300TD REAR suspension rebuild - PeachParts Mercedes-Benz Forum

dmorrison · #1 03-31-2003, 01:01 AM

Well I was under the car today assesing the rear suspension rebuild.
In the 123 Service manual I reviewed the section on the coupled semi trailing arm rebuild. I realized that this was going to be quite a job. Your basically rebuilding two axel bearing assemblies per wheel hub and require some special tools. I figure out why they designed most of the tools so I could rig or make something to use instead. This morning I was looking at the wheel hub assembly and boy was I happy to realize that I did not have this on the 300TD.
I removed the dirt and coating of grease that had accumulated over the 22 years (81 build date) the car has been around, what a mess using the degreaser,the hose and a brush to clean everything.
Disconnected the rear brake lines and sway bar link. Took the caliper off and removed the rotor. Again cleaned more of the assembly again. The caliper and rotor were replaced about 25,000 mile ago and are fine along with the parking brake shoes etc.
Now on to the Hub bearings. I rotated the hub and felt for smoothness in the bearings. I think they are fine so I will not mess with them untill I have to.
I removed the leveling actuator ( called the spring strut in the manual, its what would be the shock absorber on a 123 sedan ). Boy what a mess with all the hydraulic fluid. I was amazed at all the dirt in the trailing arm section where the spring strut attaches. Again more cleaning.
I removed the Coil Spring, more dirt, and was able to get a feel on the weight of the trailing arm. It is actually pretty light. But you dont want it falling and hitting the wheel hub section or being damaged.
I place a floor jack under the trailing arm where the shock would attach. I have the car sitting on a 12 ton jack stands just behind the holes for the Mercedes jack that comes with the car. I proceeded to release the sub frame bushing bolts ( on the right side only, one side at a time). All three at once and removed the subframe bushing using a crow bar. It came out rather easily. The 123 does not have the top bushing that is shown in the service manual.
The movement of the subframe for those who want to know. I have the differential still attached at all the normal points. The right wheel hub has the sway bar link removed, the rotor off, the brake line removed and the caliper off. The coil spring and spring strut ( shock absorber) are also removed. The supporting points for the subframe in the wagon are the forward bushing and the rear differential mount. The top of the differential is bolted to the subframe. When I disconnected the items I have listed above the subframe did not really move at all. It dropped maybe 1/2-1 inch.
To get access to the outside trailing arm bushing I had to pull down on the front of the subframe and I actually shoved the old subframe bushing into the gap sideways. It seemed like a nice amount of gap. I was able to get a socket, a universal and an extension for the Pneumatic air hammer. I had to use the 500 Ft. Lb impact wrench to get the bolt for the outside trailing arm bushing to release. But you can not lower the trailing arm yet until the inner bushing is released
I was able to get the inside trailing arm bushing nut and bolt to release with the impact wrench also ( a 125 ft/lb unit). Then I ran across my first problem.
I could not remove the bolt to the inner bushing because the flex disk for the driveshaft is in the way. I now have to lower the driveshaft so that I can move the flexdisk out of the way to get the bolt out so I can lower the trailing arm to remove the bushing. Because of the offset of the driveshaft, the left side will not require the dropping of the driveshaft. Except it will already be done.
I am considering disconnecting the axel shafts to allow better cleaning and easier working on the trailing arm since I will then be able to remove it from the car. I also figure that if I have done that I might as well replace the axels since I'm half way there.
I'll keep posting to let you know how the job goes.

Wish me luck.

Dave

dmorrison · #2 03-31-2003, 10:11 PM

Worked on the rear suspension a little to day.
Not the best day today. I fly for American Airlines and the company and union were negotiating hot a heavy for consessions. Or they were going to declare Chapter 11 bankruptsy at 5 pm today.
All the unions came to agreement this afternoon. So atleast for now the company won't declare Ch 11. Who knows what will happen in the next 6 months.

I climbed under the car and diconnected the drive shaft center bushing frame. That allowed me to move the drive shft out of the way of the inner bushing bolt. and remove it.
I decided to disconnect the axel. I wanted to be able to work on the trailing arm without shoving my hands up into a little gap in the subframe. I unscrewed the 8MM bolt holding the axel in the wheel hub and used a brass punch to move the axel out of the hub. I probably did not have to use the punch, it move quite easily. I disconnected the parking brake cable and realized that to completely disconnect the parking brake cable was going to be more work. So I just worked on the trailing arm at the wheel well with the parking brake cable attached at the trailing arm about 10 inches behind the hub. This was workable, not perfect but workable.
I was glad I decided to disconnect the trailing arm. Getting the old bushing out was a pain. I tried to hammer them out, use a punch and hammer, use a air chisel, nothing worked. I finally use the Harbor Freight universal press.

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=38335

I swear I have used this tool more than any other. I should get the expander kit for it.

Using the press I was able to get the bushing out about 1/2 an inch. Then I cut the rubber lip off the bushing and was able to use the press again to completely remove the bushing. Honed the inside and pressed in the new bushing. I then went to the inside bushin and removed and replaced the bushing using the same technique. the job took about 2 hours to R+R the two bushings.

