Generic Rear Axle Information
12 bolt
| GM Part Number | Ratio Ring/Pinion |
Fits |
| 3961404 | 4.88 - 39/8 | 65-69 All |
| 3961405 | 3.31 - 43/13 | 65-70 All, 71 All except Pass |
| 3961406 | 3.55 - 39/11 | 65-69 Pass, 66-68 Chevy, Chevelle, Camaro, 69 Chevelle, 70 All |
| 3961407 | 3.07 - 43/14 | 65-70 All and 71 Nova |
| 3961408 | 3.73 - 41/11 | 65-69 All and 70 Camaro |
| 3961409 | 4.10 - 41/10 | 65-69 All, 70 Chevelle, Camaro, 71 Malibu (Sport Coupe, Conv, El Camino [Custom] 8-cyl) |
| 3961410 | 4.56 - 41/9 | 65-69 All |
| 3961434 | 2.56 - 41/16 | 67 Chevelle w/A.I.R., 68-70 Camaro, 69 Chevy, 68-70 Pass |
| 3961435 | 2.73 - 41/15 | 65-70 All, 71 Chevelle |
10 bolt
| GM Part Number | Ratio Ring/Pinion |
Fits |
| 3961412 | 3.36 - 37/11 | 64-68 Pass, 69-70 All, 71 Chevelle, Nova |
| 3961413 | 3.08 - 37/12 | 64-70 All, 71 All exc. Pass |
| 3961414 | 3.70 - 37/10 | 64-68 Chevelle, 65-68 All |
| 3961411 | 3.55 - 39/11 | 64-69 All |
| 3961425 | 2.73 - 41/15 | 67-70 Chevy, Chevelle, Camaro, 68-70 Pass, 71 Chevelle, Nova |
| 3961426 | 2.56 - 41/16 | 68-70 Chevy/Camaro, 69-71 Chevelle, 68-70 Pass., 71 Nova |
Casting Numbers:
12-Bolt Housing: Casting #
1965 Chevelle 3859140N
1966 Chevelle 3875745N
1967 Chevelle 3894939N
1967 Chevelle-Late 3917124NF
1968-Early 1969 Chevelle 3917124NF
1969 Chevelle 3959038NF
1970-72 Chevelle 3969278NF
1970-72 Chevelle 3969278
10-Bolt Housing: Casting #
1964 Chevelle 3839390N
1965 Chevelle 3959139N
1966 Chevelle 3875744N
1967 Chevelle 3894938NF
1968 Chevelle 3917123NF
1969 Chevelle 3859037NF
1970-72 Chevelle 3969277NF
Thanks to Dave Bates for his listing of casting numbers.
The date code on a rear end housing is simple to decode. It includes the month, day and year such as J257. This decodes to October 25, 1967. Month codes are A through L for January through December.
| A - January | B - February | C - March | D - April |
| E - May | F - June | G - July | H - August |
| I - September | J - October | K - November | L - December |
Casting date example of August 20, 1964
Casting date example of June 4, 1965
Casting date example of June 21, 1967
Casting date example March 5, 1970
Foundry castings of 12345 67890
- * 1964-67 Chevelle rear ends were
manufactured by the Chevrolet Gear and Axle Division. The
housing measures 53.25 inches from backing plate to backing plate
and with the brake drums in place, the total width is 60.00 inches.
- * 1968-72 Chevelle rear end housings measure 58.5 inches from flange to flange, and with the brake drums in place, the total width is 62.5 inches. (Note: Other sources put the total width at 61.125" to 61.25".)
The 10 bolt Chevelle rear end has the 8.2" ring gear from 1964 to 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 while 1968-72 rear ends have circular spring mounting pads, which are 3/4" higher that the early flat pad.
1967 was a transition year in that A-cars might have a 1964-66 style rear end, a 1968-72 rear end (which is wider, and commonly available), or a "hybrid" rear end, which will have the 58.5" width, but with the early spring mounting pad and trailing arm brackets. (Note: For what it's worth, ALL 67 rear ends I've ever seen were the narrow variety and used the spring cup like 68-72 but were narrower like the 64-66.)
