Looking for advice on sorting quirky handling and possible bent suspension
 

Hello!

I picked up my '87 Targa earlier this year, got it on one of the big online auction sites so couldn't get a PPI done. But tons of pics and service records provided so I was fairly confident. I'm sorting a few things the car needs, nothing unusual or scary, it runs strong. I had it in my trusted indy Porsche shop to check things I cant check on my own and do an alignment and thats where the fun starts...

I wanted to check the alignment because the front end felt a bit toe'd out. Not sure if thats the term, but the front end wandered a bit at speed. More noticeable was in a bend the steering would weight up nicely and then unweight rapidly with any undulation in the road. This car would be a bit scary to drive fast in the corners, I think. I know they are known for 'quirky' handling characteristics, and what I feel seems consistent with a rear engine car, but worth having everything checked out regardless.

Results in, all four wheels were out of alignment. Fronts went back to spec with no issue, but the left rear cant get back into spec with the adjustment bolt on the spring plate fully adjusted. Mechanic thinks the trailing arm could be bent, but as you know thats very hard to measure and confirm. Also, there is evidence that the car was hit in the rear left at some point, as the left sway bar mount has clearly been welded in place. Another possibility is that there is some frame damage and the mounting point is out of alignment.

After getting the alignment as close as possible to spec the car does drive better. I'm not sure you would ever know that the rear isnt exactly right... But I know its not and that is enough to make me a little crazy.

So here's what I'm trying to decide on. Do I...
1. Leave it. If it drives fine and I'm not going to sell it any time soon then don't worry about it
2. Find a used trailing arm and have it installed to see what happens. This would also mean replacing all the bushings and likely the spring plates on both sides, so not minor work. It does need bushings, so this will happen at some point anyway.
3. talk to a local Porsche collision specialist and see if they can measure the frame to check for anything out of the ordinary. We have a very good shop locally, they just built an RWB, but i dont even know if thats something they would do...

Am I missing something else I could be looking for? Any advice on the best way to chase this down, or if its even worth it?

Thanks!

How many miles on the car? What specification is out? How much? Post your alignment measurements too. Also, what wheels and tires are you using?

Offhand, I’ll guess that your rear bushings are worn. That will affect the rear alignment. If you know you need bushings, start there and then redo the rear alignment. If you still can’t get it in spec, then look at bent arm or other problems.

Welding on the sway bar mounts does not necessarily indicate the body was repaired. Those mounts are pretty weak and people often weld in reinforcement to make them stronger.

Those trailing arm bolts are hard to undo. A few weeks of soaking, then someone who really knows how to do an alignment on a 911 do the job.

Maybe... the guy couldn't sort it in the two hours he had allocated to the job so blamed the car. I'd get some measurements done. Maybe he is right and the trailing arm needs to be altered or replaced. Measurements will tell.

I had this with my SC. They told me it was so badly damaged it couldn't be put right - Tony's Tire Service. I took it to someone else who was an expert - Dave Tunley Tires, and he said quite the opposite. The car is as tight as a button, and tweeked the alignment.

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On an older car, alignment only tells part of the story since bushings, etc. could be worn, or something could be bent as you speculated. Couple things:
The symptom that you mention about the car becoming unstable over bumps is a classic sign that either something is loose or worn. Suspension bushings are a good place to look. Jack the car one end at a time, and support it well with jackstands. Then give each suspension piece a good shake to see what moves. Check both ends of the car. Check wheel bearings too.
Your rear suspension arms are unlikely to be bent. Check everything, but your year 911 has cast arms that are very strong.

I like your option #3.

It's the safest start

The tub could be bent

The rear trailing arms don't bend, if you hit something hard they break.

What is out of spec? What was it before and what is it now?

The eccentric adjusters can be hard to get right, they can also be installed incorrectly and they interfere with each other. If the car is lowered it can be hard to get back to stock alignment.
For example you might need to run a little extra negative camber to get the toe under control.

Start by Getting specs from factory workshop manual and measure tub yourself.

Thanks everyone, this is all great info! I’ll start at the top and go down the list of comments:
Car is high mileage. I have records up to 220k. But quite a bit has been replaced and/or updated. It has 15x7 and 15x8 RS refinish wheels with Pirelli P9000 tires, which came on the car.

