Just pulled the rear axle out of my 49 GMC 250 and was looking for some info before I turn any more wrenches. Apologies if this gets wordy or if my info is incorrect:
At this time, I am considering looking for a 3/4 ton axle from the same year and swapping it out. My reasons for doing this are: -Might be easier to find brake parts? -I am not sure, but heard somewhere that 3/4 ton rear brakes are smaller 12" drums, which might help with wheel options later on. -Slightly better rear end ratio than the 5.13 I am running now
If I keep the original axle with original brakes, am I going to be able to find a stock-looking wheel that fits over those drums? I would rather not use the original rims for safety sake.
It has been hard to find any info on this, so I am hoping someone here might shed some light. My goal is a fairly stock truck. I don't need it fast or fancy. Just want an old girl I can putt around in. Thanks in advance!
1951 GMC Maintenance Manual shows rear brakes are 12"x2" on 3/4 ton (150 model) and 14"x2.5" on 1 ton (250 model). Same book shows 4.57:1 as standard rear gear ratio for the 3/4 ton rear axle, but a 5.14:1 ratio (same as in your 1 ton) was available as an option, so be sure to verify the ratio before you put any money or time into a 3/4 ton axle.
I understand that brake drums for either axle are pretty scarce. All early '47 thru '52 3/4 ton rear brakes use the same drum.
'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.
I’m not sure a stock 3/4 ton axle will help with most of what the goals are The ratio isn’t much better The brake drums are just as impossible to find old decent ones - not reproduced Many more modern rims like from fords will clear the large 14 inch stock drum on a 1 ton, same bolt pattern The offset is the bigger problem with the front tie-rod rubbing the inside of the rim -s
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)
Bigger tires will help the RPM situation. I've run 255/85x16 tires on the rear and those are about the same rolled radius as the original 7.50x17. Zero offset alloy wheels are the ticket here or Ford steelies. There are also larger 19.5 tires that may have a lower revs per mile. Those wheels can be had with the 8 on 6.6 bolt pattern. You'd have to look around. Tire rack used to have a good source of information like that but they were bought out by Discount Tire a couple of years ago and some things disappeared from their website.
If your drums are not out of spec you should have no trouble selling them to defray some of the cost of a modern 14-bolt axle if you decide to go that route. Also bendix brakes can be found to fit the HO72 axle that you have. Big tires with a 4.57 final ratio is a reasonable compromise. I found one out of a 67 3/4 ton manual trans model.
1951 3800 1-ton "Earning its keep from the get-go" In the DITY Gallery 1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.
Is it possible to buy a taller (numerically lower) ring and pinion for this axle? I'm asking because I think I will inherit one with the straight six screaming at 52mph rear gears. Not sure what Great Uncle Luke was thinking when he RPO'd that combination in a '65 C20.. but anyway.. I think a set in the vicinity of 3.73:1 or so would be much nicer.
Gear sets are NLA as far as I know unless you got lucky and found an NOS set. The lowest numerically that were offered were 4.10:1. Before you tear anything apart count the axle revs compared to the drive shaft revs. if you hold one axle still you count the DS rotations and multiply by two and that will give you the axle ratio. Look on the inside of the glovebox door of the donor truck to find the RPO code for the axle. I don't know what that is for a '65 C20 but someone here does.
From the factory the 4.10 HO52 was standard on Chev 3/4 tons equipped with 327 V8 and auto trans through '72. Otherwise it was an RPO. I believe GMCs of that era did not use the Eaton HO52 axle
1951 3800 1-ton "Earning its keep from the get-go" In the DITY Gallery 1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.
For those interested, the 1965 C20 "4.11" optional rear axle is listed as RPO "H04" as noted in the extract pic from the 1965 Chevrolet Truck Data PDF.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
hold one axle still you count the DS rotations and multiply by two and that will give you the axle ratio
Isn't it divide by 2?
'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.
