86ing the hydraulic rear suspension
 

I am removing the hydraulic rear suspension in my '83 300TD project for 2 reasons:
1. The engine is blown and I have a non-TD engine available to drop in.
2. The rear struts are leaking and cost $275 EACH!

Here are some pic of how I have removed the struts and installed sedan shocks. Once it is up and running I can report on the ride...

Pic one how the top of the strut is mounted inside the car...

Pic 2 comparison of the strut (fully extended) and the shock.

Here is the shock installed, I re-used the lower large top mount washer and used the strut rubber mounts. The top mount has a steel disk moulded into it. I had to drill the opening to a larger diameter for the shock shaft to fit. Once I am happy with the performance of the rear, I'll lock-tite the nut and cut the shaft so that it is flush with the mount and the carpet trim will fit over it.

bad news...
 

Crusher,

I have some bad news... The shock will bottom out when you hit big bumps. I'm guessing that you had to compress the shocks to bolt them in. Also, your car will be a low-rider. Don't ask me how I know...

What I did (which is fairly involved) is that I built a 1 inch cup to insert in the upper coil spring support. I installed a second rubber sandwich in the new machined cup. kinda like a lift kit. This brought up the rear end 3 inches, so now it sits right. Then I had to machine blocks for the bottom of the shocks, to be installed between the A-arm and the lower shock mounting holes. This lowered the shock a bit, preventing it from bottoming out. Not for the average DIY'er, as I needed my milling machine and lathe to make these parts.

Everything works fine now, but it's a challenge getting the shocks to line up when installing.

My advice... spend the money for the shocks and re-use your TD head with the pump.

Thanks for the advise, I did notice that the installed shocks seemed to have a reduced amount of travel space.
My thinking is that ride height is dependant on spring length. I was going to swap the springs thinking that the TD's were shorter but I counted 9 turns on the TD just like my sedan parts car. But after consulting http://skinnerbox.steaky.org/123_DISK2/program/Chassis/32-010.pdf

There are many different spring combinations and I like to be able to decipher the MB# to know the differences in spring rate....

Plan B maybe installing an electric motor to the suspension pump.....

The cup I machined was actually a 1 in. thk slice of round steel bar, which was machined to fit inside the top rubber sandwich. I welded a new lip to this cup in order to fit the second rubber sandwich. A cutout needs to be machined in this spacer to allow the shock to go through. I learned this the hard way...I don't know if MB makes a spring long enough to bring the TD rear back high enough. How low does your TD sit? Those 3 in. of lift on mine was just about right.

Springs are not cheap and are a ***** to change (and potentially very dangerous if not done right). I remember seeing the shocks for 425$/pair on ebay last year, the guy had a whole bunch of them. Maybe someone here remembers who that was.

As far as installing an electric pump.... I think that you'll be giving yourself more trouble in the long run than just refitting yout TD head. Is your head still good?

One way or another you'll have to sink some $$$ into your project. My advice is try to stick to the original system. When I did mine I was poor and naive, and looking back I wish that I had stuck to the original setup. I had exactly the same situation as you: leaky shocks and a non TD replacement engine.

Here is a pic of how the car sits now. My driveway is sloped so I measured from the ground to the top of the wheel arch, 25".

section 32-250 of the 123 manual list the springs and technical data.
The TD springs should be 115 324 38 04 unloaded length of 361mm and rate of 18.7mm per 1000 newtons.

My '79 300D donor has 115 324 34 04 springs 369mm unloaded and a rate of 18.8

So swapping the springs will give me 8mm extra height but very slightly softer springs././ not worth the trouble to swap them out.

The longest rear springs listed are 116 324 09 04 at 372.5mm and a rate of 15.2 so IF I could find them I'd get a harder ride and a real benefit of maybe 1" height, (11mm+ net ^ in rate)

The issue with the engine is unknown, besides a worn turbo, it has near zero compression, won't start, and all vapors come out of the breather. The PO said he ran it hot due to a leaking hose (the short water pump hose) and the donated it to the Kidney foundation. He said it still ran at that point. When I got it there was maybe 1 liter of oil in it and very little coolant....

Would retrofitting to airbags be possible? Would require addition of air compressor &, possibly, small air tank but may still be cheaper than repairing existing system. Thoughts?

buy a taller shock with simular mounts. Will give you increased travel and avoid all the machining. You'll probably have to call/email shock manufacturer and tell them what type and size shock you just tried and how much longer/travel you need. They can then come up with something close made for another car to match your needs.

The shock needs to be shorter, not taller. And you must remember that finding a shock that fits will not solve the problem of the rear end sagging.

As for installing an airbag setup, it would seem to me like a lot of trouble and expense for a system that will never work as well as the original setup.

How bout hydraulics?

Look at these links:

http://groups.msn.com/w123club/my230celowriderlpgconversion.msnw?albumlist=2

http://groups.msn.com/w123club/rayoslowrider280ce.msnw?albumlist=2

http://groups.msn.com/w123club/dvf280telowrider.msnw?albumlist=2

Louis.

Well the car is up and running and Lars is 100% correct, it rides like s*&^%! The rear sags and I get bounced like Iam in my brother-in law's clownmobile pick-up truck.
I've been looking into the airbag idea but that is a project and $$.
I contacted Strutmasters at strutmasters.com and they don't list a solution for Mercedes on their website but claim to know the TD rear suspension well and have a coilover shock conversion. I ordered it and will report when it arrives!!

Keep us posted on your progress. Hopefully the coils on the shocks will be strong enough to raise the rear a few inches. One thing to remember is that the opening in the A-Arm to feed the shock through is barely bigger than the shock itself, so the coil-over shocks must not be any fatter than the originals.

OK Brown just showed up and delivered the "solution" from Strutmasters. They are Tokio shocks with a coilover. From sizing things up on my spare rear suspension, The lower mount CAN be fished in the trailing arm opening from the top side. The coils and hardware are too fat to be installed from underneath but they are sa smaller diameter than the main springs.
To install it looks like I'll have to drop the trailing arms, not fun but now an excuse to replace the rubber bushings.....

hmmmm..... what about plain ol Air shocks?

Also even JC Whiteny sells air bags for an air system.