philsey
New member
.... +1
This time the brakes didn't work!
- Thread starter evtmille
- Start date
.... +1
Keemonrunnin
Member
I've had a situation while coming up to a stop light a bit hot. While I was braking (there was a good size bump in the road)as I hit that bump. My brake pedal did drop further than normal and then I had to re-apply the brake to make it work(felt like it hit the floor).Yes it did scare the crap out of me. Luckily no one was in front of me. I went back to the same spot a tried it again(same senerio) It did exactly the same thing. I don't know if it's because when I'm pressing and hitting that bump at the same time,the front wheels leave the ground and the truck senses nothing to brake on. Then when it makes contact with the road again, the brakes are already being pressed and the truck doesn't sense any brake pressure. So it drops the brake pedal down thinking I'm just applying the brakes at that moment. But,when I tried it at a slower speed not coming in hot. The truck did fine the brake pedal didn't go down any further than regular braking(not coming in hot). Anyone else experience this at all? Maybe this is what could've happened with OP wife. :shrug:
You are a brave man.......[emoji12]
Fernandina4runner
New member
I have had that happen several times with mine. It has happened several times when I have pulled off the road trying to slow down. It has also happened when I went to cross over a bumpy paved median to pull into a driveway. The brake pedal went to the floor and the brakes didn't function. I pushed the pedal again and the brakes worked. It scares the crap out of me, but I never can replicate the situation.
Danimal
New member
Rapidly locking up the brakes while the torque converter is locked up will do this. As long as the drivers foot isn't on the brake at all before stabbing the pedal - as this will unlock the TC. If you're just cruising at 35MPH plus and jam the pedal to the floor FAST and HARD the TC can't react and it'll lockup the entire drivetrain. I know this from the design and experience side of things. This happens a lot less often with ABS vehicles, but it absolutely still happens.
However, in this scenario, if you aren't altering the force on the brake pedal, the boost from the vacuum booster gives adequate braking power, even once the engine is off, because you've already applied the brakes to the floor to lock them up. So there's usually no report of loss of braking power.
Dan
ProspectiveBuyer
New member
The TC lock "can't react"? You're saying that the engine will stall, like when braking hard without stepping on the clutch in a MT. I don't buy it, such a basic design flaw is extremely unlikely to not have been eliminated a long time ago
I had this happen in my FJ back in 07. Seems to me there were a few threads about this in the Blue forum. If memory serves, it had to do with the nanny's kicking in. I seem to think it was the ABS. In my situation, I was coming up to a stop sign. The road turned from asphalt to gravel and as soon as the front tires rolled off the asphalt into the gravel (Yes there was a slight drop off) It was as though I had released the brakes and rolled right through the stop sign. I was able to repeat the situation numerous times. I guess the electronics were doing what they thought they were supposed to do. I will say the first time it spooked me. I learned to get off the brakes and then reapply.
Cheers, Steve
BlackWorksInc
New member
There's no vaccuum booster in the 4th & 5th Gen 4Runners. It is supplemented by a hydraulic motor and accumulator storage tank.
1engineer
Moderator
Seriously? You guys have had your brakes FAIL and you haven't taken it to the shop?
Here is a quick link to just one of many threads in the Blue forum about the brakes. Worst ABS brakes ever. - Toyota FJ Cruiser Forum
Cheers, Steve
Cheers, Steve
2014 Warthog
New member
I experience this frequently offroading.
One time going down a VERY steep and rough trail, the pedal ended up down to the floor (not instantly but over a short period of time) and I had to release and press again. It was OBVIOUSLY due to the action of the ABS and possibly traction control (Basically the same mechanism). I could feel the pedal going down, down, down in jerks as the ABS/Traction control was hammering loudly on the brakes. It happened quick enough (one to two seconds) that it was rather unnerving.
I couldn't explain it in infinite technical detail, but every time the ABS/Traction system hammers a brake caliper it seems to rob fluid from the brake line causing the master cylinder to drop it's volume a bit. If you have a major incident that causes dozens of hits, it can literally drain it to the point where you need to pump the brake again.
