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Help me diagnose touchy/bouncy rear end?

torch2k

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My GTPP 6spd is supercharged, and when cruising at highway speeds I notice that disengaging / re-engaging the throttle makes the rear end feel a little bit "bouncy" or "jiggly". I'm not sure how else to describe it. It also seems to squat quite a bit when under hard acceleration in earlier gears.

My guess is that I need to swap out some bushings or something, but I'd love to hear your input as I don't really know where to start.

Also, car only has about 25k miles and the only suspensions changes have been BMR Performance lowering springs. Factory 373 gears.
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BmacIL

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First question: did you have your suspension bushings clocked when you had springs installed? If no, do that first.

If yes, then it's a combination of a few things: floppy subframe bushings, oversized rear-most diff bushing bolt holes, and bushings in the suspension that bind it up and add rubbery spring rate. The BMR CB005 will take care of the first bit. Lethal Performance's diff hardware upgrade kit has sleeves to put into the rear bushings, and there are various places to get rid of rubber. The rear shock mounts and the rear lower control arm front bushings are the biggest of which. BMR SM760 shock mounts will address some it. Rear LCA bearings are a big job but have tremendous value and actually improve the ride with supporting modifications.

I would start with the CB005 and SM760 and see what you think. Bushing removal and better shocks do help a lot but then you're starting to go down the mod rabbit hole where you need other parts to go with parts you bought.
 
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torch2k

torch2k

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Thank you, that's very helpful. I'm pretty sure we didn't clock the bushings because up until now I didn't even know what it was. I think I'll go ahead and get the parts you've mentioned first and then do it all at once since it sounds like I'll need an alignment either way.
 

boB

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Assuming your Mustang did not have these problems when it was new the first step is: what changed? Before putting a lot of time and $$$ into a lot of parts that more than likely have nothing to do with the problem it is probably best to go back to as close to original as we can and take it from there. Adding a bunch of new variables could mean a much longer time to sort out the original problem.

Since the main thing that changed is the springs we can look at what may be related, alignment and bushing clocking are a good start.
 

Shouldhavegotthegt

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Probably the shocks if you are still running stock. Mine would bottom out on bumps when I changed over to Steeda progressive springs. Switched out the shocks to Koni orange and now the car rides great.
 

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VinnAY

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Much more about and is actually very common to get this rear end bouncy feel but it's more about the shocks than anything else. I put about a Grand worth of Steeda parts in the rear as mentioned above with BMR parts but that didn't and won't change anything about the rear end feel in these cars w/o going in to the shocks part of the equation.
 
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torch2k

torch2k

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Much more about and is actually very common to get this rear end bouncy feel but it's more about the shocks than anything else. I put about a Grand worth of Steeda parts in the rear as mentioned above with BMR parts but that didn't and won't change anything about the rear end feel in these cars w/o going in to the shocks part of the equation.
What shocks did you end up putting in?
 

VinnAY

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Shocks were more than I was willing to go for and the reality of my little bouncy rear end was that it was quite literally only on one section of road so I didn't find it to be problematic but it does feel weird!
 

JohnBoyNC

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I would get new shocks/struts.

FP M-18000-F is my recommendation.
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