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Since this article was written more vehicle changes have come to light. Continued research also provided more accurate dating. The most current information can be found in a new book about the CJ-3A.......

The Civilian Jeep Model CJ-3A
A guide to its features and evolution, 1949 - 1953

See the book's web-page for more information http://cj3a.info/book/index.html

Dating a CJ-3A

The CJ-3A was produced for five model years, 1949 to 1953. Two other civilian Jeep models overlapped the CJ-3A's production. 1949 was the last year for the CJ-2A and in 1953 the CJ-3B became available. Unlike modern vehicles, the difference between CJ models was not distinct. The CJ-3A had many features similar to the late CJ-2As. Likewise the late CJ-3A had some of the new characteristics of the CJ-3B. Therefore all CJ-3As are not even the same. These differences can be used to roughly date when a vehicle was manufactured. The commonly accepted description of the CJ-3A seems to apply only to the mid production vehicles. The lack of factory parts information from the CJ-3A time period makes it very difficult to decide if and when changes were made. Much information has been obtained from the CJ-2A and CJ-3A Parts List (copyright 1949) and the 1945-1949 Master Parts List (copyright 1955). Many of the listings in the 1945-1949 Parts Master List are for  years later than 1949. Both manuals contain some errors and omissions. To further complicate things Willys also had a manufacturing facility in California. Willys Service Bulletin 53-5 explains "the effective serial numbers given apply to changes made in vehicles assembled at the Toledo plant and do not apply to those assembled in our west coast plant". The CJ-3As military sibling, the M38, also went through many changes. Changes in the M38 seem to parallel a similar change in the CJ-3A with the military change happening first.

I am collecting information about existing CJ-3As to help determine when changes took place. Because anything could have happened to these vehicles in the 50+ years since they were manufactured, a large sampling of vehicles is necessary to determine which assumptions are valid. From the information I have collected to date the following differences are appearing. This information is preliminary and it changes rapidly as new information is received from enthusiasts like you. To help by supplying information about your Jeep, please answer the questions near the bottom of this page.

Vehicle Serial Numbers The CJ-2A/CJ-3A Parts Book (copyright 1949)  states that the beginning of production vehicle serial number is 10001 with engine serial number 10001. Vehicle serial number tags are attached with 4 screws to the engine side of the firewall near the air filter. The vehicle serial number had a prefix of CJ-3A for the first 2 years of production. During this time the serial numbers continued to climb with no regard for model year. Starting in 1951, and continuing through final production, a new format was used. The prefix was changed to indicate the model and model year and the serial number itself was reset to 10001 at the beginning of each model year. See Willys-Overland Production Figures 1945-61 on the CJ-3B page for a list of serial numbers of Willys vehicles.

Body TagBody Tags The earliest 1949 CJ-3As have a body number tag below the serial number tag on the firewall. Later in 1949, and for the remainder of production, the body tag was eliminated. Body tag numbers are initially close to the vehicle serial number and then skew to about 1200 less than the vehicle serial number. What does this mean? How could there be less bodies than vehicles? The body tag to the left is from a 1949 CJ-3A, thanks to Andy Testo for the photo. Early in the 1949 model year Willys began to build their own bodies. Prior to that American Central Manufacturing (ACM) manufactured the bodies. 

Engine serial number locationEngine changes The engine serial number is stamped on the boss between the water pump and cylinder head; click on the engine serial number illustration at the right for the location. The first CJ-3A engine serial number should be 3J10001 and then increase through out the remainder of production. Serial number lists of other models of Willys vehicles indicate that engine serial numbers increase at a faster rate than the vehicle serial numbers. This "skew" is probably due to engines being pulled from stock for other uses, such as replacement engines. Existing original CJ-3A engine serial numbers initially increase as expected, but then in 1950 and 1951 the skew becomes negative by approximately 2000. Then in 1952 and 1953 the engine numbers climb again as expected. The negative skew would indicate there are fewer engines than vehicles. What caused the engine serial number difference in 1950 and 1951 to account for a discrepancy of several thousand engines? The early engine timing marks are located on the flywheel and viewed through a small hole in the engine rear plate. A 1950 service bulletin explains that additional timing marks will be placed on the front cover and pulley "asap". In 1952 the engine block was changed to one with a larger flange at the rear. The 1965 Service Manual states that this was done at engine serial number (3J)130859. The bellhousing was also changed to accept the new larger starter introduced here. The early block casting number is 641087 and the late block casting number is 804380. There are also a few transition blocks with casting number 641087 and the large flange. Block casting numbers are found just above the oil pan on the passenger side. The illustrations below show the difference between the small and large rear flanges. Below the drivers side of the engine is shown ,the flanges are similar on the passenger side of the block.

