W126 Lessons Learned on R&R Front and Rear Shocks - PeachParts Mercedes-Benz Forum

stephenson · #1 06-24-2002, 04:33 PM

I want to repay all those who have helped me by posting my recent experience with F&R shock R&R on my 126 (1991 350SDL).

As usual Phil was very helpful in getting me what I needed!

My version is slightly different, but hopefully it will help someone else. This was an easy job! If I have erred, please accept my apologies and offer a better way - I will likely have to do this again, sometime.

I like the HD ride quality - firm, but not harsh.
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W126 (1991 350 SDL)

Front Shock Absorber Remove and Replace

1. Make decision between various types and manufacturers of shocks. I chose HD Bilstein for several reasons. Bilsteins have new bolts, washers, rubber rings in the package)
2. Loosen bolts on left front or right front wheel (17mm).
3. Remove protective cap and remove lock nut – measure the distance from the top of the rod to the top of the nut – this will be useful later when determining how tight to make the first nut. Loosen main nut (17mm).
4. Jack up front of car on side corresponding to the loosened bolts. I used hydraulic jack with block of wood to prevent damage to jacking pad on car)
5. Remove tire and support car (additional support is recommended)
6. Remove remaining nut, top plate (large washer) and rubber rings (another rubber ring is underneath the upper mounting area).
7. Compress the shock until it clears the top mount and then push it back and forth as needed in the wheel well to allow use of 10 mm 12 point socket on both bolts attaching the bottom of the shock.
8. Follow instructions that came with the new shock – note neither the stop buffer (auxillary rubber spring), nor the plastic protective sleeve, is included in the kit . Remove the stop buffer and the plastic sleeve from the old shock and install onto the new shock along with the bottom plate (large steel washer) in the order shown in the instructions. From shock body: stop, snap ring (was already on my Bilsteins), bottom plate washer, plastic sleeve, lower rubber ring.
9. Install the shock into position after compressing the shock enough to allow rotation in the wheel well … this will allow use of socket and ratchet.
10. Torque 10mm bolts to 20Nm (from CD-ROM).
11. Position shock and allow rod to extend through top mount opening.
12. Reinstall wheel and bolts. Lightly tighten.
13. Lower car.
14. Torque wheel bolts. CD-ROM says 110Nm.
15. Install top rubber ring, top plate, and nuts per instructions – neither of my front shock rods rotated as I tightened the nuts down – be careful, there are several warnings about this in the many postings I saw … don’t know what would happen, but it must be pretty bad so use a screwdriver or wrench to prevent this from happening! I torqued the main nut until it compressed the rubber ring to the same measurement from top of the shock rod to the top of the main nut, as when I removed it. My shocks had a single plastic sleeved locking nut that looked as if it could be used by itself, but I used the original bottom nut and then put the plastic sleeve locking nut on the top of it, locking then together.
16. Reinstall protective cap.
17. Repeat other side.

Tricks to make it easier: During removal push the shock rod into wheel well area to allow movement of shock while attached in order to facilitate the use of socket and ratchet.

Effect on car: Pretty distinctive. Ride was firm, but not harsh. Wallowing was gone (well, 126s tend to wallow a bit anyway, but it was much better). Slight shimmy from wheels gone; I had just replaced tires and was concerned they were not well balanced. New shocks appeared to help a lot.

Summary: Total time on first front shock was about an hour. Time for the second wheel was less than 30 minutes. This was really easy!
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W126 (1991 350 SDL)

