Identifying Cast Iron Powerglides, 1950-1962
driveline, flat modulator
You have to be able to read the casting code on the bottom of the transmission. It is a three or four digit number about 3/8" high, starting with a letter. "A" is January to "L" which is December, the next one or two digits are from 1 to 31 and the last digit is from 0 to 9. So K306 would be Nov, 30th, 1956, or a 1957 transmission and D47 would be Apr, 4th, 1957, also a 1957 transmission. Remember, the year breaks around the end of August, early September.
More info: If the L145 is on the bottom of the transmission in letters about 3/8" high, it would decode as Dec. 14, 1955, or a 1956 transmission. It also would have an open driveline and no modulator. If it is apart, the steel clutch plates would all be .070" thick and the frictions would be splined inside instead of the lug style.
When ordering a 1953/1954 overhaul or rebuilding kit, specify if it is a Chevrolet car or a Corvette (The Corvette has a rear metal clad seal since it has an open driveline)
**The 1950-1955 PG's use the early internal lug style friction plates, 1956 and up uses the internal spline style friction plates.
The 1957 is the only PG transmission that has three (3) .090" and two (2) .070" steel clutch plates, all of the others have five (5) .070" steel plates
Identifying 1956 TO 1967 Corvette and Chevrolet Powerglides
(and 1956 to 1962 Shift patterns)
1956-1967 CORVETTE POWERGLIDE TRANSMISSIONS
By Rev. Mike Ernst
Assisted By Pete Vanish
A well-known Corvette parts dealer recently called and said, "I have a customer who needs a 1962 Corvette Powerglide. I have a '62 Powerglide, but how do I show him, or convince him, that it's not just a passenger car version?"
My response: "I don't have the foggiest idea!"
But at the same time that I received the above inquiry, I purchased the infamous "Miss Piggy," a 1962 Corvette with Powerglide (see Corvette Restorer; Summer, 1985). Also, at about the same time, I purchased a collection of 1956-62 parts that filled the inside of a 15-foot travel trailer. Included among those parts was, you guessed it, a 1962 Powerglide that my brother-in-law had taken out of his 1962, and replaced with a four-speed. How could I determine if it was, or was not, a genuine Corvette transmission?
I turned to my 1962 Chevrolet Parts Catalog, etc., and to my most knowledgeable source, Pete Vanish of Eau Claire, Wisconsin. Pete must be credited with doing the major portion of the legwork and research for this article, in determining what makes a Corvette Powerglide different than a passenger car version. The intent of this article is primarily to assist you with visual identification, and on occasion I'll reference the transmission internal parts, but primarily I'll deal with external observations. When it comes to externals, there are great differences between Chevrolet passenger car and Corvette Powerglide usage. And there are also differences in Corvette usage between 1956 and 1967.
1956-1961 Corvette Powerglides
The major difference between Corvette and non-Corvette for the old cast-iron Powerglides used from 1956 through 1961 is readily noticeable - the transmission tailshaft housing extension is different, and bolted to it is a special cast bracket for transmission attachment to the Corvette's frame crossmember. Both the extension and the bracket are difficult to find!
The Corvette extension contained bosses on the left-hand side that were drilled and tapped for mounting the transmission's floor-shifter. Chevrolet passenger car Powerglides were all controlled by a steering column mounted shifter, and their extensions did not use the mounting bosses.
It should be noted, however, that by the 1960's the Powerglide extension service replacement part available from your local dealer (the one you'd buy for a 1957 Bel Air) was, in fact, the Corvette extension containing the cast-in bosses. So there exists the possibility that somewhere out there is a repaired 1955-57 passenger car Powerglide to be found that contains the unique Corvette extension.
There is a slight difference that occurred with this early
Corvette Powerglide extension. One version was used for 1956 through 1960; the other version for 1961 only, which
by calendar 1962 became the only service replacement part for all 1956 through 1961 Corvette applications.
Therefore, we know that they will interchange. The difference is in the speedometer drive gear adapter fitting
that attaches to the extension housing. The early fitting was 2-5/8" in length; the 1961 fitting measured just 1-7/8".
Both extensions will work on any 1956-61 Corvette, but you need to make certain that you also use the correct
length speedometer drive fitting with the corresponding extension. Both of these fittings were also used on various
passenger car and truck Powerglides, so you'll need to consult a 1961 or 1962 parts book, and a junk yard, to
secure what you need.
Another obvious difference is that the automatic transmission fluid filler tube and dipstick are longer on the Corvette Powerglide, than on the passenger car.
1956-1962 Shift Patterns
Several changes occurred with regard to the shift pattern, also indicating possible changes within the Powerglide main case itself.
The shift patterns are shown, as they would appear on the floor console transmission indicator plate. The initial version used in early-1956 had detents at the Park and Reverse positions; while the second version used on later-1956 through early- 1958 added a third detent for the Neutral position. These first two versions used a sequence (front to back) of Reverse, Low, Drive, Neutral and Park.
A third version began in mid-1958, and extended through 1961. Its shift pattern sequence ran (front to back) Low, Drive, Neutral, Reverse, and Park. It used three detents.
The fourth pattern was used for 1962, and is what became known as standard on Powerglide equipped cars. This new pattern was just the opposite of the previous pattern, and its sequence ran (front to back) Park, Reverse, Neutral, Drive, and Low.
Nineteen-Sixty-Two saw the introduction of a new aluminum Powerglide transmission to replace, in most cases, the cast iron job. The aluminum unit was used with the Chevy II four and six cylinder engines, as well as with the 250 and 300 horsepower 327 engines in passenger cars and Corvettes. The cast iron Powerglide continued use with the 235 six cylinder and 283 V-8 passenger car engines.
