37-40 LaSalle rear axle gear ratios

[rg171352]

Did all of the rear ends found in 37-40 lasalles have the same gear ratios?  Were there any cadillac rear ends that would interchange with the LaSalle units that had different fear sets?

Thank you for your help!

[Jay Friedman]

According to my 1935-55 Master Part list, all 37-40 LaSalles had a rear axle gear ratio of 3.77:1.

[Bob Hoffmann CLC#96]

Jay,
 Sorry, but you are incorrect. They came with 3,92 rear ends. Replacement rear ends made in 41 did have 3.77 rear ends. They are rare birds.
 Bob

[Jay Friedman]

Bob,

Since my parts book was published in 1955, I guess by that time Cadillac was only supplying replacement 3.77 rear ends. 

Jay

[jackworstell]

Our 1937  Seies 60...which I would think would be about the same as the series 40
came with a 3.69 ratio, Terrible on a modern highway

We switched "pigs" to a 3.07 out of an early 1950s Cadillac
( optional with the Hydramatic }
Had to switch axles to 1940s Cadillac ( used for maybe 10 years )
This to match splines of the axle with that of the 3.07 pig.

Axles had to be shortened ...about 1 1/2" each

A bit of a project...but the car nows travels at 65mph just fine

Jack Worstell

[jackworstell]

...the 3.07 pig was a snug fit...had to do a touch of grinding
on the differential housing....but it slipped in OK

Jack Worstell

[Bob Hoffmann CLC#96]

Jack,
 Don't you fid that the 3:07 is a little tall when starting out??
 Bob

[rg171352]

Thank you all for your replies.  How would I be able to determine what gear ratio I have?  Where would I potentially find a 3.77 rear if I wanted to go that route?

[LaSalle5019]

Just a comment....my 1939 LaSalle with the 3.92:1 rear axle ratio will run all day at 65 mph. The engine is turning just shy of 2700 rpm. I'll take it down the rural highways around me at 70 mph occasionally but at those speeds I would be more concerned about investing in tires (like Diamondback Auburn radials), brakes, steering, suspension, good driveline balance, etc.

[Brad Ipsen CLC #737]

Keep in mind also that a 39/40 with a 3.92 is about the same as a 41 with a 3.77.  15 inch wheels in the 41 and 16 inch in the 39/40.   

[jackworstell]

Bob Hoffman

Bob...no it turned out OK ,   We were concerned about that but
in the end we find the 3.07 OK

WE did replace the heads with 1940s heads so we have higher compression
ratio.  And we switched the distributor to one with vacuum advance
( also 1940s version)
So the end result is maybe 150hp instead of the original
135hp.  This helped offset any "sluggishness"  due
to switch from 3,69 to 3.07

Jack Worstell