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

Dear All,

I've stumbled upon some reasonably priced W126 aluminum trailing arms that I would like to fit to my W123 300D... I read on this forum that it is possible to fit them but:-

Has anyone here actually done the job?

Has anyone here got W126 aluminum trailing arms on their W123?

I've found this thread but it seems as though the poster was being messed about by people. The verdict is that it can't be done:-

http://www.peachparts.com/shopforum/showthread.php?t=246721

I'm not satisfied by this just yet (sorry!)

The seller does say that I need a different shaped anti-roll / anti-sway bar. This to my mind does indicate some different geometry if that is the case.

As usual any help will be greatly appreciated - particularly from those who have done the job.

A desperate Sunday evening (well afternoon where most of you are) bump!

I'm not getting a warm wet feeling about this one... perhaps it isn't possible after all?

At the rear, outboard end of the swingarm there is a design difference described as "anti-squat", it can be found described in the 126 Body and Chassis FSM. I suspect that is the fundemental basic difference between the standard swing arm and the aluminum versions found on 126 coupes. How does this difference manifest itself as far as what will fit and what limitations on parts that connect are not known to me other than the differences exist. Good luck!

Yet again - thanks for your help Billybob - a good shove in the right direction. The seller won't ship the parts so as I've got to go and see them, I'll take a W123 trailing arm for comparison, a camera, and a tape measure. And in the meantime I'll leaf through the FSM. Cheers!

Update - finding information
 

Hmmm I thought I'd find more information on this. It seems to be common knowledge that the steel trailing arms are interchangeable... but I can't find much information about the aluminum versions.

I've read through chapter 35 in the W126 FSM and I can't make out for sure if the trailing arms with the anti-squat geometry were aluminum or not - I guess so...

It looks like I'll have to see these parts in the flesh.

To be continued...

Did you try looking at part numbers in the EPC?

Nope - I don't have it - I'll have a chat with the friendly dealer and see if he can help out.

My memory is foggy....
 

..... but I recall looking into this....

I recall the cast arms were titanium, and were issued on the 500 and 560 models. Diesels and smaller engined cars had the stamped steel like the W123. My 85 500SEL euro car had these cast arms, so I don't think they are exclusive to the 86 and up redesign.

From what I could see, it appeared the cast arms (forged?) were interchangeable with the stamped steel.

I also recall this may involve a change in the way the disk caliper mounts, but it certainly looked like the cast W126 arms would xfer to the W123, if the different parts were also changed over.

Jim

Thanks for your input Jim. I got that impression from the FSM as well - but I need to check out the geometry of the trailing arm to make sure all of the (redundant) anti-squat stuff isn't necessary. I'm also a bit concerned about dissimilar metal corrosion... so I'll have to look into that too. (Clarification:- bunging the old W123 steel bits onto the luxurious alloy casting may not be so smart - I don't know - I'll have to see).

http://viewer.zoho.com/docs/rackve

Cross Reference List, 300d as source for pn

Hope this is useful

Wow thank you very much

1263503205 seems to be the steel one according to http://www.german-spob.de/start.php?seite=gebrauchtteile&seite_gebr=suchergebnis&suche=&language=eng

I'm not sure of the material used however, I do know that theres a right side and left side. I used those are the basis of my parts search.

• http://i.imgur.com/ghKUcl.jpg

Oh great - this is a great help - this more or less confirms that the alloy (well non steel - whether it is aluminum or titanium remains to be seen) is with the anti-squat gubbins.

I've found these pictures in the FSM:-

http://www.peachparts.com/shopforum/...1&d=1291824355
http://www.peachparts.com/shopforum/...1&d=1291824363

You can see there are extra bits by the hubs

Well it has been a long time...
 

...since I've thought about this but this picture prompted me to think again

http://www.peachparts.com/shopforum/...1&d=1318352907

This is actually a second generation W126 sub frame and trailing arm assembly... but it got be scuttling off to the Russian EPC site (EverythingBenz - Mercedes-Benz Forum and Web Search Using Google) to have a look at those lovely aluminum trailing arms.

Here's the first generation W126 sub frame

http://www.peachparts.com/shopforum/...1&d=1318352907

And these are the aluminum trailing arms

http://www.peachparts.com/shopforum/...1&d=1318352907

Part 116 must be a big bit of the anti-dive mechanism. There must be a big bit that goes across the back of the car there...

I said ages ago I'd go and make some measurements - I never did... but I might have the chance to see some real ones soon. Stay tuned!