The axels. I have agonized over replacing them. They are not giving me any problems but the cracks are "sort" of large. Not so large that I think they may split in the next 1000 miles of driving but they are 22 years old. I could have the axels serviced for $100 each. That would include new boots. But PepBoys offer lifetime garranteed rebuilds for $89. Ive come to the conclusion that if at aint broke don't fix it. Beside the R+R job for the axels is not a terribly hard job. If anything happens to one of the boots I'll replace both of them at that time.

Another delema. The hydropneumatic shock is in great shape except for the rubber boot that surounds the base and actuating rod. The rubber is falling apart. 10-20 % of it is cracked. The unit is not available from Mercedes. The purpose of the rubber sleeve is to keep dirt and mud away from the actuating rod.
I am going to try to recoat the rubber sleeve with Plastic coat. Its a rubberised material that is liquid. They advertise it by showing plyer handles being dipped into it. Then they dry like a rubber coated handle. So I'll give it a try. If that does not work I have also purchased some shower pan PVC sheet. I will make some new protectors, or glue the sheet to the old ones and see how that comes out.

Well thats all I got done today. I'll let you know how it goes tomorrow.

Dave

Capt Kirk · #3 04-01-2003, 04:26 PM

you might be able to find a generic rubber boot for the actuating rod. We use to use CV joint repair kits for our old VW which basically came with 2 new boots and the clamps. Last time I was up at Pep Boys they still had em.

dmorrison · #4 04-03-2003, 02:45 AM

The rubber boot that fits over the hydropneumatic shock is doing much better now.
The Plasti-Dip worked very well. It hardened like the rubber that made up the boot. is flexible and solid. I actually had 1 or 2 small holes in the boot and those filled in nicely.

Dave

dmorrison · #5 04-03-2003, 02:59 AM

Progress report number 3

I couldn''t work on the car that much today. To many things to do

I removed the left trailing arm of the rear end today.
I decided to completely remove the arm instead of just repositioning the unit and still have to work on it in the wheel well.
It is so much easier to work on the trailing arm on the work bench .
I had a little difficulty getting the coil spring out. I could not get the compressor to tighten the spring tight enough. I positioned it incorrectlly when I started. It was compressed enough but I could not get the spring out. So I just released the subframe bushing and I was able to remove it.
Removing the trailing arm bushing was a little difficult. This was the first time I had to use a penetrationg solvent on the car. I let it soak for 1 hour and the bolts released.
Disconnected the emergency brake cable at the pivot arm and fed it through the eyelets.
To remove the inner bushing bolt on the left trailing arm You still need the driveshaft disconnected and out of the way. Or the bolt will not come fully out.
Completely removed the trailing arm with the parking brake cable attached.
Removing the bushings I use a 3 jaw puller this time.
On the right side I had to "grind" off the rubber lip on the bushing so the ball press could work properly. I "ground off the lip using a large pair of channel lock plyers.
This time I use the ball press to move the bushing out 1/2 inch and then used the 3 jaw puller. It worked great.
Cleaned the trailing arm with a good degreaser. Painted it with POR-15 and tommorow I'll install the bushings and reinstall the arm.
Hopefully the coil spring will go back in easily.
I did mark the right spring with zip locks so I will know where to place the plates on the coil spring during installation

Dave

dmorrison · #6 04-10-2003, 12:05 AM

4/9/03 progress

Installed the rear left trailing arm today. After installing the bushings. Went easily.
Installing the subframe bushing was an easier job since I built a C shaped unit to mimick the Mercedes unit as shown in the Service manual. I used some C channel mild steel. Cut it and welded it together. Mercedes in the service manual wants you to put pressure on the outside edge of the bushing ( actually a metal section covered in rubber)to get it to fully seal. This C shaped unit presses against the outside rim as shown in the service manual. Cost about $2 to make, that is if you have a welder. The welds are not the best. My auto dimming welding helmets batteries are dead so I had to use the non-dimming unit. (welds are so much easier with an auto dimming helmet) And I'm out of CO2 gas for the welder so I have a lot of splatter on the unit. But it worked really well. The unit was used with the Ball joint press I always seem to be using on the suspension.

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=38335

The dimmensions of the press piece are (approximately) 2 inch tall
3 1/8 long and 2 1/4 wide.
Dimensions are not extremely critical. If you want to make one. check out the service manual for the concept and measure your new subframe bushing for dimensions.

The new coil spring went in after attaching the rubber hose that is slipped over the end of the coil spring. I guess this is used to prevent noise. I compressed them and they went in quickly. I had the subframe bushing unattached when I replaced the spring. I then jacked up the trailing arm to attach the screw for the subframe bushing. Released the coil spring and Saturday I will install the hydraulic shock (have to fly thurs and fri).

Re-attached the parking brake cable( done to remove the trailing arm) and the drive shaft (done to remove the trailing arm bushing bolts).

