hey yall, i just finished a full rebuild of the suspension on my 98 formula, & i was assuming that once the suspension was all redone (left no stone unturned-everything was replaced) that my rear axel shift upon acceleration out of a corner problem would be solved, thinking it was probably the sloppy factory panhard bar... but the rear end shift is still there!! ...its like u can feel the rear end shift to one side upon acceleration out of a corner, more so coming out of tight left handers or making a hard left like turning onto a side street or out of a parking lot & ur gettin on it a bit, ull actually feel the whole rear of the car shift to one side, & depending on the rate of acceleration, feels as if it could unsettle the rear to the point of loosing traction & coming around on ya?!? ...so a quick rundown just so anyone who wants to chime in will have all the specs on whats been done... the cars a 98 ls1 formula w/ 4l60e i purchased from my best friend who bought it new, so i know its never been crashed, so that rules out any structural issues... shes got founders subframe connectors, on-car adjustable panhard bar, ss brake lines, & shock tower bar, qa1 torque arm, umi 35/22 sway bars & aluminum sway bar mounts, bmr 1.5 drop springs, slp bilstien shocks, & new moog bushings (1le) in all the control arms, ball joints, tie rods, seats, isolators, & mounts, energy suspension bump stops, new set of 275/40/17 square bfg comp tires, centric cryo rotors, powerstop z26 pads, strano master cylinder brace, & a turn one pwr steering pump... the rear end is a factory 3.23 posi with 180k miles... aaaannnnd after all that, ive still got that un-nerving rear end "shift" under hard acceleration out of a corner?!? any advice or ideals of what to check would be greatly appreciated! & btw-i had a 98 camaro with almost excatly the same set up that was auto-x'd hard & it never did this?!? ...& one of my customers (although he has no f-body experience) asked if the rear axels might be the issue? ...with that many (180k) miles on them... could a worn rear axel cause that much of a shift??? ...& for the record according to my buddy whos a professional mechanic & always helps me with jobs this big, said that all the wheel bearings seemed to check out ok, but could they be the cause this mysterious issue?? ...ok, thanx yall for reading this & thanx for any advice yall could share

 

The panhard bar has asymmetric characteristics because it travel in an arc, it will pull the axle to the passengers side under compression and rebound. Plenty of people drive on panhard equipped cars and are never phased by the panhard's tendency to shift the rear end, the movement is pretty small. That said, a watts link will fix that, and is available from several different vendors.

 

thanx for ur reply... that being the case, yeah, im sure a watts link would be better, but my 98 camaro had similar suspension mods & it never did this like my 98 formula does? ...& theyre basicly the same car with different headlights... (although the panhard bar on the camaro wasnt adjustable) ...albiet, some of the brand names were different between these 2 cars, but the one big thing i can think of thats different between em was that the firebird has had subframe connectors added & the camaro did not... & i will say that it was doing the rear-shift thing before the suspension was rebuilt, so i was wondering if there was somethin i missed? or maybe the panhard bar might need some re-adjusting? ...thanx again

 

Double check the jam nuts on the panhard bar rod ends are tight. It sounds like the panhard bar is new so the rod ends on the panhard bar should be tight as well. Do the mounting bolts fit tight on the chassis and the axle? Have the holes elongated at all?

There is some play in the C-clip axles as well that can be tightened up with different thickness C-clips. These are available through various sources.

 

sounds like some good advice, thank u... ill go out & check those things... ive put a few break-in miles in on the new rebuild, so it would probably be a good ideal to do a walk-thru on everything anyhow... 'priciate the help, thanx!