W140 rear shocks...help! - PeachParts Mercedes-Benz Forum

plink49 · #1 01-30-2004, 07:40 PM

I have an earlier post this week asking if $500 was a decent price to replace the rear shocks on a '92 500SEL. I am now told by the shop (an honest indy) that the car requires self-leveling shocks with a list price from MB of an astronomical $800 PER SHOCK! I have a query in the "Parts" portion of this wonderful forum looking for a decent used one and hopefully that will produce results. My question here though is this: Does this car absolutely NEED these self-leveling shocks, or can others such as Bilstin be fitted and not loose stability/performance? If so, which model numbers will work?
Help....I can't afford $1600 for two shocks!

KenP · #2 01-30-2004, 08:36 PM

I think you'll find its more complicated than just replacing the self leveling shocks with regular shocks.
The shocks you have are able to level the car because they actually support a percentage of the weight of the car... regular shocks do not...
So, I'd expect if you want to change out to regular shocks in the back, you'll also have to change the rear springs, etc to carry the additional load.
Hope this helps.

stevebfl · #3 01-30-2004, 09:05 PM

Why would you want to replace your shocks, they are about indestructable? Are they leaking?

plink49 · #4 01-30-2004, 09:17 PM

I need to replace the passenger-side shock because the bushing is shot...causing the metal to metal thump that will probably escalate into a nightmare knowing these cars all too well!
But I love the car.

sixto · #5 01-31-2004, 01:04 AM

If the honest indy didn't know off the top of his head that a 92 500SEL is fitted with hydraulic struts for the self leveling suspension in place of conventional shock absorbers, I wonder what other critical information about the job he doesn't know.

Sixto
95 S420
87 300SDL

Peter Guenther · #6 01-31-2004, 06:55 AM

Go find a bushing, and replace. Your mechanic does not know MB very well either. The shocks are $400 ea at discount, and come with the mount, it is unique. Visit your MB parts guy, they might sell them they sell the locking nuts seperately.

stevebfl · #7 01-31-2004, 11:15 AM

Is the bottom bushing bad or the top. The top is what I see fail and cause noise. It is available separately: 140 320 09 44.

The real problem that takes out these parts and the shocks eventually are the accumulators. Long before you notice how bad they make the car ride they are doing damage. As their capacity drops they start "bottoming out". Once every bump is a "bottom out" the problem gets addressed.

KenP · #8 01-31-2004, 01:42 PM

Steve,
Then you'd be an advocate to replace the spheres based on time/mileage?
What's your recommendation based on past experience... ?
Thanks.

stevebfl · #9 01-31-2004, 02:20 PM

Yes, you could say that. I haven't actually thought to much about it but I would definitely say every 100K, but I might say every 5 years.

We have had MB station wagons for shop vehicles for about 20 years. I would say that we replaced the accumulators every 5 years, but I am very sensitive to the problem. Our first shop wagon was a euro 280TE we imported ourselves in 1985. We used it to tow our 19 foot Wellcraft bowrider for years which probably stressed them a bit. Our current wagon is a 91 300tE and we have replaced them once and will probably do it again in the next year.

KenP · #10 01-31-2004, 04:17 PM

Steve,
Good to know. I'm a huge believer in preventative repair... but, in order to be effective without throwing huge amounts of money at it, past history of the design is badly needed...
My data point is only one car... that's now 7 years old with about 95K on the clock... so, I'll put a pair of spheres on my list for when the weather warms up...
Many thanks.

plink49 · #11 01-31-2004, 07:39 PM

Thanks for all of the replies....you all have been extremely helpful! So, the top bushing is replaceable....is that what I'm reading here?
To sixto....I said he was an honest indy, not a particularly great one when it comes to MBs...obviously....LOL! His forte is BMWs

sixto · #12 01-31-2004, 07:45 PM

Quote:

Originally posted by plink49
To sixto....I said he was an honest indy, not a particularly great one when it comes to MBs...obviously....LOL! His forte is BMWs

Steve's forte is also BMWs.

Sixto
95 S420
87 300SDL

plink49 · #13 01-31-2004, 08:28 PM

Quote:

Originally posted by stevebfl

The real problem that takes out these parts and the shocks eventually are the accumulators. Long before you notice how bad they make the car ride they are doing damage. As their capacity drops they start "bottoming out". Once every bump is a "bottom out" the problem gets addressed.

I am obviously not a mechanic....what is an accumulator? Is this something that could cause a thumping on this car (W140)? Is it a replaceable part seperate from the shock?

sixto · #14 01-31-2004, 11:09 PM

The accumulator is a sphere that kinda does the job of a spring and shock. It's external to and separate from the hydraulic strut. You can replace the accumulators without touching the strut. When the ride gets really stiff, usually a sphere has failed. It becomes like an overly stiff spring.

Sixto
95 S420
87 300SDL

stevebfl · #15 02-01-2004, 12:41 PM

In the rear you have hydraulic struts. These are hydraulic pistons. If one forces fluid in the piston gets longer. View them sort of like the pistons lifting the boom of a wrecker. Add fluid and they lift.

This is how the height is adjusted in the leveling system. More pressure and the struts get longer holding the car up. That is a simple concept. Now think about what happens when a bump is encountered. The normal concept is for the strut to shorten as the suspension compresses. The above concept would have none of such. Fluid being non-compressible a strut thus becomes a rod and there is no suspension.

So along comes accumulators. They are a sphere with say a 1000psi nitrogen gas pressure inside. The gas keeps a diaphram pasted against the wall of the cylinder. Now we have a compressor that desires to make 2000psi so that it can lift the rear end of the car. Instantly the fluid in the system goes to 1000psi as any compression of fluid brings instant pressure as it isn't compressible. The full system can not accept one drop as the preesure would go to infinity in the ideal system, BUT we now have the liquid line running to the accumulator which has a compressable gas inside so that extra drop goes into the accumulator and the pressure of the now further compressed gas goes up a little.

The compressor continues pumping and fluid continues to be forced into the accumulators with the continued compression of the gas. The diaphram now has moved off the wall of the chamber and as the gas pressure raises to say 2000psi the car starts to rise.

The system is now leveling the car. The accumulator is maybe half filled with 2000psi liquid and half filled with 2000psi compressed nitrogen gas. And we hit that bump. The strut wants to shorten which causes the fluid to need to go somewhere as it is non compressable. The fluid goes into the accumulator and the diaphram is pushed further and the pressure rises to say 3000psi and the event is equalized and the pressure now rebounds like a compressed spring.

This happens over ever bump. Some bumps are small and the pressure increase is thus small. Some bumps are bigger and the strut will push a lot of fluid to the accumulator. When new the accumulator can hold the car with sufficient space left in gas to accept full movement of the struts. Remember the struts will push a finite amount of liquid out when they are fully compressed. The only space for this to happen is the space where the compressed gas exists.

Over time some of the gas passes through the diaphram and the space available is smaller when the fluid hits the pressure necessary to lift the car. Slowly the large bumps bottom out. Eventually even the dullest of drivers figures something is wrong.

When totally exhausted the spheres are full of liquid only and the struts are rigid. In this condition the force applied to the system when a bump occurs is out of this world and tears up the rest of the system. This is when the struts fail. It is some really good stuff though as there are plenty of the dullest drivers owning these cars and even after months the struts usually live through it. Always amazes me.