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  #1  
Old 09-22-2009, 07:13 PM
1990 300se
 
Join Date: Oct 2005
Location: Honolulu, Hawaii
Posts: 111
w126 guide rod mounts

Hi,

I'm going to be replacing both guide rod mounts on my car and am not sure if I should go ahead and replace the two bushings in the bracket while I'm in there. The guide rods were done a few years ago by the PO, so I don't know if I need to order a rebuild kit for them as well. Any input would be greatly appreciated. Thanks!

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  #2  
Old 09-22-2009, 07:43 PM
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Location: So Cal, No. Orange county
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What exactly are you calling Guide rods? Not familiar with that description.
Bill
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  #3  
Old 09-22-2009, 07:49 PM
1990 300se
 
Join Date: Oct 2005
Location: Honolulu, Hawaii
Posts: 111
Hi Bill,

I believe they are also called track rods, not sure what else they go by. They prevent the front wheels from going back and forth and are attached to the body by the front footwell and also to I think the lower control arms.
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  #4  
Old 09-22-2009, 08:23 PM
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Location: So Cal, No. Orange county
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They are called brake force bushings, or at least thats whet we called them. If I were doing the job I would replace all the rubber thats there. They commonly cause front end wobble or vibration after hitting pot holes or lightly applying the brakes. Pretty common repair but they will can effect alignment so it's off to the shop when finished.
Bill
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  #5  
Old 09-22-2009, 08:42 PM
1990 300se
 
Join Date: Oct 2005
Location: Honolulu, Hawaii
Posts: 111
Yes, that's exactly what I'm experiencing! It started off with a clunking noise and has rapidly evolved to wobbling. I'll go ahead and order all the other rubber parts in the area, as I definitely don't want to do this twice!
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  #6  
Old 09-22-2009, 08:50 PM
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FWIW, I Only use the genuine guide rod mounts and bushings. The aftermarkets GRM's are OK, but the bushings are total trash...

Sometimes it pays to have that Star!

Jonathan
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  #7  
Old 09-22-2009, 09:11 PM
1990 300se
 
Join Date: Oct 2005
Location: Honolulu, Hawaii
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Hey Jonathan,

Thanks for your input! The parts sold on peachparts are made by Febi. Do you happen to know if these are OEM? The local dealer is asking a little more than an arm and a leg for them, but if they are much better then I will go with them.
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  #8  
Old 09-22-2009, 09:30 PM
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Febi does not quite cut it in this case...I actually Just had a customer who did his own mounts and bushings on his 560SEL bring his assemblies back in after his Febi bits broke in a matter of months...

I can see what I can get you dealer parts for, sometimes the dealers can be Nasty w/ their mark up :-/

Jonathan
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Jonathan Hodgman
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Enthusiast Service, Restoration & Tuning.
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Specializing in all pre and post merger AMG's including Hammers and DOHC M117 engines.
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  #9  
Old 09-23-2009, 08:16 AM
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there's a nice write-up on the procedure for a 300SD (W126) here:

DIY Bearing Bracket guide rod mount replacement for Mercedes Benz 300SD.

I did this recently and left my comments there. dry fit the captive nuts before bolting up, might save you the trouble I had.
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  #10  
Old 09-23-2009, 07:26 PM
1990 300se
 
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Hi micalk,

Thanks for the link to whunter's thread. I've gone over it a few times before determining whether it would be a doable job for me.
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  #11  
Old 09-23-2009, 10:38 PM
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Yeah, that's a great write-up. I'm about to embark on that project soon too.

As to what they're called, I have seen them called "guide rod" mounts "track rod" mounts "caster rod" mounts, you name it. All are correct, though "guide rod" seems to be what is used in MB documentation.

As far as front end wobble after hitting potholes, that can also be caused by a bad idler arm bushing. In my case, I was experiencing wobbles which very quickly (a couple weeks) turned into near catastrophic oscillations after hitting potholes on the passenger side. Very scary indeed. I had just had the front end inspected and somehow this was missed. I got a thumbs up from my indie, then later that week hit a pothole at about 60mph that started an oscillation so bad I nearly lost control of the vehicle. Even more terrifying, it got worse as I tried to bleed off speed. Only after I relived this harrowing story for my mechanic was he able (or possibly willing) to find the actual problem, in my case the idler arm bushing. He fixed it for $35 and I haven't had the problem since.

My "guide rod" problem is showing up as clunking when I hit potholes at very low speed (dirt parking lots) and a slight clunk that can be heard when I sharply apply brakes. Also, I am having drifting issues which I'm sure aren't being helped by the slop down there.

In any case, I just wanted to tell you that story so that you'll inspect your idler arm bushing because I would hate for anyone to relive what I went through a year ago with mine.

-EDIT-

I also had him replace the steering damper at the same time as the idler arm bushing, and that cost more than the $35 for the bushing.
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Last edited by tinypanzer; 09-23-2009 at 10:43 PM.
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  #12  
Old 09-25-2009, 03:22 AM
1990 300se
 
Join Date: Oct 2005
Location: Honolulu, Hawaii
Posts: 111
Hey tinypanzer,

Thanks for the tip on the idler arm bushing. The bushing on my car appears to allow the idler arm to move up and down (relative to the car) very slightly. I was hoping to have the car up on a lift this afternoon but my mechanic was backed up with other customer's cars.

The symptom I'm having is that there's a clunking sound when accelerating and decelerating, rather than when going over bumps or potholes. The tire moves forwards and backwards in the tire well when braking! The PO changed the steering damper when he did the tie rods, so that's some money saved
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  #13  
Old 09-25-2009, 08:51 AM
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If the movement at the end of the idler arm is say 2-3 mm it isn't a problem. The older versions that had grease fittings etc. were subject to a lot of wear and allowed the tow in to change with driving conditions. The idler arm should be at the same hight as the pitman arm. That will have a great effect on the way a car steers over an uneven surface. I think it might also effect akerman angles and turning track. The bushings would need to be extremely loose to cause the uncontrolled steering motion described.
Bill
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  #14  
Old 09-25-2009, 12:33 PM
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+1 on checking the Idler Arm Bushing.

Like Bill said, a little motion along the axis of the idler arm bushing bolt is fine- the thing to look out for is when the axis of the long bolt can shift from side to side. To check, get the two front wheels off the ground, and see if there's any play in the steering by pushing the passenger side wheel. if there is, look at the bottom of the idler arm bushing bolt. If it's wobbling from side to side as you push the wheel back and forth, you know the bottom part of the bushing is blown.

I recently had a problem almost exactly like tinypanzer's on my '84 300SD- whenever I hit a bump at highway speeds there was a chance that I would get a scary oscillation in the steering. Replacing my idler arm bushing cleared it right up.

As for the guide rods, I don't know anything about that... Johnhef replaced the guide rod ball joints where they connect to the subframe them on my car right before I bought it from him
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  #15  
Old 09-26-2009, 05:11 AM
1990 300se
 
Join Date: Oct 2005
Location: Honolulu, Hawaii
Posts: 111
Thanks for the suggestions! The alignment guy says that the guide rod goes in and out, hence the need to replace the mounts, but I still haven't had a chance to get the car up to verify everything before I order the parts. I'm definitely going to re-cehck the idler bushing, as I'm experiencing more wobbling as the days go by!

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