  Early small flange block      Late large flange block    

Early small flange                                                               Late large flange

Starters and Generators Starter and generator numbers are found on a tag that is riveted to their housings. Three different starters were used. The first vehicles used the Autolite MZ-4137. In mid 1950 the starter was changed to MZ-4162, according to Autolite manuals. Willys Service Bulletin #50-31 lists a change in the starter and starter push rod at vehicle serial number (CJ-3A) 51911 which is in the 1950 model year. The first two starters are very similar, are activated by a foot pedal linkage, open nosed, and use a 124-tooth flywheel. The third starter is Autolite MCH-6203. This starter is key activated with a solenoid mounted to the top of the starter and is the closed nose type. It uses a 129-tooth flywheel. The 1965 Universal Service Manual states that the third starter was put into production with vehicle serial number 30973 and, on a different page, engine serial number 130859. By adding the prefixes 452-GB1 to the vehicle serial number and 3J to the engine number, the result is vehicle 452-GB1 30973 with engine 3J130859. These are credible numbers for a 1952 CJ-3A and this data fits perfectly into the information collected from existing vehicles. The engine block change to the larger rear flange also occurred at this serial number.

The generator changed from the Autolite GDZ-4817 to Autolite GDZ-6001 during the 1950 model year. Service Bulletin #50-31 states a different engine front plate was implemented at engine (3J)50551 for the new type generator and the new generator actually entered production at vehicle number (CJ-3A) 51951. Then in 1953 at vehicle serial number 453-GB1 17807 the generator and regulators were changed again to provide a greater output. According to Service Bulletin 53-5 this generator provided a nominal 45 amp output. This last generator may have been an Autolite GGW-4801 or GGW-7404. Thanks to Bill Norris for a copy of the Bulletin.

Differential CoversAxles and Driveshafts One of the common improvements associated with the CJ-3A is the model 44 rear axle. The model 41 axle was actually used in the 3A until the end of the 1950 model year. The 1945-49 Master Parts List (copyright 1955) lists this change at vehicle serial number (CJ-3A) 62488 (very late 1950 model year). On the Classic Willys Message List Todd Paisley stated that Engineering Release #6427 Rear Axles (Spicer) - Change from Spicer Model 41 to Model 44 was started on October 31, 1950 and and implemented on November 30, 1950. The rear axle can be identified by the shape of the differential cover (see photos at left). The model 41 axle uses a round differential cover while the model 44 cover has straight sides.

A larger diameter rear driveshaft appeared at about the same time as the rear axle change. Early CJ-3As used a 1-1/4" diameter rear driveshaft while the later 3As used a 1-3/4" diameter rear driveshaft. I have not been able to pinpoint when the change was made because during the 1951 model year I am seeing both small and large diameter driveshafts randomly. By 1952 all driveshafts are large diameter. The rear driveshaft on the M38, the CJ-3As military equivalent, was changed from 1-1/4" to 1-3/4" diameter on 1/5/51 according to postings on The G503 Message Forums.

Transmission and Transfer Case Shifters "The shape of the transmission shift lever was changed and the length was increased one inch on the transmission and five inches on the transfer case to provide easier shifting and better clearances on the Model CJ-3A transmission beginning with Vehicle Serial No. 18829" and "in production on the transfer case beginning with Model CJ-3A Serial No. 21712" according to Service Bulletin 49-34. Both serial numbers are early in the 1949 model year. The early shifters can be seen in the engine serial number location illustration above. The late transmission shifter had a straight shaft with a low sharp bend. Late transfer case front axle engagement shifters were longer than the high-neutral-low range shifter.

