When braking, '06 starts to spin before Trac kicks in, what to check?

[Borrowed4Runner]

Hi,

quick summary of symptom: snow-covered roads here in Milwaukee... when I brake assertively, it feels like the back tires are breaking free, and the car starts spinning counter clockwise (butt comes around on the right)... It will swing about 10 degrees, and I've either let off the brakes and/or it feels like the Brake Assist/traction control kicks in and starts pulsing the brakes to straighten things out.

Any ideas on what could be causing this? It's almost like the front left is grabbing harder than the other brakes, causing the car to spin. I've done this several times, even tried to get it with the left tires on more snow with right tires on clearer pavement, and that can lessen the issue, but if it pulls, it's always to the left.
This was noticable enough that I'm concerned if I had to truly brake in an emergency that the car would respond either unpredictably or flat-out poorly.

Any insights or thoughts on things to check would be appreciated!

It's an '06 SE5, 4WD if that matters.

Update: Found some dry pavement on the way home today... alignment seems straight, car doesn't pull if let go of the wheel driving straight. Hit the brakes and it pulls a bit to the left, even turning the wheel just a bit if not holding (very minor). So would that be a brakes issue, like the left is gripping better?

 

[ARunner]

If it is pulling on even dry pavement, sounds like something is amiss. I would recommend bleeding the brakes. Perhaps you have some air in the line at one if the calipers on the right side, if it pulls left when you hit the brake. Also, check your pads and rotors for any signs of grease or oil that could have gotten on them, as this will greatly decrease the effectiveness of the brake.

 

[DC runner]

That is classic stuck piston action. Well known issue with these trucks. No doubt about 30 other members could confirm they have replaced front brakes due to piston issues.

 

[DarenS]

quick summary of symptom: snow-covered roads here in Milwaukee... when I brake assertively...Any insights or thoughts on things to check would be appreciated!

I can't speak for the cause of this, but I would suggest slowing down and increasing your following distance so you don't have to brake assertively on a snow covered road. Once the tires start sliding on snow/ice, even the best traction control won't keep you going straight.

Just my two cents. YMMV

Daren

 

[sonerick]

That is classic stuck piston action. Well known issue with these trucks. No doubt about 30 other members could confirm they have replaced front brakes due to piston issues.

I agree with this. I've had to replace the front left caliper 3 times now due to a sticking lower inboard piston. Symptoms are similar to yours, under hard braking, it pulls to one side.

 

[DC runner]

You should also try to brake slowly on snow. Regardless of hard pack, soft, location, snow is going to behave as it wants and you shouldn't try to brake fast. This is a sure fire way to lose traction and skid, which you do not want to do. The purpose of ABS is to prevent skid by trying to prevent so called "lock up" which is what happens when you "slam" the brake. Doesn't normally matter, but in the snow; fast slam braking is what will brake the tires free and cause you to skid.

Plus, it makes the stuck piston worse. While usually just an annoyance, it can, in certain circumstances, cause an accident and for you to lose control.

A new front caliper from Autozone, with lifetime warranty, will run around 130-180. Not too bad. Takes about 30 minutes to change with a buddy helping. It will make you much more secure in the snow.

Engine braking, fyi, can be really helpful in slowing you down in the snow without breaking traction on it and skidding.

 

[Borrowed4Runner]

Thanks all for the replies... I was starting to think it might be a sticking piston, but this car is new to me, so I'm not yet familiar with the 'common quirks'. Your experiences confirm my thoughts.

As for stopping quickly, etc. Yes, I do allow a much greater following distance than most, these instances with the quick stopping was under controlled circumstances without other cars around - IE specifically testing what the car's capability was so I knew how the car would react in an emergency - and I concluded I didn't like what I would experience if I had to emergency brake.
Among other things, my braking was to test the tire capability, to find how hard I can brake before the tires do indeed break free from the pavement/snow. My car with Blizzak's is very different from this truck with Conti-Trac all-season's, etc.
Under normal circumstances I engine brake, etc, and am typically quite light on both pedals.

DC Runner - out of curiosity, how would jamming on the brakes make the stuck piston worse? Is it causing a physical binding action, that's bending one of the slides or something? Hadn't thought about it before.

 

[Borrowed4Runner]

Thanks all for your help in trying to figure out my braking issue. Thought I'd post a follow-up in case anyone runs across this thread in a search...

Took car to the dealer to have it reviewed (and tire store for 2nd opinion). In my case the front left caliper is stuck a bit closed/rubbing, and the right front caliper is siezed open and not making contact. That would certainly explain pulling left when braking, better braking force on that side than the right.
Both disk surfaces of the rotors on the outside that is easily visible through the wheel look like they're making contact (no major rust, etc), so I'm guessing the slides are getting stuck, and it's the back side not making contact as well, but I don't have that confirmed.
Scheduling to go back in in a few days to have them replaced.