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  #1  
Old 02-24-2005, 07:50 AM
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Location: Annapolis, MD
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Replaced the guide rod in my 126 300SD

A job I was dreading since my "shop" is a patch of gravel.

But the job went fairly well. There are a couple of good write ups here, so I won't get into it except the areas that I had problems.

The whole job on the driver's side took about 3 hours. It's not rocket science, but some can be a little tough.

The first problem came in loosening the guide rod mount that threads into the strut. It was very tight, even after I loosened the lock clamp and spread the threads and squirted some oil in there. The problem is that since you have already taken the guide rod mount assy off, you have to hold the assy with one hand and try to loosen with the other, and then only a quarter turn at a time. Frustrating. Once I got the guide rod mount assy off, I was able to marvel at the beauty of German engineering - a well made piece. Getting the old mount out was easier by prying than pounding from the back. Don't forget to install the star-shaped rubber mount that comes with the kit under the backing plate.

The second problem came in getting the guide rod mount/frame assy back in. You have to turn the threaded rod into the guide rod while holding up the assy in one hand. And the threaded rod does not want to turn, it's very stiff. Lining it up to get it started was the hard part. I eventually used a bottle jack to hold it up while I turned the threads. Then the tedious screwing in the mount, a quarter turn at a time. My old mount was screwed in almost the whole way.

Once that's done, getting the aft-most frame mount in is easy, but the other one wouldn't line up. Using gentle pressure from the bottle jack against the forward mount and the steering linkage horizontally got it lined up, it was just a little more pressure than I could do by hand.

Once that was in, it was just a matter of adjusting the threads and bolting the cross member back.

The difference is amazing. When I used to drive down the dirt road to my house, the front end rattled the whole way. When I would come to a stop and then release the brake, the whole left suspension would give and clunk. Now, it's smooth as it should be.

I'm a happy camper. New seat, XM, and a rattle free suspension.

Thanks to all who posted on how to replace the guide rod, your help is appreciated!
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1984 300Sd 210k

Former cars:
1984 300D 445k (!!) (Strider) Original (and not rebuilt) engine and transmission. Currently running on V80 ( 80% vegetable oil, 20% petroleum products). Actually not, taking a WVO break.
1993 300d 2.5 275k. Current 120/day commuter
1981 300SD 188k (Hans) Killed by a deer
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  #2  
Old 02-24-2005, 09:38 AM
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Good work, now go get the front end aligned.
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  #3  
Old 02-24-2005, 09:43 AM
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This repair really does make for a nice, quiet, comfortable W126 ride.

If you ever start to feel a wobble on the right side, then its time to replace the tie rods and the idler arm bushing - easier to do than the guide rod mounts.

Ken300D
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Old 02-24-2005, 10:12 AM
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Now the rear sway bar replacement will seem like a filter change
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  #5  
Old 02-24-2005, 12:44 PM
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I hated doing those things, what a pita.

Good job though now that their done hopefully you will never have to replace them again.
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  #6  
Old 02-24-2005, 01:25 PM
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I'm wondering about the alignment. I can't see how the guide rod affects it. All it does is locate the wheel assy fore and aft in relation to vertical. If it were too far one way, how does that affect alignment?

Glad to hear some of the other jobs are easier, though this really wasn't too bad.

I also replaced the kickdown cable on my son's '87 Volvo 240. That required lying on my back looking at an obscured view of a tiny cam inside the bowels of the automatic transmission and trying to get a small cable on its spring-loaded groove. And if anyone has tried to get the dipstick tube off of one of these cars (necesssary to get the pan off) I sympathise.
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1984 300Sd 210k

Former cars:
1984 300D 445k (!!) (Strider) Original (and not rebuilt) engine and transmission. Currently running on V80 ( 80% vegetable oil, 20% petroleum products). Actually not, taking a WVO break.
1993 300d 2.5 275k. Current 120/day commuter
1981 300SD 188k (Hans) Killed by a deer
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  #7  
Old 02-24-2005, 01:30 PM
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Location: Annapolis, MD
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Bill, I was marvelling at the aluminum subframe mount, not the guide rod.

The only compromise I can see that Mercedes made was in using engineering to get the ride and handling they wanted (I expect superior to past models) at the expense of having to replace parts occaisonally. I can tell you that this guide rod lasted for 24 years and 175K.
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1984 300Sd 210k

Former cars:
1984 300D 445k (!!) (Strider) Original (and not rebuilt) engine and transmission. Currently running on V80 ( 80% vegetable oil, 20% petroleum products). Actually not, taking a WVO break.
1993 300d 2.5 275k. Current 120/day commuter
1981 300SD 188k (Hans) Killed by a deer
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  #8  
Old 02-24-2005, 08:53 PM
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I'm wondering about the alignment. I can't see how the guide rod affects it. All it does is locate the wheel assy fore and aft in relation to vertical. If it were too far one way, how does that affect alignment?

The guide rod contols caster. Lengthen the rod more caster, shorten it, less caster. If you measured the distance between the mount and the LCA and put it back in exactly the same spot then you may be okay but it is better to get it aligned. Changing the guide rod length will also change the toe slightly on that side as the LCA moves back and forth in relationship to the drag link. RT
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  #9  
Old 02-24-2005, 12:55 PM
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Quote:
Originally Posted by tenknots
Once I got the guide rod mount assy off, I was able to marvel at the beauty of German engineering - a well made piece.
If this was such a well made piece why did it fail? Earlier MB suspensions would stay like new if you kept them lubed properly. At some point MB made a decision to put rubber in the suspension bushings rather than isolating the front subframe. Your witness to the results....
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