Rear upper control bushing eyes differ, and the positioning of the bushing eyes will differ. 1968-72 rear end housings will have a 3/8" forward positioning, which is farther than 1964-67 rear ends.
1964 was the only year that the rear end bushing are small, and any upper trailing arm (from any GM division) will fit 1964 rear end housings.
Upper trailing arms of 1964-67 vintage interchange, and they are 1" shorter, which will not fit into 1968-72 A-cars. 1968-72 A-cars have longer upper arms, and when switching upper arms, be careful here, in which the pinion nose angle might be affected. According to Inside '64 -- '72 A-Bodies, (Car Craft Magazine) there are 10 different rear upper control arms offered. Other characteristics include clearance bulges, common with 12-bolt differentials in A-cars, and adjustable upper arms, optioned on Oldsmobile A-cars (F-85, Cutlass). 442s had boxed upper arms, and this is a sought-after item in a restoration.
On 1968-72 A-cars, like high-performance, 4-speed, and Monte Carlo/Grand Prix, there is a triangulation brace bracket that is standard. This stiffens the chassis, and tubular versions are available from Edelbrock and Hotchkis Performance.
Note: the trailing arms fit either side, and this means that the left upper arm will fit on the right, and vice versa.
CONTROL ARMS (FRONT)
Most of the control arms for the 1964-72 Chevelle
interchange, and the lower control arm used for the front suspension
had these distinct features.
*One version was produced from 1964-66, and utilized 1.90" (1 5/16")
diameter bushings. There are two arms used from 1967-72, and the
category includes the lower control arms with round bushings (1.625"
diameter), commonly found on 1968 (all models) or 1969-72 vehicles
like Chevelle SS, Pontiac GTO, Oldsmobile 442, and the Buick GSX.
Most of the lower control arms used on the other A-cars had oval
bushings.
*The bushings described in the lower arm are located in the rear pivot area
(the TRW or MOOG manual calls this the rear control arm bushing)
on both sides of the car.
*All oval bushing arms, 1.90", and 1.625" round bushing arms (1 5/8") manufactured
used a 1 3/8" (1.375") diameter front bushing.
*The lower arms interchange as an assembly, regardless of the spring diameter
that distinguishes 1964-67 and 1968-72 front springs. You can use
a later arm on early models (1964-67), but I have not heard of a
1.90" lower arm used on a later A-body.
Note: the lower arms may differ, in case a replacement or factory mismatch are common when locating the correct lower arm for a restoration. The only problem with oval bushings is that the existing bushing cans will have to be reused, and aftermarket companies that use solid or Del-A-Lum (a Global West product) bushings as replacements might require locating a set of round bushing lower arms, either a 1.90" or 1.625".
*Upper control arms for Chevrolet Chevelles and El Caminos use cross shafts that used bolts to secure the cup washer to the bushing. BOP A-Bodies used cross shafts with threaded ends with locknuts. Due to the possibility of frame spread, MOOG or TRW manufactures an offset control arm shaft that allows the camber angles to be corrected via OEM specs.
FRONT SPRINGS
The springs vary with application and chassis packages, but there is one thing that is important: 1968-72 A-cars have a different front spring diameter when compared to 1964-67 front springs ("Knuckle Sandwich", Hot Rod, 6/87). 1969-present springs are based on computerized data concerning chassis package and body styles, but the rates vary, depending whether a softer or stiffer ride is preferred.
Note: 1964-67 front springs can be found on 1967-69 Camaros and 1968-74 Novas, but the spring rates will differ; 1968-72 A-body front springs are used on 1968-70 BOP full size cars, but the spring rates vary.
REAR SPRINGS
The data that are true for front springs is the same for rear springs, and 1964-66 rear ends have provisions for bolting on the spring to the pad.
Another difference is that 1964-66 springs are pigtailed on one end only while 1967-72 rear ends use a cup and is flanged to hold the spring in place.
