Trying to fit an aluminium W126 / 107 trailing arm to a W123 - a question of compatib - PeachParts Mercedes-Benz Forum

andydiesel · #1 12-09-2011, 07:33 PM

I'm planning on fiting the alloy arms to my 350sdl - have both steel and alloy arms in my workshop.
My guess is that the anti squat suspension is heavier than the standard one - despite the alloy arms.
Keep in mind any used parts will be at least 20 years old and will likely need rebuild. There are 5 bearings per side. A bearing supplier has quoted me $560 (CAD) for two radial bearings...you may want to change the linkage bushings - likely MB exclusive parts. There are some throwaway parts in the hub assembly...Emerg. brake cables appear different, ditto for the calipers which are mounted forward of the axle...

Tip for buying used: stay away if the steel sleeves sealing the joint connecting the arm to the hub yoke have rusted thru....The alloy will likely be pitted...also check for corrosion at the shock absorber mounting studs.
The brake shield and the emergency brake mounting base may be corroded beyond repair...

Stretch · #2 12-10-2011, 04:35 AM

Quote:

Originally Posted by andydiesel

I'm planning on fiting the alloy arms to my 350sdl - have both steel and alloy arms in my workshop.
My guess is that the anti squat suspension is heavier than the standard one - despite the alloy arms.
Keep in mind any used parts will be at least 20 years old and will likely need rebuild. There are 5 bearings per side. A bearing supplier has quoted me $560 (CAD) for two radial bearings...you may want to change the linkage bushings - likely MB exclusive parts. There are some throwaway parts in the hub assembly...Emerg. brake cables appear different, ditto for the calipers which are mounted forward of the axle...

Tip for buying used: stay away if the steel sleeves sealing the joint connecting the arm to the hub yoke have rusted thru....The alloy will likely be pitted...also check for corrosion at the shock absorber mounting studs.
The brake shield and the emergency brake mounting base may be corroded beyond repair...

Thanks for the info - you must however be fitting second generation W126 trailing arms - aren't you?

I was under the impression that the second generator rear end on a W126 was more akin to the W124 than the W123 - or have I got that wrong?

Even so if you have the time I'd appreciate a photograph or two of your trailing arms and what you are doing.

Have you checked out the prices for the radial bearings at the dealer yet? $560 sounds like a lot for bearings - but hey dealer prices can be a bit strange too!

andydiesel · #3 12-10-2011, 04:25 PM

Here's a photo showing both W126 steel and alloy arms. Note the difference in wheel carriers.
Surprise - the dealer's list price on the radial bearing was abut 30% less - still expensive.
Army - please send PM with your email address - will share full size photos etc.

Stretch · #4 06-01-2012, 08:09 AM

If you sit by the river long enough you'll see the body of your enemy float by.

If you sit behind your computer for long enough you might stumble on a bargain or two.

Last week I bought two W126 aluminium trailing arms for a very reasonable price. They took ages to get here - so long that I thought I'd have to go and fill out a form at the police station - but they got here in the end. If only people would be honest and say that they hadn't gotten to the post office just yet... oh well...

Just after ordering them I found a link (that I can't post here because it will only end up with the *****.com effect) where this guy called Kent says they don't fit! Apparently it is a case of close but no cigar - we'll have to see. At the price I paid I'm quite sure I can get my money back in the worse case scenario otherwise I'm still hopeful at this stage that I can come up with a solution.

They look almost the same from this view - except for the chunky circular casting "blobs"

Extra stuff on the back though

Notable important for fitting them differences so far

1) Caliper is in a different place - I don't know if the W123 caliper will fit yet

2) Shock mounting point is different from the steel trailing arms

Expect an update next week sometime when I make some measurements.

I'm so excited! Something new to play with!

daw_two · #5 06-01-2012, 11:20 AM

I had a set of the anti-squat non steel trailing arms. I sold/shipped them to a guy over in Little Rock but they wouldn't work for his w123 as I recall. I asked him to hang onto them and I'd pick them up sometime when I was in that neck of the woods. I didn't want to pay for return shipment.

Naturally, I refunded his money.

Stretch · #6 06-01-2012, 12:45 PM

Quote:

Originally Posted by daw_two

I had a set of the anti-squat non steel trailing arms. I sold/shipped them to a guy over in Little Rock but they wouldn't work for his w123 as I recall. I asked him to hang onto them and I'd pick them up sometime when I was in that neck of the woods. I didn't want to pay for return shipment.

Naturally, I refunded his money.

I'd like to know what the problem was - may be it will become apparent next week.

Stretch · #7 06-05-2012, 01:02 PM

Well sucess!

Hardly any problems (well as far as I can see anyway).

The aluminium version of the W126 (actually it's a 107 part according to the part number) trailing arm most definitely fits in a W123 sub frame. Here's a picture to prove it.

I've only done a rough check by measuring between the back edges of the rims (I used the same W123 disc brake and steel wheel that was fitted to the W123 parts) but there seems to be no difference between the two trailing arms in the way they fit into the sub frame. Here's a picture of where I was making my rough measurements for comparison =>

All is not 100% straight forward though.

Problem #1

W123 brake caliper does not fit on 107 / 126 aluminium trailing arms

Problem #2

Hand brake cable looks slightly different on the aluminium trailing arm. W126 cable is shorter than W123 sedan equivalent (even though they are obviously of a very similar system).

But these are pretty trivial problems - they could very easily be remedied.

Please note - the car is still in bits at the time of writing this post. I have not fitted the sub frame to the car and put the springs and shocks in place just yet - there could be another hitch...

...you have been warned (if you fancy doing this yourself).

cmbdiesel · #8 03-11-2013, 03:18 PM

Quote:

Originally Posted by daw_two

I had a set of the anti-squat non steel trailing arms. I sold/shipped them to a guy over in Little Rock but they wouldn't work for his w123 as I recall. I asked him to hang onto them and I'd pick them up sometime when I was in that neck of the woods. I didn't want to pay for return shipment.

Naturally, I refunded his money.

Did you ever get the trailing arms back?
Are they compatible with W126 300SD?

Stretch · #9 03-13-2013, 05:06 AM

Quote:

Originally Posted by cmbdiesel

Did you ever get the trailing arms back?
Are they compatible with W126 300SD?

You might be better off sending a PM for this one.

If you do and you get a replay, I for one would like to know the answer.

vstech · #10 03-13-2013, 06:49 AM

Quote:

Originally Posted by cmbdiesel

Did you ever get the trailing arms back?
Are they compatible with W126 300SD?

the 126 in 2nd gen form has different rear subframe, but it's a bolt in, so installing the arms in a 126 should be fairly simple.
I've seen them on 126 SEC's at the parts yard.

daw_two · #11 03-14-2013, 09:21 AM

Quote:

Originally Posted by cmbdiesel

Did you ever get the trailing arms back?
Are they compatible with W126 300SD?

CMB --- got your PM, but thought I would reply here, so everyone could see.

I never did get them back because I thought they wouldn't fit a w123 nor w126 diesel. After reading all of Stretch/Army's posts, I'm thinking you could make them work, but there seems to be a lot of effort in changing the other stuff. If I needed to replace a rear trailing arm, I'd just go to the junkyard and find a good one of the correct type.

I actually thought about those rear trailing arms a few weeks ago since I had that trip planned to Hot Springs, AR --- don't know where I would have put them though; traveling with 2 girls fills up the 300SDL FAST !!!!