W123 85 300D whole lot of shaking going on

[hondab100s]

So I bought this high mileage 300 for cheap, and want to make it a commute vehicle. Somehow, the climate control, cruise, sunroof, dome light, headlights, wipers and odometer works. bad news...excessive amounts of shaking and knocking coming from rear/middle of car only during acceleration forward. this occurs around 5-8 mph then comes back again around 18-25. I have already replaced the flex joints, sway bar links, center support, half shaft axles. The unjoint has no play however there is some binding off center which I figured was normal for an IRS vehicle. Also, when changing from drive to reverse the vehicle moves a lot while on the brake, and often a clunk is heard. Upon some inspecting I noticed the mounts that hold the rear subframe to the car closest to the front are squashed...almost metal to metal. And there are these brackets I am assuming are for keeping these mounts from bottoming out into the unibody that have about a 1inch gap to the bracket. The tires are old and dry rotted, however, I see no alignment wear. I'm not too familiar with MB especially this age, but it looks to me the engine mounts have excessive play. Maybe there are supposed to to make up for the vibration a 5cyl diesel may create. It doesn't appear that the mounts are collapsed enough to begin resonating into the cab/body. So I am really just worried about this knocking/shaking at the mentioned mph...also I can't go over 60 as the shaking begins to return gradually to the point where I am scared to go faster...though this is less important to me as it would be for city driving. Any ideas what to check next before sinking unnecessary money into the problem?- Thankyou in advance!!!

[Skippy]

Since the subframe mounts are collapsed, replace them. While you're in there you should probably do the diff mount as well. And change those tires before they pop. I've had blowouts before and they aren't fun. (Well actually they're kind of exciting, but they make you late for whatever it is you're going to.)

[hondab100s]

I will, but first I wanted to resolve this shaking issue. my commute is only a few miles, but a lot of lights.

[franklyspeaking]

Sounds to me like the motor mounts are loose in front and the sub-frame loose in back, and the only thing keeping the drive-train in tact is the center drive line support and possibly the transmission support. Hence, all your vibration is being transmitted through the good tight points of contact. You are always going to have some slight unbalance, but it all magnifies with bad mounts.

[hondab100s]

Well that is true, but since the clunking sound shaking only happens in drive I figured it had more to do with the rear as the subframe is bottomed out on the front mounts. So I am guessing when I go into drive the subframe lifts up clunking against the unibody?? The thing is I can get over that...it's the shaking at the speeds mentioned that's alarming. As if the drive shaft is binding or the half shafts are falling out. I was just wondering if anyone had this problem and the remedy. I don't want to throw money at this for mounts (especially ones that may still be good) and still have the problem. So to help me with subframe mounts, has anyone here ever seen any so wore out that it caused the driveshaft to bind or come so misaligned it shook the vehicle like mine?? if not then I simply won't replace them yet as there are other things of more importance like tires as mentioned earlier.

[franklyspeaking]

If it is vibrating at 5-8 mph, perhaps you could put the rear securely on jack stands and view what is going on? Of course, not suggesting you do anything unsafe.

[Maki]

Vibration at 5-8 mph? Tires.

[hondab100s]

I wish it were tires, but this only happens at certain speeds, only during acceleration, only while moving forward. I probably could jack up the vehicle and put a load on the drivetrain at the mentioned speeds, but this is dangerous and a 2 person concept. I was hoping to get some input before such a strategy be used.

[Maki]

A rule of thumb with whipping old Benzes into shape: If it's made of rubber, replace it. Motor mounts, subframe bushings, differential mount ... and check the proximity of the power steering belt to the oil cooler lines. Collapsed motor mounts tend to drop the front of the engine so the ps belt and pulley cut into the upper oil cooler hose, allowing the motor oil to bleed out quickly.

[hondab100s]

I recall reading about the ps belt cutting oil cooler hose...and it's nowhere near it. Actually it has a separate oil cooler off to the side. Which makes mounts particularly difficult to judge for wear as that's been what to watch for. That being said I believe I shall do rear subframe mounts and recheck diff mounts. I did a brake stand and saw no play on rear differential so I assumed they were done already. How many mounts are there on rear subframe? I only see 2, but there has to be at least 4. Do they all have to be done?

[Hirnbeiss]

What is high mileage? I don' think you can rule out the u-joint, esp. if you say it has some binding.

[hondab100s]

odo broke at 196k, and the oil change sticker said it was done with 194k about a year ago. So I am guessing around 200k. the ujoint has no play, but with excess bend it binds. I'm assuming this won't be an issue as long as its deflection is minimal. Which it isn't if the subframe is moving up and down in the front.

[steeleygreg]

I agree with replacing the rubber, i.e. trailing arm bushings, sub frame bushings. In metal there is something called a resonant frequency or frequencie(s) in which loose metal will vibrate causing noise.
It could be the tires but I wouldn't think so at slow speed. The OE stated it occurred at 2 different slow speeds. I assume it smoothed out at higher speeds ! Chances are the rubber is old, loose, cracked causing the car to shack.