Pinion Seal Replacement - How to determine Friction Load

[jimkari]

I'd like to replace the rear pinion seal on my 87 300E. The manual speaks of determining the friction load. Does anyone know how this is determined?

Thanks,

Jim

[Chas H]

An inch-pound torque wrench is used to measure the turning resistance of the pinion.

[Arthur Dalton]

If you do not have the tools for measure, you can index mark the pinion flange nut so it goes back to the original position. That usually gets you back to where it was before, but not a true torque spec procedure.

[Chas H]

Originally Posted by Arthur Dalton

If you do not the the tools for measure, you can index mark the pinion flange nut so it goes back to the original position. That usually gets you back to where it was before, but not a true torque spec procedure.

This is the way I do it.
And I have an inch-pound torque wrench.

[Arthur Dalton]

Me Too..

I only use the torque pre-load procedure if I change a pinion bearing.
I have one of those old Snap-On Torque-O-Meter from the Navy...kinda cool tool.

[charmalu]

I have a Differential out of a W126 that Iam going to install in my 85 300D. I need to use the flange off the 300D and install on the W126 Diff.

The 123 has a smaller flex disc than the 126.

I purchased a new pinion shaft nut and oil seal. thought this is a good time to replace it.

I bought a new nut figuring using the old nut it wouldn`t stake in properly and might loosen up.
So how do I get the proper torque with the new nut?

also how would I use the inch pound to determine the torque preload. I have never done this before. splain it to me . Iam a dummy in this dept.

I read another thread where the guy said the nut is a little more that finger tight. something like 0.75 in lb.

Charlie

[Chas H]

Changing the pinion flange takes the easy way off the table since it's likely not the same height as the original. Use the torque wrench to measure the turning torque before you dis-assemble. When all is back together, tighten the pinion nut in steps until the initial turning torque is attained. A little more turning torque is OK.

[charmalu]

Thank you for the reply.
I have one more question. do I unstake the nut first? or is that possible?

It would take a lot of torque to over come the staked part.

I also read to use an impact gun to remove the nut, or break it free.

I under stand torqueing it back on to get the proper tightness.

Charlie

[Arthur Dalton]

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Are you sure ?? That is tightening torque on the nut..and that only effects the turning torque of the pinion shaft.
One is very high Ft/lbs and the other is very small In/lbs.
It is the in/lbs force required to rotate the shaft [ bearing load] that determines how many ft/lbs you torque/tighen the nut...not the other way around...... the final measure is always the rotational in/lbs..and you use small increments on the ft/lbs b/c you do not want to excede the bearing in/lb loading spec b/c you can not take it back.

[charmalu]

I just reread post#7 "use the torque wrench to measure the turning torque before you dis-assemble"

so I put the in lb wrench on the pinion nut, pull down on the wrench, and see what the reading on the wrench is to move or turn the shaft?

then when I reassemble the unit, I tighten the nut in small increments, check what it takes to turn the shaft with the inch lb wrench. add more as necessary to achieve the final number I startd with, w/o going past where I started.

now I have the Differential sitting on the bench, that would give me a different reading compared to it being installed in the vehicle with the axles in place. am I right with this thought? I then would have two different readings.

Charlie

[Chas H]

The torque wrench readings will be valid if the task is started and completed with the rear in place, or if the task is started and completed with the rear on the bench.

[charmalu]

CHAS H, you use a inch lb torque wrench. which type? clicker, digital, beam.

I apprciate the information given here, the muddy waters are clearing up.

Charlie

[Arthur Dalton]

>

Yes..what you are measuring is the force it takes to turn the shaft..this is the friction of the bearing loading. That has a spec so that the pinion does not move lateraly when power from the engine is applied.
An easy way to invision this is a simple/generic front wheel bearing adjustment...as you tighten the WB nut , the wheel gets harder to hand turn..that is bearing load. Too much and you burn up the bearing, too little and you have a loose wheel.

So, if you measure the needed force to turn/rotate the pinion before dis-assembly, you know where you have to go when you put it back together. It is the final in/lb reading you are concerned with..regardless of what it takes, be it 125 ft.lbs or 165 ft/lbs , on the pinion nut to get there ,it takes what it takes. If you just used a set torque in ft/lbs on the nut, you would have no way of converting that into bearing load , as every case would be different.. That is why CH said Small Increments as you approach the correct in/lb loading spec. So you tighten the nut and then take a reading each time until you get the proper in/lb reading. There are factory specs for this if you do not want to use the original that you had before dis-assembly.
The problem can arrise if one where to go to far b/c you can not loosen back..that is the trick.
And that is why most guys just index the pinion nut and put it back where it was originally..the problem with that is you don't know if a guy was in ther before you at some time, but if the diff has been fine except for the seal, it is a good guess that all is OK.

[charmalu]

thank you Arther for the fast reply.

I see you use a Snap-on Torque o meter wrench.

I have an old Sears beam type I bought years ago for an old Toyota head project, about 1974.
And I have a Sears Digitorque 250 ft lb.

since I will need an inch lb wrench, which I should have anyway, which one should I purchase for this project?

seem like some type of digital gauge, as I pull down I could see the # add up.

charlie

[Arthur Dalton]

Yes

You want the lowest one you can find as that torque is usually 15-30 in/lbs....and a dial is very nice b/c you can see it creaping up there as you add torque.

Some guys use those 1/4/drive torque screwdrivers..they work great and are cheap...you can preset them cuz they have a clicker.

As CH said, you can go a little more on the in/lb reading b/c you have bearings with normal wear on them, so a little extra won't hurt any...but not much..1-2 in/lbs.
Many guys that use the index mark procedure will go a hair past the index knowing there is wear in the diff and that will tighten them up a bit,but caution is the name of the game here...which is why I always go get a final in/lb reading before putting driveshaft back on..then you know for sure.

Don't guess on differentail bearing loads ..I have seen too many in the dumpster b/c of foolish nut tightening w/o regards to load.

An added Note **

There is also a procedure where you wind a string on the pinion and pull the string with a scale [ like a light fish scale] ..that tells you the required force to rotate the shaft and you then just duplicate it when you re-assemble.
That trick is actually in the Benz Book for vintage cars , but most likely from when wrenches were not so available to the adverage Joe...get a in/lb wrench capable of low reading and do it right ..........