Rear Differential mount on the 300TD wagon. Go to Thomaspin's site. He did a great phototechnicalmanual for changing the mount on the 300SD.
What I will add is the wagon presents some space problems for your tools. The wagon fuel tank is behind the rear suspension along the floor of the back of the wagon.
This makes getting a wrench into the space to remove the two large bolts that attach the mount to the differential a problem.
The 4 attaching bolts at the top are no problem. The 2 differential bolt required some creativity. OR removal of the fuel tank.
I was able to use a box wrench, 22MM, on the top bolt. The bottom bolt was removed by using a 22MM socket and a small piece of 3/8 square steel. This allowed me to use a open end 3/8 inch wrench to grab the piece of steel. And remove and install the lower bolt and the upper bolt. I kept the 2 bolts loose while installing the 4 mount bolts at the top. Them used the setup I have described to tighten the 2 large bolts.
I could not torque the bolts due to setup. I remembered the loosening strengh required and tried to duplicate it upon instalation.
This is a problem only in the wagon.

One additional lesson I learned. When you unbolt the rear differential to replace the differential mount. You can now lower it, Your supporting it with a hydraulic floor jack. BEFORE you lower it you need to unbolt the brake lines to the calipers. As the rear suspension drops the only thing holding the unit will be the brake hoses, which are very short. And the sway bar. Which was not a problem. The front of the subframe is attached and will hold the assembly but the problem is the brake lines.

The attached picture shows the socket, small 3/8 drive and the C press I built.

Dave

whunter · #7 05-13-2005, 05:52 PM

I added this link to my forum.

ShopForum > Do It Yourself Links & Resources > DIY Links by Parts Category
Suspension:
Suspension:

dmorrison · #8 08-18-2006, 01:23 AM

Put your center seats down. Located in the front of the rear floor you will find a couple of screws, hard to see in the carpet. Remove these screws and remove the panel to the floor. The tops of the shocks and such will be visible now.

Dave

tom gaines · #9 08-21-2006, 12:21 AM

Many thanks. Strong glue had me worried-hate to use force. almost stripped one fitting. Now "rides good, sounds bad". Just need more parts & labor.
Next I'll finish the 450 SL.

Tom

Paul Ellis · #10 10-19-2006, 03:30 PM

Question, I can't seem to loosen the bolt holding the subframe so that it can be lowered to remove the bolt in the trailing arm pivot. The bolt is tighten to 120 NM, but when I put a breaker bar and cheater on it to remove it has a rubbery feel and I am bending the breaker bar. Impact wrench will not remove bolt because of the rubber absorbs the impact. Do I just pull harder with a longer cheater? Help help

whunter · #11 10-19-2006, 04:26 PM

Quote:

Originally Posted by Paul Ellis

Question, I can't seem to loosen the bolt holding the sub frame so that it can be lowered to remove the bolt in the trailing arm pivot. The bolt is tighten to 120 NM, but when I put a breaker bar and cheater on it to remove it has a rubbery feel and I am bending the breaker bar. Impact wrench will not remove bolt because of the rubber absorbs the impact. Do I just pull harder with a longer cheater? Help help

Typically this means the bolt is corroded into the sub frame mount metal sleeve.

The only cure I have found is the massive application of torque; enough to shred the sub frame mount rubber from the sleeve.

Note:
You will need a vice, (minimum of propane torch) heat, SAE 30 oil (you don't want more flammable lubricants), and a good breaker bar to separate the bolt from the sleeve, after it is removed from your car.
Wrecking the sleeve is OK, the bolt is roughly $20.00 USD plus S&H.

Paul Ellis · #12 10-19-2006, 08:32 PM

Thank you for the information. I went to your web page and read where someone had used a tourch to heat the head of the bolt and let cool several times to loosen the bolt. This was on a 126 , is the 123 the same design? Had a 4 ft cheater on the breaker bar, i quess I need a 6 footer. Thanks again, paul

whunter · #13 10-20-2006, 12:32 AM

Quote:

Originally Posted by Paul Ellis

Thank you for the information. I went to your web page and read where someone had used a torch to heat the head of the bolt and let cool several times to loosen the bolt. This was on a 126 , is the 123 the same design? Had a 4 ft cheater on the breaker bar, i guess I need a 6 footer. Thanks again, Paul

Yes.
I use the exact same procedure on the W123.

Paul Ellis · #14 10-20-2006, 07:08 PM

Thanks again Hunter, I drilled a little hole from the top down....to the top of bolt, injected wd 40 and I finally got the bolt out. But, stripped out all the rubber from the bushing....so $ 80 bucks more for two bushing kit. Oh, the 20 ton press from HF really made the removal of the rest of the rubber from the bolt easy. Now, I will then be ready to replace the trailing arm. There is a lot of rust under the left side. So a pretty 81 300d will be going to market. What is a 81 300d worth? Thanks again for all the help. regards paul

starrywhite · #15 08-18-2009, 02:16 PM

Hello
I am in the process of wanting to replace the trailing arms so that I can install a new sls
The old system was removed and the trailing arms severely damaged to accommodate a horrible hospital job using std shocks.

The unknown for me is the compression of the springs.

It sounds from your post that it was a piece of cake.

Please walk me through it if you can, I would love to know how you did it, and what tool you used for the compression itself.

I watched the wrecker take the arms I now have, off its previous location and that seemed to be easy to do in reverse.

Thanks

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