WEEKEND WORKSHOP
Save £500 in 48 hours
Ed explains how to diagnose and fix a rear-axle final drive in a weekend or less
ED'S JOB CARD
REFRESH YOUR FINAL DRIVE
Today's job is to fettle a leaky or noisy final drive. I'll show a number of jobs that you could easily do in situ, in a day. Then I'll move on to show how to strip, assess and reassemble a typical unit. Bearings and seals should be widely available – you can read the number/size off the old ones. Shims could be made by an engineering firm. Other parts may be difficult to find.
How tough?
You’ll need:
► Basic tool kit
► Dial gauge
► Torque wrench
► Large hammer
► Soft hammer (eg. nylon)
► Feeler gauges
► Small cold chisel
► Puller (optional)
► Small press (optional)
Will take: 3+ (HRS)
Will cost: 0 (£)
Cash saved: 500 (£)
START DAY 1
Need to know
The pinion is forced forwards and backwards during acceleration and overrun. To resist this, it's held in opposed taper-roller bearings. These are set with no play – in fact slightly 'preloaded'. There's a spacer between them which ensures the preload is correct when the pinion nut's tight. A collapsible spacer deforms to the correct length on initial installation; a rigid spacer is shimmed to give the correct length.
Methods of setting preload on pinion shaft bearings.
Collapsible spacer tube (A) Rigid spacer tube, (B) Collapsible shim (C) Rigid spacer tube (D) Standard shims (E) (add/remove as required).
► Vital differences
Rigid spacer: the nut is done up very tight at all times. Collapsible spacer: only done up tight on initial installation, to set the correct length. If the nut's removed and replaced, it's nipped up lightly.
► Fix pinion noises
If the final drive grumbles at speed on a light throttle or just entering over-run, the pinion bearings are not preloaded. Collapsible spacer type: Remove propshaft. Jack up one rear wheel. Tighten pinion nut gradually while rotating pinion flange. When you feel lumpiness in the rotation, stop, then back the nut off slightly until the roughness – just - completely disappears.
► Torque rigidspacer
Rigid spacer type: It should be enough to remove the propshaft and retorque the centre nut to spec. Perform the smooth rotation test afterwards: the loss of preload may signal issues.
► Change pinionseal
Remove pinion nut. You can count turns, but it's not really necessary. Remove pinion flange (it may knock off or may need a puller). Then carefully pierce and lever out the old seal.
TOP TIP Be prepared to catch a flow of oil when the seal is removed.
► Insert newseal
Replace single or double-lip se
