A 1940- 1941 Buick question regarding rear end gearing.

[Brooklyn Beer]

Can someone tell me if changing the gears in the rear end of a 40-41 Buick is any different then any other year? A car was presented to me in a trade offer and the car was delivered new to a very , VERY, hilly and mountainous area. It seems the owner had the gearing changed for that hilly area in order to get up and down the inclines better. Car has 15 inch tire right now and combined with the gears, it is really turning some higher then normal RPMS for sure.  It is pretty flat here so going back to factory specs (or even a little more highway friendly ratio) would be on the ticket for sure.  So would like to know how big a job it is as the cost could be a deal breaker.  And who has the gears for sale? 

[Ben Bruce aka First Born]

On the '50 on the bottom of the rear end is a number above another that if gears have not been changed will indicate the ratio. Bet yours has that as well.

 

  Rear end gears will interchange from 1940 through 1955.  I installed a 1955  3.36/1 in my 1950.  A bit of work, but doable .  Not much cost except for the gears.  Willie [ Old Tank} has a tutorial on his website.

 

 Going from the original 4.1 to the 3.36 dropped the third gear rpm's by about 650-700.   70 mph is 2700 rpm. 

 

  Ben

[Matt Harwood]

What year & series is the car? There were always optional gear ratios available. For instance, the '41 Special came with 4.44s as standard, but you could get 4.10s as an option and it sounds like the car you're talking about has the 4.44s. With the 4.44s, it will spin pretty fast at highway speeds with those gears. I've found 3.90s to be a good compromise on the small series cars, but taller gears like the 3.36s Ben mentions are good for the highway, although you'll lose some off-the-line punch and around-town usability. A fair trade-off, I'd say. 

 

You can determine what gears you have by removing the rear cover and looking at the gear ratio stamped on the pinion gear.

 

Changing them isn't as easy as most cars because of the torque tube. Most guys will change the pumpkin and Ben is correct in that the pumpkins are mostly interchangeable between the years. However, pulling the torque tube out and reinstalling it properly is a BIG job. Many have done it and it's not a bad solution, but it's not really a quick and easy project. 

[gdmn852]

One of the hardest things when I changed the rear gear set on my 49 was getting the sleeve that connected the pinion to driveshaft apart,there is a difference between the 48 to later differentials but the whole carrier will interchange.

[gdmn852]

Made a mistake, picture is actually assembling it.If you look closely there is a difference between the two, later carrier is larger due to bearings at pionion area.

[gdmn852]

Later gear set is the red color 

[Brooklyn Beer]

So say a shop was given this job to do. price estimate being it looks time intensive ?

 

[jackofalltrades70]

I removed the rear end and did the gear change in around 5 hours. I have a 47 Roadmaster convertible.  Used the gears from a 54 Special I believe.

 

Matt

[jackofalltrades70]

As you can see, these are the different gear sets.  The original is stamped 41  10.   Take 41 and divide it by 10.  4.10 gears

likewise, the one I put in, is a 43  12.  Take 43 and divide it by 12.  3.58 gears.

 

Matt