The first CJ-3As utilized a bottom-mounted radiator, like the 2As. The bottom of this radiator was bolted to the frame crossmember and had a rod that extended between the bracket on the radiator top tank and the firewall. Later CJ-3A radiators were side mounted. The side mount radiator was bolted to the grill on both sides instead of the frame, and lacked the top connecting rod. The last bottom mounted radiator was CJ-3A 21656, according to the 1945-49 Master Parts list (copyright 1955). Service Bulletin No. 49-57 lists this change at a different serial number, CJ-3A 31374. Keith Buckley also added that the Air Deflector portion of the grille changed from 22 gage to 18 gage at this time. This logically was done to support the extra weight of the radiator. The vehicle frame also changed as the two radiator mount tabs were eliminated with the side mount radiator. Surveys of existing vehicles indicate that the CJ-3A 21656 serial number is most likely the correct point of change. Existing vehicles also show the possibility of a short run of bottom mounted radiators after the side mounted radiator had been put into production. It is interesting that Service Bulletin 50-4, Installation of Monroe Hydraulic Lift Pump on Models CJ-2A and CJ-3A, mentions "During the production of the Model CJ-3A with the side mount radiator, it was necessary to use a small quantity of bottom mounted radiators".

Air Inlet The large majority of existing 1949 CJ-3As surveyed have Oakes manufactured air filters. Most 1950 and newer vehicles have Donaldson air filters. The Oakes air filter has a flat top while the Donaldson air filter top is dome shaped. At serial number (CJ-3A) 62692 the Air Cleaner Tube and Bracket was changed according to the 1945-1949 Master Parts List (copyright 1955). The new "crossover tube" did not have a dimple in the top which was previously needed for clearance between the tube and the top radiator support rod. The photo below illustrates the early tube, with a dimple, in a CJ-3A without the radiator support rod.

Dimple in crossover tube

Hood  On early CJ-3As the location of the hood blocks is not equidistant from the hood center seam. This is a leftover characteristic of the CJ-2A. Service Bulletin 51-4 explains that "the right hand hood bumper has been relocated an equal distance on the right hood side, as compared to the left hood side for better appearance. This change was made effective with serial number (451-GB1) 13783".

Left Front Fender  The left (drivers side) front fender attachment on early 3As had additional bolts holding the splash apron to the frame. The 1945-1949 Master Parts List (copyright 1955) indicates that two 3/8"-24 x 3/4" bolts, washers and lock washers for attaching the left front fender to the frame were only used up to Serial No. (CJ-3A) 62505. This serial number would fall very late in the 1950 model year. The fenders also changed eliminating the extra flange with the bolt holes. The fender part number did not change possibly because both types of fenders could be interchanged. Later vehicle frames are also different as the threaded holes for the fender splash apron bolts were eliminated.

 Early Left Fender  Late Left Fender 

Early and late style left fenders, click on photos for a larger view

  A minor change was made to the tailgate in mid 1951. The M38, a sibling of the CJ-3A, required four cutouts in the top flange of the tailgate to allow for rear seat bracket and spare tire carrier attachment. This modified part carried over to the civilian Jeep although it was not necessary on the CJ. The photo below shows a late tailgate with 3 of the 4 cutouts visible. The 4th cutout is the longer oval type on the far left side of the tailgate. See the excellent article, Tailgate Reading, on the CJ-3B Page for more information about tailgates.

Tailgate Notches

Tail Lights
Late in the 1950 model year, at serial number CJ-3A 53768, the rear tail light changed from steel stamping to zinc die casting according to Service Bulletin 50-40. NACO tail lights were steel stampings and ALA tail lights were zinc die castings. There is a good article on The CJ-3B Page that shows all the different CJ tail lights.

Horn Button Horn buttons change from the button inside the steering wheel nut to the rubber cover over the nut type. This was done to make it more waterproof. The change is appearing at approximately the same time as the 1950 to 1951 model year change. The 1945-49 part book lists this change at vehicle serial number (CJ-3A) 57215. Surveys of actual vehicles show that both types of buttons were used into 1951.  The rubber cover is often missing from the late style since the rubber deteriorates over the years.

 Early Horn Button      Late Horn Button    Late button w/o cover  

Early horn button inside nut             Late button with rubber cover           Late style with cover missing

Gauges According to Service Bulletin 50-8 the temperature and oil pressure gauges style changed at serial number (CJ-3A) 43699 in the 1950 model year. The "dial" type was superseded by the "lever" type gauges.