Rear Shock Absorber Remove and Replace

1. Make decision between various types and manufacturers of shocks. I chose HD Bilstein for several reasons. Bilsteins have new bolts, washers, rubber ringss in the package)
2. Remove rear seat back
- release catches on left and ride side of bottom seat cushion
- carefully remove and stow (there are always things to tear or damage leather)
- unscrew three screws (right, center, and left) at the bottom of the back seat frame
- lift up seat (two sets of hands are easiest) and carefully remove and stow
3. Remove plastic access covers to get to the top mount.
4. Loosen bolts on left rear or right rear wheel (17mm).
5. There are no protective caps on the rear shocks, so remove top nut and measure the distance from the top of the rod to the top of the nut – this will be useful later when determining how tight to make the first nut. Loosen main nut (17mm).
6. Jack up front of car on side corresponding to the loosened bolts. I used hydraulic jack with block of wood to prevent damage to jacking pad on car)
7. Remove tire and support car (additional support is recommended)
8. Remove remaining nut, top plate (large washer) and rubber ring (another rubber ring is underneath the upper mounting area).
9. Unbolt the two hex head bolts from beneath the trailing arm (lower mounting area). The CD-ROM says there are two different types of schema here – mine simply had two 17mm bolts from below.
10. Remove the shock by lowering it and rotating one way of the other as you pull it out to clear the hole – you may have to jack the rear you are working on up a bit more to allow it to clear.
11. Follow instructions that came with the new shock – there is no stop buffer or plastic sleeve on the rear shock assembly. From the shock body: snap ring, bottom plate washer, lower rubber ring.
12. Install the shock into position and install the two bolts from beneath. I had some trouble with this on one shock because the lower mount on the shock was a few degrees out of alignment with the trailing arm mounting area. I pulled shock back out and rotated the mount bracket a few degrees in the shock (it is set in a bushing) and then it went in easily – it was no more than 5-10 degrees). Make sure shock rod has extended through the upper mount opening.
13. Torque lower mounting bolts to 45Nm (from CD-ROM).
14. Reinstall wheel and bolts. Lightly tighten.
15. Lower car.
16. Torque wheel bolts. CD-ROM says 110Nm.
17. Install top rubber ring, top plate, and nuts per instructions – only one of my rear shock rods rotated so I used an adjustable wrench to hold the rod while tightening with an open ended wrench. I torqued the main nut until it compressed the rubber ring to the same measurement from top of the shock rod to the top of the main nut, as when I removed it. Be careful, there are several warnings about the rod turning while tightening in the many postings I saw … don’t know what would happen, but it must be pretty bad! My shocks had a single plastic sleeved locking nut that looked as if it could be used by itself, but I used the original bottom nut and then put the plastic sleeve locking nut on the top of it, locking then together.
18. Repeat other side.
19. Reinstall plastic access cover, seat back, three seat back screws, and seat bottom. Be careful with seat back frame as it is sharp edged and can cut you and other interior pieces.

Tricks to make it easier: Use a helper to hold the shock rod as you push shock up through spring and upper mount opening – it will make it easier to deal with minor alignment issues on the bottom mounting bolts.

Effect on car: Pretty distinctive. Ride was firm, but not harsh. Wallowing was gone (well, 126s tend to wallow a bit anyway, but it was much better). Slight shimmy from wheels gone; I had just replaced tires and was concerned they were not well balanced. New shocks appeared to help a lot.

Summary: Hardest part was dealing with the bottom mount bolt alignment. Total time on seat cushion removal was about 15 minutes, then first shock was 30 minutes, then second shock was an hour (alignment issue). Easy, but time-consuming due to the interior work.

#2 05-11-2005, 10:58 AM

That is one well written set of instructions. Thanks for taking the time to document this process. Last week I purchased a 1981 300sd for a $1000.00. It has the worst set of shocks on it of any car that I have ever owned. It drives fine until you hit a bump of any kind in the road, and then hang on and try to keep it in your lane. The rear comes up quite a bit and then continues to bounce, the front wallows quite a bit. Makes driving it exciting in all the wrong ways. I am going to use your instructions to replace all the shocks this weekend. Ordered a set of hd bilsteins from Phil on monday. Body is straight on the car, although it has a couple of rust spots completely through about the size of a silver dollar just behind the headlights in the front fenders. Car is from salt lake area. Too bad, because other than the shocks and a slightly strangely shifting tranny it is in good condition despite the 277k miles on it. Apparently it was a one owner car for the first 275k miles. I am replacing my 1980 300d that I bought for $800.00 a couple of years ago. The 300d runs ok, but is non turbo. I can't believe the difference the turbo makes. Almost like driving a gasser. I have put about 40k on the 300d. It has been a pretty good car, except for the fact that it has a small short that will kill the battery in two to three days if it is not driven daily. I will try to get my $800.00 back out of it. Shouldn't be too tough, the body is really straight with no rust. Anyway, thanks again for taking the time to write all that stuff down. I thought I would take the time to say thanks.

nglitz · #3 05-11-2005, 11:58 AM

Nice procedure.

thombenz, you might also want to look at all of the bushings in the rear end. A loose one here can allow the rear toe to change, essentially steering the car at the rear tires. Exciting.

stephenson · #4 05-25-2005, 08:37 AM

thombenz,

Glad it helped ... this is the sort of simple mechanical thing that can be made VERY easy by someone publishing the "gotcha" things ... I read several other posts on the topic prior to trying it ... learned a lot from them - sort of an iterative learning process!

Still have car - my daily 70 mile commuter. No major issues right now.

Brian Carlton · #5 05-25-2005, 09:19 AM

I'm struggling with a rear ride height issue on the SDL. I posted a separate thread regarding this.

Can you tell if the rear ride height increased when the brand new Bilsteins were installed in the rear? If so, by how much?

invisik · #6 07-08-2006, 08:53 PM

Great instructions! Changed the front shocks on my 1989 560 SEC. Only other item I can suggest is there's a wire that runs right where you have to put the socket to remove the outer 10MM bolt. If you loosen the holder, you can move the wire down and out of the way--just don't forget to tighten it afterwards or you'll have a rattle!

-m