My 88 300SE vibration at 40 MPH

[carnut]

I have a shudder, vibration in the car at approx 2000 RPM which matches 40 MPH. The vibration is very slight in the floor of the car. If I turn a hard left turn leaving a stop sign, the vibration quits until the car is parked and starts up again as I get to 40 MPH. Some days its more pronounced than others? I'm thinking rear CV axle but which one? Turning left loads the right axle but slightly stretches the left. It's as if the joint is in a new position after the turn. If the boots are intact how do you confirm a binding CV joint.

[junqueyardjim]

If it were mine, (and I can do the labor and it is not difficult), I would switch the axles shafts right for left. About half the life should still be in those joints if the rubber is good, and by switching them to the other side, you reverse the way they have been running and you can get a lot more life out of them.

[carnut]

Thanks!! done many axles in my day and this should be the easiest. No stub shaft in the differential. AND no money spent

[dlssmith]

Inspect the motor and trans mounts, just in case.

[carnut]

Well, I spent 4 hours attempting to swap axles left to right. Got all the bolts off at the flanges except one. It backed out 3 turns then bound up. I managed to round off the internal 12 points so now the 12 point tool wont grip it. Some say to drive a 12 mm 12 point socket over the bolt head to grip it. I dont think theres enough clearance away from the axle flange to do that, but next Monday I'll try it. Any other ideas?

[neanderthal]

Does it happen in 3rd gear at the same rpm too?

[S-Class Guru]

You could get creative with a dremel tool; grind some flats on the outside of the round head. You could cut the head off if you have the bolt loosened out enough, but then the issue is getting the axle off the remaining bolt, probably would not come off without moving the diff over or moving the swing arm (big job). You could try to drill a hole sideways thru the bolt head and stick a hardened pin thru it and find a way to grab and turn it (but it's hardened steel). You could use lots of Liquid Wrench and heat - probably should do that no matter what you do. If you can devise a way to turn it, try to work it back in, then out a bit - back and forth until it loosens up a bit.
Huge vise grips and the above penetrating oil, heat, and loosen/tighten routine.

As to the problem, you might have a center driveshaft bearing and/or u-joint bad. They can definitely act differently whan turning one way of the other.
The bearing is easy, the u-joint is $350 minimum. When my u-joint got old at 200k it vibrated slightly only when accelerating thru about 15-18 MPH, so maybe that's not it.

DG

DG

[carnut]

It happens at 2000 RPM after it shifts once. One shift would be into 3rd as it takes off in 2nd. I ordered 2 bolts this morning from the local MB dealer. $7.50 for 2! I'll try the 12 point socket over the old bolt next Tuesday. I dont think there's enough room to grind 2 flats on the bolt. Thought about heat but there's the rubber boot that's too close. I let it soak 30 min with PB blaster. I will do this bolt 1st because the axle will be flush with the flange to the differential. We initially thought the flange being loose and slightly at an angle was binding up the bolt so I reinstalled 2 bolts to realign the flange but to no avail! Thanks all for the insights! The saga continues. So as to not have a completely wasted day, I did adjust the parking brake shoes and replaced the original woven fuel line from the tank to the fuel pump!