What's causing my rear to scoot sideways??
12-08-2008, 10:47 AM
#1
Racer
Thread Starter
What's causing my rear to scoot sideways??
Whenever I shift or apply throttle on my 1996 CE/LT4 6 speed coupe, the rear end scoots to one side and then corrects back to center. This is more pronounced above 60 mph and is ocurring even after installing new:
rear differential, positraction, bearings & yokes;
drive shaft u joints;
ZFdoc C Beam beam plates;
Dennys half shafts w/ u joints;
rear spring, QA1 shocks & Baniski trailing arm; and
rear wheel bearings.
I'm to understand that this can ocurr if your C Beam is loose, but mine should be tight as a drum.
Any informed thoughts on what might be causing it would be appreciated.
rear differential, positraction, bearings & yokes;
drive shaft u joints;
ZFdoc C Beam beam plates;
Dennys half shafts w/ u joints;
rear spring, QA1 shocks & Baniski trailing arm; and
rear wheel bearings.
I'm to understand that this can ocurr if your C Beam is loose, but mine should be tight as a drum.
Any informed thoughts on what might be causing it would be appreciated.
Last edited by 89FX3; 12-08-2008 at 12:10 PM. Reason: spell check
12-08-2008, 11:45 AM
#3
Race Director
Random thoughts:
Does it happen with and w/o traction control engaged? Could me malfunctioning system? (Doesn't this work by pulsing brakes on spinning wheels? What if one side is working and the other is not?)
Are you sure rear alignment is correct?
Are you sure new posi is working correctly? (Maybe have someone trail and watch to see if both tires react the same under WOT).
Have you done any work on rear brakes....
And, of course, tires & tire pressure.
Does it happen with and w/o traction control engaged? Could me malfunctioning system? (Doesn't this work by pulsing brakes on spinning wheels? What if one side is working and the other is not?)
Are you sure rear alignment is correct?
Are you sure new posi is working correctly? (Maybe have someone trail and watch to see if both tires react the same under WOT).
Have you done any work on rear brakes....
And, of course, tires & tire pressure.
12-08-2008, 11:55 AM
#4
Racer
Thread Starter
I'm suspicious the C Beam & plates aren't tight.
But, if that's the case, wouldn't I feel movement in the shifter when it happens??
Last edited by 89FX3; 12-08-2008 at 12:10 PM.
12-08-2008, 11:59 AM
#5
Racer
Thread Starter
Random thoughts:
Does it happen with and w/o traction control engaged? Could me malfunctioning system? (Doesn't this work by pulsing brakes on spinning wheels? What if one side is working and the other is not?)
Are you sure rear alignment is correct?
Are you sure new posi is working correctly? (Maybe have someone trail and watch to see if both tires react the same under WOT).
Have you done any work on rear brakes....
And, of course, tires & tire pressure.
Does it happen with and w/o traction control engaged? Could me malfunctioning system? (Doesn't this work by pulsing brakes on spinning wheels? What if one side is working and the other is not?)
Are you sure rear alignment is correct?
Are you sure new posi is working correctly? (Maybe have someone trail and watch to see if both tires react the same under WOT).
Have you done any work on rear brakes....
And, of course, tires & tire pressure.
It's doing the same "scoot" it did before installing all new parts.
Rear brake pads (not calipers) & bearings are new.
Are you saying to punch off the ASR??
Bart
Last edited by 89FX3; 12-08-2008 at 12:11 PM.
12-08-2008, 12:01 PM
#6
Team Owner
Did you add the GM Posi additive after the diff work? What weight of gear oil went in??
Check the rear toe arms at the center; are the bolts that hold the center part of the tie rod assembly to the batwing tight? Also check that the batwing itself is mounted properly and the bushing at each end are in place and in good condition. Also check the sway bar connections and bushings.
I would think that there would have to be a major difference in tire pressure to get the car to move sideways at a shift outside of a loss of traction by one wheel. It would be evident at WOT shifts, but if you feel/see it at part throttle shifts, the problem will most likely be in the rear suspension somewhere, the posi, or the C-beam.
With the ASR left on, the first thing the system does to keep the car straight is change throttle position. That would be felt as a pulsation in the gas pedal. Input to ASR is from the lateral accelerometer and the wheel speed sensors. If the car doesn't yaw a lot in this case (not geting sideways on WOT acceleration) then the VSS input kicks in the ASR.
After throttle modulation by the ASR, then there is a reduction of ignition timing, followed by brake application through the ABS system. I would think that if what you feel is just a quick and short movement, then the problem is in the back of the car.
Check the rear toe arms at the center; are the bolts that hold the center part of the tie rod assembly to the batwing tight? Also check that the batwing itself is mounted properly and the bushing at each end are in place and in good condition. Also check the sway bar connections and bushings.
I would think that there would have to be a major difference in tire pressure to get the car to move sideways at a shift outside of a loss of traction by one wheel. It would be evident at WOT shifts, but if you feel/see it at part throttle shifts, the problem will most likely be in the rear suspension somewhere, the posi, or the C-beam.
With the ASR left on, the first thing the system does to keep the car straight is change throttle position. That would be felt as a pulsation in the gas pedal. Input to ASR is from the lateral accelerometer and the wheel speed sensors. If the car doesn't yaw a lot in this case (not geting sideways on WOT acceleration) then the VSS input kicks in the ASR.
After throttle modulation by the ASR, then there is a reduction of ignition timing, followed by brake application through the ABS system. I would think that if what you feel is just a quick and short movement, then the problem is in the back of the car.
12-08-2008, 01:09 PM
#7
Burning Brakes
My 95 also has had the side "scoot" for as long as I can remember. I tend to drive the car pretty gently but, on the occasional time where I start sharply from a stop, there is a definite "shifting" I can feel (I think the rear shifts leftward) which is most noticeable when I have the ASR disengaged.
