NUTS ABOUT AXLE PINIONS
QI’ve read and re-read a number of books and manuals, but I’m still confused by the tightening torques for rear axle pinions. Can you help? Maurice Elwin, Kircaldy
Ed says:
AThe pinion shaft runs in two opposing taper roller bearings, like many wheel bearings. These must be pushed together by the pinion nut so that endfloat in the shaft is eliminated, then very slightly preloaded (tightened) so the shaft turns with a very small amount of drag. This is done by setting the distance between the bearings very precisely.
The distance may be set using a slightly-short rigid spacer tube plus a few shims to make up the correct distance. Home assembly will require a few trial-and-error attempts. If the drag becomes too great before the nut is fullytightened, dismantle and add extra shims until it’s correct at the prescribed (usually high) nut torque. If you’re simply replacing the pinion seal on the car, then you should be able to retighten the nut to its full torque without altering the shim pack.
Some pinions have a crush tube or ‘collapsible spacer’. The tube or spacer is over-length and the nut is tightened until play is just eliminated (this requires a high torque to initially compress the spacer) and the desired light drag is obtained. Thanks to the pre-compressed spacer, when changing the seal, the nut only needs be done up to restore the desired drag – i.e just nipped up and no more. Use a new selflocking nut which will hold itself in this perfect position.
When replacing a pinion seal in situ on the vehicle, chock one rear wheel securely and jack up the other, placing an axle stand under it. Rotate the pinion shaft as you incrementally tighten the nut. The pinion should have no endfloat and should rotate smoothly when you turn it. If movement is stiff and clunky as you rotate it in a single direction, it’s too tight. You may be able to back the nut off a little to restore smooth rotation. If you greatly overtighten a collapsible spacer or can’t achieve smooth rotation without fore-aft play, then the final drive will need to come apart to replace the spacer for a new one or to increase the number of shims.