These aluminum Powerglides were manufactured at Toledo, Ohio, in 1962, and they received a "B" character prefix in the unit identification date of manufacture stamping to indicate Toledo. Initially, these stampings were located on the right front corner of the transmission, covered by the converter cover. During the second week of November, 1961, the stamping location was changed to the right-hand side, on the base of the pan. As illustrated, "B1204N" indicates a Toledo Powerglide manufactured December 4th, during the night shift.
Internally, there were significant differences between the lighter aluminum Powerglides built for the Chevy II's, as opposed to those built for the V-8 engine models. In general, fewer clutch disks and smaller clutch piston areas wouldn't allow these lighter transmissions to survive under the requirements of the larger V-8's.
Externally in 1962, the major difference was that the passenger cars required a tailshaft extension housing that was 9-3/64" long, while the Corvette required an extension that was 11-1/4" long with three cast-in bosses for floor-shifter mounting. This is the primary difference (see photos). If you were to simply lengthen the driveshaft to compensate for the difference in extension length, the shifter still will not mount to the shorter housing, nor would it come through the floor in the correct position. A bit of help is to locate a 1962 Chevy II Powerglide, because it is of the correct extension length (11-1/4" long). The only problem is that the Chevy II Powerglide transmission was not heavy enough internally to handle the power of the Corvette 327 engine.
In 1963, both the Toledo and Cleveland plants were manufacturing aluminum Powerglides; however, only the Toledo plant produced the automatic transmissions used in the Corvette. Now, a Toledo built Powerglide was prefixed with the letter "T" (rather than "B"), so an identification stamping of "T0320N" would be a Toledo Powerglide built March 20th, during the night shift.
The tailshaft extension housing for a 1963 Corvette remained 11-1/4" long, while the passenger car unit remained 9-3/64" long.
There was a part number change from 1962 however, which reflected the fact that the 1963 Corvette Powerglide extension now used five mounting bosses for the shifter. Pete Vanish researched that one and found that the 1963 Series 10 and 20 Chevrolet (and probably GMC) trucks used a Powerglide with a slightly different shifter location, and they are a direct Corvette interchange. So there is your challenge! Find a 1963 10 or 20 Series truck with its original Powerglide. This tailshaft extension can also be found on 1963 Chevy II's and 1964 Chevy II Super Sport models, but again, this transmission is a lighter-duty model.
Incidentally, what I call a direct interchange above (from the 10 or 20 Series truck) fails to take into account that linkages, vacuum modulator lines, neutral safety switch, and the oil filler tube and fluid dipstick are unique to the Corvette, designed specifically to clear the body floor pan shapes. For any model, these become the truly tough parts to locate for a restoration.
Nineteen-Sixty-Four found little change in the external configuration of the Corvette Powerglide transmission. It was very much like the 1963 Corvette except that the output shaft was changed from 16-splines, to 27-splines on a 1964. The 1964 Chevrolet passenger car also changed to the 27-spline configuration, but the Powerglide itself remained the shorter type with the 9-3/64" long tailshaft extension.
Also, the 1964 Powerglide (and possibly later 1963's) used an external oil cooler. Previous Corvettes had always had an excellent power-to-weight ratio that made an oil cooler unnecessary. The engineers apparently changed their minds, and added a cooler consisting of an aluminum heat exchanger mounted in front of the radiator, with fluid lines routed back to the transmission. The use of this cooler extended through 1967 on all Corvette 327 cubic inch engines, while 427 engines with Powerglide used a heat exchanger located inside the tank of the new heavy-duty copper core radiator.
These are the easy ones! In 1965 the new passenger ar body style allowed Chevrolet to equalize transmission output extension lengths at 11-1/4". Since the shifters were bolted to the body floor pan in both the passenger cars and the Corvette, there also is no problem with the bosses for shifter mounting on the extension. So the Powerglide transmission itself (not including linkages, oil filler tube and dipstick) is a direct interchange.
The preceding information hits on the peaks and high points of information available on the Powerglides. If you want greater depth, send me a long #10 envelope with two stamps, and $3 for duplicating costs, for significantly more 1962-1967 Powerglide information with part numbers, hints on visual identification, etc.
I've noticed a renewed increase in Powerglide equipped Corvettes over the past year. I attribute this to three reasons: 1. A number of restorers have finished a body-off restoration on an Fl or heavy duty brakes model, and now that that car's finished, and too nice to use, they're looking for a "driver" for the spouse or themselves. Powerglides tend to be very reliable and not "high-strung." 2. Powerglide Corvettes, if they are still Powerglide equipped, tend to have lived a more stable life than their manual shift counterpart that was more thrashed around by a number of different owners. 3. In 1962, for example, there were roughly only 1,500 Powerglide Corvettes produced. How many remain? 300? Less? Those older cars were much more easily converted from Powerglide to a four speed than the other way around, and so many were.
Editor's Note: Mike's preceding story does not include the 1953-1955 Corvette Powerglide transmissions. In formation concerning the Powerglides used in 1953-55 six cylinder Corvettes was published in the Winter 1982 issue of The Corvette Restorer Magazine. For the 1955 Corvette V-8 Powerglide it should be mentioned that the output shaft extension housing is the same as that of 1955 through 1957 Chevrolet passenger cars, as the 1955 Corvette floor-shifter was mounted to the under-body and therefore did not require the shifter mounting bosses on the extensions as used on 1956 and later Powerglide Corvettes.