VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Rear end gear ratios on 1939 Chevy

Hello,
I am new here and would like to ask a question. Why do 1939 Chevrolet cars have two different qear ratio's for the rear end. I did a search and found out that some of the members have switched out the rear ends for the 3.73 that came in the master 85's. My question is "Why did Chevrolet make two different gear ratio's on such similiar models?" I have a 39 four door Master 85 that had the rear end replaced with a MD many years ago. I have not driven the car for many years but would now like to get it going. Should I look for the original gear ratio that came with the car? Thanks for your replys.

The engineering features manual states that the reason is to give the car greater fuel economy. Since the Master model was the low cost version that would make sense, if you can't afford the higher priced Master Deluxe, you probably can't afford the extra gas. Thus the gear ratio seems to be a way to sell cars to borderline buyers.

Brian

Hi Gabes,
It's up to you, but I would recommend using the higher ratio rearend gears. You'll enjoy the car more and the engine won't work as hard either trying to maintain 55 mph.
I just replaced my 4:11 gears with 3:50's in my '32 and I cannot tell you how much more enjoyable the car is. Starting out in first gear is no problem since first is so low, and the car pulls much harder now in second gear - if that makes sense. High gear is a dream. Now 55 mph doesn't even seem to strain the engine at all. FYI, I bought my 3:50 gears from Larry Jackson.
Anyway, the 4:11's are just too low for today's driving.
Just my opinion.
Jim

The Master DeLuxe had 4.22 gears for "maximum performance"
The Master 85 had 3.73 for maximum economy.
At 60 MPH the M.D. engine was running at 3145 MPH and the M. 85 2766 RPM.
After changing to the 3.73 ratio my '39 will cruise at 65 MPH and fuel milage increased about 1 to 2 MPG at high speed.
The M. 85 had larger cooling fins in the radiator and a larger fan blade (more noisy) to compensate for the engine pulling "harder" under load.My car does fine with the M.D. cooling.Power on hills will be reduced but well worth the change for todays driving conditions.

Is Larry Jackson a vendor and will 3:50 fit my 38 M? Thanks.

The 3.50 gears that Larry Jackson makes fits 1930-32 only.

:( :( :(

I agree :( thanks.

Thanks to everyone for the answers. I guess I will try to find the Master 85 rear gears. I guess I am not in any hurry, but just wait until some hot rodder decides to not use the original drive train. Just like I did 25 years ago with another 39 that I had. I wish I still had the parts from 39's that I trashed many years ago.

The gears from a 1937-39 Straight front axle cars will all work

I have a excellent set of 3:73 gears in the parts for sale. Thanks Ross

I have the whole rear end off of a 40 chevy (don't know if M or MD) that I would let you have if you come get it. It will need bearings as it sat outside. It's the complete housing & torque tube with wheels. I don't know the gear ratio, it came with my car when I bought it.

TO PUT 3.50 GEARS IN A 39 I USED A 53 53 POWERGLIDE RING AND PINION AND TOOK THE SPLINED PART OF THE 53 54 DRIVE SHAFT AND PUT IT IN THE 39 THEY WORKED GREAT.

The 39 has a propellor shaft lists at 59 1/4" overall length with 10 splines in the 27-54 parts book. It doesn't match the length of the 54' propellor shaft in the parts book?? What do you mean by the splined part?
Mike

MIKE THE SPLINED PART OF THE 54 DRIVESHAFT
YOU REMOVE AND PUT IN THE 39 SHAFT. THIS IS THE REAR OF THE SHAFT WHERE THE PINION GEAR GOES.