712Setting pinion depth

Press the inner and outer pinion bearing cups into the differential housing and then lubricate both bearings. Slip the standard pinion head spacer (thick shim washer) and the larger inner bearing over the dummy pinion and align assembly into the pinion housing (Fig. 7.2). Slide the other bearing and centralizing cone handle over the pinion shank,

Fig. 7.1 Stretching axle housing to remove differential cage assembly

then screw on the preloading sleeve. Hold the handle of the dummy pinion while winding round the preload sleeve nut until the sleeve is screwed down to the first mark for re-used bearings or second for new bearings. Rotate dummy pinion several times to ensure bearings seat properly. Check the bearing preload by placing a preload gauge over the preload sleeve nut and read off the torque required to rotate the dummy pinion. (A typical preload torque would be 2.0-2.4 Nm.)

Place the stepped gauge block and dial indicator magnetic stand onto the surface plate then swing the indicator spindle over selected gauge step and zero indicator gauge.

Clean the driving pinion head and place the magnetic dial gauge stand on top of the pinion head. Move the indicator arm until the spindle of the gauge rests on the centre of one of the differential bearing housing bores. Slightly swing the gauge across the bearing housing bore until the minimum reading at the bottom of the bore is obtained. Repeat the check for the opposite bearing bore. Add the two readings together and divide by two to obtain a mean reading. This is the pinion cone distance correction factor.

Pinion Depth Gauge
Fig. 7.2 Setting pinion depth dummy pinion

Etched on the pinion head is either the letter N (normal) or a number with either a positive or negative sign in front which provides a correction factor for deviations from the normal size within the production tolerance for the pinion cone distance.

If the etched marking on the pinion face is N (normal), there should be no change in pinion head washer thickness.

If the etched marking on the pinion face is positve (+) (pinion head height oversize), reduce the size of the required pinion head washer by the amount marked.

If the etched marking on the pinion face is negative (— ) (pinion head height undersize), increase size of the required pinion head washer by the amount marked.

The numbers range between 5 and 30 (units are hundredths of millimetres). So, +20 means subtracting 20/100mm, i.e. 0.2 mm subtracted from pinion head washer thickness, or —5 means adding 5/100 mm, i.e. 0.05 mm added to pinion head washer thickness.

Calculating pinion head washer thickness For example,

Average clock bearing bore reading = 0.05 mm Pinion head standard washer thickness = 1.99 mm Pinion cone distance correction factor = 0.12 mm

Required pinion head washer thickness = 2.12 mm

7.1.3 Adjusting pinion bearing preload

Setting pinion bearing preload using spacer shims

(Fig. 7.3(a)) Slip the correct pinion head washer over pinion shank and then press on the inner bearing cone. Oil the bearing and fit the pinion assembly into the housing. Slide on the bearing spacer with the small end towards the drive flange. Fit the old preload shim next to the spacer, oil and fit outer

Crown Wheel And Pinion Design
Fig. 7.3 (a-e) Crownwheel and pinion adjustment methods

bearing to pinion shank. Assemble the pinion drive flange, washer and nut (Fig. 7.3(a)).

Using a torque wrench gradually tighten the nut to the correct torque (about 100-130 Nm). Rotate the pinion several times so that the bearings settle to their running conditions and then check the preload resistance using the preload gauge attached to the pinion nut or drive flange. Typical bearing preload torque ranges 15-25 Nm. If necessary, increase or decrease the spacer shim thickness to keep within the specified preload.

If the preload is high, increase spacer shim thickness. Alternatively if the preload is low, decrease the shim thickness. Note that 0.05 mm shim thickness is approximately equivalent to 0.9 Nm pinion preload torque.

To alter pinion preload, remove pinion nut, flange, washer and pinion outer bearing. If pre loading is high, add to the original spacer shim thickness, but if preload is too low, remove original shim and fit a thinner one.

Once the correct pinion preload has been obtained, remove pinion nut, washer and drive flange. Fit a new oil seal and finally reassemble. Retighten drive flange nut to the fully tight setting (i.e. 120 Nm) if a castlenut is used instead of a self-locking nut fit split pin.

Setting pinion bearing preload using collapsible spacer (Fig. 7.3(b)) Fit the selected pinion head spacer washer to the pinion and press on inner pinion bearing cone. Press both pinion bearing cones into housing. Fit the outer bearing cone to its cup in the pinion housing and locate a new oil seal in the housing throat with the lip towards the bearing and press it in until it contacts the inner shoulder. Lightly oil the seal.

Install the pinion into the final drive housing with a new collapsible spacer (Fig. 7.3(b)). Fit the drive flange and a new retainer nut. Tighten the nut until a slight end float can be felt on the pinion.

