Generic Rear Axle Information

12 bolt

GM Part #/Teeth
Individual Part #s
Ratio
Ring/Pinion
Fits
3961404 (39/8T)
(3862528/3862516)
4.88 - 39/8 65-69 All
3961405 (43/13T)
(3862689/3862693)
3.31 - 43/13 65-70 All, 71 Chevelle/Nova, 72 Chevelle
3961406 (39/11T)
(3853010/3853008)
3.55 - 39/11 65-69 Pass, 66-68 Chevy, Chevelle, Camaro, 69 Chevelle, 70 All
3961407 (43/14T)
(3863691/3853003)
3.07 - 43/14 65-70 All and 71 Nova
3961408 (41/11T)
(3862525/3862513)
3.73 - 41/11 65-69 All and 70 Camaro
3961409 (41/10T)
(3862526/3862514)
4.10 - 41/10 65-69 All, 70 Chevelle, Camaro, 71 Malibu (Sport Coupe, Conv, El Camino [Custom] 8-cyl)
3961410 (41/9T)
(3862527/3862515)
4.56 - 41/9 65-69 All
3961434 (41/16T)
(3871038/3871041)
2.56 - 41/16 67 Chevelle w/A.I.R., 68-70 Chevelle, Camaro, 69 Chevy, 68-70 Pass
3961435 (41/15T)
(3869788/3869785)
2.73 - 41/15 65-70 All, 71-72 Chevelle

10 bolt

GM Part Number Ratio
Ring/Pinion
Fits
3961412 (37/11T)
(3880044/3790628)
3.36 - 37/11 64-68 Chevy, Chevelle, 65-68 Pass, 69-70 All, 71-72 Chevelle, Nova
3961413 (37/12T)
(3880043/3790629)
3.08 - 37/12 64-70 All, 71 All exc. Pass, 72 Chevelle
3961414 (37/10T)
(3880048/3849722)
3.70 - 37/10 64-68 Chevelle, 65-68 Pass
3961411 (39/11T)
(3880046/3790627)
3.55 - 39/11 64-69 All
3961425 (41/15T)
(3910818/3910823)
2.73 - 41/15 67-70 Chevy, Chevelle, Camaro, 68-70 Pass, 71 Chevelle, Nova, 72 Chevelle
3961426 (41/16T)
(3917184/3917185)
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 NF3894939 ~ N3894939
1967 Chevelle-Late NF3917124
1968-Early 1969 Chevelle NF3917124

1969 Chevelle 3959038NF
1970-72 Chevelle 3969278NF
1970-72 Chevelle 3969278

10-Bolt Housing: Casting
1964 Chevelle 3839390N
1965 Chevelle 3859139N
1965 Chevelle 3863495N *
1966 Chevelle 3875744N
1967 Chevelle 3894938N
1968 Chevelle 3917123NF
1969 Chevelle 3859037NF
1970-72 Chevelle 3969277NF

The casting numbers/letters on rear end housings appear to have either a prefix or suffix of "N" or "NF" and no reason has been found yet why they may have one or the other.

* Although this has been reported on a few 1965 Chevelles it may, MAY, be from a different GM A-body line.  Research on this is continuing.  See also 1965 Chevelle rear axle information page.

File Photo - 07/20/2009

File Photo - 07/20/2009

Anyone having photos of rear end casting numbers with "N" or "NF" different from those above are encouraged to email me a photo of it. Please be specific about the year and, if possible, include a photo of the casting date. My email address is on my Contact page.

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

Recently I've been asked a couple of questions about, what appears to be, McKinnon Industries-built (GM of Canada) rear ends that seem to have odd - or non listed - ratio ID codes as far as Chevelles are concerned.

One is casting number 3969278 (1970-1972), dated F 20 9, and coded XT 0911K and another 3969278 coded LJ 1128K. Another two are casting number 3959038 (1969), no casting date as of yet, and coded LE 1115K and LE 0822K.

I cannot find information in either my U.S. or Canada parts & accessory catalogs. Any help in identifying axle ratios for these two prefixes or any other McKinnon Industries rear ends with other prefixes not listed on this site would be welcomed. The XT, LE and LJ prefix codes to appear for Pontiac 1970 GTO/GP for 3.07, 2.73 and 2.56 respectively. Although no casting numbers are given, all of the codes (XT, LE and LJ) can be found at http://ronspontiacpage.com/reference-pages/rearendcodes.htm for 1970 model years and XT for 71 & 72 as well.

ELCAMINOSTUFF  All Rights Reserved
Casting date example of H 20 4 for August 20, 1964

ELCAMINOSTUFF  All Rights Reserved
Casting date example of F 4 5 for June 4, 1965

ELCAMINOSTUFF  All Rights Reserved
Casting date example of F 21 7 for June 21, 1967

ELCAMINOSTUFF  All Rights Reserved
Casting date example of B 18 8 for February 18, 1968

ELCAMINOSTUFF  All Rights Reserved
Casting date example of C 5 0 for March 5, 1970

File Photo - 07/20/2009
Casting date example K 9, 1 for November 9, 1971

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Foundry castings of 12345 67890 and rear casting date of L 19 8 for December 19, 1968.

Often anomalies occur. The two photos below are from a 1970 Chevelle with the correct casting number, 3969278NF, but a casting date that appears to be December 22, 1968 (L 22 8). It has been suggested that possibly the casting date was set wrong and it should be L 22 9 for December 22, 1969 as it should be.

10/28/2009
10/28/2009

ELCAMINOSTUFF  All Rights Reserved
ELCAMINOSTUFF  All Rights Reserved

All Chevelle rear ends are of the Salisbury design. A Salisbury rear end is very easy to distinguish from the Hotchkiss design. The Salisbury rear end has a removable cover on the rear of the center section where the Hotchkiss does not.

typical Chevrolet Salisbury rear end
Typical Salisbury rear end found on 1964-1972 Chevelles.

typical Ford/MoPar Hotchkiss rear end
Typical Hotchkiss rear end found on 1957-1985 Fords.

The Hotchkiss is generally favored over the Salisbury in racing circles due to the fairly quickly removable center section allowing a racer to have several gear ratios available to be swapped relatively quickly as the situation warrants.

* 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. Axle tube flange-to-flange is 54.25 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".) Axle tube flange-to-flange is 55.25 inches.

* A second measurement to check is centerline distance between spring perch seats.  1964-1967 are 35 1/16 inches between seats where 1968-1972 are 34 31/32 inches.

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.

8.2 versus 8.5

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, most 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 but have seen several with May/June casting dates from 1967 model year Chevelles. However, a June 1967 casting date rear end such as this might have found its way into very early 1968 model year Chevelles as well and could be the basis for the statement in the article.)

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.