of this before I go to the dealer and ask him to take a look at the ABS Actuator for me. I have terrible luck when it comes to replicating an issue at the dealer, hence it'll help me immensely if I can just walk in and tell him what he needs to look at for sure.

Thank you Galaxee (and DH)!

 

<div class='quotetop'>QUOTE(Tom_06 @ Apr 19 2006, 05:52 AM) [snapback]241999[/snapback]</div>

I live some 100 km from the Toyota dealership and they never have another car in stock. They can't get enough to meet demand.
I only have 450 km to go to the first chechup (1000 km) so I will wait and see if the braking problem improves. Having said that, I notice I am now subconsciously correcting by easing up on the brake pedal at the last minute.

 

<div class='quotetop'>QUOTE(Kross @ Apr 19 2006, 10:24 AM) [snapback]242047[/snapback]</div>

can you feel the grabbing in the brake pedal? any kind of vibration when this is going on? where does the vibration feel like it's coming from?

trying to sort out if everyone here has the same issue. will take some looking.

does this happen every day? or just now and then?

does it feel like it takes longer to bring the vehicle to stop when this is happening? or no? (this could be reworded to ask, does it feel like the brakes are less effective when this is happening?)

the whole no-symptoms-in-neutral thing has him thinking it's not the ABS in this case. we'll take a better look at this thread, i just looked at a post or 2 and he said "oh i've done that"

this sounds different though, now that we're getting into it. let him do a little digging around in this thread and at work.

 

<div class='quotetop'>QUOTE(galaxee @ Apr 19 2006, 10:51 PM) [snapback]242452[/snapback]</div>

Yes, I can feel it in the pedal but it isn't really a vibration. To give you something to compare it to, if you're driving a normal automatic transmission car and are at a red light (while in Drive) facing downhill, you'll have to press down on the brake a little harder than you normally would (since you're facing downhill)... if you don't press down on the brake harder than usual, you can feel the car slip a little...THAT is the feeling I get in the prius, except it is for a second... it goes: *slip* --brake-- *slip* --brake.


<div class='quotetop'>QUOTE(galaxee @ Apr 19 2006, 10:51 PM) [snapback]242452[/snapback]</div>

Unlike the other posts above, mine isn't really coming from one side in particular. In fact, mine isn't even a vibration, just the brakes slipping and grabbing quickly.


<div class='quotetop'>QUOTE(galaxee @ Apr 19 2006, 10:51 PM) [snapback]242452[/snapback]</div>

I just began noticing it four days ago. It didn't happen at all this morning but it usually happens (for the three-four days before today) in the mornings on my commute to work when it is a little cooler out. Not sure if the temp has anything to do with it though.



<div class='quotetop'>QUOTE(galaxee @ Apr 19 2006, 10:51 PM) [snapback]242452[/snapback]</div>

Not really less effective, more like they're bieng applied in a "stammering" sort of fashion (for the lack of a better word). Usually when it happens, I press down harder on the brake and the Prius complies swiftly and stops the car quickly (without the grab-release-grab).

To tell you the truth, I doubt mine is really a technical problem at all. In the evening today, I actually forced myself to brake normally as if I were in a normal car (not braking lightly in advance, instead pressing pedal harder and closer to stop) and the Prius responded just fine (no brake-grab-brake-grab)...so my problem COULD just be:

1) In my love for the brand new hybrid, I may have been a little light on the brake pedal when stopping and may have hit that precise spot in the brake pedal system where the brakes switch over from regen to conventional. Since that borderline spot is where I'd probably go light on the pedal, the Prius probably applied the minimum amount of conventional brakes and would switch back over to regen (and back and forth)...?

2) The conven brake pads or rotors were severly under-used due to my light and sensitive braking patterns in the beginning and may not have been polished enough to grab right away...?

I will update if I notice the brake grab-release happen on my end again. For now I will continue to not be completely feather-footed on the brakes.