Oil Gauges

Early "dial" and Late "lever" oil pressure gauges

Canvas Body Top Willys parts manual illustrations show the CJ-3A with a 7 piece canvas top and small metal framed windows similar to the CJ-2A. The 1945-49 parts book (copyright 1955) states there is a "New front top kit with larger curtain lights and eliminating window frames. New door assemblies and side curtains may be serviced for the old type with smaller windows in pairs only." According to Service Bulletin 50-14 the window change was made at (CJ-3A) 46180 which would be just after mid 1950. The door frames were also changed to make room for the larger windows. This was done by relocating the diagonal brace from above the door handle to below it.

 Early Canvas Top    Late Canvas Top

Early small window top with metal frames                        Late large window canvas top        

Colors The first CJ-3A windshield frames were painted the body color. Most original vehicles after mid 1952 seem to have black windshield frames instead of body color windshield frames. This is consistent with the CJ-3B, which had black windshield frames. This change appears at about vehicle serial number 452-GB1 20000.

Original wheel colors are difficult to find. The wheels on many vehicles have been replaced since wheels are easily exchanged. The "Gray Jeep" as seen on the CJ-3B Page has reddish orange wheels (Sunset Red?) so we can assume that in 1951 there were several different wheel colors depending on the body color. Did the last 3As use just black or white wheels like the later CJs?

From the G503 CJ Technical Knowledge Base comes this information; Engineering Release #5248 Gas Tank Assey. (Painted Black) - Revise Paint Spec. From body Color to black Enamel started on  1/27/49 and issued 2/15/49. This indicates that the early 1949s had body colored fuel tanks. The change to black fuel tanks may have occurred at about the same time as the body serial number tag was eliminated.

Other Minor Changes  Click here for a list of other minor changes that were made to the CJ-3A.

I would like to thank everyone who has helped by providing information. There are far too many people to name. All the people who took the time to provide data about their CJ-3A deserve credit as this couldn't be done without them. Special thanks to Harold West for help with the data and ideas about how to analyze the information.

More data is needed to confirm these findings. Much of this information does not seem to be written down anywhere so your input is very important to document the changes. If you own a CJ-3A, or have any information about the 3As, please fill out the following survey and e-mail it to me. The answers to any of the questions are helpful even if your Jeep has been modified or you can not answer all the questions. Your input can help record the history of the 3A.

All comments are welcome
Bob Westerman
Click here for contact information.

Willys CJ-3A Questions
Please answer the questions as your Jeep was originally equipped.
1. Owner Name
2. What is the model year of the Jeep?
3. What is the original body color?
4. What is the original color of the windshield frame?
5. What is the original color of the wheels?
6. What is the original color of the gas tank?
7. Original soft top color, bow color and window size?
8. Are the hood blocks located equal distance from the hood center seam?
9. Does the tailgate top flange have cutouts? (see photo above)
10. Oil and temperature gauges, dial or lever type? (see photos above)
11. Is the horn button bakelite inside the steering wheel nut or a rubber cover over the nut? The rubber cover is often missing. (see photos above)
12. Does a push rod pedal, floor switch, dash button, or key activate the starter?
13. Are the transfer case shifters approx. the same height or is the front drive lever taller?
14. Does the transmission shifter have a bend in the middle or is it straight with the bend at the bottom?
15. Is the radiator side mount (grille mounted) or bottom mount (frame mounted)?
16. What is the vehicle serial number? (located on the tag screwed to the firewall near the air filter)
17. Is there a body tag, or holes for a tag, below the serial number tag? If so what is the body Number?
18. What is the engine serial number? (stamped on the boss between the water pump and cylinder head)
19. Is there a dimple in the air filter crossover pipe? (see photo above)
20. Does the air filter have a flat or dome shaped top?
21. Generator part #
22. Regulator part #.
23. Distributor part #
24. Starter part #
25. Does the engine block have the late large flange at rear of block? (see illustrations above)
26. What is the engine casting number? (passenger side just above the oil pan)
27. Is the rear axle a model 41 or model 44? (41 round cover, 44 straight sides)
28. Rear driveshaft small diameter (1-1/4") or large diameter (1-3/4")? (The front driveshaft is always 1-1/4" for comparison)
29. Left front fender splash apron bolted to frame? (see photos above)
30. Overall, is the vehicle original or modified on a scale of 1-10 with 10 being original?

Click here for contact information.

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