pinion bearing nut and preload question
 

I am putting a 2.47 diff from a W126/1 380SEL into my 1982 300TD. I obtained a spare input yoke from a 1982 300D diff, and i am now swapping it onto the 2.47 diff. I changed the seal and I'm using a new nut.

I measured the turning resistance prior to taking the nut off of the 2.47 diff by using a strange rig I made, but the results are repeatable so that's all that matters. I noticed that it is harder to turn than the original 3.07 from my 300TD.

Here's my problem. With the nut off, the turning resistance was the same, i.e. a little hard to turn. I used my in/lb clicker torque wrench to try to measure the actual torque and it's somewhere between 10 and 20 in/lb. I'm guessing that's normal for when the nut is tightened down and the bearing is loaded, but with the nut off, shouldn't it turn freely?

I measured the resistance with my strange rig, and it's exactly the same as with the nut on. So..... how am I supposed to tighten down this nut without over-tightening? I thought I would tighten it down until the turning resistance came back, but I can't see how I can do that.

The Haynes book says the minimum torque on that nut should be something like 132 ft/lbs. I don't know.... it came off with maybe 75 ft/lb. I just used my hands and a 24" breaker bar. If that is the correct torque, should I just torque it and measure the turning friction, and if it's still the same, just leave it at that? Something tells me if I do that, it will be too tight.

Thanks for your help.

My Pinion Seal is leaking so I will be facing this Myself if I decide to change it.

It sounds like you already know this but inside is a Crush Sleeve similar to the one on the Rear Wheel Hub. If you over tighten it you crush the Sleeve more and change things.

The other methods I have read about on this Forum in the DIY section are something like counting the number of exposed threads and marking the Nut so it goes back to the same spot.

The service manual method or the other methods; none sound really good.

I think the best that can be done is to pick a procedure that has worked for others and put thread locker on the threads so the Nut does not want to move.

Before someone starts on this sort of project it might have been interesting put a Dial Indicator on the Shaft and see if there was any end Play.
You would assume there would be not but you never know.

20 inch pounds is not that much. I find that this is typically the case with a previously crushed crush-sleeve and that the new nut is pretty much snugged instead of really tighten down. Striking the nut would lock it in place.

The spec for 132ft lbs is when you are installing a new crush sleeve. The mistake people make is to tighten it down to that spec on an already crushed sleeve. Doing so puts more pre-load on a bearing that has already been seated.

If your confident on your measuring setup, then go ahead with it. But the actual tool to use is a dial style inch pound torque wrench, preferably the 1-30 or 1-50 inch pound type.

Mine, pictured, is 1-150 but works just fine.
http://www.peachparts.com/shopforum/...1&d=1337271479




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I haven`t done this procedure, a while back I was going to use a 2:47 Diff in a 300D. Did some searching and got some great answers and help from Arther Dalton. hope ther is something in this thread to help.

www.peachparts.com/shopforum/showthread.php?t=233540

then this one.

www.peachparts.com/shopforum/showthread.php?t=81784


Charlie

Does someone have the part number for the crush washer? I don't want to spend a fortune and wait a week for a stupid washer but if it makes this whole job come together properly it might be worth it.

Can the pinion bearing be changed easily? Or does the whole diff have to come apart? Looks like the latter.

I didn't think counting threads would work in my case because I was not putting the same input flange/yoke back on. I read the service manual and it just says the same thing. You measure the initial turning torque (with a N-cm torque wrench, or in-lb), tighten the big nut incrementally, and measure the turning torque every time until you get back to the original reading. My problem is, even with the nut OFF I'm still at the original reading. Right now I have about 40 ft-lb on that nut (the diff is on the ground, and it keeps moving, so I need to mount it in the car to finish torquing). It still has the same turning torque. Does it sound to you like the pinion bearing is bad?

So is this crush washer similar to the washer on a new spark plug? I know those can be reused, with the same torque setting, but it just feels different when you reach that torque the first time compared to every time after that. I've done wheel bearings on VWs and Porsches, and I've never seen a collapsible washer. There are washers for holding preload, and I know how to set them, but they're solid.

I'd love to have a small in-lb torque wrench like that, but lately I've been reevaluating how much money I dump into tools, which is a lot, and I know I've never use this torque wrench again. Being tight on money at the moment, I just didn't want to buy one. I'll post a pic of my method. It's ghetto, but repeatable.

Thanks for the links, I already read those threads when I was getting ready for this job but I couldn't find anything on what to do if the turning torque is still the same with the nut off as it was with the nut tightened down. How do I know when to stop tightening the big nut?

Technically I was referring to the thrust washer, but I don't have the part number for that. I found in some diffs there is actually there is no thrust washer there after pulling the seal. The flange was seated directly to the bearing. So it might be hit or miss on that.

I found some of my notes of the specs when I swapped out the fanges. The 3.07 diff and 2.47 diff had the same 5 inch pounds of turning resistance in both directions with the diff out of the car. Looking at the notes, I recall just tightening the nut on the 2.47 down to about 55 Ft lbs resulted in 5 inch pounds of turning resistance.

