300TD Rear Suspension - PeachParts Mercedes-Benz Forum

Swampy · #1 04-30-2003, 01:02 PM

Hi All.. A couple of months ago, I picked up a 79 300TD in need of engine rebuild.. My plan was to swap the block from my 78 300D -- it's got a bad case of the rusties, but relately low mileage -- and the head off of the 300TD.. Thus, I'll be able to keep the hydro-leveling system deployed. However, when I took the head off of the 300TD, I discovered a crack in the 3rd cylinder. Clearly my options are: (1) get the head repaired, or (2) look for another head (if I understand correctly are getting and expensive).. Either way, I'm probably going to spend much more than the car is worth.. My question is: Although this is not the best option, has anyone, or know of anyone that has had some success with converting the hydro-leveling system to a conventional spring/shock system? In the archives, there was some mention about an air shock system?

Any and all assistance would be greatly appreciated..

Kerry Marsh
79 300TD
78 300D
87 Toyota Landcruiser (BJ70 --3.4 L diesel)
98 Subaru Legacy
82 Toyota Landcruiser (BJ42)

leathermang · #2 04-30-2003, 03:37 PM

You need to go look at the rear system you have on your 79 wagon... it may not be the self leveling type.... I have a parts wagon in my yard.. and it is not the self leveling system.... I had a 1981 wagon which was.. and I picked up this parts car as a back up for that.... was I surprised when I found out it did not have it ? yes I was.....

Swampy · #3 05-01-2003, 08:18 AM

I'm sure that it has the hydro-leveling system.. I can remember taking the pump off of the head, and following the lines back to the fluid resevoir.. Under the rear, you can clearly see the suspension strut with the pressure lines leading from them..

#4 05-01-2003, 10:32 AM

You will need a head made for the pump.. They were common a few years ago and used for other things besides cars.. As you said you can use a turbo or non turbo head as I remember.. But watch close that the oil and water passages are right.. .. I have two friends that just looked around the salvage yards and got stronger springs.. I talked to both but they have forgotten what cars they came from.. But perhaps S cars.. They both just replaced the rear shocks with air shocks.. You only need to remove the shocks and check the travel and get a replacement that fits and has the right travel.. However you really need to have springs that will carry the car.. Many of the old TD's have rear springs that have sagged and the level system now carrys the rear of the car more than it should.. For some reason here in the US we seldom replace a spring if not broken.

Ken

leathermang · #5 05-01-2003, 11:29 AM

"you really need to have
springs that will carry the car.. Many of the old TD's have rear springs that have
sagged and the level system now carrys the rear of the car more than it
should.. For some reason here in the US we seldom replace a spring if not
broken."--Ken

Amen ! A much overlooked or underlearned fact.

gsxr · #6 05-01-2003, 12:12 PM

I do know that anyone who has attempted to convert a self-leveling rear to non-SLS (standard spring & shock) has never had good results, and usually end up re-installing the SLS system and making it work properly. Good luck...!

leathermang · #7 05-01-2003, 01:43 PM

" I do know that anyone who has attempted to convert a self-leveling rear to
non-SLS (standard spring & shock) has never had good results "--gsxr

That is an incredibly sweeping statement, implying you know all the people who have ever converted these rear suspensions... Would you like to restate that using some 'qualifier' words... like ' that I have known,' ' that I have read about' ,'most', etc...?

gsxr · #8 05-01-2003, 01:54 PM

Let me put that another way. I have not heard from anyone on the MBZ.org email lists (in the past 4+ years), nor on Mercedesshop.com, who have tried swapping to non-SLS and liked it, or even left it that way. I'd love to hear from someone who did find a way to make it work.

From what I understand, the issue is all wagons have SLS, and the sedan springs either don't physically fit (??), or are simply not strong enough for the extra weight of the wagon body. Hence no non-SLS springs exist (that I know of!) to support the heavy wagon rear end. The hydro shock supports a decent amount of the rear weight, 20-30%, IIRC? If you put in sedan springs & standard shocks, the rear end sits way too low. None of my cars have SLS so I never did major research into this. Like I said, I'm all for finding a way around it, but thus far it's not looking promising...

