McDar

Differential interchange

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How many years will interchange with a 40 Series 26 3rd member. Is there anything online that is similar to a Hollander's interchange manual? Replaced the transmission and 39-54 had many interchangeable parts but don't know if rear center sections are also like this. The trans was like this and by the terrible sound I'd bet the rear is the same.

post-57926-143138951654_thumb.jpg

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1) All 3 speed transmissions from 1939 thru 1955 can be installed in your 1940 Pontiac.

In 1949 the mainshaft / tail housing was lengthened so, you obviously need to use a '39 - '48 mainshaft.

In 1947 a felt seal was used on the input / main drive gear shaft which replaced the ''reverse screw'' oil slinger machined

onto the earlier main drive gears. >> NOTE: The Bell Housing was also changed in 1947 WHICH MEANS that an 'earlier' shaft (with the

screw) may be used in a later application because a felt seal can be slipped over the reverse screw HOWEVER, to PROPERLY install

a ''later'' (felt-style) shaft in an earlier vehicle a 1947 - 1954 bell-housing must be used.

2) For the differential: 1939 thru 1955 3rd members can be interchanged from vehicle to vehicle. '39 thru '46 units are designed

with a different pinion bearing arrangement than are the '47-'55 units. This means that the ring & pinion sets cannot be interchanged

between the 2 designs but does not prevent the use of the complete 3rd member ass'y from one car to another.

3) FYI:

The smaller series Buicks and 'earlier' Oldsmobile transmissions are also the same design and can be used with the appropriate use

of main drive gears and mainshafts (Buick used a 'torque tube').

Also, the rear-end 3rd member from Olds in the '40's can be used in a Pontiac.

~~~~~~~~~~~~~~Hope this is helpful. ~~~~~~~~~~~~~~~

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if you're wanting to change the complete rear axle and differential assembly, 1941 to 1948 are the same, if you just want to change the 3rd member center pumpkin, 1939 to 1948 are the same. charles coker, 1953 pontiac tech advisor.

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2) For the differential: 1939 thru 1955 3rd members can be interchanged from vehicle to vehicle. '39 thru '46 units are designed

with a different pinion bearing arrangement than are the '47-'55 units. This means that the ring & pinion sets cannot be interchanged

between the 2 designs but does not prevent the use of the complete 3rd member ass'y from one car to another.

~~~~~~~~~~~~~~Hope this is helpful. ~~~~~~~~~~~~~~~

Does that mean 1956 third members are a stand alone unit? , as 57 - 64 are the same.

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hi don, there is no major difference in the pontiac differential from 1949 to 1956 other than rear brake related parts. i know in 1956 the pontiac dual range hydra-matic got a different driveshaft yoke. getting back to the differential, why bill didn't cover 1956 i don't know, might have just been a typo or overlooked. charles coker, 1953 pontiac tech advisor.

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Yes,

In '49 -'52 the axles housing is narrower (shorter-left to right). (I don't know how '53-'54 or'55 compare to the 'others').

now bill, that is not correct, according to pontiac's printed 1946 to 1957 pontiac specifications manual, 1949 to 1956 pontiac differential housing, rear axles, wheels are all identical, resulting in the having the identical rear track of 59.0 inches.

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