And here's the rear anti-roll bar
 

It looks very similar to the W123 set up...

http://www.peachparts.com/shopforum/...1&d=1318357726

Here's a start of the week bump (now it has been rehoused to DD - thanks mbdoc!)

It looks like if you use the compatible anti sway bar and the entire a arm plus hub assembley you will be good. My queston though is the mounting bolts for the aluminum assembly. The anti squat parts look like they will stress the sway bar with for and aft loads which the original standard steel parts would not do.

I am guessing there will be modification necessary there to make them work.

Thanks for the input.

I don't know for sure but the anti-roll bar in the picture below (number 5)...

http://www.peachparts.com/shopforum/...snapshot17.png

...looks very similar to a W123 one. It even has the kinks in the corners. Number 8 looks a bit different and beefier at the mounting points (that's the bit for the anti-squat variation).

According to wikipedia the width of the SEC was 1828mm instead of 1820mm for the other W126s - I guessing the extra 8mm was in wheel arch flares though!

Mercedes-Benz W126 - Wikipedia, the free encyclopedia

The W123 has a width of 1784mm

Mercedes-Benz W123 - Wikipedia, the free encyclopedia

So I think the anti-squat anti roll bar from a W126 would have to be cut / modified or perhaps the anti-squat fittings added to a W123 anti roll bar...

126 alloy trailing arms
 

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!

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.

Update!
 

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.

http://www.peachparts.com/shopforum/...1&d=1338552339

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

http://www.peachparts.com/shopforum/...1&d=1338552351

Extra stuff on the back though

http://www.peachparts.com/shopforum/...1&d=1338552360

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!

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.

Update
 

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.

http://www.peachparts.com/shopforum/...1&d=1338915337

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 =>

http://www.peachparts.com/shopforum/...1&d=1338915497

All is not 100% straight forward though.

Problem #1

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

http://www.peachparts.com/shopforum/...1&d=1338915624

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).

BUT!
 

And there is a but!

I'm not really sure if it is worth it now!


I measured the weight of the two trailing arms. The W123 steel version is lighter than the aluminium one. The W123 one comes in at a gnat's cock lighter than 16 kg and the W126 / 107 aluminium version weighs in at 21 kg.

I'm going to have to do some unsprung weight / suspension calculations to see if I need to change the rear springs as well.

I had the feeling that the aluminium trailing arms were going to be lighter than the steel as well as being more corrosion resistant. Unfortunately with all of the anti-dive gubbins on there it seems as though the reason why the large proportion of these trailing arms were made out of aluminium was probably more to do with stiffness...

...well that's my guess anyway.

Is there any point in fitting ant-dive to the rear end of a W123 300D non turbo?

I think not.

Do I want the warm wet feeling of having corrosion resistant aluminium trailing arms rather than the steel ones?

Yes - kind of

Is it worth the extra 10kg in weight?

Well that's not really what I wanted to discover...





...what do you guys think?


Would it be a cool upgrade?

Would it even count as an upgrade?

Well those rear trailing arms, at least on the 126, seem highly subject to corrosion. Avoiding that problem may be worth it.

That's the only benefit I can see with them.

Now if I go ahead with my OM648 conversion then I'd probably have the torque needed for the anti-dive otherwise with only a N/A OM617...

The rear calipers on the aluminum setup are floating caliper, similar to the 124 chassis. It looks to me like the conversion is way too complicated for the value offered. (Sorry)

I was very high on the idea originally but after seeing all the differences it looks impractical to me.

the extra weight would be a deal killer for me too.

I think I'm going to get some prices for the bits that I would need to make these trailing arms totally new and post up that information before I make a final decision. At least that sort of information might be of use to others...

It doesn't look like I'll be going ahead with it at the moment though.

TRUTH! Passenger side seems most common. My SD and my buddies old SE.

http://www.peachparts.com/shopforum/diesel-discussion/303427-w126-trailing-arm-rear-lower-control-arm-rebuilt-replacement.html

I forgot to say about the caliper difference...

I don't consider it to be a problem at all just use the caliper that is designed for the aluminium trailing arm. I haven't checked it out yet but the piston diameters look the same - so I don't expect a difference in braking force.

One of the trailing arms came with a caliper fitted - and if it is OK that could save a bit of cash. It is an ATE by the way... they might all be ATEs for aluminium trailing arms... I don't know I'll have to check with the dealer...

Anyway here are some more pictures.

