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#873775 - 05/17/11 03:01 PM Re: Car sways back and forth under heavy acceleration [Re: BladeOfAnduril27]
555ss Offline
Member

Registered: 12/07/06
Posts: 272
Loc: NH
I just saw this topic and my monte when still stock back half did just about what you describe.
It felt like the car was mounted on a rod thru the middle of the car in thru the trunk and out thru the grille, and it rotated left and right under hard accel. It handled well every where else. The cause of it was just too little rear shock dampening, A tighter shock and the stock style rear ran a best of 8.88 in the quarter with the same shocks.
_________________________
84 Monte SS 555 BBC on spray runs 8.40's at 160+


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#873791 - 05/17/11 04:03 PM Re: Car sways back and forth under heavy acceleration [Re: 555ss]
MAP Offline
10+ Year
Member

Registered: 05/11/02
Posts: 3541
Loc: Yuma, AZ
Hi Folks,

Something jumped out at me when I read your post, 555: because of the rear's self-steering design, which is intended normally to increase understeer and thus make the car more stable for typical drivers under typical conditions, I could see that with soft, tall sidewalls, and with lots of torque applied to the rear, that the angle of rear roll, and thus rear steer, could get significantly modulated by the rear's torque input. That is, as torque input is varied (gear shifts mostly,) rear roll gets varied too, and the roll variation is finally reflected as a variation in the car's direction of travel. The result is "weird" steering. Another kind of modulation happens too: with tall, soft sidewalls, sidewall height will vary from one side of the rear to the other, as the rear's torque input is varied. This variation in side-to-side sidewall height alters the effective rolling radius from one side to the other, and this will tend to steer the rear as well.

I would think that stiffening the shocks, and especially the rear suspension roll stiffness, should ameliorate this. Or better still, eliminate the rear's self-steering behavior directly. Stiffer sidewalls would help too in this respect, but this may have other kinds of negative impacts that may preclude this option.

Best,
MAP




Edited by MAP (05/17/11 04:10 PM)

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#880323 - 06/19/11 10:44 PM Re: Car sways back and forth under heavy acceleration [Re: MAP]
montesleeper83 Offline
Member

Registered: 04/08/10
Posts: 167
Loc: Lino Lakes, MN
Ever figure out the issue???
_________________________
83 Monte CL "rat rod" project
95 GMC Safari daily driver

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#883548 - 07/07/11 11:09 PM Re: Car sways back and forth under heavy accelerat [Re: 84supersport]
Toecutter Offline
My First Post!

Registered: 07/07/11
Posts: 1
Loc: San Juan, Texas
Originally Posted By: 84supersport
Could be the tall sidewalls. I've noticed on mine since I put the tall 275/60s on mine that it will sway from side to side if I let the pressure get low. Kind of like how you can see a car with the tires aired dopuwn do at the end of the race track. Kinda feels like its skating side to side.


Hi, I'm a newb. This exact same thing happened to me in my '87 Buick T-Type. And I was also running a 275/60-15 radial. The side to side sway was so bad that my kids could see it from the starting line. Inside the car it was one of the scariest things I have experienced. I really thought I was going to lose the car. This same car went an 11.20 @ 119mph a week later on a 26x8.5 Hoosier slick without any problems. Never did figure out what happened.

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#883741 - 07/09/11 12:21 AM Re: Car sways back and forth under heavy acceleration [Re: montesleeper83]
baaboo Offline
Member

Registered: 07/24/09
Posts: 8604
Loc: Racine, WI
Originally Posted By: montesleeper83
Ever figure out the issue???


Looks like no, huh? frown
_________________________
1987 Aerocoupe, 383 Super Ram and 20-gallon custom aluminum tank. Car retired (for now) from open road racing, but I'm not.

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#1007941 - 07/19/14 12:14 PM Re: Car sways back and forth under heavy acceleration [Re: Black Rocket]
Black Rocket Online   content
Member

Registered: 12/27/06
Posts: 370
Loc: MN
Sorry I forgot about this thread. Since posting I have installed Currectrac adjustable upper control arms and Currie Johnny joints in the axle housing.

I do admit the condition got better, but is not completely gone. Its most noticeable at higher speeds under heavy load.

I have 295/50/R15 tires in the rear and aftermarket upper and lower control arms. I believe that takes the bushings/arms out of the equation.

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#1007968 - 07/19/14 08:15 PM Re: Car sways back and forth under heavy acceleration [Re: Black Rocket]
BadSS Offline
10+ Year
Member

Registered: 05/30/00
Posts: 1201
Loc: Pearl, MS, 39208
I ran 12.5" section width, 28.5" tall bias ply slicks (extremely soft sidewalls) on 10" rims and it ran straight and true up to 146mph.

The only time I've ever experienced a sway like you're describing was when I was running a Detroit locker and had a slow leak causing unequal pressure in the tires. I suspect that one of your tires is actually a little taller than the other or there's something internally wrong with one of them allowing it to "grow" more than the other.

Could you borrow a set of rims/tires from someone to check to see how there's work?

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