Hello all,
TLDR; video shows my rear toe and camber changing with differing loads, braking, and changing gears. I would like to know what could be causing this issue and how I can fix it.

This is my first post to these forums, and my first time dealing with a troubling suspension issue on my 2003 C5 (base/A4/226k miles). I recently did a DIY job on my C5 to replace transmission seals (input and output seals - so far, no leaks!), torque tube (chose to replace with used TT with ~40k miles), transmission and differential fluids, and brake pads and rotors. When reassembling the car, I made sure to use new nuts for Rr Xmember Mounting Nuts (to 81lbft), and of course new Rr Drive Axle Spindle Nuts (to 118lbft) - all while car was up on jacks, and I made sure to torque everything to spec. After reassembling everything, I noticed that the rear left wheel was moving when I changed gears, braked, or accelerated slightly - I took a video of this, you can see the YT video linked below. Before doing this job, I was able to do spirited driving, and the suspension felt pretty solid. Now:
1. It fishtails on straight roads at anything over 35mph and gets worse with more speed or turning,
2. The rear brakes make a grunting (not squealing) noise,
3. The rear toe seems to change under changing load,
4. Light rear tire squeal at low speeds when turning.
I would like to understand what could be causing this issue, and what possible solutions there are. I am just trying to get this car to be reliable and do (at most) some spirited back roads driving.

Please see link to YT video here (apologies for no sound - I can take another video if sound is required):

 

Moved to C5 Tech for assistance.

 

Inspecting the rear suspension while in an unloaded condition does not mean much in my opinion. Start with the basics, have the car aligned (4-wheel alignment) and, have the technician check the suspension bushings and ball joints for excess play while it it on the rack.

 

I would add to this that any good alignment includes first checking the tire pressures and ride heights. Also, before- and after-alignment printouts should be provided.

Request that the alignment settings be set at the preferred values [or as close as possible], not just within the allowable ranges.

 

At 226K miles, all the a-arm cast in rubber bushings are probably shot. The usual fix is to remove the rubber and replace with urethane bushings, that will tighen up the suspension a lot. There also might be a place that will replace the old rubber bushings with new cast in rubber if you want the same type of ride.

 

I agree - all of that suspension looks original. I would consider all bushings and balljoints to be suspect. At that age and mileage, just rebuild the rear suspension. Even if you manage to catch the "1" bad component, that others could fail tomorrow.

 

Really? Without even setting the correct wheel alignment and checking for excess play in the suspension components?

 

Parts cannon away!

 

At 226K miles on a 20+ year old car, absolutely

 

The only movement I'm seeing in that vid is the suspension reacting to the unhealthy angle of the CV joints, due to the suspension droop.
Maybe I'm missing something?
It is very likely that the suspension bushings have deteriorated on a high mileage car, but there's seldom any excuse for replacing parts without knowing why you're doing it.
Ball joints can be tested and measured for play.
Rubber bushings can be inspected visually, and with a little creativity, monitored for movement.
Try a front end/alignment shop for help, but find a real one, not a tire store/gas station...

 

Thanks everyone for the inputs. Haven't gone MIA, so here is a small update - I went to a Firestone, and they told me the same thing - the control arm (esp. upper) bushings are bad. I have ordered all 4 [edit - mistake; 8 bushings, top and bottom] control arm bushings (poly) and 2 upper ball joints (bottoms seem good for now - probably coming due soon, but no issues yet). Once I have them in and have a chance to do a test drive, I will update this forum so people in the future can see.

 

A-Arms have to come off for the bushings, kinda silly not to do the lower balljoints at the same time - they're only ~$40 each

 

Definitely looks like your A-Arm bushings are gone...I went with Polygraphite.....supposedly you dont have to lube them as much

 

Unless you add grease fittings now while everything's apart, the only way to lube them in the future is to disassemble everything again and realign after.

 

Final update:
Thank you everybody for the help. I replaced the [rear] upper and lower control arms with poly bushings, replaced the rear inner tie rods and outer ends (they were stuck together so I just got new rear tie rods), and got an alignment (firestone). The result is that the car is now driving straight, and does not fishtail when hitting bumps, or on the highway.

Here are some things I would do if I had to do this job again:

• Use a local shop to install some bushings: The lower rear bushings were really slippery - I tried using various methods including a 12-ton press and a ball joint press kit - all other bushings went in, but this one would not. I paid a local shop to install them, which really helped. They had them installed in about 2 hours, including the sleeves and washers. They also removed the top bushings including the sleeves - I installed those myself later.
• Burning rubber off the sleeves, or the whole bushings by covering in acetone, allowing time to dissolve, and then (safely) setting aflame: By doing this I got the rubber down to the sleeve - after that it would not burn anymore, so while the sleeves were hot, I used a wire brush/wire wheel to remove the rest of the rubber, while making sure not to damage the soft metal sleeve.
  • On the metal sleeve - I am not sure the exact material but because of the low weight and softness I think it's aluminum (correct me if I am wrong) - regardless, I made sure to not overheat the metal via propane torch nor quench it after.
• Using a ball joint press kit to remove bushings: This made it really easy to get the bushings out of the control arms. Also great for reinstalling the sleeves.
• Used lots and lots of grease - I used super lube compatible with poly bushings generally - although in the future I would use more of the grease that comes with the bushings - it's just that my kit came with 2x ~1-inch tubes, which were not enough at the rate I was using them.
• Using leverage to get control arms back into the car/subframe: Relative to the original bushings, I found that these new bushings made a much tighter fit in the subframe. Before I used to be able to just stick them into the subframe, put a bolt in to hold in place - this time, I had to get one in at a time. Using a jack helped to lift up the control arm, light taps with a hammer, and leverage via crowbar, I was able to move the control arms just enough that the bolts could go in. A thin, stiff L-shaped tool may be helpful in fine-tuning/aligning the bolt hole to the nut on the other side.

Here are things that could be done better:

• I creased one of the washers in toward the bushing because I did not know that would come off. This later had to be straightened out before pressing back in.
• I did not change the ball joints, nor the sway bar end links, because I did not see issues there - these are probably coming due at the age/mileage of this car, but I should be good for some time. I see this as cutting a corner, but I feel I had to due to time constraints. The suspension shop rep agreed he also did not see any current problems with the ball joints.