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Bringing up an old post I found and hoping to get some help..



I'm having an issue with the following set-up: 2015 Silverado, Black Widow edition - 6" Fabtech & 35x12.5x20 MT ATZ's. I bought the truck last week and noticed the wheels hopping/sliding when fully turning left or right. Thinking it was an alignment issue, I brought it back to the dealer to check. They made some minor adjustments but nothing was out of GM spec and the problem remained. I contacted Fabtech to see if there were any other specs i should use for the alignment other than what the manufacturer recommends after the lift but they said "not really". i did get the alignment specs for one of the trucks they (Fabtech) own with the same lift and the only thing i can see different than mine is the slightly increased caster angle. No idea what the issue is but very annoying and sure it will wear my tires prematurely.



Based on my knowledge, it seems like whether turning left or right the outer wheel is over-steering and/or the inner is under-steering causing the outer to either slide or hop. Driving straight or in slight turns is great. Only see the issue at full turn. Also lost turning radius but kinda expected that with the lift/tires. I'm sending Fabtech pics of tread marks and tire wear and see what they recommend. Seems like the Ackermann angle is off but not sure where to start with ruling it out. The truck is back at the dealer today to align according to the Fabtech specs but not sure what to expect when I get it back.



Always in 2WD and rarely use the auto 4WD feature.


Disengaged the traction/stability control to see if anything changes but nothing. Other than that...Stumped



Pic is of the skid marks left after turning left. Same is happening at a full right turn.



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Sounds like a faulty differential.

 

This truck was brand new when you bought it?

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I bought it with 8500 miles (used). Could possibly be a faulty diff. I did put it in some wet grass with the front wheels on a brick to see what the rear would do and did get the initial one-tire spin before it locked both wheels. Any idea how to check the differential? I haven't noticed the back tires binding/sliding when turning.

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Also, the inside tire seems to follow the correct path. Only the outside tire is sliding. Something seems off with the Ackermann angle but not sure how to check that other than the Fabtech design specs (which i oubt that I'll be able to get).

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I did put it in some wet grass with the front wheels on a brick to see what the rear would do and did get the initial one-tire spin before it locked both wheels. Any idea how to check the differential?

that's how it's supposed to work. If the front tires are sliding in sharp front turns like that, I wouldn't be surprised because of how big your tires are

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I've had a range of trucks from small to large, Ford and Chevy, most with same size tires and even bigger and never had this problem. I expect a little chirp or even light skid at a full turn but not to this extent. And note that it's only the outside tire sliding when turning in either direction. I give these tires 20k miles max if i kept it this way.

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Brought it back to the dealer and had it aligned to specs that we got from a Fabtech rep on their test truck...Made it worse. Re-aligned back to factory specs and better but still not right. Next step is to have the Southern Comfort (company that installed the lift) rep come take a look. I have 2 service advisors, 1 lift mechanic, two alignment techs completely stumped. All were on board to get this truck fixed and the problem resolved but several are using the "it's normal" excuse when nothing seems to be fixing it.

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Only at full steering lock in either direction? I had factory size tires on my 08 and it did it. i thought it was normal. You can't, at least i don't think you can, align a truck to go straight down the road and to make turns at full wheel lock as the tires are turned to the same degree right? Let's say it's 45* on both tires, the outside tire needs less than 45 degrees to make the same turn with the same friction. Again, i thought screech from the outside tire was normal for thie reason i just mentioned. But i am not sure, mechanics is a hobby, electricity is my job LOL

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You are correct on thinking that if both tires turn the same angle one will slip/squeel/bind/etc since they are traveling around circles of different diameters. This is accounted for by what is called the Ackermann angle which allows the inner wheel to turn sharper than the outer and thus follow the correct path. In my case, it seems as though the Ackermann angle is reversed and my outer wheel is turning sharper than my inner wheel. This is binding the front end when steering and causing the outer to slide as the truck follows the path of the inner tire. I know chevy's have a tendency to squeak the tires a bit at a full turn by I've lost so much turning radius that I'm not even 3/4 of what a stock truck should be. I'm assuming something was done incorrectly when installing the lift or something is bent somewhere. I'm going to look at another truck at the dealership that just had the exact lift put on and compare the two.

