DaGunit

Hello all and thanks for thinking about this and sharing any ideas you may have. Most of this is back-story / explanation. Skip on down to bottom to get cliff notes starting at "SYMPTOMS":

I have a 2010 GS 350 awd with 92k. It has been lowered on Megan Racing C/O's and 20" wheels/tires. Wheels are 9" wide in front, 10.5" in back. I have 245/35/20's on the front with 275/30/20's on rear. It has been setup like this since about 45k miles (about 4 years) with no real probs (slight rubbing until proper ride height dialed in and the all-too-common vibrations at stop/low speed wobble - lived with it a while).

Many more mods but those are the applicable ones for the purpose of this thread. Now for the embarrassing part....

Had a wheel repair scheduled for one day a couple weeks ago and forgot about my appt. until I was headed out the door to work. Running late (and obviously not thinking clearly), I grabbed one 17" wheel and a jack to throw in the car so I could remove the curb-rashed wheel (20") from the rear of the car to be repaired. In total, drove about 37 miles (a few of those at highway speed, say 65mph) until I got home and put the another 17" wheel on the other side so at least the rear had the same size wheels on. Drove to work and back like that (maybe 15 miles total - no highway) but not until after I started noticing some vibrations especially when accelerating. Now, it is possible (likely even) those vibrations were there before the two 17's and two 20's (front to back) meaning they were (likely) there when it was three 20" and one 17" but I'm just mentioning when I absolutely recall noticing the vibrations. Got home, put all 17" wheels on until 20" wheel fixed.

Wheel fixed, go to pick up, noticed tire bald on repaired wheel while other rear tire had about 5/32 left. Obviously, I had already been driving around on mismatched rears (due to certificate replacement from nail in tire not long after I bought both rears but apparently my left rear wears faster (another issue I realize, but for another time)). Thus, I had been driving around for quite some time with mis-matched rears (estimate 10k miles), then did the stupid thing with the 17" while 20" was being worked on.

Since then, bought new tires, rotated all sorts of different ways with both sets (17" and 20"), two alignments, independent Toyota shop diagnosis., Lexus dealership diag, endless trips to discount for remounting/rebalancing/Hunter road force machine calibrations/checks and all to no avail. Indie Toyota shop and Lexus dealerships refuse to continue diag. without returning vehicle to stock 100% claiming the mods are the cause. That is non-sense. This clearly came up while driving on mismatched sized tires/wheels and is not tire/wheel nor suspension related. Damaged a coilover when lifting the vehicle up so many times is highly unlikely but the only possible way (I can think of) that the suspension would be the cause.

SYMPTOMS: Shudder/vibration through body when accelerating especially between 3 - 5k rpm range. Pull to right when accelerating (wasn't there before and both alignments were within spec - checked twice). Coasts straight, no vibs/shudder when in neutral. No hard shifting going on though. No whining of diffs. All mechanics believe all parts (suspension and driveline) are tight and check out well. No leaks. Tires checked so many times, the guys at Discount know me by name and laugh when I come walking back in. Wheel was not damaged enough to cause any bends and that theory eliminated with stock 17" test.... after test... after test.

All that said, my research now is leading me to differential or transfer case and hopefully not any transmission damage.

QUESTION: If I have damaged the drive line due to mismatched wheel/tire size, for those of you who understand the AWD system on the GS 350, where would you start throwing money at replacing parts? Rear Diff? Front Diff? Transfer case/tranny? Ever heard of this sort of problem with any other Lexus owners before?

I thought about trading it in but even a quick test drive would raise eyebrows. Think I'm going to have to own up to my mistake and figure out best/quickest way to resolve which is why I'm reaching out! Already know it won't be cheap. I'm already at about $1,000 between tires and diag fees.

Sorry about the novel but I truly thank you for any ideas/input as I'm not familiar with the AWD system. Not sure if damage is more likely to be left to right, front to back, in the diff, or in the transfer case, or what?

Haven't done a drain of the diff to see if I have a lot of crap in there. Maybe that should be my next step?

DaGunit

Bump.... Additional thoughts: Don't believe the pulling to the right to be related. When I switched front wheels/tires, pulling stops (possibly due to previous wear patterns and just mixed them up when re-installing first time - only rear tires were replaced - fronts only had about 10k miles on them or less - showed 7/32's). Vibrations/shudder still prevelant. Seems most noticeable, however, when light load. Ex. pushing on gas pedal just to maintain speed on slight incline. Also seems worse when needing low end torque like bottom (2k rpms) of 4th gear. However, it seems to shift when it should and has no problems doing so. And still does it under heavy acceleration but not as bad as when light acceleration needed. In fact, if I can accelerate in between (at the sweet spot), it is hardly noticeable (most people probably wouldn't know anything was up).

Just occurred to me: Aren't the front and rear diffs open diffs? If that is the case, and they are not LSD, then wouldn't mismatched tire/wheel size damage most likely be in transfer case? Maybe torque converter or tranny but less likely? Anyone?

Now thinking transfer case drain/fill to check for bits is better place to start than front or rear diff drain/fill.

ibidu1

iTrader: (1)

I had the same issue you had on my 08 AWD, and had the same wheel setup but on stock suspension.

What cured my issue was completly replacing all the bushings in the car. I would replace 2-4 arms at a time hoping the problem went away it didnt. The pulling to the right, I also had! I think the majority of the issues came from the front lower control arm rear bushing. It looked good, but after I replaced it and got a new alignment the issue went away. Also on the rear I replaced the top chamber arms to an adjustable arm, and had the alignment shop add positive chamber to the rear to help flatten the rear tread.

But def. replace all your suspension bushings at once, and then get it realigned. It will save you a lot of headache, trust me I chewed up a set of 20" tires trying to figure it out.