And THEN you may get the panic brake reaction (I have). In fact besides actually hitting it fast, a press release and press again in rapid succession may also trigger it.
Pulling off the road onto dirt at some speed, going over a very rough road/board bridge and braking down steep rough terrain are all exactly the kind of scenario that causes this.
And in deference to what someone recently said, I don't think that the reaction indicates a specific failure. It seems to be endemic to the system given the number of people that experience it.
2014 Warthog
New member
So after all that, in this very case here... what were the road conditions and did the ABS/Traction control systems actually activate? Was there a stuttering noise during the first braking? Or was this just nice smooth sailing and the pedal smoothly went to the floor with no noise at al all?
The latter would be a faulty unit. Bad presure pump or controller, etc.
But most of the other responses here are something I think most anyone can experience given the right road conditions... So just be aware of it and be ready to double pump the breaks if necessary when braking hard on rough bumpy terrain.
The latter would be a faulty unit. Bad presure pump or controller, etc.
But most of the other responses here are something I think most anyone can experience given the right road conditions... So just be aware of it and be ready to double pump the breaks if necessary when braking hard on rough bumpy terrain.
Keemonrunnin
Member
My guess is what they'll say is, "well since you have added aftermarket parts suspension,bigger wheels,front & rear bumpers etc.. you changed the dynamics of this vehicle". Sorry can't help you here. So for now, I have pretty much changed my driving habits just because of the added weight to the 4Runner. (Braking a lot earlier,double pumping the brakes just because,not pushing the skinny pedal as hard anymore,and a bunch more of other little stuff).
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Keemonrunnin
Member
My experience was on dry road conditions. When I did hit the bump,the brake pedal did pulsate a bit while going lower to the floor before re-applying it. Now what I do when coming to a stop is hit the brakes earlier,then let off,re-apply. It's turned into a habit for me now. When I drive other cars I happen to do the double pump as well.
I think those are symptoms of 'ice mode'. I've experienced it in my Accord and now in my Prius v a few times.
While on the brakes going over railroad tracks or some uneven surface the brakes seem to quit working. In my Prius v, it feels like the car is actually accelerating. A quick release and re-apply of the brakes gets things back to normal.
1engineer
Moderator
Question: Do you think it is a symptom of the brakes failure to operate correctly or a symptom of the road conditions, i.e. railroad tracks cause tires to momentarily leave the surface and the same thing over bumps. I ask that because by the time you release and re-apply the brakes the terrain conditions could change.
I will say on a dirt washboard road at medium speed the brakes don't work well. Why? Because the tires are not in contact with the ground half of the time. I guess I could install air brakes....
I think it is a poor reaction from ABS to rare road conditions.
From what I've read, ice mode reduces available braking force until reapplication of the brakes. I'm conditioned to pump the brakes, so I've never tried just stabbing them continuously the few times it has happened to me. It's never occurred in the 4Runner, but I'm not the primary driver.
Not saying this is what happened to the OP's wife as ice mode requires some type of disturbance in the road to activate and the ABS is going nuts, which is certainly not 'nothing happened'.
It sounds like there might be a problem with the ABS program in some situations. Not something a shop could fix.
On railroad tracks (or pavement discontinuity, or whatever) the tires are momentarily unweighted or on a slippery steel surface, but as soon as you are past them and the suspension settles down, you are on dry pavement so the brakes should work like normal. Hitting the brakes while crossing the tracks triggers the ABS, as expected because otherwise you lock up the wheels. The problem is that the ABS keeps going after you cross the tracks and it continues to act like it's on an extremely slippery surface, severely limiting braking power as if you are on ice, rather than allowing braking force that you would expect from ABS on dry pavement (a little less than braking without ABS, but still very hard braking).
I've noticed this in my last car, a Honda, but I don't think I've been in a situation yet in my 4runner where this might happen.