Doug
Doug
12-08-2008, 01:27 PM
#8
Racer
Member Since: May 2004
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I also have a 1996 CE LT 4 and had the similar problem. After doing everything to the rear it still did the scoot... It always seemed there was just to much power and it wouldnt hook. Then someone pointed me in the direction of tires. I did have the runflat tires and I had heard that that could be a problem. Well I put the new Goodyear Tires on, non runflats and like magic it was gone. Stright ahead at all speeds. I dont know what kind of tires you have on but if its the runflats I would take a look at them, good chance that might be your problem....G
12-08-2008, 02:03 PM
#9
Racer
Thread Starter
Did you add the GM Posi additive after the diff work? What weight of gear oil went in??
Check the rear toe arms at the center; are the bolts that hold the center part of the tie rod assembly to the batwing tight? Also check that the batwing itself is mounted properly and the bushing at each end are in place and in good condition. Also check the sway bar connections and bushings.
I would think that there would have to be a major difference in tire pressure to get the car to move sideways at a shift outside of a loss of traction by one wheel. It would be evident at WOT shifts, but if you feel/see it at part throttle shifts, the problem will most likely be in the rear suspension somewhere, the posi, or the C-beam.
With the ASR left on, the first thing the system does to keep the car straight is change throttle position. That would be felt as a pulsation in the gas pedal. Input to ASR is from the lateral accelerometer and the wheel speed sensors. If the car doesn't yaw a lot in this case (not geting sideways on WOT acceleration) then the VSS input kicks in the ASR.
After throttle modulation by the ASR, then there is a reduction of ignition timing, followed by brake application through the ABS system. I would think that if what you feel is just a quick and short movement, then the problem is in the back of the car.
Check the rear toe arms at the center; are the bolts that hold the center part of the tie rod assembly to the batwing tight? Also check that the batwing itself is mounted properly and the bushing at each end are in place and in good condition. Also check the sway bar connections and bushings.
I would think that there would have to be a major difference in tire pressure to get the car to move sideways at a shift outside of a loss of traction by one wheel. It would be evident at WOT shifts, but if you feel/see it at part throttle shifts, the problem will most likely be in the rear suspension somewhere, the posi, or the C-beam.
With the ASR left on, the first thing the system does to keep the car straight is change throttle position. That would be felt as a pulsation in the gas pedal. Input to ASR is from the lateral accelerometer and the wheel speed sensors. If the car doesn't yaw a lot in this case (not geting sideways on WOT acceleration) then the VSS input kicks in the ASR.
After throttle modulation by the ASR, then there is a reduction of ignition timing, followed by brake application through the ABS system. I would think that if what you feel is just a quick and short movement, then the problem is in the back of the car.
There's been no ASR throttle kick-down involved when it yaws on part-throttle acceleration.
And we did put in the GM slip diff additive w/ Mobil 1 synthetic diff fluid (75-90 wt).
Yeah, I need to make sure they check the whole drive train for alignment & tightness.
Thanks-Bart
Last edited by 89FX3; 12-09-2008 at 11:53 AM.
12-08-2008, 02:07 PM
#10
Team Owner
This may be one of those urban legends, because I have no first hand experience, but I've heard that synthetic is too slippery for a conventional posi to work correctly, even with the additive. You might look into this, and try some conventional lube.
12-08-2008, 02:09 PM
#11
Racer
Thread Starter
I also have a 1996 CE LT 4 and had the similar problem. After doing everything to the rear it still did the scoot... It always seemed there was just to much power and it wouldnt hook. Then someone pointed me in the direction of tires. I did have the runflat tires and I had heard that that could be a problem. Well I put the new Goodyear Tires on, non runflats and like magic it was gone. Stright ahead at all speeds. I dont know what kind of tires you have on but if its the runflats I would take a look at them, good chance that might be your problem....G
It did the same thing w/ a set of Yokohama performance summer tires.
Last edited by 89FX3; 12-09-2008 at 11:54 AM.
12-08-2008, 02:10 PM
#12
Racer
Thread Starter
Interesting point.
12-08-2008, 02:11 PM
#13
Le Mans Master
What I wanna know is how can you drive that thing and hang your head out the window far enough to watch the rear end slide sideways under full acceleration
Hence the two headed dragon????
Hence the two headed dragon????
12-08-2008, 02:30 PM
#14
Melting Slicks
I gotta tell ya I am trying to figure out how anything other than tires would cause this. Isn't the batwing bolted directly in? There should be no flex at the differential even if the c-beam is loose. I could see noise caused by the tranny to diff case flex but that is it.
I am just trying to understand this as I have a "scoot" but i dismiss it as a traction issue. I have a bit of a traction issue
I am just trying to understand this as I have a "scoot" but i dismiss it as a traction issue. I have a bit of a traction issue
12-08-2008, 03:37 PM
#16
Racer
Thread Starter
Last edited by 89FX3; 12-09-2008 at 11:55 AM.
12-08-2008, 05:00 PM
#17
Safety Car
My 92 does the same thing now. I just assumed it was from the batwing and 4 bar bushings being worn out.
Since our stuff is all new I have to hazard a guess that some how your getting rear toe change under acceleration.
Will
Since our stuff is all new I have to hazard a guess that some how your getting rear toe change under acceleration.
Will
12-08-2008, 09:21 PM
#19
Race Director
i would do this along with checking your u-joints. if a needle bearing broke and one has slop you will get exactly what you speak of. also worn rear end bushings can cause this under load since the rear end will shift with the power being applied. energy bushings cured my problem of walk and of breaking u joints.
12-08-2008, 09:28 PM
#20
Le Mans Master
