Monday, July 2, 2012

FIAT 131 1975-77 Drive Axles Repair Guide

Rear axle assembly uses an integral carrier type differential having hypoid type ring and drive pinion gear set. Drive pinion bearing preload is maintained by a collapsible spacer and differential bearing preload is obtained through the use of shims between the bearings and rear axle housing. Semi-floating axles use ball bearings retained on the axle by a press fit retaining ring and the axle is secured in the housing with a retaining flange. A removable rear cover permits inspection and service of differential assembly.
The fiat 131 uses only one rear axle assembly. The axle ratio is 4.44-1; a nine tooth drive pinion with a forty tooth ring gear.
Axle shafts and Bearings
Removal - 1) Raise and support vehicle. Remove rear wheels and brake drums. Remove bolts retaining axle shaft retaining flange to brake backing plate.
2) Attach slide hammer to axle flange and pull axle from housing using care to guide the brake backing plate off the axle as if it is extracted.
3) Remove axle bearing from shaft using an arbor press and suitable support tools. Discard axle shaft bearing retainer. Inspect retainer seat on axle shaft and if seat is scored or damaged, replace axle shaft.
Installation - 1) Place retainer flange and bearing on axle shaft. Heat bearing retaining ring to about 600°F (300°C) and place heated retainer on axle shaft.
2) Using an arbor press and appropriate support tools, press bearing retainer onto shaft until bearing is locked between retainer and shoulder on axle shaft. NOTE - Do not exceed 13,000 lbs. force with press as damage to axle shaft assembly may occur.
3) If axle is to be installed at this time, replace oil seal inside axle housing (if required), and install axle in reverse order of removal.

Removal - Raise and support vehicle. Release parking brake and remove spring from parking brake bracket and support. Pull cable housings away from bracket and remove cables from bracket and support. Remove propeller shaft from drive pinion flange and stabilizer bars from rear axle housing. Remove brake hose from "T" connector and slip link out of slot in bracket on axle housing. Support rear axle assembly floor jack(s), remove shock absorber-to-axle housing bolts and lower and remove axle assembly.
Installation - Reverse removal procedure then bleed the brake system and check for proper operation of parking brake.

NOTE - Overhaul of differential assembly can be accomplished with rear axle assembly installed in vehicle
Differential Case Assembly - 1) Raise and support vehicle, remove axle shafts as previously described, and separate propeller shaft from drive pinion flange. Remove cover from rear of housing and drain lubricant.
2) Install spreader (8064), on housing, mark differential bearing caps for reference at time of reassembly, the remove bearing caps. Spread housing and remove differential case along with bearings and shims, noting position of bearing outer race and shims and keeping all left and right side components separated.
3) Using a puller, remove differential bearings from case. Keep bearings separated with other components. Put locating reference marks on ring gear and case, then removing eight ring gear-to-case retaining bolts and remove ring gear. NOTE - Drive ring gear from case (if required) using a soft headed mallet.

4) Using a soft drift, drive differential pinion gear shaft out of case. Remove pinion gears, side gears, and side gear thrust washers.
Drive Pinion Gear - Hold drive pinion flange and remove flange nut and flange from drive pinion gear. Remove oil seal and dust shield from pinion shaft then push dive pinion gear out of rear housing. Remove drive pinion  bearing outer races from housing. Using an arbor press, remove rear bearing from drive pinion shaft and retain shims found between bearing and gear.

Drive Pinion Gear - 1) Install pinion bearing outer races in rear axle housing. Before installing rear bearing on drive pinion gear, establish pinion depth adjusting shim thickness as follows (all values given are in hundredths of a millimeter):
NOTE - If the original ring and pinion gears will be used for reassembly, and right-to-drive pinion gear tooth contact pattern is satisfactory, use original shim(s).
Note marking on original drive pinion shaft. Measure original shim thickness and add it to the value give on the pinion shaft to establish the nominal dimension.
Example: Pinion marking is +10 and original shim thickness is 2.90. Nominal dimension is 3.00 (2.90 plus +10).
Note marking on new pinion gear and subtract this value from the established nominal dimension and this will give you the new required shim thickness.
EXAMPLE: Nominal dimension is 3.00 and marking on new drive pinion is +20, then new shim thickness is 2.80 (3.00 minus +20, then new shim thickness is 2.80 (3.00 minus +20).
2) Place new (or original) pinion depth adjusting shim on drive pinion gear, and using a press install rear bearing on drive pinion gear. Lubricate bearing and install drive pinion and bearing in housing. Install new collapsible spacer, front pinion bearing, dust shield, new oil seal, and pinion flange in housing.
3) Start pinion flange nut on shaft and as nut is tightened, keep checking rotating torque of pinion shaft (pinion bearing preload) using an inch pound torque wrench. Tighten nut until pinion bearing preload is within specifications. NOTE - If pinion bearing preload torque is exceeded, do not back off nut to obtain preload. Install new collapsible spacer and repeat procedure.
Differential Case Assembly - 1) Place thrust washers on side gears and install side gears in case. Install pinion gears by rolling them into position and install pinion shaft. Check rotating torque is not to specification, install new thrust washers on side gears. NOTE -Thrust washers are available in thicknesses from .0709" (1.80 mm) to .0817" (2.10 mm) in increments of .002" (.05 mm).
2) Install ring gear on case and tighten bolts to specified torque. Press differential bearings onto case, and if using original bearings, spread housing and install case using original shims. If using new bearing or case, install case in housing and insert enough shims equally on both sides to eliminate any end play.
3) Install bearing caps and bolts and tighten bolts. Measure ring gear backlash using a dial indicator mounted to hoousing ring gear backlash using a dial indicator mounted to housing with plunger contacting ring gear at right angel to the gear teeth. Block drive pinion flange from turning. Zero dial indicator. Rotate ring geaer back as far as possible and note backlash reading on indicator. If backlash is not within specification, adjust backlash by changing size of shims. To increase backlash, increase size of shim on pinion side of carrier, and to decrease backlash, increase size of shim on ring gear side of carrier. When changing shims, be sure to install shims of equal size to opposite side of carrier.
4) After determining correct shims to be used, add .002" (.05 mm) more shim thickness to each side. Install spreader on housing, spread housing and install bearing outer races and shims. Remove spreader and install bearing caps and tighten bolts. With differential completely assembled, check ring-to-pinion gear tooth contact pattern to ensure all adjustments are correct.