doctormoreau

Tried disabling my ABS because I was getting this strange sudden stop and shuddering feeling accompanied by some vibration noise when I'd quickly hit my brakes in a parking lot.

Damn, problem is not fixed. It's so strange, if I take off and drive and come to normal stops I'm fine...but if I come to a quick stop right after starting up and going into gear (for instance you start up the truck and pull out of a parking spot but have to stop suddenly because the car in front of you does) then it "feels" like the ABS brakes kick in and you come to a really harsh stop (as opposed to the 4Runner's normal soft stop). Funny thing is I CAN'T get the ABS to kick in by going 40mph and smashing the pedal, in most cars I can.

It's a series of rapid pulses that you feel through the brake pedal and it also makes a noise and varies in intensity from time to time.

I can replicate it nearly every time if I just let the truck sit for a few minutes, then put it into gear, let it roll forward and quickly tap the brakes. Once I'm rolling for a short distance under power it won't do it again. Really strange.

I've seen others complain about judders from the driveline, is this possibly something related to the driveshaft?

Ideas?

toyota4x4907

Check your wheel bearings andU-joints

doctormoreau

I do have a slight front end shimmy under normal braking (not what I was talking about above, that only happens with a quick stop when barely moving). I've never seen a wheel bearing do anything like that but I guess it's not impossible.

It's been a while since I owned anything with u-joints so I suppose that could be the culprit and it's only acting up when there is a quick load on it. Still, seems like something in the brake system to me. I'm telling you it feels like when the ABS kicks in on most cars except it happens at extremely slow speeds and the truck kinda shudders to a stop. Imagine stalling out a 5-speed because you left it in gear and stopped, it feels JUST like that and I keep expecting it to be stalled but it's still running.

I suppose I need to get the driveline lubed up, guess that could cause some strange stuff too.

wyoming9

iTrader: (1)

I am no Auto trans person but I think you might have a transmission problem.

Or is it the engine that is shuddering ??

Like the massive amount of vacuum drawn by the brake booster at low rpm

Just a guess.

doctormoreau

No it's not the engine stumbling, but it does feel almost exactly like when you come to a stop with manual transmission still in gear.

It's hard to explain. Most of the time I find that the brakes on the 4Runner are nothing like on my Yaris. On my Yaris I can mash them and make them lock up quite easily but on the 4Runner they won't lock no matter how hard I jam them on. Except if I first start up the truck, put it in gear and let it lurch forward in idle (like in a parking lot), then, and only then if I hit the brakes they grab super hard and lock up and it feels like the ABS is kicking in or I'm stalling a manual tranny car. It makes a rapid clunking/popping noise and comes to a halt. Again, I've disabled the ABS so it's not ABS but that's what it feels like.

Also, again, once I drive a hundred feet or so above a couple of MPHs it doesn't do it again.

I had someone look at the drivetrain and he said all of the u-joints are nice and tight.

I really, really hope it's nothing with the transmission, but I wouldn't think it is because it shifts out really nicely. No clunking at all or anything when going into/out-of gear and shifts are very clean. Though I suppose it's possible that it could be well overdue for a fluid change or there could be some kind of valve or electronic control making it go wonky in certain situations.

doctormoreau

I also get some wheel shake when I start braking so I'm thinking something may be up with my brakes. Going to tear them down and inspect them real soon. I just go the truck so I have no idea when they were last inspected.

maachine

warped rotors. you can get them turned at an autoparts store as long as they are within spec.

doctormoreau

doctormoreau

the video makes it sound like a single "crash" but it's more like a quick series of GUG-GUG-GUG! and you feel it through the brake pedal. it's like the brakes grab super hard and something shudders.

funny thing is that once cruising the brakes are really soft and I can't get them to lock no matter how hard I try, they only do it when first taking off. I didn't even notice it for days because normally I take off and it's a short distance before I have to stop, the reason I noticed it the first time was because I went to take off in a parking lot and immediately had to stop hard because the jerk in front of my slammed on his brakes.

this article makes me think it is indeed warped rotors. http://www.aa1car.com/library/brake_pedal_pulsates.htm

i have some new ones on order and will be changing them in the next week or so along with pads.

wyoming9

iTrader: (1)

You must remember your 4 runner is quite a bit heavier then your little car.

Just how did you disable the ABS if you did not remove the valve the fluid still has to go through it.

a locked wheel is sliding and if it is a front wheel means you have no control.

Is this a 4Runner or Tacoma??

doctormoreau

It's a 4Runner.

I just pulled the ABS fuse because at first I thought it was the ABS kicking in when it wasn't supposed to.

Yeah, I'm thinking it's one of the brakes grabbing really hard while the other one doesn't or something strange like that. Going to be replacing both rotors and pads in the next couple of weeks. It seems to only happen when the truck is first started up so I'm thinking when they brakes are cold. (or at least not warm yet) since it won't do it when coming to a stop from speed (which warms them up).

tantacoma

I had a similar problem that stumped me for a while. I do NOT have ABS brakes, and do have manual hubs though, so this might not help you.

Symptom only occurred when going REAL slow (say in a parking lot, or a drive-thru) and braking to a complete stop. The brakes seem to 'grab' rapidly, like your shudder. No noise, just that annoying shudder. Brakes worked great otherwise.

I first assumed the calipers were grabbing, so I replaced them. No go.
Then, greased the driveline, No go.
Then replaced the rear diff fluid (I have an LSD) No go
Then added a clamp-deal to the front of my leaf spring pack. No go.

Finally, replacing my rear shoes (plenty of lining left) with OEM shoes did the trick

maachine

the grab you are describing, my truck is really bad about doing that when they are cold. but i dont have any pull or shudder. after about 5 seconds of braking slowly or using my brakes more than 3 times, the grabbing stops.