8.25 8 1/4 Rebuild and modification

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for 1996 and newer 29 spline 8 1/4 rebuilds:

DIFFERENTIAL BEARING PRELOAD AND GEAR
BACKLASH
The following must be considered when adjusting
bearing preload and gear backlash:
The maximum ring gear backlash variation is
0.003 inch (0.076 mm).
Mark the gears so the same teeth are meshed
during all backlash measurements.
Maintain the torque while adjusting the bearing
preload and ring gear backlash.
Excessive adjuster torque will introduce a high
bearing load and cause premature bearing failure.
Insufficient adjuster torque can result in excessive
differential case free-play and ring gear noise.
Insufficient adjuster torque will not support the
ring gear correctly and can cause excessive differential
case free-play and ring gear noise.
NOTE: The differential bearing cups will not always
immediately follow the threaded adjusters as they
are moved during adjustment. To ensure accurate
bearing cup responses to the adjustments:
Maintain the gear teeth engaged (meshed) as
marked.
The bearings must be seated by rapidly rotating
the pinion gear a half turn back and forth.
Do this five to ten times each time the
threaded adjusters are adjusted.
(1) Use Wrench C-4164 to adjust each threaded
adjuster inward until the differential bearing freeplay
is eliminated (Fig. 57). Allow some ring gear
backlash (approximately 0.01 inch/0.25 mm) between
the ring and pinion gear. Seat the bearing cups with
the procedure described above.
(2) Install dial indicator and position the plunger
against the drive side of a ring gear tooth (Fig. 58).
Measure the backlash at 4 positions (90 degrees
apart) around the ring gear. Locate and mark the
area of minimum backlash.
(3) Rotate the ring gear to the position of the least
backlash. Mark the gear so that all future backlash
measurements will be taken with the same gear
teeth meshed.
(4) Loosen the right-side, tighten the left-side
threaded adjuster. Obtain backlash of 0.003 to 0.004
inch (0.076 to 0.102 mm) with each adjuster tight-
ened to 14 N·m (10 ft. lbs.). Seat the bearing cups
with the procedure described above.
(5) Tighten the differential bearing cap bolts 95
N·m (70 ft. lbs.).
(6) Tighten the right-side threaded adjuster to 102
N·m (75 ft. lbs.). Seat the bearing cups with the procedure
described above. Continue to tighten the
right-side adjuster and seat bearing cups until the
torque remains constant at 102 N·m (75 ft. lbs.)
(7) Measure the ring gear backlash. The range of
backlash is 0.006 to 0.008 inch (0.15 to 0.203 mm).
(8) Continue increasing the torque at the rightside
threaded adjuster until the specified backlash is
obtained.
NOTE: The left-side threaded adjuster torque
should have approximately 102 N·m (75 ft. lbs.). If
the torque is considerably less, the complete
adjustment procedure must be repeated.
(9) Tighten the left-side threaded adjuster until
102 N·m (75 ft. lbs.) torque is indicated. Seat the
bearing rollers with the procedure described above.
Do this until the torque remains constant.
(10) Install the threaded adjuster locks and
tighten the lock screws to 10 N·m (90 in. lbs.).
After the proper backlash is achieved, perform the
Gear Contact Analysis procedure.

8 1/4 INCH AXLE
Axle Type . . . . . . . . . . . . . . . . Semi-floating, hypoid
Lubricant . . . . . . . . . . . . . . . . . . . . . . . SAE 80W-90
Lube Capacity . . . . . . . . . . . . . . . . . 2.27 L (4.8 pts.)
Trac-Lok Additive . . . . . . . . . . . . . . . . 148 ml (5 oz.)
Axle Ratio . . . . . . . . . . . . . . . . . . . . . 3.21, 3.55, 3.90
Differential
Case Clearance . . . . . . . . . . . . . 0.12 mm (0.005 in.)
Case Flange Runout . . . . . . . . 0.076 mm (0.003 in.)
Ring Gear
Diameter . . . . . . . . . . . . . . . . . . . 20.95 cm (8.25 in.)
Backlash . . . . . . . . . . 0.12-0.20 mm (0.005-0.008 in.)
Runout . . . . . . . . . . . . . . . . . . . 0.127 mm (0.005 in.)
Pinion Bearing
Preload . . . . . . . . . . . . . . . . . 1-2 N·m (10-20 in.lbs.)