 

okay. first off, to reply to all the "there must be a TSB for this issue now" people.

there is no way to call someone up and say "hey this should be a TSB." toyota analyzes the number of service records to determine whether a problem is prevalent enough to put out a TSB. basically the whole point of a TSB is to say "hey people, this is a common problem and here's how to fix it."

as most of the dealers seem to say "this is normal" you're not going to see a TSB out of this, they're concluding you're not used to the way the car drives.

as far as there being an existing bulletin and techs being instructed to automatically state that there is no problem... that's not true, and whoever told you that was either being a jerk or yanking your chain.

also, calling the NHTSA will not give you the TSB you're looking for.

call the toyota customer experience center.

------------------------------------------------------------------

now. there seem to be two problems here. one is a problem where near the very end of a stop when you're letting back off the pedal, there's a feeling of the brakes re-engaging momentarily just once. this is a problem if the people experiencing this are not actually pushing back down on the brake pedal. he doesn't know what's causing it, but if this is a serious issue to you, explain the problem directly to the tech (don't just let the service writer take notes) and let the tech drive your car for a couple of days. this gives you more than a five-minute shot to reproduce the problem, and obviously it's much easier to diagnose something you've had the chance to feel yourself. no tech is going to go around chasing after a problem they don't see because there's no way to know if it's fixed.

rule number one of working on cars. if you can't make the problem happen, you can't know if you fixed it.

another problem is the brakes grabbing multiple times during a stop, which some people have described as an ABS in slow motion kind of effect. this could be caused by a number of things, one is the ABS actuator as skijapan decribed and as DH has diagnosed in the past. if it is the actuator, there should be some audible noise from the brake system. you may hear something from the affected wheel. another could be a regen-related issue which may or may not be a transaxle issue. given that regen is accomplished within the transaxle, one could make the connection. a warped rotor is going to feel more like a vibration in the front end of the car during hydraulic braking from high speed. at its most severe, a warped rotor can cause steering wheel shimmy at low/near stop speeds. however if your rotors were warped that badly, moderate to heavy braking from 70 mph would feel like being in an earthquake. it would not feel like a grab-release pattern.

the fact that at least for one of you, this isn't happening in neutral points to regen, whether software of hardware related....??? we can't tell.

just to repeat this because it's important... the tech NEEDS to experience this to begin to correct the issue. if they insist it's normal and they are actually experiencing the problem: take another car out for a drive and immediately point out the differences.

for a test drive: first you should drive. make the problem happen and say "this is the problem." make sure you tell him what exactly you're doing when the problem happens. then let him drive. describe again how you produced the problem so he can reproduce it. then if he insists it's normal, repeat the process in a car of the same model year and point out the differences immediately. most prius techs don't have a heck of a lot of experience driving normal prii. that is probably the single biggest problem in communication between owners and techs.

--------------------------------------------


well that got long but i hope it stimulates some discussion and some more descriptions of the problem and maybe helps someone have a solution figured out sometime here.

and if anyone cares to drive over to durham nc... he can give it a look over.

 

Kross:

in a car with a "normal" braking system, braking lightly in advance pretty much feels the exact same way as braking lightly in advance in a prius. you will get the slight feeling of contact from the brake pads with the rotors and that should be it. then you brake and then you stop.

if you press suddenly on the brake pedal, the by-wire detects that as a potential panic stop and ramps up brake power accordingly. that should be the only difference.

that's the only real difference...

so could the feeling in the pedal be light enough vibration to be considered just a "tactile response?" it wouldn't have to be severe vibration.

does the brake slip at a complete stop?

does this happen at high, medium or low speed?

if this keeps happening, do this soon since it's starting to warm up. but what you want to do is take it to the dealer at night, and have them leave it parked overnight. tell them it happens when you start up in the morning and it's been sitting and cold all night. have them drive it first thing in the morning around the same time you'd get it going and they will be better able to diagnose the problem.

 

wow, the thread that will not die.
.
Mildly glad to hear of another bad or questionable brake actuator
in the field, though. Internal pressure sensors, perhaps, like
mine? That required a whole actuator changeout too, and yes, it
took the poor tech a day and a half in sweltering heat. Half of
that was probably getting the air bled out correctly.
.
_H*

 

So any progress ? cause i lost hope of ever getting this fixed.

