I have a w126 300se '89.My vibrations are only in drive. When stopped I only have the vibrations at low rpm like below 600rpm, say 500-550rpm. Then all go away unless heavier acceleration. But no matter how light I am on the accelerator it vibrates starting at 30ish on up if it is under load. As soon as I let off the pedal the vibrations go away, yes even at 80mph so no high speed vibrations like I keep seeing. Also I tend to have a horrible shaking if the right side of the car goes over a bump, the left seems to be very tight in relation. Do I need new motor mounts? Tranny mounts? Suspension parts? Any help would be appreciated.

You may have a flex disc coming apart on you. Use a flash light and raise the driverside using safty jack stands as well. Look forward of the driveshaft where the driveshaft connects to the tranny, you will see a disc.
Look for the obvious cracks or chunks missing from the disc. Check carefully in the area of the bolts for cracks and/or tears.
There is alot of info here doing a search on flex disc repair if you are a DIY kind of person.

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thanks for that info, I will definitely go check it out 2moro. I have some spare time.

Make sure the engine and trans mounts have not collapsed. The engine, trans, driveshaft and differential are all supposed to be aligned, or the flex discs will be flexed too much and go bad.

Looks for cracks in the areas between the bolts. if you need to replace the flex discs, they only go in one way and there is confusing information on installation.

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Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

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Ok will do. I suspect that the mounts have gone bad, and now probably the disks too. I know the engine was rebuilt at 150k miles, and now Im at 250k. Dont know where in there the mounts were replaced. Where are the tranny mounts? and for that matter the engine mounts, I looked under the car earlier and wasnt sure if what I saw were them.

Ok so I lifted the car up. The flex disks both look fine, although I could be mistaken. But The right engine mount is definitely shot. And my guess is the left one too. Could not tell with the tranny mount but probably could use a new one anyways. Any specific brand of mounts good? I know I get what I pay for, but I am trying to save money. I found a URO brand one for like $10 each. My guess is that they might go out quickly.

Is the oil pan strong enough to lift the engine with a 2x4 or 2x6 and a floor jack?

How hard is it to replace the flex discs? Any idea about how long it takes, barring unusual cricumstances? I need to replace the front on in my SEC, so it seems like replacing the back one at the same time would be a good move.

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Yes, you can jack up the 6-cylinder using the oil pan, no problem. Just be careful and unhook the motor mounts first; don't try to jack up the whole car with the oil pan -Ha. Yes, you will need to raise the motor a bit to slip in the motor mounts. Unhook the air intake and check the hoses and wires for binding as you ease the motor up an inch or so.The right mount is the first to go, as it is torqued downward when the engine is under load. This can cause the exhaust to rub on the cross member, makes a terrible banging noise.
This may be what you are hearing on that side.
Another noise-maker is the guide rod bearing. they clunk loud when tapping the brakes or going over small bumps. Search herein for how to replace them - not too difficult.

The tranny mount is on the very rear end of the tranny shaft - just a couple of bolts, put the jack under the tranny first of course. You can't usually tell if this mount is bad, it just sags a bit. cheap and easy, just do it.

The front flex disk is pretty easy; because there is room to work it out without removing the driveshaft on the 126 (that's a real pain). I'm not sure if other models can be replaced without removing the shaft.
The only trick is getting the disk in correctly, and the right bolts/washers in the right holes, etc. There is writing stamped on the disk in German, that says "this side to the rear". Then the bolts are different lengths. Just really look over the old disk and how it's mounted, and make some notes on bolts, positions, etc; and it's no big deal.

if the mounts don't fix things, it's possible you could have a driveshaft center bearing going bad. in that case you will have to remove the entire exhaust, and the heat shield, then drop the driveshaft - lots of work, but pretty straight-forward.

DG