StapleGun

I have a 1998 ML320 - I'm having trouble removing the rear 32mm bolt - this is the bolt for the input shaft to the rear differential, aft of the universal bearing flange. The seal is leaking and needs replacement. Anyone have a WIS diagram they could share with me or email (cohibas4u@yahoo.com) Many thanks in advance..that 32mm bolt ain't budging.

MBTech21

Just the fact that you are asking about that nut suggests to me -STOP!!! That nut is holding the pinion flange to the pinion gear and applies the correct preload to the two pinion bearings (they are held in there against a collapsable spacer,). If it gets done too tight, the spacer collapes more-diff is ruined, if it's too loose-pinion shaft doesn't have correct preload-diff is ruined. This adjustment is CRITICAL and should never be done by someone with out experience in rear ends!!
Hope you read this in time...

StapleGun

Thanks for the response, it's why I tossed a 'line for help' - anyone have a WIS schematic? I have changed diff seals before but I'm missing something here...Any thoughts on how this gets replaced?

C32AMG/02

Some pinions have a notch and the nut is staked in if you have this set up use a small chisel and undo the stake. The easiest method is to use an impact air gun to remove the nut. You will also need a jaw puller to remove the flange.


The first step is measure the differentials friction torque, how much toque does it takes to turn the differential. You will need a dial indicator torque wrench.

With the car safely off the ground, transmission in neutral and park brake off, place the torque wrench on the pinion nut, set the dial to “0” turn the nut CW and note the torque reading the pinion flange turns; which is, the differentials friction torque. Once the seal is changed tighten the nut, (you will need a breaker bar and use a new nut) in stages until you reach the differentials friction torque.

If not set to that recorded number + or - one haft Ft-lb, you will change the pinion bearings per load friction torque, causing a premature bearing failure.




NOTE: let a professional do it.

StapleGun

Thanks for the response C32AMG/02 - at this point in time, the 'nut' in question is not budging. Is it counterlocked from behind or is it reverse-threaded? I understand the pre-loading procedure as well.

The impact wrench has not budged it and it and there's no staking on it so I'm at a loss as to what to do....

StapleGun

Went to Brumos and got to look at the WIS and parts schematics - from what I gathered it's jammed. One more question... anyone have ANY idea torque spec on this bolt???

C32AMG/02

The other method to retain the pinion nut is by a locking plate, a round piece of metal placed over the nut and staked to the flange. The torque on the nut from memory is 170Nm, confirm it first, But you can’t use this number; the pinion pre- load is already set up, you need to use the friction torque number to re- torque the pinion nut after the seal is changed.

StapleGun

Again, my thanks...the nut finally came off. Thanks for that number, I understand that 170Nm is what it will require for initial seating and the pinion pre-load. If I use your method the amount (in ft-lbs) will not be much right - do you recall how much by chance (ballpark)???

C32AMG/02

You are welcome.

The friction torque number varies, there are a lot of variables involved, model, tire size, LSD, torsen or open differential, type of gear lube, the method I posted is the trade way.

Please do it this way, it’s the right way, if you don’t, that rear will fail. Since the differential is set, you don’t need much torque to re torque the nut, use a new one.

You can buy a good, less expensive Dial indicator toque wrench on E bay or you can rent one from an equipment rental store.

StapleGun

Thanks for the help C32AMG/02 - it makes sense, and I truly appreciate your taking the time to post. I purchased the nut, lock tab and seal already. Took pictures of everything so I can post and hopefully help others that have contemplated the job. Only challenge was removing that nut, it was seized bad. Again many thanks to all that offered their invaluable help!