 

well, some more detailed explanation of what you're experiencing would help, but obviously there's no clear diagnosis possible over the internet.

some of the advice in post 90 may help you make some headway with the dealers.

without seeing it in person there's not much we can do other than suggest and offer advice.

 

Does anyone know if the brake system uses an accelerometer to calculate braking force required?
If it does and sets a force to the mechanical brakes to give a constant deceleration then it may account for some of the results that some of us are getting. When electrical braking is applied and a set deceleration established a change to mechanical braking at low speed could cause the mechanical brakes to over compensate.
With a constant pressure being maintained on the pedal, if deceleration is too much then the mechanical brakes could be partially released. If deceleration then becomes insufficient then the brakes would be applied with greater force. Hence the ABS effect.
In my case where the car stops abruptly when the speed gets below about 2-3 km/h can be explained by the vehicle maintaining a constant deceleration that suddenly ceases when a complete stop is achieved. My 2-3 km/h is only a guess and the figure could be zero.
During deceleration, my body would attune itself to a constant decelerating state and the stop would then cause it to continue on, hence the feeling of being thrown forward.
Just a thought.

 

After taking the car to the 5000miles oil change ... I haven't had this problem ... coincidence ?

The car also started making the old familiar noise of releasing pressure when standing still. (used to have it on the 04 prius)

 

Well, my problem, which seems to be a little different from everyone else's is BACK <_<

During the past week and a half I have been experimenting with exactly how it happens, and here are the results: For the past week I have been having it almost ALL the time, regardless of whether it is cool out or not (it has reached high 70s here in the afternoons now).

What basically happens is that to me it seems like there is a precise spot in the brake pedal at which the brakes are sort of sporadic. This spot incidently seems to be hit EXACTLY when you're coming to a complete stop (not a sudden one, just your regular red light) and you're slowing down at a constant normal rate, then towards the end you ease off the pedal just a little so your car doesnt jerk to a stop. When you're easing off the pedal that tiny bit is when this happens...instead of lessening the pressure on the brakes corresponding to me easing off the pedals, the brakes at that point sort of "slide" and then grab, then slide and grab. I don't think it is a "release-grab" because the brakes are still bieng applied, they just go back and forth in the pressure for a few seconds at that precise spot.

Anyhow, I am taking the Prius in today to the dealership to have one of their people drive it and tell me what's going on. Unfortunately the dealership that I prefer (and bought the car from) is now a little far from where I live (I moved ), so I don't know if I can leave the car with them for a while.

If they need to test out what I complain about, would that warrant a loaner car from their end or not? Or does that vary depending on the dealership itself?

 

<div class='quotetop'>QUOTE(Kross @ May 9 2006, 08:30 AM) [snapback]252064[/snapback]</div>

This is what this thread is about.

 

Did a search for "brakes slip" and found this megathread.

Bought a '05 / 10K Pri several weeks ago and having this experiece as well. I've tried braking slow, fast, hard, soft and all with the same results. The brakes work great, but right at 8mph, there's a momentary loss of braking. It feels like i've lifted my foot slightly, but I ain't. I've let friends take test drives and they have the same spooked experience, unprompted by me.

At 8mph, the brakes feel like they have let go, and the car almost speeds up from the loss of resistance. A second later, the brakes reapply and the car resumes what feels like normal braking. From reading this thread, I see that the friction brakes cut in around 7mph. But there's a momentary lag in my car as it switches from regen to friction braking. I don't experience it as a "grab", but more like the brakes stopped working for a moment and then started working again.

Anyone gotten a Dealer to fix this problem on their car, or is it just the way it is?

 

That's how it is. (unless it's really feels like you don't have brakes.)

That's when the regenerative braking transitions to mechanical only brakes.



(but have it checked anyway, you can never be too safe)




<div class='quotetop'>QUOTE(cagemo @ Jul 3 2006, 02:57 AM) [snapback]280428[/snapback]</div>