Attach the pinion preload gauge to the drive flange and measure the oil seal drag (usually around 0.6 Nm). To this oil sealed preload drag add the bearing preload torque of 2.2.-3.0 Nm.

i.e. Total preload

Gradually and carefully tighten the drive flange nut, twisting the pinion to seat the bearings, until the required preload is obtained. Frequent checks must be taken with the preload gauge and if the maximum preload is exceeded the collapsible spacer must be renewed. Note that slackening off the drive flange nut will only remove the established excessive preload and will not reset the required preload.

7.1.4 Adjust crownwheel and pinion backlash and differential bearing preload

Setting differential cage bearing preload using shims

(Figs 7.3(c and d) and 7.4) Differential bearing preload shims may be situated between the differ

Fig. 7.4 Setting differential cage bearing preload using shims ential cage and bearings (Fig. 7.3(c)) or between axle housing and bearings (Fig. 7.3(d)). The method of setting the differential bearing preload is similar in both arrangements, but only the case of shims between the axle housing and bearing will be described.

With the pinion removed, press both differential bearing cones onto the differential cage and slip the bearing cups over rollers and cones. Lower the differential and crownwheel assembly with bearing cups but without shims into the final drive axle housing. Install the dial indicator on the final drive housing with the spindle resting against the back face of the crownwheel. Insert two levers between the final drive housing and the differential cage assembly, fully moving it to one side of the housing. Set the indicator to zero and then move the assembly to the other side and record the reading, which will give the total side float between the bearings as now assembled and the abutment faces of the final drive housing. A preload shim thickness is then added to the side float between the differential bearings and final drive housing. This normally amounts to a shim thickness of 0.06 mm added to both sides of the differential. The total shim thickness required between the differential bearings and final drive housing can then be divided according to the crownwheel and pinion backlash requirements as under setting backlash with shims.

Calculating total shim thickness for differential bearings For example,

Differential side float Differential bearing preload allowance (2 x 0.06)

Total differential bearing pack thickness

1.64 mm 0.12mm

1.76 mm

Fig. 7.4 Setting differential cage bearing preload using shims

Setting crownwheel and pinion backlash using shims

(Figs 7.5 and 7.6) After the pinion depth has been set, place the differential assembly with the bearing cups but without shims into the final drive housing, being sure that all surfaces are absolutely clean. Install a dial indicator on the housing with spindle resting against the back of the crownwheel (Fig. 7.5). Insert two levers between the housing and the crownwheel side of the differential assembly. Move the differential away from the pinion until the opposite bearing cup is seated against the housing. Set the dial indicator to zero. The levers are now transferred to the opposite side of the differential cage so that the whole unit can now be pushed

Back Lash Shims
Fig. 7.5 Setting crownwheel and pinion backlash using shims

towards the pinion until both crownwheel and pinion teeth fully mesh. Observe the dial indicator reading, which is the in-out of mesh clearance between the crownwheel and pinion teeth (shims removed). This denotes the thickness of shims minus the backlash allowance to be placed between the final drive housing and the bearing cone on the crownwheel side of the differential cage to obtain the correct backlash.

Backlash allowance is either etched on the crownwheel or it may be assumed a movement of 0.05 mm shim thickness from one differential bearing to the other will vary the backlash by approximately 0.05 mm.

Example From the following data determine the shim pack thickness to be placed on both sides of the crownwheel and differential assembly between the bearing and axle housing.

Differential side float with shims removed = 1.64 mm Differential bearing preload allowance each side = 0.06 mm

In-out of mesh clearance = 0.62mm

Backlash allowance = 0.12mm

In-out of mesh clearance

= 0.62 mm

Differential bearing

preload allowance (add)

= 0.06 mm

Backlash allowance (subtract)

= 0.12 mm

Required shim pack crownwheel side

= 0.56 mm

Total differential side float

= 1.64 mm

Differential bearing

preload allowance (add)

= 0.06 mm

Crownwheel side shim pack without

preload and allowance (subtract)

= 0.50 mm

Required shim pack opposite

crownwheel side

= 1.20 mm

Alternatively,

Required shim pack opposite crownwheel side

Total differential bearing pack thickness

Shim pack crownwheel side

0.56

To check the crownwheel and pinion backlash, attach the dial gauge magnetic stand on the axle housing flange with the dial gauge spindle resting against one of the crownwheel teeth so that some sort of gauge reading is obtained (Fig. 7.6). Hold the pinion stationary and rock the crownwheel backwards and forwards observing the variation in gauge reading, this valve being the backlash between the crownwheel and pinion teeth. A typical backlash will range between 0.10 and 0.125 mm for original bearings or 0.20 and 0.25 mm for new bearings.

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Responses

  • Destiny Simpson
    How to check for pinion height on a differential unit?
    2 years ago
  • eric
    How to increase pinion height?
    2 years ago

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