car feels twitchy in the back
 

hey guys, i can really use some help here. I had a new set of BC coilovers installed professionally. it felt fine for a while but i noticed the back feeling loose on certain highway pavement & in the rain. I checked the rear tires & they were worn on the inside pretty bad. so i got 2 new tires & it feels even worse now. I didnt do an alignment. so my question is could it be that or could the coilovers springs have an improper preload. really would appreciate some insight on this.

Get your alignment checked. Whenever you change the nominal height, you need to realign. Start there and let us know if you still have an issue.

^ This. Preloading coilovers shouldn't be hard from the get-go, but preload them again just in case before you get an alignment. Also check difference in dampening.

^ Good point. Before you have it aligned, make sure it is at the height you want. This includes making sure the suspension bushing are not preloaded.

coilovers do NOT need preloading. the only time spring preloading is done is during a corner balance. Else, the perches should be snug against the spring while still allowing the spring to rotate easily by hand (please note rotate means along the vertical axis, it does not mean that the spring should be loose enough to wiggle left and right).

I believe the preloading that the OP is talking about deals with the control arm bushings on the chassis side. Yes, I know that is not what real preloading is, but it is what everyone around here calls it.

I was referencing this particular line:

Gotcha, missed that detail.

Alignment. Also, stiffer springs and/or bars will make the car more touchy on iffy road surfaces. It's analagous to how one walks on dry vs icy sidewalks.

ok so Im doing what guys said. Im going to check to see if every thing is ok with the coilovers . (dampening, spring preload, etc) BC racing also has a video stating that the spring needs to have 4mm of preload & they show you how to achieve that setting. Im thinking that when it was installed & they set the height maybe the locking collar that adjusts the spring preload was moved & now its out of wack. so after i will get an alignment. will post results. thanks guys.

take note that the 4mm preload is just enough to allow you to spin the spring. The reason they say 4mm as opposed to 0mm is since you aren't using helper springs you run the risk of having the spring unseat when the suspension expands all the way

ok so how do I adjust to 0mm of preload. i adjusted to 4mm preload & it still feels bad. feels like the back is swaying when im cornering.

preload isn't your problem. 4mm of preload is absolutely nothing. Preload would not cause this:

Like others said get your alignment specs and post here for further advice.

The only other thing you may want to check is your swaybar and endlinks. Make sure they arent binding, arent broken, and are properly aligned.

Ok got it, going for alignment now. Thanks

ok so i got my alignment & it was off especially in the rear, so i know im on the right track, thanks to you guys. It feels ok , better , but not all the way good. i will test it in the rain tomorrow to get a feel on how bad or good it is. Monday i will take it to my mechanic . now i know swaybar & endlinks were mentioned but is there anything else i should have inspected at this point. could the alignment still be off a bit.

What are your alignment values? The shop should have provided them for you. The factory spec range is very wide, so you can be in spec but still have shitty numbers.

When I installed my coilovers, they increased over steer, to reduce it you can soften the rear or stiffen the front, add a stiffer front sway bar, reduce rear tire pressure and/or increase front tire pressure.
However the most important thing is the alignment and you need to make sure all the bolts are secured correctly.
Are there and knocks where the rear feel loose? If there are you might have a few loose nuts that is the first place to look.

Quick general handling reference
Setup Matrix

yeah i saw that the alignment spec were in the green but i wasnt issued a copy. It was a local tire shop not the dealer or my mechanic. But i will go to my mechanic on monday to get more of a in depth look at the values.
Now I do have a low speed clunking noise on the right rear of the car, i had this checked out about 3 weeks ago & nothing was found. it has gotten worse & I have spoken to BC racing about it last friday & they told me to check that the top nut that it might be loose. I didnt have all the proper tools to do it properly. tried my best & it did seem tight. I will try again tomorrow with the proper tools. i have searched about the clunking noise & everyone that has this issue is saying check top nut , preload. but none have complained about handling issues.

The issues may or may not be related. Besides the top nut, also check the anti sway bar link. Sometimes they loosen over time, or the link itself has too much play in the joints.

I doubt the shop kept your alignment numbers, buy I guess it is worth a shot.

Do you have any other suspension modifications besides the coilovers?

ok will have my mech. check the anti sway bar link. yeah i dont think so either, but i will let my guy put it on his alignment lift. so not really worried about getting it to better specs. No other suspension mods. only running 18" staggered wheels. But Ive had them for about 3 years now with out any problems. before my coilovers i had stock shocks with tein S techs. i had coilovers installed in july.

Ok so I went to my mechanic today & he saw that my alignment was still off. He attempted to do a complete alignment but the bushings at all my alignment points are shot. he can only adjust to a certain point. so I know that I can replace front lower control arm bushings but my question is can I replace the rear control arm bushings. My mechanic is saying that it doesnt look like i can replace the rear . Is this correct. & if not what would you guys recommend.

Also the adjustments that were made has the car feeling way better. maybe 75% better.

The rear bushings are replaceable, just like the front bushings. I recently had the front control arm bushings replaced because I had the same issue (seized bushing sleeve to cam bolt). I ended up having my local dealer do the labor since I wasn't able to break the bolt loose. They ended up having to cut the bolt out, and then they were unable to press out the old bushings. Mind you this is a Mazda dealer, which has a press designed to push these bushings out, and they were unable to. The dealer ended up taking them to a local machine shop with a larger tonage press and finished the install.

Just a warning if you were considering doing this work yourself.

I just had my camber and caster bolts and bushings replaced: They had seized so that turning the adjuster bolt was twisting the bushing and loading the suspension.
It took the mechanic (Green & Ross) 6 hours with air hammers and penetrating oil to get the old parts out... not something to attempt yourself.

Free advice: Spend some time or money to apply anti-seize to the adjuster bolts and bushings before they seize.

Good advice, and I did the same. I even took the joints appart after getting it back from the dealer to apply anti-seize. I didn't trust that they would have done it.