Chevelle Rear End |
El Camino Rear End
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 |
Stamped Axle Code Location
The gear ratio code, date, and rear axle assembly plant are
generally stamped into the right (passenger side) axle housing
facing forward and exact locations may vary slightly. This is an
example from a 1967 Chevelle and is stamped CB 1012 W. The
"CB" letters are the original ID code for a 3.36:1 ratio, 1012 is
the assembly date of October 12, and the "W" indicates the plant
code for Warren, MI. This identification may not always be stamped
clearly and the area is often covered with years of road grime so it
may take some scrubbing to reveal it.
Individual gear ratio identification codes can be found for their respective years on this website.
Casting Numbers
12-Bolt Housing: Casting
1965 Chevelle 3859140N
1966 Chevelle 3875745N
1967 Chevelle NF3894939 ~
N3894939
1967 Chevelle-Late - 1969 3917124N
1967 Chevelle-Late - 1969 NF3917124
1967 Chevelle-Late - 1969 3917124NF
1969 Chevelle 3959038NF
1969 Chevelle X3959038NF
1970-72 Chevelle 3969278
1970-72 Chevelle 3969278N
1970-72 Chevelle 3969278NF
10-Bolt Housing: Casting
1964 Chevelle 3839390N
1965 Chevelle N3863495 *
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 may 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. The same has been found with the letter "X." But, here's my theory based on what I've seen. Feel free to comment on it. The "N" and "NF" is reportedly for the Neenah foundry located in Neenah, WI.
- The model year 1967 is a transition year in two ways. Two rear
end casting numbers have been found on 12-bolt rear ends, #3894939
on 'early' models and #3917124 on 'late' models. Research shows
1967 used both the early, narrow width rear end and the later, wider
width rear end; hence the two casting numbers.
The early, narrow width rear end also saw both the early model years (64-66) use of the single letter "N" with the casting number while later, wider width rear ends saw the later model years (68-72) use of the two letter "NF" casting. Occasionally the casting identification will also include the letter "X." Its meaning isn't known. Maybe a new mold being tested...?
* Found on several 1965 Chevelles. See also 1965 Chevelle rear axle information page.
1967-1969 ~ Variations of casting number 3917124
1969 ~ 3959038NF and X3959038NF
1970-1972 ~ 3969278, 3969378N, 3969278NF
Two photos from different distances showing the location of the axle housing casting number NF 3917123 X. The GM 5 casting on the driver side is a mold casting identification and will, of course, vary from center section to center section.
Anyone having photos of rear end casting numbers with "N" or "NF" or "X" in 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.
Casting date example of H 20 4 for August 20, 1964
Casting date example of F 4 5 for June 4, 1965
Casting date example of F 21 7 for June 21, 1967
Casting date example of L 14 7 for December 14, 1967
Casting date example of B 18 8 for February 18, 1968
Casting date example of D 19 8 for April 19, 1968
Casting date example of I 8 9 for September 8, 1969
Casting date example of C 5 0 for March 5, 1970
Casting date example K 9, 1 for November 9, 1971
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.
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 Salisbury rear end found on 1964-1972 Chevelles.
Typical Hotchkiss rear end found on full size 1955-1964 Chevrolet, Ford
and MoPar.
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.
One way to tell the 8.2 from an 8.5 is by the ring gear bolts. The 8.2 rear end has 3/8" ring gear bolts with 9/16" head where the 8.5 rear end has 7/16" ring gear bolts with 3/4" head and are left-hand threads.
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 many 1966-72 A-cars, like high-performance versions, SS396 series (66-68), Chevelles and Monte Carlos there is a frame reinforcement 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.
