VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Rear end ratio stamping

Where on the '37 differential case is the gear ratio stamping? The book isn't clear, but on a unit I just bought today, supposedly from a '37 Master with the 3.7 gears, there are markings on the upper right side of unit. The numbers include the Chev. part number, a number 225, with two circles having diagonal lines through each circle (like the no smoking symbol) before and after the 225 number, a letter S or possibly 2 nearby, and a raised area with the number 10 stamped. My service manual says the 3.7 ratio rear end number on the case would have a C prefix before the number. I am I looking in the right place? This rear end came from a car having a straight axle, which I did buy too for possible conversion of my MD from the troublesome IFS knee actions. I wonder now (I know, check the numbers before you buy) if this car was a Master Deluxe converted to the straight axle long ago. It had only a single taillamp, which was a Master signature, I think. So, after long commentary, I ask again, am I looking at the right place for this C prefix and number -- any help, thanks. e-mail jleman@newsletterbureau.com

My "Chevrolet 1937 Specifications" states the following: Rear Axle Serial Numbers & Prefix, (numbers and Locations) Numerical sequence #1001 and up, stamped in casting on top forward end of differential carrier. Master Deluxe GA 4.222:1 ratio does not have a prefix mark. Master GB 3.727:1 ratio has a prefix C.

I assume you purchased the complete axle assembly. You can count the ratio by, "holding one brake drum/axle shaft from turning", mark and turn the opposite brake drum/axle shaft two full turns while counting the number of turns on the drive shaft (input end). It should be easy to determine 3.7 turns vs 4.2 turns. You'll need some help of course.

Another method would be if you could count the number of teeth on the ring gear and on the pinion gear provided the unit is apart. The 4.222 axle will have 38 teeth on the ring gear and 9 teeth on the pinion gear while the 3.727 axle will have 41 teeth on the ring gear and 11 teeth on the pinion gear.

Jim,Congratulations on your find.The Master will have a thicker steering wheel and smaller horn button and lack some of the chrome trim that your Master DeLuxe has on the dash.And of course it will not have a Starterator.The only sure way will be to remove the rear cover and count teeth.(and inspect for wear and rust) Good Luck......also if you get the car remove the speedo gears to correct the error due to gear change...Also I believe the C will be a stamped letter not raised.

Thanks gentlemen! My heart sinks though, as Chev Nut's response brought shudders to me -- the car was largely apart. I did see the steering wheel and it looked very much like the one in my Master Deluxe. The dash had been stripped for hot rod. The engine was a 235, so the foot-operated starter mechanisms were gone. I'll count the wheel turns tonight to get a better idea, but lacking the stamping indication and Chev Nuts observation about the steering wheel.....Perhaps I'm back in the market.

Jim, I think if it were my rear end I would do as Chevy Nut suggested, pull the inspection cover and count the teeth, You should drain the grease and clean the differential (third member) with naptha or kerosene any way, try to see if there is any metal particles in the grease and bottom of the housing. Do it while it isn't on the car and you will know for sure what you have, and go back with a new cover gasket, if you can't find a Tailor made one they aren't that hard to cut useing the cover and the face of the housing for a pattern. any how that is my opinion.

Gentlemen -- Pulled the cover from the new rear end mentioned at the start of this string and thanks to Chevy Nut's data, counted the ring gear teeth and yes sir re bob -- 41 teeth. I have a 3.7 rear end after all. Thank you everyone for important input. I've used this forum many times for help, advice and troubleshooting. Together we always seem to solve one another's concerns. See you on the road!

oopss -- it was Oldie's teeth data that I used. Thanks. And thanks again to all.

Well ,that is correct if you also counted 11 teeth on the pinion gear in addition to the 41 on the ring gear. ( 41/11) =3.7272....... and did the inspection look like you have a keeper?
no large hunks of metal riding in the bottom? no really sharp , jagged edges on the gears? I have come to believe that these old torque tube rear ends are very durable and rugged when they are maintained well and kept lubed. The older ones sometimes suffered from the rivets comeing loose that hold the ring gear on. (that often caused a lot of excitement!)

Didn't count the pinion teeth, no. However, after scrapping away 60+ years of crud from the case, etc, did discover the stamping number with the C prefix (was on the most forward snout of case, just before torque tube) the factory indication for the 3.7 rear. The gears were clean, no metal in the gear oil, oil wasn't burned nor did it appear to contain any water. It also has new brakes shoes, wheel cylinders, springs, etc., put on by the prior owner before he decided to go the hot rod route.