1937 Rear End Or 1940 Rear End

[John Washburn]

Folks,

Got an easy one for ya. I have a nice 37 LaSalle Coupe, but as always the gears are a bit low for driving on the highways and byways of Colorado.

I just recently was given a full rear end off a 1941 Cadillac that had an automatic transmission.

My simple question is if I take the third member out of the 41 Cadillac can I then pull the 3rd member out of the 37 LaSalle and install the 41 in its place?

I have a spare 37 LaSalle rear end so I can check before I try it for real, but was hoping someone has experience or knowledge in this area.

Thanks

John Washburn
CLC #1067
Elizabeth, Colorado

[JIM CLC # 15000]

07-17-05
John, IM thinking that the gear ratio from the 41 will be very close to the one in the 37. I would be for finding out before doing much work.
Good Luck, Jim

[baxter culver #17184]

Johnny,
This subject has come up on the message board before.  And as I recall that discussion, while the 3rd member will bolt into your differential housing, there the compatibility stops.  The axle splines are different after 1940?  and if you were to suggest also switching the axles to obtain the right (correct) splines, the length of the axle is also different.  So, you could lay both units out on the garage floor, open a Pale Ale, and begin a critical examination process--including careful measurements.  If my memory is correct, shortening/resplining the 41 axles is one possibility.  And there may be more. Perhaps others can weigh in here.

[Harry Scott (4195)]

According the the Master Parts Book, the 37 LaSalle has a 3.77 rear, stamped 377 and the 41 ratio, 3.36, is stamped 6. These stampings are on the bottom of the differential just behind the yoke. It may be easier to adapt the entire 41 housing than to try and swap the differential and axles.

[Brad Ipsen CLC#737]

The 3.77 was not the original ratio in the 37.  This was the replacement 3rd member if you went to your Cadillac dealer in later years.  This is another example of why the Master Parts Catalog is not the authority on authenticity.  I dont know the exact mix of parts required but if a longer axle from 41 and newer can be found it is a lot easier to machine the tapered end shorter than cutting new splines.  A local member here in the north Seattle area has done that to several cars for use of the 3.36 axle in earlier cars.

[John Tozer # 7946]

Brad,

I have a 38 75 series rear end that I have considered for replacement of the (relatively speaking) glass diff that was in the 37 75 series. Again, the rear axles are longer in the 38. I am interested, therefore, in how your friend turns down the tapered end of the axles.


Regards,



John Tozer

[Doug Houston]

One of our guys near me (Fred Swan) has a Cadillac 36-60 coupe that he drives a lot. As with many cars in the pre-1940 era, the axle ratio was in excess of 4:1 (as Brad Ipsen has pointed out). He obtained a 41 Hydra-Matic rear axle (3:36-1) and had the end flanges cut off and the housing shortened. Had the flanges re-welded on, then had the shafts cut to size and the tapers and keyways machined. This gave him a correct rear axle for his car. I believe that the spring pads had to be re-located as well. Hes happy as a lark with it, and its so much easier on the engine. I cost a bit more than a grand, but was well worth it.

It was in 1941 that faster highways appeared and the need for engines to run slower was immediate. For the 41 cars, except the 67 and 75, the standard rear axle ratio was 3.77:1, and the no-cost economy axle became 3.36:1. The 3.36 ratio stayed on for many years after even into the later engines. When Hydra-Matic appeared in 1941, all axles for the H-M models were 3.36:1.

[John Washburn]

Guys,

Thanks, now to figure out what to do. I think I will start with the 41 rear end to see how much work it will be to install in the 37 LaSalle. I need to see if the 16 wheels will work. Will keep you updated.

John Washburn
CLC #1067

[John Tozer # 7946]

Doug,

So from what you say all I am doing in swapping the 38 75 for the 37 75 is getting out of spiral bevel and into hypoid? Doesnt seem much when you consider the work involved - axles too long, spring pads and shock absorber connections in the wrong place, wheel studs different (pressed in with a wheel nut as opposed to a screw in bolt)....

I havent been able to find a ratio on the 38 75 diff yet under all the crap.

....and you dont want to know how much it all cost to get to Australia!

Regards,


John Tozer