Measuring Pinion Preload


Please excuse me that even though the main thread is at the XJ forum, I am also posting here but I need all the info I can find, it’s a job no one wants to do twice…!

I think that my pinion bearings don’t have enough preload (Salisbury LS diff with crush sleeve).
The diff has a very faint whine on deceleration.
I changed the Pinion seal so now that the cage is out it’s time to check that out.
But measuring drag between the backlash, on a 2mm travel area, is difficult and non conclusive to say the least.

So I have a plan:

  • Measure the pinion turning torque with the pinion nut loose (no preload). This measurement will be the total torque required to overcome the pinion seal, the output shafts and seals, and the crown bearings.

  • Tighten the pinion nut to original place and measure again. Then, subtract the first measurement and the difference will be just the pinion bearings preload, no?

  • Tighten the pinion nut until correct value is obtained.

And some questions about the preload values:
The extract from the manual that I have found states: “The torque required to turn pinion shaft should exceed by 5 to 10 (0.06 to 0.12 kgf.m.) the torque recorded in operation 3 (just the seal, no preload)”

But then it adds that “If the torque is below 25 (0.29 kgf.m.), tighten flange nut further until torque figures is between 25 and 30 (0.29 and 0.35 kgf.m.). If, however, torque required to turn pinion shaft exceeds 45 (0.52 kgf.m.), final drive overhaul, operation 51.25.19 MUST be carried out.”

It’s quite confusing…
I guess that the 25 - 30 is the combined torque for the whole diff assembly ?
It sounds like a lot of force to me.

Any suggestions welcome.

Aristides …

Check this out …

I had the same problem with my a XJ40 differential. After reading this article I tightened the pinion nut
a very small amount and it completely eliminated the whine I was experiencing on deceleration. This was about 6 or 7 years ago and I’ve had no problems since.

A lever with a load applied can certainly be used as a torque device. However the article doesn’t address how much pre-load is being applied to the bearings, only that drag (pre-load) is being increased; to what?

Its not difficult to calculate the amount of torque being applied; its simply based on the actual weight, and the distance from the centre of the pinion along the lever its being applied.

The author of the article needs to brush up on simple imperial to metric conversion math. He repeatedly used 6mm for 1/8" and 12mm for 1/4" conversion throughout, so it could hardly be a typo. Doesn’t really instill a lot of confidence regarding the rest of the article.



Yes that’s what I did in the end.
Details over at the XJ forum thread:

“The author of the article needs to brush up on simple imperial to metric conversion math. He repeatedly used 6mm for 1/8” and 12mm for 1/4" conversion throughout, so it could hardly be a typo. Doesn’t really instill a lot of confidence regarding the rest of the article."

Looking back at that link I posted in 2004. If I remember correctly I finished late that night and made a feebly attempt at conversion by putting a regular ruler next to a metric one. Once posted I usually don’t re-read the links
Amazed it took this long for someone to call me out on this. (smile) I have spent some time fixing the conversion numbers on the link.

To angelw: I say Thanks

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Hello Bernard,
There are many things stated in Jaguar Work Shop Manuals that are incorrect. For example, when dismantling the Rear Extension (Oil Pump Housing) of an early Manual Gearbox, a point is made regarding marking corresponding teeth of the Oil Pump Gears to ensure correct fitting. Why? They have different number of teeth and therefore, each tooth of the small gear will visit each tooth of the large gear through multiple rotations.

The Workshop Manual also emphasizes that if the Pinion Shaft Nut is over tightened, the Crushable Spacer must be replaced with a new one, as intimated by the text from your article.

If no spacer was used and the Pinion Shaft Nut tightened to the specified torque, then the whole of the load would be applied to the Tapered Roller Bearing Cones and their Cup. Accordingly, the Collapsible Spacer is used to soak up much of that Load as the Bearing Cones are forced towards each other as the Pinion Nut is tightened and the Collapsible Spacer Collapses,

The Collapsible spacer is free to collapse until the Cones of the Tapered Bearing Sets make intimate contact with their respective Cups, (No End Play, No Preload). Further tightening of the Pinion Shaft Nut would further Collapse the Collapsible Spacer to the extent of a small amount of distortion of the Differential Housing. After that, no further Collapse of the Collapsible Spacer occurs; I have tested this many times by exceeding the recommended torque of the Pinion Shaft Nut and the Preload of the Pinion Shaft Bearings dismantling the whole system and measuring the length of the Collapsible Spacer. This test was carried out by measuring the length of the Collapsible Spacer after each small incremental increase of the Bearing Preload from Zero (No End Play, No Preload) to way past recommended Bearing Preload.

From a certain point, as the torque of the Pinion Nut is increased, no further Collapse of the Collapsible Spacer occurs, but Preload of the Bearing increases as the Pinion Shaft Nut is tightened further. This is due to the stretch of the Shaft, particularly through the Threaded Section (smallest diameter) of the Pinion Shaft. This stretch is the principle behind applying a certain torque to a bolt to keep it tight. The Bolt is acting like a spring; exceed the natural elasticity of the bolt and that affect is lost.

Liken the situation of the Bearings coming together, via the tightening of the Pinion Shaft Nut, to putting two blocks of steel together under the ram of a Hydraulic Press. As the pressure is increased, the two blocks don’t come closer together (they started out in intimate contact with each other), but the load on each is ever increasing as the load applied by the press increases.

I dislike the Collapsible spacer with a passion and haven’t used them for many years. Instead, I use a Non Collapsible Spacer. I use a Master Spacer that when assembled results in measurable End Play. Based on the End Play measured, I select a Spacer that will give me the correct Preload on the Bearings. Through many years of rebuilding Differentials and using the Solid Spacer, I’m able to select the correct size the first time. Shims can also be used (as per the method used prior to the introduction of the Collapsible Spacer), but having a multitude of Solid Spacers works well for me as I have a very well equipped machine shop.



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