How much play in drivetrain?
 

I spent Saturday putting a used, 80K mile differential and new diff mounting bushings in the rear suspension subframe on my 94 E320 wagon.

to date it has new:
front and rear driveshaft flex discs
new rear axles
new diff mounting bushings, all 4
and the "young" differential that felt great out of the box from the wrecking yard.

Driving the car, it shifts beautifully once underway. Even "sort of raced" a Cayenne Hybrid yesterday and did very well. The car moves.

The problem is in first getting it into gear, whether reverse out of a parking spot, or just forward and driving away. There is way too much "clunk" in the rear of the car as the drivetrain engages. Getting under the car again yesterday, the driveshaft can rotate maybe a degree or 2-4 (hard to tell) of free rotation before engaging.

Interestingly, the clunk seems to be in 2 parts. Nothing violent, just more than I think should be going on, and I did drive a similar wagon and the drivetrain engagement from rest was butter.

Even though the transmission shifts perfectly and smoothly in all acceleration modes, could the trouble be in the transmission? Should any car's drivetrain be free of "free rotation" of it's parts?

Love the car, just put the 17s on it, but this issue is getting tiring. I even think that whatever might be wrong with the car is what killed the old diff. Though at 170K, it could have just been its time.

Some backlash is normal. There are a lot of gears and they cannot be too tight or they will wear out very fast. Make sure your CV joint bolts are tight, however.

There are still a lot of small components that can each have a little bit of wear and play, and everything is cumulative. Your description sounds like a U-joint, but can be a bit here and there through the whole line.

Our lexus GX did the same thing. It was a common u-joint issue on those cars.

Sounds like a u-joint. They're relatively cheap and easy, that's the first place I'd look for a drivetrain clunk.

If this W124 is like my dad's old car, I don't believe there are any u-joints. It has flex disks at the transmission and diff.

Based on the work done, I'd suspect the transmission.

Shaun, if you disconnect the front guibo from the transmission, do you have any backlash from there to the rear wheels?
Jurgen

Thanks Guys,

Jurgen has it. Drivetrain is:
Transmission
Flex disc/guibo (new)
Driveshaft
Flex disc/guibo (new)
Differential (newish, now I'm starting to second guess it)
axles (new)
Wheel hubs (no bearing noise, so assuming wheel assemblies are good)

Just ran some errands and twice it shifted smooth as silk going into reverse, a little more clunk thank it should going into drive.

I think it may be the transmission too. Will have to pull the front apart to check, maybe this weekend. Will do a filter and fluid change in the transmission while I'm in there. What I haven't been able to is have someone shift while I'm visually inspecting the rear end. There's enough sound that I should be able to see what's going on.

Does it clunk ONLY upon engagement? That's a typical solenoid / valve-body symptom

Yes, so perhaps the transmission is sending too much "energy" to the rear end when going into gear.

All other aspects of the transmission shifting are excellent, from cruising to punching it.

Usually it is the electromagnet that engages the hydraulic circuit/piston getting weak. A new solenoid fixes it. Or the piston itself is "sticky" and engages all at once. It "delays" engaging the circuit, then BAM it does it harshly.

Sound right?

Try hitting the throttle immediately after you ask for reverse from park. If you can count a second, then "bam" that's not the driveshaft

Do you have a center carrier bearing on the drive shaft? Those can make some violent noises if the rubber they are mounted in becomes too compliant.

just went out to do some testing, revving before and after asking for a drive gear, both Drive and Reverse.

Got to end it here until I can get a friend to be in the car doing the same thing with me at/under the car. There is definitely something loose/broken in the right rear of the car. I've got the front passenger seat out and rear seat bases for max cargo capacity, but also a clear earshot to the back of the car.

It sounds more like the new CV joint in the back is bad.

Going to go out now and see if I can "videotape" the sound on my camera.

Rick, you may have it actually, though the sound in the back rear is real. Doing a search, I found this too. There are U-joints on this thing.

http://forums.pelicanparts.com/uploa...1334009265.jpg

Is it actually laying on your converter?

Well, I'll be a sob. That's like my brother's W123. Just did a rear suspension refresh, and those adjusting nuts look familiar. I must be getting old.

You and me both. I thought it was a one piece tubular driveshaft.

Rick, that's a pick I found on a Benz site doing a search on W124 bearing carrier.

Just went out and snapped my own pics. U-joint is bad I think. lot of play.

to get to it, I have to drop the exhaust, worst possible job. I hate exhaust work of any kind.

going to call the yard I got the diff from and hope they have the driveshaft.

http://forums.pelicanparts.com/uploa...1334011343.jpg

http://forums.pelicanparts.com/uploa...1334011352.jpg

That bearing assy is rebuildable. You don't need a drive shaft for just the carrier.

Yes, you can get just the bearing, pretty cheap. But since I'm keeping the car long term, I think I should do the shaft if I can get the one out of the 80K car I got the diff from. That was only $100, so I imagine the drive shaft will go for $50 or less, which is good piece of mind for me, especially while I'm under the car. Worst case would be pulling it apart to find the u-joints are bad and then I'm screwed without another good one, I need the car every day.

Stay tuned, and thank you for your help Rick!

Consider tapping in a new ujoint before swapping in the junkyard shaft. Also make sure the junkyard one hasn't been dented or bent while at the yard because thats going to cause a ton of vibration and burn up this differential. Are you sure the old diff wasn't fine and it was just the bad center bearing/ujoints?

I think the bad center support bearing (and possible U-joints) chewed up the diff. it's definitely bad, I'll open it up this weekend and take pics if I find anything interesting.

Just ordered a new support w/ bearing, all of $11. URO isn't the best brand, but it will work.

inexhaustive searching yielded very little on the u-joint itself. I'm sure I can have it rebuilt if I can't find them.