2015 DCSB unstable at highway speeds

I recently sold my 2002 Tacoma DCSB TRD Off Road and purchased a 2015 DCSB SR5. The same day I bought it I installed the following:
255/75R17 BFG MT'S at 32psi (Wrangler Rubicon Tires)
17" 4runner trail wheels (2016 MY)
5100's at the 1.75" setting with stock springs
Single rear Add A Leafs (2" lift with stock rear shocks)
A 2012 ELD rear axle with home made wire harness and momentary switch
Caster: 2.0L 1.9R
Camber 0.09L 0.12R
Toe: .05 total
Stock upper and lower control arms

I really did not drive the truck much before I did the mods but have had it a few months now I have noticed it kind of sucks to drive on the highway. The steering I way to sensitive at high speeds, any movement and you dart back an forth. I get way to much steering wheel feedback, this is annoying at low speeds also but when mixed with the twitchy steering at high speeds makes ruts in the interstate a handful. If there is packed snow or slick spots on the road surface and you are doing more than 40 mph it is scary, you have absolutely no idea what the truck is going to do. I could drive the same roads/conditions with my old Taco (exact same tires and psi) and do 60mph+ with confidence. On curvy mountain roads it is super difficult to get the line right and any slick stuff gets under steer followed by over steer, all of which is very unpredictable again the old truck was way more predictable. Any advice on how to settle this thing down and make if feel more planted (alignment specs, suspension parts, different steering rack???) Love the truck, just wears me out to drive on long trips or at high speeds.

 

Have you gotten an alignment since installing your lift?

Wheels/Tires balanced using a "Road Force" balancer?

Are the tires new? Rubber compounds break down over time.

 

The tires were off of a 2017 wrangler with 200 miles on them and have 2017 date codes. Yes on the alignment, Caster: 2.0L 1.9R, Camber 0.09L 0.12R, Toe: .05 total. And I did not ask if they road force balanced or just used a regular spin balancer on my tires but there is no vibration at any speed from the tires.

 

Is the stabilizer bar still intact?

 

Yep stock sway bar is still there and attached

 

I'm not buying the alignment numbers.

I've seen good numbers given by machines that were in need of calibration.

And both camber and toe should be about 0 on a truck. You're numbers, while 'low', would indicate a twitchy vehicle to me. Which is pretty much what you describe.

 

Sounds like a simple lack of traction to me. You mention you get understeer on slick stuff... then oversteer (i.e. traction suddenly gains and now that you've got the wheel turned the tires redirect movement).

MT tires (such as the BFG MTs) aren't really designed for slick surfaces like ice/snow. They're designed for... wait for it... Mud Terrain. They're best on sand or mud where you need paddles to push you.

 

Does it like being all over the road and kind of a chore to drive? Your caster is way too low. You may not be able to get it higher w/o different upper control arms. I would also try rotating the tires front to back is see if there is a difference.

 

With stock suspension I too notice the over sensitive steering. Anyone wanna chime in with some answers ?

 

I had a similar issue, scary to drive over 60mph

Took it in to get an alignment and my buddy was not able to get it perfect...

I purchased upper control arms (total chaos) and it made a huge difference, 85 on the freeway with confidence..

My tires are Michelin ltx at 2’s 265/75/16, I believe they are similar size to yours....Warren

 

Pit the exact same tires on my 17'. After going from stock I can confirm it felt...a bit outta control. Since then I have gotten used to the feel of the MTs, but will be changing to a AT, mostly bc of road noise. BTW I damn near wrecked the first time I drove them in rain, actually slid sideways under hard braking. I would bet it's 90 percent the tires, maybe 10 percent alingmment.

 

Clearwater Bill I think we are on the same page. I've grown to believe that alignments are probably one of the biggest scams going in the automotive business. The problem is two fold: technicians who do not know how to operate the machines, and equipment that may not have been calibrated since new. I recently caught an alignment company cheating the numbers.....oh yes that keyboard on their fancy machines can do other things. I went in and asked for the preferred values -- and they gave them to me in a printout -- perfect. But my truck was never on the rack but in the way back of the place supposedly out of view -- at least they thought -- and they only scribed the front tires the old fashioned way to give a toe-and-go but nothing else.

 

You might want to look into changing out the steering rack bushings. Energy Suspension makes the kit, because Toyota only sells a whole new rack. Four Wheeler Magazine has a write up here. On my DCSB I changed out almost EVERYTHING (UCAs, LCAs, Inner & Outer Tie-Rods, Coilovers, Cam-Bolts and I still need to put in the bushings) but I think the driver side tie-rod was causing the problems with steering. I took off the boot and it was full of grease and the outer felt loose.

 

Thanks for all the feedback, as far as tires go I ran these exact same tires on my old tacoma for about 40,000 miles and I guess I have kind of ruled that out as the cause. My first thought was alignment, should I go more than 2 deg. (not .2 but 2 deg) of caster? As far as camber and toe go I agree 0 all the way around would be best but it is basically that near as makes no difference. Alignment machine calibration could be a small factor here but I definitely had a wicked caster pull and super bad bump steer after I did my lift and after the alignment the truck drives straight and the bump steer was significantly reduced. I am defiantly inclined to believe the numbers they gave me. Would something like 3* caster and a little negative on my camber be the ticket?? I dont have my own rack so I am paying around $100 a shot to get it done and they really don't like it when I give them my own number. I had to do that last time, I think the factory specs had caster way down at like 1-1.5*. I was also thinking about dropping my front end down a slot on the shocks, thinking maybe the control arms were at a little to steep of an angle making the tires move to much (in and out) when the suspension moves up and down?

 

Check the control arm bolts /cams and make sure 1 didn't loosen up. Lie under the truck and have a buddy crank the steering wheel back and forth. Look for the steering rack moving around (like the sloppy bushings mentioned above)

 

Cool, will do. Also worth noting the truck only has 40,000 miles on it so everything seemed pretty tight (new) when I took it apart.

 

Forget factory specs as they can't be used anymore once the suspension is altered, the ride height changed, and larger tires used. Try to bump the caster up to 3 degrees if your upper control arms will allow. Your steering will become a little heavier but less vauge and more stable. Leave camber alone for now and definitely do not go with negative camber.

 

Oh, and see if they are doing toe correctly as I still would not rule out some bump steer. They should be adjusting the tie rod ends equally on both the left and right sides. Measure from the jam nut on the TRE the threads exposed that are left. You can use a 3X5 card or anything else and mark the card. It should be the same L-R and Toy only allows a max of 1.5 threads difference.

 

Take some pics if you can of your adjustment cams on the lower control arms of the left and right sides, front and rear, and I'll tell you if there appears to be much of any additional caster that can be had.

 

Thanks! Might be tomorrow before I get a chance though. From what I have been reading it sounds like it might be hard to even get the numbers they gave me with stock UCA's at the 1.75 setting.