Rocking in the rear under acceleration or quick lane changes... Car feels unstable

[Big Blue]

I have thought for a while that my car felt very unstable in the rear, under hard acceleration or swift lane changes I get a substantial amount of rocking or wagging in the rear suspension. I had chalked it up to me being over critical until I let a friend drive my car while I drove along side in his car. When he went to do a fly by so I could hear my exhaust he had to make a lane change under acceleration and I was able to see the car rock very noticeably and he felt it and said that is scared him pretty good. I don't know what could be causing this to happen. I have bmr performance springs, bmr sway bars, and a set of super noisy Viking warriors as well as new p-zeros. Please help I have no idea what this could be but I know my friends car doesn't drive like his and he has similar parts in the rear. Any help would be appreciated.

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[BmacIL]

I have thought for a while that my car felt very unstable in the rear, under hard acceleration or swift lane changes I get a substantial amount of rocking or wagging in the rear suspension. I had chalked it up to me being over critical until I let a friend drive my car while I drove along side in his car. When he went to do a fly by so I could hear my exhaust he had to make a lane change under acceleration and I was able to see the car rock very noticeably and he felt it and said that is scared him pretty good. I don't know what could be causing this to happen. I have bmr performance springs, bmr sway bars, and a set of super noisy Viking warriors as well as new p-zeros. Please help I have no idea what this could be but I know my friends car doesn't drive like his and he has similar parts in the rear. Any help would be appreciated.

Sounds like your suspension is overdamped. Try softening your shocks several increments. How new are the tires?

 

[Big Blue]

I tried that but it didn't help. It was doing his with the factory pp shocks as well.

 

[BmacIL]

I tried that but it didn't help. It was doing his with the factory pp shocks as well.

If your tires are very new they still need to burn off their release film and 'break in'. This usually takes 80-100 miles. What setting is your bmr sway bar set to?

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[Big Blue]

The tires have about 2000 miles on them now and the bars are on the softest setting. Could it be faulty bushings or something like that?

 

[BmacIL]

The tires have about 2000 miles on them now and the bars are on the softest setting. Could it be faulty bushings or something like that?

Possibly. Sounds like something is broken/loose.

 

[Big Blue]

yeah it seems that way. I have torqued everything to spec but I'm still getting the rocking, my best friend was a ford master tech but now he is a diver in the oil field so he's is gone a lot but when he gets back I'm going to look it over with him and see what he thinks I should do. With that being said any ideas should be helpful, I'd like to get this taken care of fast. It doesn't make sense for me to be uncomfortable driving this car like it was meant to be driven.

 

[BmacIL]

yeah it seems that way. I have torqued everything to spec but I'm still getting the rocking, my best friend was a ford master tech but now he is a diver in the oil field so he's is gone a lot but when he gets back I'm going to look it over with him and see what he thinks I should do. With that being said any ideas should be helpful, I'd like to get this taken care of fast. It doesn't make sense for me to be uncomfortable driving this car like it was meant to be driven.

Have you taken the car in for alignment since you installed everything?

 

[Big Blue]

Yeah that was the first thing I did.

 

[rvlyssup]

Either something is broke, loose, or installed wrong.

OP, did you remove anything else other than the upper shock mount when installing the rear springs or did you do what Ford recommends? Can't really install the springs wrong unless they were made wrong. :shrug:

I have the same springs and then some & my car is like a go-kart on roids.

 

[leszek]

Check your rear sway bar links. What you describe is what happens when the rear sway bar is not doing its job.

 

[Big Blue]

Well I followed the bmr instructions to put them in, which is a nightmare. I should have dropped the subframe but oh well. The car was doing this before but not as bad. I just installed the sway bars last weekend and it all went in just as it came out so that's shouldn't be the problem especially since the problem predates the sway bars. Possible and messes up hum bearing. It's not a slight side to side wobble or wagging in the rear end, it's very visible from outside the car and it is very unsettling. I've also noticed that it causes the car to rock side to side with the bumps in the road but more pronounced. I thought it might be worn bushings but I can't tell over the the loud annoying rattle and bumping of these poor fitting Viking shocks.

 

[rvlyssup]

Yeah I believe BMRs instructions mimic Ford's tear-down procedures. Also, I think you need to pre-load the suspension when torquing them to specs or you'll encounter binding.

 

[zuki_dan]

Do you have any kind of cradle lockout installed on the car? If not it is probably play the the sub-frame bushings.

My car handled weird after installing all of my BMR parts but after an alignment all turned out great.

 

[BmacIL]

Well I followed the bmr instructions to put them in, which is a nightmare. I should have dropped the subframe but oh well. The car was doing this before but not as bad. I just installed the sway bars last weekend and it all went in just as it came out so that's shouldn't be the problem especially since the problem predates the sway bars. Possible and messes up hum bearing. It's not a slight side to side wobble or wagging in the rear end, it's very visible from outside the car and it is very unsettling. I've also noticed that it causes the car to rock side to side with the bumps in the road but more pronounced. I thought it might be worn bushings but I can't tell over the the loud annoying rattle and bumping of these poor fitting Viking shocks.

Did it do it without the Vikings? If not, take 'em off. It really sounds like the body is not being controlled properly when it gets lateral acceleration, so it keeps pointing to dampers.

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