ABS Engaging and Bucking w/ Lift

[SgnDen]

Thought I'd share this issue and dealer feedback.

I installed my Toytec lift + wheels/tires within weeks of my '13 Limited landing in my driveway.

Under hard braking and/or big bounce conditions where the ABS engages, the nose would of course drop a bit and ABS engages. However, on the un-weighting of the front end caused by typically slight release of pressure on the brake pedal and/or simply gaining traction, the nose pops-up and the ABS again engages heavily/abruptly causing sever bucking action. Pretty wild but I just dealt with it. However, after a few incidents where it involved dumbass drivers/bicycle riders (I live in a college town) where emergency braking an maneuvering was required, the edge of control thing was well, no bueno.

Took 'er into the dealer. They abused it for a while and 100% experienced the same thing.

Diagnosis - When I had the lift installed (the lowest ToyTec makes), they had to disconnect the XREAS. I knew it would need to be disconnected but the new suspension did just fine keeping things leveled as XREAS would've.

S, when the nose dives, ABS kicks-in, traction is gained, ABS release, nose comes up...BUT it "bounces" up more that normal due to the new suspension..that unweights the front end and re-engages the ABS and sends the whole shebang back into nose dive.

Any of you guys with lifts experience this?

Yeah, if it's icy (today), I can just hold the pressure, let ABS do it's thing and no kicking/bucking around as long as I do NOT let-off the brake until nearly stopped. Not an optimal maneuver of course.

-S

 

[Intruder]

What about doing a zero point calibration?

 

[1engineer]

I don't understand. You brake hard, ABS kicks in and you either come to a stop or slow down sufficiently for the condition. Right? Why would you let off the brake until you slowed sufficiently (or stopped)? I guarantee you that if I were going 60 mph, slammed on the brakes hard enough for ABS to kick in, immediately let off the brake and then instantly slammed them on again hard enough to bring ABS back into play my 4Runner would buck and jerk too. It has nothing to do with nose dive or suspension just driver input. Usually when you brake hard enough to bring ABS online you hold it until the maneuver is completed. Now, throw our brake assist on top of ABS and it would be a wild ride indeed if you did it consecutively!

 

[SgnDen]

I don't understand. You brake hard, ABS kicks in and you either come to a stop or slow down sufficiently for the condition. Right? Why would you let off the brake until you slowed sufficiently (or stopped)? I guarantee you that if I were going 60 mph, slammed on the brakes hard enough for ABS to kick in, immediately let off the brake and then instantly slammed them on again hard enough to bring ABS back into play my 4Runner would buck and jerk too. It has nothing to do with nose dive or suspension just driver input. Usually when you brake hard enough to bring ABS online you hold it until the maneuver is completed. Now, throw our brake assist on top of ABS and it would be a wild ride indeed if you did it consecutively!

Hi Greg:

Yeah, this is absolutely not a matter of being a s*tty driver who can't operate or feel the right degree of input required for any given situation (like landing a '50 Globe Swift at 90kn in a 15kn crosswind). That's why I tried the dealer so they could be sure things were calibrated properly.

The up/down movement is not so much the issue (which would of course occur normally), it's that the ABS re-engages at the "top" of the un-weighted action. So the ABS does fine on first required engagement (e.g. emergency braking), I then release pressure as appropriate (ABS disengages), slightly reapply pressure as appropriate and "balmmo" (technical term) the ABS re-engages full tilt.

Dealer said it was due to the stronger front suspension causing the front to "pop-up" more abruptly than stock + no XREAS. That's all they said and of course blamed it all on after-market components so they wash their hands of the interesting phenomenon.

However, I certainly get what you are saying in general.

 

[Intruder]

I then release pressure as appropriate (ABS disengages), slightly reapply pressure as appropriate and "balmmo" (technical term) the ABS re-engages full tilt.

Didn't catch this before. Don't pump the brakes with ABS. I remember when ABS started getting more mainstream there were a lot more rear end collisions in the winter around here because people were still using threshold braking along with ABS so it was taking them even longer to stop.

 

[SgnDen]

Didn't catch this before. Don't pump the brakes with ABS. I remember when ABS started getting more mainstream there were a lot more rear end collisions in the winter around here because people were still using threshold braking along with ABS so it was taking them even longer to stop.

