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Old 06-19-2016, 08:37 AM   #1
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Rear end lurching side to side....

Okay, looking for a little guidance. I just did a full suspension refresh. I bought a used 2002 Boxster S suspension take off (shocks, springs, sway bars). All of the other components were new (control arms, sway bar end links etc.). I had an alignment done at a shop as well.

Car details (anything I can think of that may help) - 1999 Boxster base. Has larger Porsche wheels than the stock with 20mm non-hub centric lightweight spacers (have new hub-centric on the way). Engine was replaced approximately 40k miles ago and I do not know if they put in new engine mounts. I would air on the side of saying they did not as it was done by the previous owner. I have a durametric (really just hooked up first time today)..there are no faults. Engine runs smooth, 5 speed shifts smooth.

Here's what is occurring. When I hit the gas the entire car seems to shift left in the rear and when I let off the gas it seems to shift right. It feels it bit like a swerve when you are in the car. It also happens when you shift. Really any time there is torque applied. Now the suspension refresh may have nothing to do with this. It didn't do it before the refresh that I recall. There is no noise associate with the lurch/swerve.

Anyone have any ideas or troubleshooting steps to check?

Last edited by Jthoms1; 06-19-2016 at 08:41 AM. Reason: Added vehicle detail
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Old 06-19-2016, 10:06 AM   #2
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I always use the "what was the last thing that was done" theory when troubleshooting. So the most probable point that could cause this, and that was touched, would be the forward end of the LCA. Might check the torque on those bolts.

PS The rear arms.

Last edited by 911monty; 06-19-2016 at 10:37 AM. Reason: PS
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Old 06-19-2016, 10:07 AM   #3
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Hello,

first, i don't know if it's a good idea to put a 2002 S suspension in 1999 non S, because of the engine/transmission weight difference. Also the S setup takes the different unsprung masses into account (S brakes and wheels weight more).

I don't think that is a engine / transmission mount problem. Maybe if all engine and transmission mounts are totally worn. But that would only have a short momentum and should be balanced out by the drive shafts of the car.

I suspect there is a problem with suspension and sway bars.

Regards, Markus
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Old 06-19-2016, 01:04 PM   #4
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Thanks guys...going to go over the install again to look at torque on the nuts and the sway bars.
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Old 06-19-2016, 01:48 PM   #5
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Originally Posted by Jthoms1 View Post
Thanks guys...going to go over the install again to look at torque on the nuts and the sway bars.
Easyest solution would be the spacers, insure they are installed properly & you have proper thread engagement with the lugs. Did you torque suspension bolts while loaded on the wheels?
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Old 06-19-2016, 02:09 PM   #6
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One of my first posts was a very similar problem. I could nearly change lanes with throttle change. Stand on it and it would change direction, chop the throttle and back it came.
Slightly mismatched tired. New sneaks and the problem was gone. Incidentally, 02 S model.
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Old 06-20-2016, 02:17 AM   #7
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I'm going to head out and check everything shortly. I had a thought and did some research last night. Given the fact I installed the "S" suspension my sway bar sizes changed. I ordered 19.8mm bushings for the rear and recall them seeming a bit to not fit the way I though they should. I can't recall what I put on the rear size wise. Last night on Pelican I saw it actually calls for 19.2mm. I ordered them and they will be hater later this week

My question...if the rear bushings are the wrong size could that cause it?
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Old 06-20-2016, 02:40 AM   #8
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Hello,

if the sway bar didn't have a chance to move / flex - too tight, that might cause that symptom.

But it sounds more that a rear wheel can move a bit back- and forward.

I would also check all suspension components including control arms and wishbones and of all nuts and bolts are fastened to specs.

Eventually you should recheck the alignment parameters from the shop with the Porsche specs. I had in the past, that a shop did an alignment for another car to a similar but different car, which didn't work at all.

Tyre profile could be a problem. But i think you don't have changed tyres, or especially only one tyre. Or mounted it vice versa – one in driving direction, the other not.

Regards, Markus
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Old 06-20-2016, 06:17 AM   #9
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I doubt if it's the sway bar bushings. It's most likely something to do with locating the wheels under torque, which would point to the rear trailing arms. Those are the arms that bolt to the body behind the firewall.

It could also be tires, but you didn't say that you had changed anything around that. You might try taking the spacers out from the wheels and see if that makes a difference.

Lastly, it could be a bad alignment. Did the shop give you the specs? The toe could be way off.

Last edited by Racer Boy; 06-20-2016 at 07:50 AM.
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Old 06-20-2016, 07:45 AM   #10
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You didn't mention having a four wheel alignment done, but after I swapped out my entire suspension the car drove so wonky down the road I was sure I screwed something up terribly. The back end warbled around like I had a wheel on with shims on one side of it or something.

I told the shop I took it to that every bolt on the suspension needed to be loosened and torqued down with a load on the wheels and tires and it needed to then be aligned.

They did their job right and I got my boxster back and it drove like a Porsche after that.
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Old 06-26-2016, 08:49 AM   #11
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Thanks guys. I did get a four wheel alignment, double checked the torque on all of the nuts and had the tires balanced.

I did finally discover what it was! The bolt on the forward end of the rear trailing arm had fallen out. So what I was feeling was that trailing arm sliding in its spot. Just put a fresh bolt in and it handles great.

Thanks for all of the help.
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Old 06-26-2016, 09:25 AM   #12
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Originally Posted by 911monty View Post
I always use the "what was the last thing that was done" theory when troubleshooting. So the most probable point that could cause this, and that was touched, would be the forward end of the LCA. Might check the torque on those bolts.

PS The rear arms.
Should have found that the first thing.
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Old 06-26-2016, 09:27 AM   #13
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Should have found that the first thing.
True. Like my father used to say, "thats the way the cookie crumbles".
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Old 06-26-2016, 09:30 AM   #14
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These bolts being inserted from the bottom up are IMO poor design. I brought it up in a different post. The bolts should be inserted top down. That way if the nut falls off or bolt loosens, it can't fall out, as yours did.
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Old 06-26-2016, 01:55 PM   #15
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I have had the problem you described to TEE. I am not saying this is your problem, but mine was my tire pressures. One was way low and it looked ok. When I checked it with the gauge, one side was much lower than the other.

Just a thought.
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