1966 Chevelle

Rear Axle Section Links

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Rear Axle Gears and Driveshaft

1964-67 Chevelle rear ends were manufactured by the Chevrolet Gear and Axle Division and were the same width. Measuring two different 10-bolt rear ends, I found the following:

Rear end #1 not in car. From backing plate-to-backing plate, 53.3125 inches. Wheel mounting surface-to-wheel mounting surface (outside brake drum-to-brake drum) measures 59.875 inches. The tape measurement photo below shows 60.1875 inches but there is the extra length of the tape going up/down the brake drum. If you measure close to 60 inches and not as much as 62 inches, you can be assured the rear end is from a 1967.

Rear end #2 in car. From backing plate-to-backing plate, 53.250 inches. Rear wheels were not removed to measure the outside drum-to-drum because the inside measurements are within 1/16-inch and I didn't feel the need to jack up the car and remove the wheels.

Note: Other sources put the total width at 60.5 inches, so measure carefully. I did find that by using a steel tape and 'bending' it over the top of the brake drums I came up with 60.1875 inches; see photos below.

1968-72 Chevelle rear end housings are about 2 inches wider overall, but again, be careful what you measure to/from and how much slack is in your tape.

The 10 bolt Chevelle rear end has the 8.2" ring gear from 1964 to early 1972. It wasn't until late 1972 that the 10 bolt 8.5" ring gear was used in Chevelles.

Rear spring mounting pads differed in that 1964-66 rear ends used a flat pad with a hole drilled in the center.  1967 rear spring mounting pads had a raised 'hat' design and tapered coil springs.

1966 spring perch
Note lower spring retention plate on the 1966 rear end above as opposed to 1967 rear end below with tapered lower pigtail and 'top hat' design lower spring perch.
1967 spring perch

Courtesy Dale McIntosh
Backing plate-to-backing plate - 53.3125 +/- 0.165 (1/16")

Courtesy Dale McIntosh
Outside drum-to-outside drum - 60.1875" (60 3/16 inches).

Quote from the Chevrolet P&A Catalog: "1965 to 1969 production numbers are stamped on the bottom left or right axle tube either adjacent to the carrier housing or about 8"-10" inboard from the backing plate - usually on the passenger side."

Courtesy Dale McIntosh
Although this is from a 1967 Chevelle as noted by the spring lower perch, the focus is the location of the identification information.

Courtesy Dale McIntosh
Close-up of above 1967 rear axle housing. CB 1012 W decodes to CB=3.36:1, 1012=Month [Oct] and Date [12], W=Warren, MI.

Decoding the stamped information is as follows:
* The first two letters indicate the gear set ratio that was installed. See table below to decipher these first two letters.
* The assembly date of the axle assembly is shown with 4 digits; the first two being the month (01..12) and the second two being the date (01..31)
* The last letter is the plant of assembly letter code
* If the gear set is a Positraction unit, normally the original equipment supplier letter code is stamped below the above 7-character codes.

Plant Codes:
* G=Detroit Gear & Axle
* B=Buffalo, NY
* W=Warren, MI.
* K = McKinnon Industries

Positraction Codes (Original Equipment Suppliers to GM)
* D=Dana Positraction
* E=Eaton Positraction

A typical rear axle code stamping will look like one of those shown below.

File Photo
CW 0923 decodes to CW=3.31:1 Positraction, 0923=September 23. (Plant not captured in photo)

File Photo
KF 1014 B decodes to KF=3.55:1 w/metallic brakes, 1014=October 14, B=Buffalo, NY

10/30/2009
CF 1015 E decodes to CF=3.31:1 Positraction, 1015=October 15, B=Buffalo, NY,  E=Eaton (original equipment manufacturer for GM Positraction).

File Photo
CW 1112 B decodes to CW=3.31:1 Positraction, 1112=November 12, B=Buffalo, NY

10/05/2009
CX 0104 B decodes to CX=3.07:1, 0104=January 4, B=Buffalo, NY
I purposely cropped this one a little wide to show how road grime can accumulate on the rear axle housing.


KM 0114 B E decodes to KM=4.56:1 Positraction, 0114=January 14, B=Buffalo, NY, N.Y. E=Eaton (original equipment manufacturer for GM Positraction).

File Photo
CF 1127 E decodes to CF=3.31:1 Positraction, 1127=November 27, E=Eaton (original equipment manufacturer for GM Positraction).  (Plant not captured in photo)

File Photo
CI 0503 E decodes to CI=3.73:1 Positraction, 0503=May 3, E=Eaton (original equipment manufacturer for GM Positraction).  (Plant not captured in photo)

11/24/2009
CF 0509 B E decodes to CF=3.31:1 Positraction, 0509=May 9, B=Buffalo, E=Eaton (original equipment manufacturer for GM Positraction).

Courtesy David Armstrong
CX 0727 B decodes to CX=3.07:1, 0727=July 27, B=Buffalo, NY