 

Anyway.. Here is a good article explaining the Ackermann Angle if interested.

 

http://www.super7thheaven.co.uk/glossary/ackermann-angle/

 

 

Also, I can feel it gradually increase as I continue turning. At full lock it's the worst (obviously) and has me completely stumped...

 

Best way to visually explain my problem:

 

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Edited by only1adam12

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Just went and inspected the front suspension and found this (pic). Extreme and uneven wear on the front of the lower a-arm where the spindle has been rubbing. First, Isn't the steering bump-stop on the rear of the spindle? Even if this is (another) bump-stop on the front of the spindle, why is it so worn with only 9k miles on the truck? Fabtech claims that this is normal but really doesn't seem normal. If it is, what will be left at 50-60k miles? It's the same wear on both sides and I have the problem when turning either direction. Coincidence?

 

I'm thinking this is either a cause or result of the issue I'm having. Any ideas?

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Edited by only1adam12

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Hey Adam,

 

Getting slightly off track here, but I think you are saying that you bought the truck used a week ago correct? If so, did you get a carfax or other printout showing that the truck was never wrecked?

 

I ask because I have seen a wrecked and repaired truck once that would turn sharper to the right, than to the left. it was hitting the steering bump stop on right turns, not on the left ones. Ended up having to change a steering box and a upper and lower control arm that was residual damage that was not fixed from the accident.

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Correct, I bought it on New Year's Eve and did get a carfax. Everything looked clear and even showed the first round or normal maintenance performed. It only has about 9k miles and does it turning in either direction. I brought it to another tech today and he is stumped as well. Said that he's never seen a bump stop wear that much but he normally deals with steel suspension and this truck has aluminum.

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Silly me i thought the stops were in the rack and the stops to the control arms were secondary stops. A lot of four wheel driving may cause that because that's a lot of full steering on 9k miles.(unless it occured while you had it after the lift) So, after reading the Ackermann tech sheet, i suspect when you modified the lift, (forget how much you lifted), you changed the angle of the tie rods from the rack. Essentially your tie rods went from horizontal to 30+ degrees angled down.

 

Now, after you set the toe, castor and camber back to original specs, does the travel of the tie rod change since the angle of the tie rod changed? I would guess after they set the toe to spec, (likely some outward turns on the tierods to make up length) the turning radius of the inside tire increased and the outside tire decreased screwing up the Ackermann angle from the increased angle of the tie rods. If the rack was moved with the lift then all of the above is moot. lol

Edited by Willshire

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I haven't had much time to inspect all elements but assuming the tie rod angles aren't changed much since the new Fabtech spindle compensates for the height. With a 6" lift, I don't expect the truck to perform like factory and don't mind the loss in turning radius but do expect it to turn properly and not destroy my tires after 20k miles. I highly doubt these bump-stops should be worn to this extent especially with only 9k miles. Seems like they held the wheel at full lock and ran over speed bumps (A LOT) in both directions. I also did some simple geometry to see how much the outer wheel will turn after losing 1/4" of the aluminum bump. Based on what I assumed the dimensions are, the front of the wheel will turn an extra 1/4" or ~1.1 degree compared to no wear on the stop. Might not sound like much but really is when there are 35" tires on it. This seems to be the exact problem I'm having but Fabtech seems to think the wear is totally normal. Most of the techs I showed the wear to haven't seen this before but mainly work on/lift trucks with steel suspension. My biggest questions now are is "is this wear normal"? and "is it the reason my outer tire is over-steerng"? Also, "why isn't the inner (rear of lower control arm) steering bump worn at all"?

 

At this point I'm still scratching my head on why no one knows what the cause of the problem is. I've been in contact with the dealer techs, lift techs, lift designers/manufacturer, and the company that installed it. Everyone looks at it and says "That's not right" but then when they can't come up with a solution they say "well, maybe it's normal". If it can't be fixed I'll have to start looking into returning the truck (even though i really don't want to) but can't/won't pay for something that isn't working properly.

 

Apologize for the rant but this is getting very frustrating...

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