Note that on the 124 chassis there are a wider variety of springs available, and the tallest/strongest *might* work on a 124 wagon. But most of the time this question arises, it is in reference to the W123 SLS system. Well there was the guy with an E420 and SLS who wanted Sportline, but he ended up getting the proper Euro Sportline SLS springs to fix it.

#9 05-01-2003, 02:01 PM

Are the weakened springs related to the failure rates of the older systems? I'm assuming that as the springs fail, the hydro system is required to counter more force and so must tax the hydraulics?

gsxr · #10 05-01-2003, 02:08 PM

That's one theory. Some "experts" claim that springs almost never sag or fail - was that Stu Ritter? Can't remember. However that defies laws of physics, spring steel does change in rate over time & usage (doesn't it?). And I have heard of a lot of people who put new springs in their cars (due to sagging) and been happy with the increase in ride height. Probably wouldn't hurt, new rear springs will be $200/pair.

leathermang · #11 05-01-2003, 02:35 PM

Dave, your statement "From what I understand, the issue is all wagons have SLS" indicates you did not read my above post, stating that my 1979 wagon parts car does not have SLS.. and I only found that out when another person said their wagon did not have it....
Further, there is a possibility , given the above, that the SLS was designed to bolt onto some of the basic frame which the wagon already had... Since we are talking the same body style.. and like the situation where the clutch pedal mounting is included on automatice trans vehicles... to reduce the number of different mold, etc... to reduce cost....
Many springs are available for all the MB's ... and I know for sure that TWO DIFFERENT heavy duty springs are available for the rear of the wagons.... one described as " for countries with poor roads".... they are color coded from the factory....
So , while no one may have posted about changing over, or has posted but did not fulfill the necessary physical criteria, I believe that a suitable changeover is certainly possible with a little information and care in choosing components...

gsxr · #12 05-01-2003, 02:58 PM

Yup, you are right, I missed the details in your first post. Note that the 1979 is a 123.190, and according to the EPC is should have SLS! The EPC shows no non-SLS parts for the rear suspension, which is really weird. Maybe you have a Euro parts wagon? I dunno. Would need to check the Euro EPC. The early 123.193 (turbo) wagons used the same SLS springs as the .190, but later ones used a different spring - there's a chassis VIN number break. But there were no other optional springs shown. I'd need to check the TDM for th 123, and also the Euro EPC.

A note on the alternative springs. MB springs are color coded with a red or blue stripe, indicating "long" or "short", for the SAME spring part number, to allow for manufacturing tolerances. You don't get to pick which you get unless the dealer has one of each.

The spring part number is stamped near the end of the coil that sits in the control arm, at least on the 124 springs. I don't believe the other stripes indicate anything, it's the part number that's important, and the blue/red only indicates which thickness rubber pad should be used. But yes MB normally does offer a HD spring for "countries with poor roads", and I have seen that before.

Believe me, if you can do the swap and post the part numbers required, there will be a lot of happy people anxious to read the "how to"!

#13 05-01-2003, 03:11 PM

I would be one of the grateful should a successfull conversion be documented. My hydro system has at least two leaks (corroded lines and a wet sphere). This 81 wagon is a decent car but not worth rebuilding the hydro. I'd like to replace the springs and install gas shocks. Maybe I'll be the one documenting the process.

gsxr · #14 05-01-2003, 03:21 PM

leathermang, could you post (or email) me the VIN to your parts car wagon without SLS? I'd like to see if I can find out what springs that has in it.

lrg · #15 05-01-2003, 03:23 PM

I'm not 100% sure of this but I remember someone telling me that the SLS was optional (but almost always installed) on non US wagons but was standard on US wagons. That doesn't mean there wasn't a wagon or two that made it to the US without SLS but it suggests that they would be very rare and unlikely many if any dealers would carry parts for the conventional setup. For those that wish to explore a factory conversion I'd suggest they look abroad, especially places where the simpler setup might be favored.