Ha, for sure. Still happens when you see all of the folks around here new to serious ice/snow driving...you can see it a mile away for sure.

My situation in these instances is where it doesn't make sense (or safe) to get all of the speed scrubbed-off by applying steady/reasonable terminal pressure to dead-stop.

Also kicks-on when going over a large speed bump...a bit faster than I probably should. ;^)

 

[Intruder]

I'd go with zero point calibration as a starting point then. It's not difficult to do and has been documented in a thread on this forum. If that doesn't solve your problem then you can look at other things that might cost money to fix.

 

[1engineer]

Hi Greg:

Yeah, this is absolutely not a matter of being a s*tty driver who can't operate or feel the right degree of input required for any given situation (like landing a '50 Globe Swift at 90kn in a 15kn crosswind). That's why I tried the dealer so they could be sure things were calibrated properly.

The up/down movement is not so much the issue (which would of course occur normally), it's that the ABS re-engages at the "top" of the un-weighted action. So the ABS does fine on first required engagement (e.g. emergency braking), I then release pressure as appropriate (ABS disengages), slightly reapply pressure as appropriate and "balmmo" (technical term) the ABS re-engages full tilt.

Dealer said it was due to the stronger front suspension causing the front to "pop-up" more abruptly than stock + no XREAS. That's all they said and of course blamed it all on after-market components so they wash their hands of the interesting phenomenon.

However, I certainly get what you are saying in general.

Pretty sure your dealer is full of shit. That said, I don't think ABS is technically to blame here either. It sounds like your brake assist function is the causation of your consternation or really, the actuation of the brake assist feature.

Here is what I know from personal testing:
When applying the brakes on the 4Runner with a slow, steady force, you can get to the ABS actuation without the brake assist function kicking in. If you "panic" brake, that is stab quickly and hard on your brake pedal, you will bring in the brake assist and MAN does it assist! I did this test when I owned the 2011 SR5. I was intrigued by this braking system after panic braking for a deer and stopping right. now. so I went out to a stretch of deserted highway and decided to figure out how this works. I got up to 50 mph and slammed on the brakes. I mean hit it hard and fast just like a panic stop. The brake assist kicked in and I stopped really really fast. I then got up to 50 mph again and gradually (by gradually I mean less than a second but not instant) applied increasing force to the brake pedal. The ABS kicked in but no brake assist! I did it a few more times with varying degrees of actuation force and speed and determined that the brake assist actuation has to do with the velocity over time before it was activated. What does this mean for you?

Take your 4Runner out, much as I did, to a deserted stretch of road and start testing. Make your maneuvers as you would normally do, then go back and do them using a slower actuation speed, meaning don't instantly but gradually push the brake pedal. Report back.

I actually changed the way I brake with the 4Runner after my testing. Brake assist is a great tool to augment stopping but I, like you, would prefer more control during the braking process. Now in a true panic stop brake assist is going to happen (instinct) but for all other situations slow(er) than instant actuation might just help you.

 

[BlackWorksInc]

What suspension did you install (spring weight, shocks, ect) and what other mods do you have? (i.e. tires, front bumpers, ect.)

We need to start parsing through some details a bit.

 

[3wbdriver]

I'm wondering if Toyota can re-flash the ECU so it's not looking for the XREAS? And whether this could possibly change how the braking system works? I don't know squat about the system but it seems like if this started after you disconnected it your 4R may be having a brain fart (technical term).

 

[bimrunner]

I'm wondering if Toyota can re-flash the ECU so it's not looking for the XREAS? And whether this could possibly change how the braking system works? I don't know squat about the system but it seems like if this started after you disconnected it your 4R may be having a brain fart (technical term).

XREAS is hydrolic and not electrical so there isn't any ECU input/reading. It shouldn't make a difference to the truck's brain if it has XREAS or not. I don't have this issue fwiw.

 

[Jhalko]

Agree with [MENTION=89562]bimrunner[/MENTION] I've got the toytec boss coil overs and no issues at all since taking out xreas.

 

[3wbdriver]

XREAS is hydrolic and not electrical so there isn't any ECU input/reading. It shouldn't make a difference to the truck's brain if it has XREAS or not. I don't have this issue fwiw.

In my defense I did admit ignorance of the system. It was just a thought. Thanks for the clarification.