2002 S80 Sideways jerk (rear) over bumps

puntmeister · Post by **puntmeister** » 09 Jan 2014, 09:36

The rear of my S80 jerks sideways over bumps. There is no "bump-stear" - ie, the steering wheel doesn't move, nor does the car turn. Just the rear of the car feels like it swings out, and back in, real quick.

I recently changed the rear shocks (figuring this to be the problem) - the new shocks definitely reduced the sideways jerk, but didn't completely eliminate it.

From what I can find, in googling this issue in general, could be:

1) Bad alignment (in particular, thrust alignment)
2) Bad bushings
3) Bad spring/springs

When changing the shocks, I took a look at the various rear bushings, but didn't see any that were obviously bad.

Anybody have a similar experience, or thoughts/knowledge on the likely issue?

Thanks

Post by **MoVolvos** » 09 Jan 2014, 10:50

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Volvo's are usually not affected by the Thrust (Angle) Alignment or Offset unless you been in an accident. The chassis/suspension combo is fairly stout. Most side sway type jerks as in the case of a quick jerk when encountering a bump at speed on a large overpass sweeper is usually caused by the Toe. Without knowing the rear alignment which can't be adjusted by the DYI my guess would be Positive Toe or Toe In on the front tires.

Take a measuring tape and with a helper measure the front and backside distances of the front tires. Try to use the most centered tread of both tires and find a height that is about the same on both the front and back sides and go as high as the chassis or suspension will allow and see how much they differ whether it is Toe In or Out.

Blessings,

BKM

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puntmeister · Post by **puntmeister** » 09 Jan 2014, 11:31

Thanks for the reply

Forgot to mention there is some play in the front wheels - side-to-side - no play in the tie-rod ends, so gotta be the inner tie rods - I have a couple new ones, will install this weekend.

I was thinking the play in the front might be the issue - but, the front doesn't sway at all, nor does it stear funny at all. Just the same, perhaps the tie rods on the front are the issue? (will find out soon one way or another).

It is hard to believe the thrust alignment is the issue, given the car otherwise tracks perfectly straight (even with bad inner tie rods...).

Post by **MoVolvos** » 09 Jan 2014, 11:47

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A bad Tie Rod may or may not be causing the problem. If the suspension is otherwise tight and wheels balanced the forward motion will just push/pressure it to seat in a position and not cause any tracking or vibration issues (yet).

Measure the Toe before changing the Tie Rod to give yourself an idea where it's at but it won't be exact due to the looseness of the Tie Rod of course. You'll will need an Alignment from a shop if you have not done a DIY Alignment before.

Blessings,

BKM

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Post by **precopster** » 09 Jan 2014, 14:57

How old are the tires and what type are they? Also are they a match for the fronts?

Reduced grip can also cause sideways slip. If the tires have been through 2 or 3 seasons of extreme tempreatures the rubber may not have the pliancy it used to have.

puntmeister · Post by **puntmeister** » 09 Jan 2014, 18:26

I just recently bought this used, so not sure how old the tires are, but they are in very good condition, minimal tread wear, no signs of uneven wear at all, and are the same tires all the way around (Firestone, would have to check the model).

It doesn't feel as if the tires are slipping on the road at all - feels like the car keeps tracking straight (no skid sounds, no stearing wheel play/jerk) - just the rear end swings to the side & back.

Post by **precopster** » 09 Jan 2014, 18:41

Tread depth unfortunately isn't a measure of grip or rubber condition. Are there any build dates on the tires?

In my experience if miles haven't been achieved in 3 years of use any tire will give very unpredictable handling besides have you seen how Firestones compare with Continentals in handling tests?

Post by **MoVolvos** » 09 Jan 2014, 21:23

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I've been interested and playing with suspensions for a long time and it is caused by the Toe setting assuming everything else in the chassis is in decent shape. I've performed a few alignments also in my short live career at Acura on the Hunter Rack's as an entry level tech. Use to against my better judgment 3 wheel my Rabbit GTI around not that I was a good driver by any mean and don't that any more of course.

I've done half dozen basic alignments with basic hand tools in the last couple of years and they're usually within specs when put on the machine. (Audi A8, LX470, S70 T5, Odyssey, CRV...). Measure the rear Toe and if it is less than an 1/8 of an inch front and back it is OK then proceed to the front tires.

Although this is for "Bump Steer" the concept is the same. The Volvo front end is so tight the kick goes to the rear. Toe and Tie-Rod Ends which are used to adjust Toe can both be contributors to the issue.

http://autos.yahoo.com/maintain/repairq ... 108_3.html

Blessings,

BKM
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puntmeister · Post by **puntmeister** » 09 Jan 2014, 21:39

I'm with ya - no particular fan of Firestones.

So, what you are getting at: Could just be the tires.

Other than replacing the tires, how would one diagnose this for certain?

(I'm getting deja-vu....I chased an 'alignment' issue for months on my Jetta, only to find it was one bad tire)

Post by **precopster** » 09 Jan 2014, 23:38

Well an alignment check of both front and rear axles would be a good place to begin. You seem to have a handle on whether there's worn components.

Take a look at IPDs video regarding their rear adjustable rods for P2 chassis; it gives you an idea on where the rear toe-in adjustment is performed.