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  #1  
Old 10-22-2008, 06:15 PM
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1983 300TD, Rear suspension shakes at highway speed

ok, so i'm trying to diagnose this problem and thought i'd come on here for some advice.

first, why i think the front is fine:
* i got an alignment last week, the tech inspected all the suspension parts and gave it a clean bill of health.
* the steering wheel doesn't shake when the car does, and the steering box is tight enough that it would if the front suspension was the source of the rattle.

things in the rear suspension that i know are fine:
* my SLS system works, i put in new accumulators a few months ago and no issues since then.
* the boots on the axle shafts are not torn, so i don't know for a fact they are OK but i don't have a reason to think they aren't. this problem has been going on for over 6 months now, based on previous axle issues i'd expect them to have deteriorated much more if they were the problem.
* the tires show no sign of uneven wear, bulges or anything that would make me think they're the issue.
* the brake pads were replaced about a year ago, and there is no asbestos buildup on the rims. i have one caliper that locks up sometimes, only wearing down one pad. this is the best thing i can think of so far.

here's what happens: the shaking occurs mainly from 55-70 MPH, getting worse as speeds increase, but if you make it past 70 it subsides untils 75MPH, where it basically goes away. usually braking helps make it better, but that's subjective because braking will often reduce the speed below the 55MPH threshold anyways.

any ideas?

thanks,
nick

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  #2  
Old 10-22-2008, 07:44 PM
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Here are a couple of ideas.

Do you get any pulsing from the brake pedal when you press it lightly as you are comming to a stop? If so you have warped rotor, which might cause some vibration at high speeds.

You might have lost one of your wheel weights.

It could also be a flex disc or the center bearing on the drive shaft. I'd climb under the car a look at those to make sure they look okay.

Also look at your sway bar links. I've never heard of them causing a vibration but they are easy to check. Might also look at the sway bar bushings.
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  #3  
Old 10-22-2008, 08:21 PM
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i'll try the brake pedal tonight or tomorrow, good idea. the vibration gets pretty unruly though, i doubt a warped rotor would be capable of it.

i'll also look into the unbalanced wheel possibility, but the problem has persisted over a few different tires, so i doubt that's it.

the flex disc is fine, i pulled the transmission in march and it was in great shape.
the sway bar is fine too,i check it every time i pull a tire, which is surprisingly often.
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Old 10-23-2008, 01:02 AM
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While under the car check the sub frame mounts and the trailing arm bushings. I bet it's a trailing arm bushing.

Dave
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  #5  
Old 10-23-2008, 01:28 AM
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where are the trailing arm bushings?

thanks,
Nick
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  #6  
Old 10-25-2008, 04:14 PM
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OK, sway bar links are fine, trailing arm bushings and subframe mount bushings appear fine, i can't find any slop in any of them and they seem to be in fine condition, a but cracked but nothing like the worn control arm bushings i replaced on the front last year. there is no pulsing in the braking, so i'm ruling out a warped rotor, i looked at wear on the rotors too and it seems even.

can anybody think of anything else? should i replace the trailing arm bushings anyway, it seems like a PITA. it's hard to believe this kind of shaking comes from an unbalanced wheel.

thanks,
nick
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  #7  
Old 10-25-2008, 04:22 PM
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you most definitely can get bad vibes from a wheel or bad tire, you can also get cheap tires that balance perfect on the machine and still vibe bad on the car due to an out of round tire or bad belt that allows the tire to go out of round at speed

switch your wheels front to back and see if it moves.

also, I have had vibes come and go just by removing a wheel and putting it back on the same place. I now mark the wheel and rotor with a paint pen before I remove the wheel.

also, remember to always torque lug nuts and to do so in the skip pattern
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  #8  
Old 10-25-2008, 05:27 PM
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you know what the problem is.
you stated the issue I bet it is in your OP
brake caliper. if it's sticking, it's getting hot. ifit gets hot, it will mess with the bearings. pull the caliper that's sticking and replace it.

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