DaGunit

ibidu1: Good to hear from you again! Long time, no talk. Much appreciate you sharing your experience (as always!). Bummer to chew through $$$$$ tires but better than some of the possibilities I've been fearing with my situation so I'd chalk that up to a lesson well learned (if it were me).

I am down to driveline and suspension at this point so certainly think you could be on to something. The only issue I take with your theory is that this 'change' was realized in 1 day. The day after I swapped those wheels. I def. understand that it could just be a conicidence but kind of doubting it. In fact, I'm thinking, if it is suspension, possibly something I caused when raising/lowering the vehicle (too much stress on some point and whatever was weak/failing just failed right then and there from the stress).

I'd be lying if I didn't have a raised eyebrow at the LCA bushing though. Even though it looks fine, maybe it has failed? In my opinion that theory is better justified when you consider the vibration is under load but I'm reluctant to believe it is suspension related.

What I find myself continuing to think about is "torque". I even say it out loud (when driving by myself) as I'm contemplating all the working pieces taking place as I am experiencing the vibrations.

Regardless, I was thrilled to see a reply and I thank you much for your ideas/experience! I will start looking more down that road to widen my gaze. The independent shop and Lexus both said all suspension elements were checked and seem to be tight and in good working order. Is there anything you can do (besides just replace bushings) to test for problems? All I know is inspect for unusual movement with pry-bar. Were yours showing any signs or just by replacing them was how you got your confirmation?

I am thinking of raising the car up this weekend (on the coilovers) to see if there are any changes due to ride height, suspension angles/geometry as the Lexus Dealership is so convinced is the issue (of which I think is total crap). That is the cheapest/easiest next step.

Then, probably schedule drain/fill of transfer case.

If still an issue, bushings could likely be next.

I do raise the car high enough on one side when changing wheels/tires that I can do both the left front and rear at the same time. I'm wondering what parts that stresses and if that may have caused some sort of damage.

Please feel free to throw out any other ideas/suggestions! Would still really love to know if front/rear diffs are open diffs and if I have my understanding correctly that mismatched wheels/tires would not affect open diff. Any takers?

ibidu1

iTrader: (1)

When you installed the 17s did you get an awd error light pop up? I got that once when one of my 20"s had a flat tire and had to use my spare tire. It freaked me out and I didnt go past 50mph. Putting one off sized tire I assume would be ok because of the differantial, but when you threw on both 17"s I think that may put tension on the driveshaft into the transmission but certain awd transmissions have a awd clutch. When you replace your diff fluid, look for metals or any shiny bits I doubt you will find much. I also doubt you did any internal damage!

As far as the tire wear issue in the rear, I tried pry bar, all my bushings looked and preformed fine under the car. That was the odd issue! It would pull to the right slightly. I tried many shops and I couldnt figure it out. But it was costing money from the tire getting chewed up as I do lots of highway driving. But after replacing all of the bushings minus the front control arms. The issue went away my car doesnt track and doesnt have tire wear issues. Replacing the LCA bushing fixed my issue with the car pulling to the right.

Try putting your ride back to oem, and get the car realigned if you have purchased yearly package for free alignments.

DaGunit

ibidu1

iTrader: (1)

Actually Dagunit traditional 4wd have mechanical transfer cases, awd do not. Awd system would usually give you different power to each wheel. For instance an awd you may get 60% power to the rear wheels and 40% to the front depending on clutch or computer that tracks from speed sensors. If you had a traditional transfer case you for sure would have heard the tires in the back slip as there is no clutch in a transfer case, just gear driven.

My theory for the abnormal tire wear i believe is coming from the bushings.

But for vibrations while under load, that maybe caused from a bent rim, or not having hubcentric shims, abnormal tire wear, driveshaft or cv axle has an imbalance. I suspect its your rims, being bent or warped. Have a job spin them on a balancer and look for any whobbling in the face of the wheel and more important in the rear of the wheel.

DaGunit

Interesting.... Than what is this? Maybe I'm misinformed? Lexus GS 350 Transfer Case

And then HERE you can see where the transfer case actually attaches to the transmission with the rear drive shaft going straight back from the transmission and the jetting out part of the transfer case attaching to the front drive shaft. It is my understanding the clutch pack lives within this unit. I could be wrong of course.

DaGunit

Or maybe I am misunderstanding what you're saying. If you're saying, they don't have mechanical transfer mechanism but they do have one (it's just clutch, not mechanical), than I agree with you. My concern is that I damaged that clutch within by running too long on mismatched tires and then added the different sized wheels, sending it over the top of what it could handle. Probably generating too much heat and damaging parts. That's theory #1 anyway.

DaGunit

An additional mention is that the shudder I feel when on the gas reminds me of what a bad clutch on a motorcycle feels like when taking off from a stop; shudders because torque isn't transferred correctly/smoothly. Additionally, I'm wondering if it isn't currently applying power/torque correctly between front and rear (due to the possible damage) which might be lending to greater torque steer (in the front) causing the pull.

Obviously, I have been thinking about this too much lately. I just wish there was some sort of bread crumb trail so I don't have to waste money guessing. I'm ok with spending money on the car, just don't like the thought of wasting money on the car. I'm sure most of us have been there at some point with at least one of our vehicles though! Cest la vie

ServerTech

Transfer case is part of the AWD transmission and uses ATF from the transmission for lubrication. That's why the AWD car has a bigger transmission fluid pan and filter than RWD cars. That shudder you feel sounds like slipping forward clutches from dirty ATF. You should drop the AWD pan, clean up the magnets and replace the factory AWD filter like I did at 62k.

https://www.clublexus.com/forums/gs-...er-change.html

Good luck with your car.

DaGunit

DaGunit

DaGunit

DaGunit