8 1/4 INCH AXLE
DESCRIPTION TORQUE
Diff. Cover Bolt . . . . . . . . . . . . . . 41 N·m (30 ft. lbs.)
Bearing Cap Bolt . . . . . . . . . . 136 N·m (100 ft. lbs.)
Pinion Nut–Minimum . . . . . . . 285 N·m (210 ft. lbs.)
Ring Gear Bolt . . . . . . . . . . . . . . 95 N·m (70 ft. lbs.)
Backing Plate Bolt . . . . . . . . . . . 64 N·m (48 ft. lbs.)
RWAL/ABS Sensor Bolt . . . . . . . 24 N·m (18. ft. lbs.)
 
Last edited:
As RRR commented, I am a believer in the 8.25" rear for STREET/STRIP use, especially with pump gas and no transbrake use. The bearings and axles seem equivalent or superior to say, 12-bolt Chevy stuff, and you know they get raced. The ones who use C-clip eliminators on the Chevys, we would upgrade to an 8.75 or Dana 60 by that stage. I made hundreds of runs at the 12.50 level with a 360 (400hp?) and over a hundred with a 416 running low 11's, with slicks. No transbrake and a 904 wide-ratio trans. I even was running the small (gasp!!) 7260 U-joints, with zero failures. Up to 500hp (flywheel) and under 3500# I think it's fine for general purpose use. MoPar's camshaft test mule was a mid '70s Duster with a 4.30 geared 8.25 and they were using a low compression 400 BB running 10's eventually.
 
dodgedude37 said:
Thanks that previous thread had me worried.
Click to expand...

I think the carrier break is 2.45 and numerically lower and "whatever" is just above 2.45 and numerically higher.....I think that's right.
 
I'm not sure but doesn't the 2.45 gear axle housing have a different offset than the the higher gear ratio's?
 
So I have 8 1/4. 2.45 open diff. This replaced 7 1/4. 3.23 open. Now I want to get my gearing back with a limited slip. Change to a limited slip carrier for lower gears like 3.55, sound right?
 
dodgedude37 said:
So I have 8 1/4. 2.45 open diff. This replaced 7 1/4. 3.23 open. Now I want to get my gearing back with a limited slip. Change to a limited slip carrier for lower gears like 3.55, sound right?
Click to expand...

Getting your gearing "back" would be going "back" to a 3.23. Going to a 3.55 would be using a lower gear. But that's a decent gear.
 
So was the big bolt pattern the only option on a-bodies and 8.25?
 
Last edited:
As per my earlier post I am regearing an 8 1/4 diff. Upon removing the pinion races I discovered a shim behind the large race & no shims behind bearing. Was wondering what was up. I was expecting just the opposite.

Dave
 
dodgedude37 said:
As per my earlier post I am regearing an 8 1/4 diff. Upon removing the pinion races I discovered a shim behind the large race & no shims behind bearing. Was wondering what was up. I was expecting just the opposite.

Dave
Click to expand...
Has it been apart before? It's easier to knock out the race vs pulling the pinion bearing off to put a shim behind it to set the pinion deeper....
 
I don't know the history, but I can't imagine putting 2.45 gears into an 8 1/4 on purpose. So my guess is oem. The diff & K frame were transplated from a 73 donor to give me power front disc & larger bolt pattern.
 
I guess my question should I put that shim back? I have a shim kit for behind the bearing & my original bearing modified to a slip fit, easy on easy off.
 
dodgedude37 said:
I guess my question should I put that shim back? I have a shim kit for behind the bearing & my original bearing modified to a slip fit, easy on easy off.
Click to expand...
If you're not looking to change the pinion depth, yes or put the same thickness behind the bearing instead of behind the race. Both ways does the same thing....
 
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