"clunk" sound 300D

Yes, it's me again. I'm going on a long
trip tomorrow in my 81 300D and i've noticed
a few things I hope to get a little feedback before leaving.

When i put on brake and almost come to a stop, i can hear and feel a distinct "clunk"
sound under the car. I can't yet figure
exactly where it's coming from, but possibly toward the back. Any ideas? Everything along
the tranny looks fine to me underneath, but
then I'm not 'really' experienced in that
area.
Thanks

[Ed Richardson]

Well, here I go again on the flex disc. I had a similar sound and it was a bad front disc. Crawl under again and take a look and wiggle the drive shaft. Ed

[REX CARLE]

If this clunk happens just before the car comes to rest, then most likely there is little or no vaccum to the modulator with the throttle in the rest position. Therefore the transmission is downshifting to first gear. First gear should engage upon applying throttle after coming to rest. Check vac lines, valves on valve cover and at injection pump.

Ed, new brakes, discs, calipers, the whole works were just replaced on the vehicle 5k miles ago. I would think they are fine, unless one is faulty. Also, I got under it yesterday, the driveshaft and works seem fine, tight as a drum.

Rex, I just went over vacuum lines this past weekend and looked like all connected, but i'll look them over again, expecially at pump. That makes good sense what you say.

It's definitely not a bottle or somehting rolling around, it does it distinctly just before I come to complete stop where there's not really any 'force' to cause something loose in car to shift, that would happen before this sounds happens...if i make any sense. What I need to do I guess is let somebody drive it and see if i can pinpoint where under the car it comes from. Hard to tell from driver seat, but it almost sounds like from the rear.
Thanks

[mark300d]

I seem to have a similar problem on my 123. A lot of times when I come to a stop the car makes a thump/thud. I have not checked any or the parts sugested, yet. I also have a small shimmy at 55mph+, the steering just vibrates left and right, but I think this is because I need an alignment. The thunk seems to be coming from the front left area of the car. I want to say that it is coming from the (forgime the lack of technical language) the connector that ties the wheel to the chasis, the one that goes back and inwards from the lower arm and into the chasis. Is it possible there is some play and it makes the thump?
Mark.

Mark,

The MB nomenclature for this part is the guide rod. Most people call it a strut rod. Yes, if loose, this would certainly cause the problem you describe. I've had so little trouble with the front suspension of a 123 car, I don't know if this is a very common failure. The best thing is to get the car up where you can shake and pry around on the components to determine where your problem is. Don't do this unless you have experience with raising a car to safely perform these tests. If I encourage you too much to jump under the car to do this, I will receive the "wrath of Deezel", (the mercedesshop safety officer) and rightfully so. We have no way of knowing what equipment you have to work with, or what your experience level is, so we don't want to encourage you to do something that may prove unsafe.

But the only way you can know what to replace is to shake and pry. Be careful.

Good luck,

------------------
Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

[be459]

If it is the strut rod bushings, you can feel and hear the clunk by tapping the brake while the car is rolling slowly. The tapping cause the front wheels to lock up while the body is try to push forward. The wheels then push the strut rods against the body causing the noise. If someone is watching from outside, he could see the front wheels move backward relative to the body while braking. Either way, Phill, the flex disc should be inspected regularly.

Good luck and have a nice trip.

David

[stevebfl]

I often don't get into these noise problems as the question being asked often involves to many assumptions by the one asking. When done at the service desk a series of follow up questions is always necessary.

In reading the replies, I like the reply by Rex. The downshift from second to first is normally so soft that it is indistinct. If that shift is made with no vacuum the shift is a distinct "klunk".

I would verify the vacuum on the modulator. It should be around 20in on the 80-81 vac shifted 722.1 diesel trannies with the throttle closed. In this position the trans is in second gear. With the slightest throttle linkage movement the microswitch on the valve cover closes and the vacuum is dropped to around 12in at which time the trans downshifts to first.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician