108 Hydropneumatic Compensator Replacement

[neelyrc]

My 280SEL 4.5 has the standard compensating unit but it appears to be growing weary.  To the casual observer the appearance is quite good but I can tell that it is sitting low with no remaining camber.  Niemoller will rebuild the unit for around $1500 if your core is in suitable condition.  I understand that the units are actually rebuilt by ZF Tradition (www.zf.com) and some savings can probably be realized if bought direct. 

Alternatively, the original compensator can be replaced with a spring kit (MB part No. 9003290501). Apparently these were once plentiful and many 108s were converted.  So far I have only found very pricey used ones on line in the USA.  There are at least a couple of vendors in Germany selling new kits for about 20% of the cost of a rebuilt compensator.  I have been told that the ride and handling may suffer somewhat but the camber is restored.

Has anyone here installed such a conversion kit on a 108?  If so I would be interested in hearing whether the results were deemed suitable. Any comments will be appreciated.

[wwheeler]

My W111 had the axle spring when I bought it. When I rebuilt the rear axle years ago, I decided to go with the Hydro compensator. At that time, these were just beginning to be rebuilt by ZF in Germany. The Classic Center's price was substantially higher at the the time. I obtained a core and sent to ZF in Germany. It was a giant pain to sort out the payment but it got done and is on the car now.

I was hoping for a better ride but really did it for originality. I will report I saw no difference in handling or height. Pretty much the same before and after the coil spring. So unless you plan to load the trunk up or are a stickler for originality, I don't see that the hydro compensator is worth the effort. The spring will never fail, where as the compensator will at some point. How long? Who knows. My understanding is they fail when fluid drips from the unit indicating the seal is blown.   

Do you know if the unit that is on the car now is original? That would be a pretty good service indicator about how long they might last.

You will have to weight the pros and cons, But dealing directly with ZF may still be a giant pain as it was when I did mine. Niemöller may be an easier path. Also check the Classic Center's price. All the exorbitant shippng to Europe and tariffs will be taken care of. Is that $1500 US or E1500 euros?

[neelyrc]

Thank you for your informative reply, Wallace.

I would prefer to stay original but in this case I am leaning toward replacing the compensator with the spring kit.  If I go this way I will retain the Boge unit in case I later decide to go for the rebuild. 

I have heard that the life of the compensator in normal service was possibly 15 to 20 years.  I do not know if my unit is original to the car.  I doubt it. My car has 138,000 on the clock and this mileage is well documented .  I have fairly extensive maintenance records from the original owner covering the first 90,000 miles.  I need to dig through these to see if there is any mention of a replacement in the early life of the car. 

I have not contacted ZF but only reviewed their online site.  I did pull down the price from Niemoller and it is €1400 which is roughly $1500 at current exchange rates.  In addition the customer must supply a rebuildable core.  Of course shipping and tariffs would be on top of this. I believe that Niemoller have the units rebuilt by ZF so I guess that it would be a bit cheaper to deal directly with ZF.  I have not contacted the Classic Center.

The German spring kit suppliers I am looking at have the kit in stock for approximately €150 with three to five day shipping.  There is a €40 difference in shipping cost between the two as they use different shippers.  The vendors are:

mbclassics.de

and

dbdepot.de

I would be interested to hear if anyone here has experience with either of these vendors.  They are both listed in our suppliers list in the Technical Manual.


Thanks again for your help, Wallace.

[wwheeler]

I have dealt with mb classics many times  and they are easy to deal with. A solid company and have not had any issues. I find them easier to order from than Niemoller. Done business with both. Shipping from Germany to the US is shockingly low. The reverse is not true.

[neelyrc]

………….Do you know if the unit that is on the car now is original? That would be a pretty good service indicator about how long they might last………..

I had a chance to look through the original owners fairly comprehensive maintenance records and found that a new compensator unit was installed at 108,350 miles on September 17, 1987.  Considering the completeness of the records, I believe this was the first replacement.  The car has done exactly 30,000 miles since then.  Records for this period are fairly sketchy but it would appear that the unit now in the car is the second unit the car has seen and it has not lasted nearly as many miles as the original unit but has lasted many years longer.

The cost of replacing the Boge unit in 1987 was $530 plus $98 labor.

[wwheeler]

Good info and thanks. I wonder if the replacement was new or a rebuild? It seems reasonable that a rebuild would not last as long as a new unit. My understanding is that these fail with time as well as just mileage. First one lasted 108K and 20 years. The second lasted 30K and 35 years. 

[neelyrc]

Pretty sure the replacement in 1987 would have been a new OEM unit as receipts show it was supplied and installed by a MB dealership.  I do not know when rebuilt units first became available.

I guess we can’t conclude much from the 20 years and or 30k mile potential lifespan indicated by my car’s experience to date.

I ordered the spring replacement kit from dbdepot.de and will give it a try.
.   

[neelyrc]

The replacement spring kit is now installed and the ride height in the rear is back to normal. 

The recently installed rear shocks were practically fully compressed all the time before removing the hydropneumatic compensator and therefore were not able to do their job. Back at normal height they are working well and the overall handling is greatly improved.

So far I have only driven about 50 miles with the new set up. It seems the ride is not as “soft” but it is not overly stiff and it is as I like it.

I am holding on to the old compensator for use as a core in case I decide to revert to the original setup sometime in
the future.

[wwheeler]

sounds good and thanks for the update.

[PS1971280SL]

I had a 1969 280SE and had the rear spring replacement done when the original  set up failed and I could not tell the difference in the ride or handling.

[jjbrooks]

For what it’s worth I recently had the hydropneumatic compensator on my ‘69 280SE cab replaced with a ZF rebuilt unit purchased from MBCC. Cost was about $1600 with core exchange (not including labor).  Car has just over 111,000 mikes on it and both ride height and handling are much improved. I briefly considered going with the steel spring solution but glad I opted for with hydro compensator to preserve originality.  YMMV.