Measurements after alignment:
Left Rear: camber -1.1, toe 0.49 (out of spec)
Right rear: camber -0.9, toe 0.23
Total toe: 0.71 (out of spec)
Thrust angle: 0.13

Rear bushings at spring plate mounts do look at least partially collapsed, and now that I think about it that makes sense that it could impact the alignment. It’s just more off on the left side so that’s why we thought there could be damage. Same for sway bar mounts, its only welded on the left so I assume it was a repair.

I do trust the tech though. He races P-cars on the weekend and tried a number of other adjustments before he was convinced we couldn’t get it in line. He had the car for a week and walked me through it all in person when I picked it up. I got under the car with him and saw everything firsthand.

Good call on checking each end while on a jack stand. Maybe something moves more than it should and that would tell me something useful.

I'm heading out of town next weekend so might be a little while before I can dig back in, but thanks for the thoughts!

Cheers!

Deformed bushings in the control arms have a big affect on alignment and if they haven’t been replaced, they are surely deformed. Unless the adjustment ranges are on wildly opposite ends of the adjustment range per side, likely nothing is bent.

The stock rear swaybar chassis mounts are very weak, extremely common that they have gotten ripped off or fatigued out over the years and been repaired or replaced with beefier mounts. WEVO makes a nice investment cast mount.

great to know! Thank you!

I didn’t read all the replies so I don’t know if this was mentioned yet.

But very often the toe eccentric will foul the camber range of adjustment. To avoid this, you can remove the toe eccentric, set the camber, the reinstall the toe eccentric and set toe.

What happens is the toe eccentric can be facing upward or downwards. If it’s upwards, you can get max negative camber adjustment range. If it’s facing downward, you can get the most upright camber settings.


I’ve seen a lot of techs blame a bent arm on this issue. May not be the problem in yours but it’s worth trying.

Ahh, very interesting. So in my case the toe is what is out of spec. So would what you're saying still apply? That the toe adjustment range can be effected by the camber setting if the toe eccentric is installed opposite of what it should be?

The steel trailing arms certainly can get bent, my '72 had such a condition, they can be straightened by a good metal man

I suppose that it's also possible for the aluminum semi trailing arms to be tweaked as well, but I never ran into that.

Be aware that the rear sway arm mount on these cars are known to break and is NOT conclusive evidence of impact. Many cars have had these break and rewelded. In fact there are manufacturers who sell a more robust mount for exactly this reason.

Try not to jump to conclusions based on what you see.

A snap over steer will tweak the rear of the engine compartment. To check run your hand under the back corner reinforcements, the radius of the corners is large and smooth if you feel any buckling of the radius in the sheet steel then the diagonal measurement of the engine compartment is off corner to corner. Also with the car on the ground after a drive go to the rear with a flashlight, get down flat and look straight forward along the spring plates sightline, the gap from the inside of the spring plate to the frame should be the same for both sides, something like 10mm each side.
Does this make any sense? Or should I get a pic for you tomorrow.

Interesting, I think I understand sighting the inside of the spring plates (I'll do that tonight), but I'm not sure about where the corner reinforcements are. I'll poke around and see if they jump out to me, but if you have a pic that would be awesome!

What! A snap over steer does NOT tweak the car.

I bet it does if you hit something ;) Regardless, its easy enough to check the gap on the inside of the spring plates and feel for irregular corner bracing.

well, I didn't get the car up on stands tonight but I was able to get under it enough to look a little closer at some things. I couldnt see anything out of the ordinary in the frame or bracing around the engine so I assume I'm ok there. I did, however, notice a different gap between the spring plate and the subframe comparing the left and right side. The left was tighter by a bit for sure. And I knew that the bushings were worn, but now that I know more I REALLY know the bushings are worn. They look completely collapsed to my eyes. Yikes. So even if I do have other issues to sort out in the rear the bushings will be task #1. ...that and some new spring plates at least. With any luck that will take care of the issue.

So the question is (and I think I already know the answer), could I attempt to DIY this task over the winter while its not driving weather?http://forums.pelicanparts.com/uploa...1699326678.jpg
http://forums.pelicanparts.com/uploa...1699326678.jpg