Hello I recently acquired a 1962 C20 that, to my surprise has trailing arms and coil springs in the rear (and torsion bars up front). Somewhere along the line someone replaced the 3-speed transmission with an 'old process' granny low four speed. Even more recently the original motor was replaced with a GM 'crate motor' 350. My current concern is that the rearend is much too low geared. It is low geared enough that I can take off in third easily, and the motor is winding it's little heart out at 55mph. My question is two-fold. I was hoping to find out about any bolt-in complete rear axle swaps..interchanges. Where I can merely unbolt the old, and bolt in the new. I am capable of swapping yokes, but am not equipped to deal with altering spring perches, etc. The next part of this question is how to identify a spicer, from a dana, etc. I've been around these old trucks for a lot of years but that is one thing I never needed to know. Oh...one more thing...I have a 1972 Open Road motorhome chassis that has a 350/TH400 and dually rear axle. Is it possible that the third member will swap into my housing? Thoughts? Thank you ahead of time.
Some people will tell you that slow is good — but I’m here to tell you that fast is better.
You probably have a 3.90 ratio. A 3.38 was available, so a bolt-in will be "possible". Correction in next post from Fred. Use the search function on here to read all kinds of info on this issue. Swapping dropouts would be nice and easy. If not found, then consider 1965 and above for non dropout/modern diff.
It's no surprise, they had torsion bar till 63. Coil rear up into the 70's. You don't need to identify Spicer from Dana. They are the same company and the axles are called corporate now. GM is the "corporation".
Complete diff swap: You need to decide on what ratio you want 3.08-3.73 or what. Your basic task is the width. Find a differential width that is close and has the ratio you want from a donor Chevy or GMC (Dana 44). A 10 bolt or a 12 bolt. You may have to find someone who can do perches/trailing arm mod. Leaf springs were an option about 1971 or so. You may run into one of those and modify to fit. Of course you will need to find a 3/4T so that the lugs are same as front.
Last edited by bartamos; 07/28/20187:02 PM.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
A 62 C-20 (3/4 Ton / 8 lug) would have the "corporate" Eaton HO52/HO72 rear end which has a 4.57:1 ratio. The only known alternative without serious modifications to just about everything connected to the rear housing on this series truck would be the 4.10:1 rear end from a 67-72 truck that came with an auto trans. It is a bolt in 3rd member. As with everything that has a lot of interest, they have become relatively scarce and of course priced accordingly. There is extensive discussion about this subject in this forum. There is a current thread on this very issue. Fred
1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes 1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes 2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans 1947 Willys CJ2A w/F-Head engine
Your truck has had a lot of changes over the years (engine, transmission, double radiator, ?) so I wouldn't be surprised to find that the rear end was changed too. Follow 3B's advice and post some pictures.
A 62 C-20 (3/4 Ton / 8 lug) would have the "corporate" Eaton HO52/HO72 rear end which has a 4.57:1 ratio. The only known alternative without serious modifications to just about everything connected to the rear housing on this series truck would be the 4.10:1 rear end from a 67-72 truck that came with an auto trans. It is a bolt in 3rd member. As with everything that has a lot of interest, they have become relatively scarce and of course priced accordingly. There is extensive discussion about this subject in this forum. There is a current thread on this very issue. Fred
If you can find a 4.10 gear from another HO52 the swap is easy. Pull the axles, disconnect the driveshaft and swap out the pumpkin. A better swap is to locate a 14 bolt corporate that is the same width between the drum faces, so your tires will fit in the fenders. Most of these had 4.10 gears, but there are many with 3.90 and 3.73 gears, which I would look for. Best to find a junkyard that specializes in Chevy trucks. They will be a big help, especially if you can talk with an old guy. You will need to weld on your spring perches. And if needed, the housing can be narrowed by cutting and welding.
