Opinions on weird rear suspension situation

[cutlass389]

Quick synapsis, my basically stock rear susp. car has dead hooked ALL year until recently. I didn't change or touch anything. Fourth round two weeks ago it suddenly torqued up and twisted(the body) and I spun like crazy with wheel hop and everything. Haven't hooked since. I looked and had a super stock guy look and nothing is visually broken or amiss. Changes since are welding axle tubes, installed new solid lower control arms from UMI and rotated tires side-to-side. This past Saturdays race with changes above I spun on the first two passes and only started hooking when I lowered the leave rpm from 1400 to 1000. I had a couple of guys watch the launch and they both said that at the hit the left rear of the car came up a lot even though I had 20 psi in the right bag as always. Any ideas as to what would cause this sort of change to suddenly happen?

 

[UMI Sales]

Hello
Are the tires still in good shape? Are they a drag radial or a slick? Either way if they are shot then you aren't going to hook. And are you using a rear sway bar? If not its not allowing you to distribute weight evenly throughout the rear end. I just wanted to throw this out there for you as another suggestion.
Thanks
Brad

 

[cutlass389]

Hey Brad, thanks again to you guys for getting those arms out to me in time for my points race on Saturday. The tires are Hoosier drag radials with 70 passes on them. I ran a pair of the same ones all last season without any problems. It 60's around 1.58 weighing 3130 with me leaving @ 1400 off the footbrake so I don't think I'm really killin' 'em. I run an air bag rather than an ARB which would be the better way to go but it's been workin' fine for the last 4 years 'til all of a sudden.

 

[StreetBu]

First thing I would look at is the body mounts. Was the car rusty at all underneath? Just thinking that one of the body mount bolts broke and is letting the body separate and unload the rear tires....Just a thought.

 

[Supe]

Have you checked the bag for leaks?

 

[grizwald]

what are the rear shocks like?

 

[cutlass389]

That's the kind of expanded thinking I was in need of. I never thought of a body bolt breaking. The only rust in the car is the front footwells, the frame is perfect. I've launched it hard over 600 times so it's quite possible. The air bag reads 20 psi and passes the poke test but sometimes the line gets pinched and gives a false reading. The back shocks are stock type and ancient. I'm going to check the bag line, put more weight in the trunk, double check the upper control arms aren't under preload, physically check the shocks and try to inspect the body bolts. Thanks for the ideas guys.

 

[cutlass389]

OK, well the body bolts are all there although a couple were slightly loose. The upper control arm on the passenger side was under preload so I backed it off to neutral. I added 65 lbs in the trunk and made sure the airbag lines aren't kinked. The shocks aren't physically broken but when compressed they just kinda' stay there for a while and eventually stretch back out. I guess that's normal for a non gas shock but I may replace them anyway.

 

[CutlassRacer]

If the car is suddenly awkwardly twisting, you should really look over the mounting points on the frame and make sure nothing is cracked.

 

[Supe]

Check your front suspension as well. A dead/collapsed front spring can do some strange things out back.