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Help! Death wobble

S

slowwgtp

New member
Hey guys, new member and this is my first post. I have a 99 gtp that has been a great car, but about 9 months ago the transmission broke and due to time and money, I have not been able to repair it until yesterday. Replaced the trans with a low mileage junkyard unit, and when I pulled the old trans I found that it had the non hd model in it so naturally I had to buy a new passenger side cv axle to fit the correct transmission. Bought duralast from autozone. Finally got it on the road this morning and it drove and shifted great... until I got on the highway and as soon as I hit about 50 + it starts to shake so badly it literally feels like the wheels are falling off. Checked some things out and replaced a bad tie rod end but that didnt fix the problem. Did some more digging and found the passenger front wheel bearing to be in bad shape so replaced that too, still didnt fix the violent shaking. If I am heavy in the throttle, it feels much less wobbly, but then as soon as I let off the gas and until I am back under 50 it shakes like you wouldn't believe. I have already spent more money on this car than I can afford right now so replacing too many more parts is out of the question. I would like to find the one magic part that is causing the issue. Any ideas? By the way, never did this back before transmission went out
 


I think a big problem is that you replaced your transmission with one not correct for it.

The gear ratio's in the non-HD unit are different than the HD unit you once had. Perhaps it's trying to figure out it's speed and what gear to be in and starts to shake.

Also, check your steering rack bolts. A loose rack can make a shake too and if you replaced a tie rod you still need an alignment done.
 
stop driving the car asap. or you'll be buying another tranny. you need the gears changed in your pcm.

no idea if the wobble is related, but ive seen a hand full of cars eat the new tranny due to not have the pcm tuned for the gear change.
 
The transmission I pulled out was not an hd trans. The one I put in is an HD trans which is correct for the car. So unless someone replaced or flashed the pcm when they put the wrong trans in, I should in theory be running the proper trans and pcm gearing combination. Rack is tight, have no play in the steering whatsoever, as soon as I turn one wheel by hand the other is turning with it. I somewhat feel like it is something in the trans or the new duralast axle I bought, but cant really see anything obvious
 
I know I need an alignment, but made sure that the tie rod was the same length and threaded on the exact same amount as the original. Just dont want to get an alignment and then have to mess it back up to replace more parts
 


if you bought the car with the wrong tranny it may have had the pcm tuned for the gear change. and thats why its not happy now.

sadly the only way to find out for sure is to use a tuner to read the pcm and look at its bin file. tuner means a dhp or htp tuner. not a scanner. a real tuner.

as far as the alignment goes. once you took the old tie rod end off, it needed an alignment. if you got more front end parts to change change them before the alignment for sure. like you said not worth tossing cash at the same job twice. but do it all quickly cause tires can wear f ed up pretty fast.
 
I have no idea either. That's the problem LOL. I've dealt with tons of separated tires and this definitely does not feel like that. It is torque dependent and very sudden and drastic when it happens. It will go away the second I slow down to 50 miles per hour. I just noticed I have a bad bushing on my passenger side lower control arm but the bushing is all still there, just broken. There isn't really any yet or anything where it should be wobbling around so I don't feel like that would be the issue, would it? To me it seems like it would almost have to be something rotational
 
Yeah, I know all about bad tire wear patterns. Need tires soon anyway so I'm not worried about that, was going to get tires and Alignment at the same time. Just need to figure out this stupid wobble so I can drive my car that I have been missing for 9 months. I feel like I may have ruled out hearing because it will do it no matter what gear I am in or whether or not I am at low load or no load. I was thinking of getting on the highway and trying to accelerate to 60 or so and then shift to neutral to see what happened there. If the wobble goes away, then I would think it would definitely have to be something in the trans, right?
 
Update... found the culprit. Turned out to be tires in conjunction with bad wishbone mounts. I guess my tires were putting off a vibration which was somehow transferring to the engine/trans and turning the car into a giant paint mixer. Thanks guys for the helpful input.
 


if the car sat in one place for 9 months the tires could be flat spotted, and that will feel pretty damn bad at speed.

the lower control arms, buy on line, they run about 40 a side vs the local parts store.
 
Yup. You were experiencing harmonic resonance. The vibration was always there to some degree but once you hit 50 your bad tires vibrated at the resonance frequency of the suspension assembly, with the help of the bad bushings and viola, death wobble. If you had the guts to keep accelerating you would have found the upper limit of the resonance, if the car didn't fly apart and it would feel like the vibration would go away or at least reduce the severity. I don't advise doing that by the way. It's pretty common on big trucks because their tires aren't usually balanced, just throw them on the rim and go.
 
Good you found the problem. If you need your PCM read in the future, I'll be living in Knox county and I'll help you if I can.
 
even a std snapon scanner will be able to read the calculated gear ratio, at low load cruise in 3rd gear the ratio should be .98-1.02 if the pcm is programmed for the gears
 
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