Identification Code Ratio
CA (10-bolt) 3.08:1
CB (10-bolt) 3.36:1
CC (12-bolt) 3.73:1
CD (12-bolt) Positraction 3.07:1
CE (10-bolt) Positraction 3.08:1
CF (12-bolt) Positraction 3.31:1
CG (10-bolt) Positraction 3.36:1
CH (10-bolt) w/metallic brakes 3.70:1
CI (12-bolt) Positraction 3.73:1
CJ (12-bolt) w/metallic brakes 3.07:1
CK (12-bolt) Positraction w/metallic brakes 3.07:1
CL (10-bolt) w/metallic brakes 3.08:1
CM (10-bolt) Positraction w/metallic brakes 3.08:1
CN (12-bolt) w/metallic brakes 3.31:1
CO (12-bolt) Positraction w/metallic brakes 3.31:1
CP (10-bolt) w/metallic brakes 3.36:1
CQ (10-bolt) Positraction w/metallic brakes 3.36:1
CR (10-bolt) Positraction 3.70:1
CS (10-bolt) Positraction w/metallic brakes 3.70:1
CT (12-bolt) w/metallic brakes 3.73:1
CU (12-bolt) Positraction w/metallic brakes 3.73:1
CV (10-bolt) Overdrive 3.70:1
CW (12-bolt) 3.31:1
CX (12-bolt) 3.07:1
KC (12-bolt) w/metallic brakes 2.73:1
KD (12-bolt) Positraction 2.73:1
KE (12-bolt) Positraction w/metallic brakes 2.73:1
KF (12-bolt) w/metallic brakes 3.55:1
KG (12-bolt) Positraction w/metallic brakes 3.55:1
KH (12-bolt) Positraction 3.55:1
KI (12-bolt) "396" w/Powerglide 2.56:1
KJ (12-bolt) 3.55:1
KK (12-bolt) Positraction 4.10:1
KL (12-bolt) Positraction w/metallic brakes 4.10:1
KM (12-bolt) Positraction 4.56:1
KN (12-bolt) Positraction w/metallic brakes 4.56:1
KO (12-bolt) Positraction 4.88:1
KP (12-bolt) Positraction w/metallic brakes 4.88:1

Note some differences listed for GM of Canada Chevelles & Beaumonts.
Codes KC, KD, KE, and KI are not listed.  Codes KF & KH have different types and brake linings.
Courtesy Tom Lloyd

File Photo

The date code on a rear end housing is simple to decode. It includes the month, day and year such as I245. This decodes to September 24, 1965. Month codes are A through L for January through December.

A - January D - April G - July J - October
B - February E - May H - August K - November
C - March F - June I - September L - December


File Photo
File Photo
I245 casting date of September 24, 1965

File Photo
J65 casting date of October 6, 1965

11/24/2009
D146 casting date of April 14, 1066

File Photo

Rear Gear Assembly - Group 5.529
GM did not sell the ring or pinion gear separately but rather as a unit. Part numbers below indicate the unit number with the ring gear part number followed by the pinion gear part number, again, not sold separately.

12-bolt gear ratios

Chevrolet Part Number Ratio
Ring/Pinion
Fits
3961404 (39/8T)
(3862528/3862516)
4.88:1 - 39/8 65-69 All
3961405 (43/13T)
(3862689/3862693)
3.31:1 - 43/13 65-70 All, 71 All exc. Pass
3961406 (39/11T)
(3853010/3853008)
3.55:1 - 39/11 65-69 Pass, 66-68 Chevy, Chevelle, Camaro, 69 Chevelle, 70 All
3961407 (43/14T)
(3863691/3853003)
3.07:1 - 43/14 65-70 All and 71 Nova
3961408 (41/11T)
(3862525/3862513)
3.73:1 - 41/11 65-69 All and 70 Camaro
3961409 (41/10T)
(3862526/3862514)
4.10:1 - 41/10 65-69 All, 70 Chevelle, Camaro, 71 Malibu (Spt Cpe, Conv, El Camino [Custom] 8-cyl)
3961410 (41/9T)
(3862527/3862515)
4.56:1 - 41/9 65-69 All
3961434 (41/16T)
(3871038/3871041)
2.56:1- 41/16 67 Chevelle w/A.I.R., 68-70 Camaro, 69 Chevy, 68-70 Pass
3961435 (41/15T)
(3869788/3869785)
2.73:1 - 41/15 65-70 All, 71 Chevelle

10-bolt gear ratios

Chevrolet Part Number Ratio
Ring/Pinion
Fits
3961412 (37/11T)
(3880044/3790628)
3.36:1 - 37/11 64-68 Pass, 69-70 All, 71 Chevelle, Nova
3961413 (37/12T)
(3880043/3790629)
3.08:1 - 37/12 64-70 All, 71 All exc. Pass
3961414 (37/10T)
(3880048/3849722)
3.70:1 - 37/10 64-68 Chevelle, 65-68 All
3961411 (39/11T)
(3880046/3790627)
3.55:1 - 39/11 64-69 All
3961425 (41/15T)
(3910818/3910823)
2.73:1 - 41/15 67-70 Chevy, Chevelle, Camaro, 68-70 Pass, 71 Chevelle, Nova
3961426 (41/16T)
(3917184/3917185)
2.56:1 - 41/16 68-71 Chevelle, 68-70 Chevy/Camaro, 68-70 Pass., 71 Nova

Courtesy Matt Tucker
Ring gear of 3.07:1 ratio 12-bolt - Chevrolet lists the ring gear as part #3863691.


File Photo
File Photo

The original tag reads, "USE POSITRACTION DIFF. LUBRICANT ONLY" while replacement tags like those shown reads, "USE LIMITED SLIP DIFF. LUBRICANT ONLY."

File Photo

File Photo

Driveshaft - Group 5.544

Part Number Reference Fitment
3898244 P&A Catalog 67-67 Chevelle, 68 Chevelle (4-dr) El Camino
     
Rear Flange for center housing - Group 5.545
3878972 P&A Catalog All w/12-bolt cover
3997957 P&A Catalog All w/10-bolt cover

File Photo

1. 3868910 Axle Asm
1. 3868912 Wagons & Pickup Delivery
1. 3868930 13817-67
2. 102634 Nut(1) 3. 103320 L. Washer 4. 1358938 "U"-bolt
5. 3868653 Prop. Shaft Asm
5. 3881652 13817-67
6. 358501 Nut(2)    
(1) 12-16 lbs. ft.
(2) 55-75 lbs. ft.