W115 differential swap.

[scraf]

My W115 long wheelbase originally had a petrol engine but now has a OM617 3 litre diesel.

The differential it currently has is a 3.46.

Issue; when accelerating there is a lot of vibration if I change gears " too early ". Meaning that car's driveline likes the engine to be revving a lot higher when accelerating that I would like for an old diesel motor.

If, and this is a big if, I understand what I've researched on the internet, what I am looking for is a diff with a lower ratio, that would be with a higher number.

Thus, I'm considering swapping for a 3.92 differential.

Maximum obtainable speed doesn't concern me, neither does speed of acceleration, or for that matter correct speedo readings.

All comments or advice greatly appreciated.

[rumb]

I'd start with checking motor mounts, trans mount, and driveshaft, subframe mounts.

[Sugar Bear]

I wouldn't expect a 3.46 to be causing "lugging." As stated I'd be checking for worn driveline components, exhaust, subframe mounts etc. first.

Can the vibration be felt if the car is stationary? Was the transmission and engine an assembly or separate units? Do higher RPM's make it better or worse?

Look for a worn driveshaft center support and bearing.

Good luck???

[scraf]

Originally Posted by Sugar Bear

Can the vibration be felt if the car is stationary?

Nope

Originally Posted by Sugar Bear

Was the transmission and engine an assembly or separate units?

No idea

Originally Posted by Sugar Bear

Do higher RPM's make it better or worse?

Better

Originally Posted by Sugar Bear

Look for a worn driveshaft center support and bearing.

All very new, but will be checking everything before doing the diff transplant.

[Todd Miller]

Since you state the center support is "new," I would suggest loosening the mounting bolts and sliding the support bracket just slightly forward, to give the bearing a little pre-load. You might find this cures the issue.

I'd also inspect the exhaust system, heat shields, and both engine mounts and the transmission mount, in order to make sure there's nothing that is rubbing or making contact with something, that, when the engine is lugged and loaded down, things flex enough that there's a vibration of sorts.

[Frank Reiner]

Originally Posted by scraf

My W115 long wheelbase

The differential it currently has is a 3.46.
Issue; when accelerating there is a lot of vibration if I change gears " too early ".
Thus, I'm considering swapping for a 3.92 differential.

Long wheelbase = 3-piece driveshaft
A 3-piece driveshaft has two u-joints, and can easily be assembled with the u-joints out of phase. Look to the phasing as a first step.


Changing the final drive ratio will only change the road speed at which the disturbance occurs; it will not change the driveshaft speed at which the disturbance occurs.

[scraf]

Originally Posted by Frank Reiner

Long wheelbase = 3-piece driveshaft
A 3-piece driveshaft.

Downgraded to 2-piece at the recommendation of the shop that reconditioned the shaft.

Originally Posted by Frank Reiner

Changing the final drive ratio will only change the road speed at which the disturbance occurs; it will not change the driveshaft speed at which the disturbance occurs.

My shade tree mechanic friend who says he has fixed the same problem with a diff swap would probably bring torque into the conversation now.

I'm trying to get more rotations to the wheels with less revolutions of the engine, if I drive it like I would a petrol engine the issue is far far less apparent.

[scraf]

Originally Posted by Todd Miller

Since you state the center support is "new," I would suggest loosening the mounting bolts and sliding the support bracket just slightly forward, to give the bearing a little pre-load. You might find this cures the issue.

Thanks for that, that's definitely going on my list of possible fixes.

Originally Posted by Todd Miller

I'd also inspect the exhaust system, heat shields, and both engine mounts and the transmission mount, in order to make sure there's nothing that is rubbing or making contact with something, that, when the engine is lugged and loaded down, things flex enough that there's a vibration of sorts.

You're probably underestimating the amount of shudder there is, even for a 50 year old car. I'll try and figure out a way to video tape the issue for prosperity.

[Todd Miller]

It is impossible to "estimate" anything via someone's attempt at describing something, via keyboard. What you are getting, is free advice, from people willing to help out a fellow enthusiast, on a car that's been modified.

[Frank Reiner]

Originally Posted by scraf

Downgraded to 2-piece at the recommendation of the shop that reconditioned the shaft.

All bets are off.

[scraf]

Originally Posted by Todd Miller

It is impossible to "estimate" anything via someone's attempt at describing something, via keyboard.

Fair call, it was not my intention to criticize anyone's powers of deduction, was trying to make the point that I'm dealing with a serious shudder as opposed to something rubbing, which didn't translate well, via keyboard.

[scraf]

Originally Posted by Frank Reiner

All bets are off.

I still have the receipt for the work should, heaven forbid, I need to return to the shop.

[cth350]

Do you still have the old three piece shaft?

If the shop does not have lots and lots of Mercedes experience, they didn't fully understand what a benz is capable of and probably gave you less than ideal advice.

-CTH

[aluminum]

like Frank Said " easily be assembled with the u-joints out of phase. "
whatever driveshaft >
Run the Car upon stands while watching for this Vibration from the side of the Car >
If its the driveshaft you should be able to see it> Check to see if the Drive line / Driveshaft
is running true or not ( at different speeds with someone in the Car changing speeds )

When changing U Joints you Need to mark them before "disassembly"

All in All sounds like you need another driveshaft returning to a original type .