1) The slightly different although similar looking caliper

http://www.peachparts.com/shopforum/...1&d=1338993388

2) The anti roll bar connection

http://www.peachparts.com/shopforum/...1&d=1338993465

3) The shock mounting bits (also no problems there from what I can see)

http://www.peachparts.com/shopforum/...1&d=1338993479

http://www.peachparts.com/shopforum/...1&d=1338993490

bump

Ok this Kilo gram stuff means absolutly nothing to me, sooooooooo.........
Since Google is our friend ;)

16KG = 35.27lbs

21KG = 46.30lbs

11.03lbs difference.

Charlie

I'm sorry Charlie - I'll try and remember to convert any future measurements into old money as well!

So what do you think of the whole idea then? Would you consider doing it? (for the right price of course)

Army,

With this upgrade, can you use the bigger calipers and rotors ? Seems like a nice trade off. I would swap 11 pounds for the bigger and better brakes. I would rather lose 11 pounds off my gut. My .02. So, does this whole sha-bang just bolt in ?

I don't think the brakes are any different operational wise.

I have to check them out still but the caliper that was left on one of the aluminium trailing arms that I bought looks like it has the same sized brake piston in there as the calipers that are fitted on the steel trailing arms. It looks like only the casting is different so that it fits into the slot on the aluminium trailing arm whereas the calipers on the steel trailing arms just bolt on (as I'm sure you know).

I guess this "upgrade" on a W126 would be very straightforward as you'd just remove and replace. The only problem that might occur would be fixing the thicker anti-roll bar to the chassis for the anti-dive mechanism. But that might not be a problem.

As for doing this to a W123 I know that that anti-roll bar needs to be narrower. The W126 is a wider car. The rest of the stuff seems to me to just be a bolt on job though - I might be able to use a W123 coupe rear anti-roll bar or shorten a W126 one for the anti-dive attachments... I haven't gotten that far yet. (And like I've said I'm not sure if I'll go that far!)

The anti-dive mechanism should in principle be a handling advantage when fitted to a vehicle with a powerful engine - but when fitted to a N/A OM617 I guessing it isn't going to have much of an effect...

...oh yes there's a difference of 5kg / 11lbs per side.

That extra 11lbs will give the rear tires that extra downward force to help eliminate Burn Outs. :D

You know with the Turbo added, helps the 617.952 unleash all that awsome power. :eek:

Charlie

Right that's it I'm not doing it then!

Caliper differences
 

I'm quite lucky having both the W123 ATE and W126 ATE brake calipers to compare. If one set had been of another make it might not be so clear.

I can confirm that

1) the brake pads are the same
2) the discs are the same
3) the brake pistons in the calipers are the same
4) the caliper mounting bolt diameters are the same but the bolts are of a different length
5) the distance between the centres of the mounting bolts are the same
6) only the thickness of the mounting side on the W123 caliper is thicker - the casting is slightly different in this area - that's it.

Here are the pictures

http://www.peachparts.com/shopforum/...1&d=1339069778

http://www.peachparts.com/shopforum/...1&d=1339069788

http://www.peachparts.com/shopforum/...1&d=1339069798

I am sorry, I am certain that the rear calipers were different on my 84 500sec so assumed that all the aluminum arm cars would have them. Those look to be pretty much the same as on the 123 cars.

Thanks for your input Tom - I have no idea which W126 these came from - they could in fact have been from a R107. I have no idea and no reliable way of finding that information.

All I did was buy these bits from a bloke selling them on marktplaats (that's a Dutch variation of ebay that's very popular 'cos for lots of stuff you don't need to pay for the advert). In his advert he has a picture showing racks of these parts already removed from the cars - it could be his picture - it might not be! I have no idea. I didn't go and see him - I just got him to put them in the post for me.

I'll spend some time doing a bit more research for part numbers then we'll know what's what.

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.

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.

So the bottom line would be to remove the whole rear suspention from the SEC and move it on over to the 300SD?

Trailing arms, Sub Frame, Axles and Diff. So should be around $300 for the whole packafe + - .

Charlie

I don't think so Charlie. The trailing arms seem to be the same dimensions whether they are steel or aluminium to me. The only problem I have for my W123 is how to fit the anti-roll bar so that the anti-dive set up works. I'm going to have to modify either the W123 roll bar or shorten a W126 one to make it fit - but then again I might make a custom one (in my dreams!)

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 !!!!

Thanks for the update daw_two

Note to self
 

(Sorry to use this forum as my personal note pad!)

SEC rear caliper left hand side P/N is 126 420 04 83

SEC rear caliper right hand side P/N is 126 420 05 83