Hello ! I have a factory 1949 3600. I need to change the rear diff so I can go faster than 2 miles per hour. I was told the truck has Farm Gears. Any suggestions would be great ,!
What rear end do you have? Post stamping numbers if you don't know.
What transmission and engine do you have?
1950 Chevrolet 3100 (Ol' Roy)
1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)
I have a 1950 216, 3spd, 4:11 rear end and I have no problem reaching 65mph. I can cruise on the interstate comfortably at 55-60 without undue stress on the engine.
When the truck came to me the owner said he couldn't go faster than 30mph and blamed it on the "low gearing." Of course it turned out that the clutch was slipping badly at about 30 mph and on any hill.
It also had crappy 15" wheels on it with tires of too small diameter. They were also too wide. You could barely steer it.
Installing a new clutch and original size 16" wheels an large diameter tires made getting up to 60mph easy as pie.
If your truck can't reach 55-65mph, you have problems other than a low geared rear end.
1950 Chevrolet 3100 (Ol' Roy)
1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)
But Otto's truck is a 1/2 ton with a 4.11 rear gear while 49.3600 is a 3/4 ton probably with 4.57 gears. Don't know what his rear tire diameter is, but if you assume 30 inches it would take 3072 RPM to get it to 60 MPH. Not impossible, but certainly a scary engine speed for someone who isn't deaf, young or used to abusing his 70+ year old engine.
Last edited by Bill Hanlon; 08/24/202312:17 AM.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
OOps, sorry. Too many different trucks on here. My mistake. Seems like there was a '49 3100 that needed something.
1950 Chevrolet 3100 (Ol' Roy)
1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)
Standard 3600 would be a 4.56 rear axle ratio (mine was), but I bleieve there was an optional rear end that was even higher numerical ratio (5.??) that he may have.
Regardless the tire size has a significant influence so it will be helpful to hear what he actually has.
A kid raised on Hotwheels, Matchbox and Tonka cannot be reasonably expected to own only one vehicle as an adult.
1949 Chevrolet 3804 In the Legacy Gallery | In the Gallery Forum 1973 IH 1310 Dump 1963 Kaiser M38A1 2001 International/AmTran RE3000 "Skoolie" 2014 Ford E-350 4x4 (Quigley)
My Apologies to everyone trying to help. The truck is a 4 speed and the tires are 7.00-15. I was told that the truck was built with Farm Gears from the factory ?
Standard 3600 would be a 4.56 rear axle ratio (mine was), but I bleieve there was an optional rear end that was even higher numerical ratio (5.??) that he may have.
Regardless the tire size has a significant influence so it will be helpful to hear what he actually has.
Correct, in 1949 there was an "RPO 3600" that had 5.14 ratio rear axle gears. Here's a page from the 1949 Vehicle Info Kit with that stuff highlighted. It's possible that people referred to the 5.14 ratio as "Farm Gears".
It should be a fairly simple swap to the more common 4.56 gears.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
My 47 3600 has the 4:56 rear end. It is in very good condition so I opted to put a Gear Vendors overdrive behind my SM420. It gives me a 3.56: 1 final ratio. My 235 rpm is very comfortable 2400 at 60 mph. I have the original 8 bolt 15" rims.
What is the outside diameter of your tires? 7.00x15 sounds like they would be pretty small compared to the original making your engine vs. vehicle speed issue worse. My '50 3600 tire size is roughtly a 34.5" outside diameter. If your tires are closer to 30" your engine speed will be more than 10% higher for the same vehicle speed.
