1979 6.9 SEL..guidence needed

[Vladamir]

Hi,

A question for al you 6.9 owners out there.

I've been looking at a late 1979 6.9 SEL over here in the UK. Its a low mileage car for the year with just 96,000 miles on the clock and a full Mercedes History. This is a car I saw last year which was sold through a classic car auction and its just come back on the market

When I went to have a look at it today, the front suspension was down over the tops of the tires and did not pump up when the engine was switched on. When I saw it go through auction last year the suspension was at the right height and every thing about it looked right.

Took the car out for a drive and the front of the car was all over the place...wallowing and pitching due to the low suspension.

Mechanically the car is in great shape, ie; engine nice and smooth as was the transmission. Good brakes etc etc.

So whats with the suspension.....I've done a search and it could be a number of things. Is anybody able to tell me what the most common fault is on the front suspension and possibly a couple of other idea's.

Many thanks

[wbain5280]

There has been a lot of 6.3 and 6.9 discussion lately.

http://www.peachparts.com/shopforum/search.php?searchid=320243

(a search on m100 in the vintage forum)

or

1970 300sel 6.3

or

Engine Rebuild on 6.3

or

W116 advice needed

Read Gerryvz's presentation.

Make up your own mind.

(Bottom line, buy a 500E/E500 W124.)

[Vladamir]

Thanks for the links.....a lot of interesting stuff, but not much on suspension and the most common causes of front suspension problems on 6.9's

Any other information gladly received.

Many thanks

[Emmerich]

The system is simple, it has a pump, 4 hydraulic struts, 5 nitrogen spheres, and 2 leveling valves. If only the front goes down it is something on that end. If you are losing fluid in the reservoir you have a leaking strut. If the leveling valve for the front is leaking internally, you will see no fluid loss but the front will go down.

Any car like this needs to have the suspension gone over by someone with knowledge of the system. You might fix one thing now, but shortly have to do more work. Its best to diagnose and repair everything at once.

Struts are expensive. N2 spheres are pretty cheap. Leveling valves can be rebuilt, I don't know if they are available anymore.

[diametricalbenz]

How much were they asking for the car in its current condition? Is the vehicle in private hands now or is it back at the auction house?

[alabbasi]

I think there is a company called Pleades in London that specialises in the Citroen CX, DS range that should be able to charge them for you.

[gerryvz]

Fred is pretty much right on, with the exception of there also being a master level control valve underhood right on top of the hydraulic reservoir.

Generally, a 6.9 going down on its haunches is due to fluid/pressure loss -- a hydraulic leak -- either at the strut or at the hydraulic pump and sometimes at one of the level control valves on the axles. Struts do leak from a couple of internal o-rings that sustain a fair amount of friction, and they can leak internally so that you can't see the problem; but most commonly they leak externally so that just by getting underneath the car you can see leakage in the immediate vicinity of the strut.

A hydraulic pump leak is generally obvious by either hydraulic fluid on the ground, or leaking down the front of the block directly underneath the pump (which is mounted on the front of the block, driver's side, driven off the crankshaft).

The best bet if you purchase this car, is to have a specialist replace the entire suspension to a known-good condition. You can purchase rebuilt or new front/rear leveling valves and master valve from MB, and this is a recommended route over going rebuilt. The accumulators run under $200 apiece; and I believe the struts are now in the neighborhood of around $1,000 apiece give or take.

I believe the hydraulic radial piston pumps run around $800 these days (list). They are well-lubricated by the hydraulic fluid, but do after 20+ years tend to begin seeping from the gaskets. They can be rebuilt, but the pumps are EXCEEDINGLY difficult to screw back together properly so that the new gaskets seat correctly. I have found that it's just easier in the long run to purchase a new pump and go that route.

A moderate to experienced DIYer can handle the suspension on a 6.9 -- everything is accessible and fairly easy to get at.

Yes it's expensive, but preferred to replacing individual parts to patch up a faulty system. By going with new components, you will have a suspension that operates as the factory intended. The 6.9 suspension at factory spec is not too bad, but is rather soft (particularly when compared to a 6.3). Some people say that it firms up when pushed, but my experience has been that by the time things are "pushed", the heavy car is near its limits and that entails a whole nother approach to keeping things in line. The 6.9 is definitely more geared toward luxury and high-speed cruising than performance, and there's little that can be done to make it a "handle like on rails" type of car.

The engines tend to be very long-wearing and durable both on the bottom and top ends. Major problems that one would see involve the K-Jet fuel injection system, which many if not Bosch specialists have the expertise to diagnose and fix.

I'd take the prospect of taking on a 6.9 (or 6.3 for that matter) very seriously, and know what you are getting yourself into, in order to have a car that's proper (and thus the best ownership experience). Some of my previous posts have been designed to give folks a bit of a dose of reality about these cars, because they often seem to have become rather "impulse" type purchases, and they suffer from neglect from these owners who cannot provide them what they need. They are demanding but rewarding cars to own if the ownership experience is approached the right way and from the right financial perspective.

I'd recommend you (and anyone reading this) to visit the sites at http://www.m-100.cc and http://www.m-100.info if you are interested in learning more about the cars. You will learn A LOT from the bulletin boards at these sites and observe all of the little and big problems that owners experience with these cars -- should help you make up your mind.

Good luck!

Cheers,
Gerry