sfjohnson

Trying to diagnose strong sway / pendulum from back end under power. For example, while under power if something disrupts straight line driving a strong oscillation sets up in the rear with strong body roll requiring wrestling the wheel straight. For example pulling a hill in a cross wind or a gentle flick of the steering wheel starts the rocking; straightens right out once accelerator is lifted. Originally thought it was the tiny sway bar so swapped in the old one from my (now vey stiff) WRX. Then KYB struts and standard height King Springs. Also did engine and transmission mounts (stock, not group-n), now wondering if differential mounts (front 'K' and back hangers) or trailing arm bushings. Nothing seems overly loose or sloppy compared side by side to the WRX. Any ideas? Thanks in advance!

flstffxe

Any current alignment numbers?

__________________
His - 08 X Prem 5mt
Hers - 08 X 4EAT
Subaru oil filter comparison

sfjohnson

Thread Starter

All within specifications. It's done this since I bought it used 4 years ago and through a half dozen alignments. Thought it was just standard for a Fozzy with Dunlop Wintersport M3s and I was over-critical after driving my WRX. But after Kings/stuts, mounts, and the sway bar, the pendulum persists and figure it has to be something worn/shot/loose. Or at least want to correct it.

flstffxe

Subarus specs are almost wide open for alignment numbers. You can have a alignment that will cause handling issues and still be with in those factory specs.

I would also be curious about the differences in the numbers between those half dozen alignments. Both our '08s needed to have the alignment corrected shortly after being purchased new, both had too much toe and had every thing else dialed in. Have not had a alignment since on either, no abnormal tire wear, tracking or pulling. If the numbers are moving around a lot it may be worth looking at some of the suspension bushings. But there shouldn't be a need to have an alignment done on an average of 8 months.

Tires and tire pressure can play a huge roll.

__________________
His - 08 X Prem 5mt
Hers - 08 X 4EAT
Subaru oil filter comparison

sfjohnson

Thread Starter

Just got back from the stealer. Mechanic says: 'worst handling Subaru I've driven.' Immediately blaming KYB struts / King Springs, which went on to try and improve the sway (which did improve some). Alignment was ok (numbers below). Next idea: junkyard transmission and the differential gearing wasn't matched properly (80k miles since I got it, and 150k total; figured it would have worse problems than sway under power if the real case). Last resort is to leave it with them to tinker with and get charged hourly. When asked about diff carrier/outrigger bushings, tire flex, etc., was met with blank stares. I've had good experiences with Dunlop Wintersport's in the past on other vehicles; currently have M3's. Feels like the whole front end is 'light' all the time, and under power the back end humps up and moves. Alignment numbers:

Camber: LF 0.2, RF -0.2
Caster: LF 2.3, RF 2.9
Toe: LF 0.01, RF 0.01
Total Toe: F 0.02
Steer Ahead: F 0.00;

Camber: LR -0.4, RR -0.5
Toe: LR 0.09, RR 0.10
Total Toe: R 0.19
Thrust Angle: 0.00

Any other ideas?

sfjohnson

Thread Starter

Problem solved! Tried my 235/40r17's of my WRX to eliminate tires, and it was much improved (much less resonance with the pendulum - remember your freshman physics simple harmonic oscillators?). So dropped it off at a drive-live line specialist/friend. No way I was going to give the stealer to 'think about it' for $80 an hour.

Turns out it was a broken link bolt on the rear driver's side hub. On the ground, and on the rack, there was enough tension not to be evident with any loose arms, but putting a jack under the arm while on the rack, the wheel was floppy. He noticed there was an odd appearance to some rust coming out around the bolt, evidence of rusting - shining - re-rusting.

While he was in there, replaced all the bushings with Whiteline/Prothane. Next up are both rear wheel bearings - the wiggle for 80k wore them out. Still has a bit of body roll that the WRX sway isn't taking care of, but we're on the right track now.

So recap - bought from a Subaru dealer, half dozen alignments at Firestone, and then checked by another Subaru dealer - none of whom could figure it out. And thankfully it didn't let go in the 80k I've had the vehicle...

Aaron'z 2.5RS/WRX

Wow.. so an alignment shop/dealer couldnt find a broken suspension bolt?

I feel so much safer knowing that these people are ASE Certified.....
. :facepalm:

Sent from an other planet (Tapatalk)