Since I had an extra diff, the 3.07, I tried tightening down the nut to 120 ft lbs resulted to about 10 inch pounds of turning resistance. I did not test the resistance with the nut off the diff. So I don't know if they were the same. I would just go and tighten down until you think there is 1 inch pound increase from the original setting. I'm guessing it would be around 50-70 ft lbs on the nut.


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Now that you mention it, I did not see a thrust washer inside the 2.47 diff when I took the yoke off. When I was taking the yoke off of a 3.07 on a 300D at the junkyard, I did see a thrust washer in there. Maybe I should have taken it just to have it.

Alright, I like your suggestion, I'm going to just go to 50 ft-lb and check the turning torque. Then I'll add 5 ft-lb and check, and repeat.

So on your 2.47, you left the pinion nut at 55 ft-lb? And everything is ok? The book says 180Nm or 132 ftlb minimum but I'm totally cool with 55 if you say it's ok.

Yes the pinon nut was left at 55 ft lbs. It has been fine so far.

Your plan sounds good to me. Good luck.




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I'm somewhat doubtful of this.

If it took 132 lb-ft. to crush the sleeve and apply a specific preload to the bearing, it will take the same 132 lb.-ft. to maintain that preload after installation of a new pinion seal.

I recently went through the same scenario when changing the yoke on the 2.47 diff. I procured an inch-lb. torque wrench..........required for this procedure............and measured the torque required to rotate the pinion. The measurement was in spec at approx. 8 inch-lbs. (somewhat less than one ft.-lb.) Upon removal of the yoke and installation of the smaller yoke, I attempted to duplicate this same value. However, the application of torque, beginning at approx. 50 lb.-ft. and ending at approx. 130 lb.-ft. had no effect on this running torque. It remained at the same value.............8 inch-ounces.

I would suspect that the crush washer maintains a certain preload on the bearing, even when the pinion nut is removed. However, this preload won't necessarily remain forever if the applied torque with the new nut is significantly less than 130 lb.-ft.

I made the decision to leave the torque on the new nut at 130 lb.-ft (about the maximum that I could apply without restraining the diff in some type of vice).

I started at 50 ft-lb, and I went up to 85 ft-lb before I had a thought...

If my 2.47 diff does not have a thrust washer....... then is there any reason to even be worried about over-torquing? There's no washer to crush, so why can't I just go to 132 ft-lb and see what happens? Obviously there's no risk of damaging the pinion bearing, unless I go way up to like 160 ft-lb.

Do you mean 8 inch-pounds? 8 inch-ounces would be 0.5 in-lb, or 1/24 ft-lb.

Sorry, my bad.

It's 8 inch-lbs. The spec is 4.4 to 8.8 inch-lbs.

How would this be possible?

The friction of the pinion flange splines against the pinion gear are most likely maintaining the preload. In some cases, the bearing race itself could be stuck so tightly to the pinion gear that pulling the pinion flange back some would still not reduce the preload.

You could pull the flange back to set the preload again with the nut, but I would just apply a generous amount of torque to the nut again without disturbing the flange. The risk of going back with torque as low as 55lb ft is that it may allow the flange or the front pinion bearing race to back off of the pinion gear a little and reduce preload once you start driving again.

Park Tool makes a perfectly sized, affordable, non-clicker torque wrench for checking preload- the TW-1. I bought the Snap On wrench, which has less resolution than the TW-1 at such low torque values, and found out a couple of days later that I could have bought a few TW-1 torque wrenches for what I spent on the Snap On.

There are no “thrust washers” or thrust bearings in the pinion assembly. They are pre-loaded Taper Roller Bearings with a crush sleeve between the two bearings that will only collapse further at a torque of more than 132 ft-lbs. Since you said that the nut released at “maybe 75 ft/lb” you should reset the friction.

http://i508.photobucket.com/albums/s...fferential.jpg

The pinion should have turned freely when you released the nut. Taper Roller Brgs are a very close fit onto the shaft, zero to 5µ clearance, and it is the pre-load that locks them onto the shaft.

To reset the friction:

1) Turn the nut back 2 to 3 turns and tap the pinion shaft with a brass drift until you can feel a little side and end play on the pinion shaft.

2) Tighten the nut gently until you can just feel a measurable friction and then set it at 8 inch/lbs. If the crush sleeve has not been over-crushed you should then be able to continue to torque the nut to 130 ft-lbs without increasing the friction any further as 130 ft-lbs is too low to further crush the sleeve.

If further tightening increases friction then the crush sleeve must be replaced.

The reason why I ended up with 55 ft pounds is when I backed off the original nut I torqued it down to the original stake to get a test value. It definitely did not take 132 ft pounds to remove, much lower, and when I retorqued it down to the original stake, it was around 50ft lbs or so.


There is a thrust washer in some differentials, but not all, as shown in this FSM section.

http://www.peachparts.com/shopforum/...1&d=1337352383



I appreciate the schooling on this subject, that is very good information.


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