I'm considering swapping out my 3.90 gears in my 56 Chev P/U for a set that would allow me to get in the passing lane to actually pass someone. However, the ones that are out there are identified by a couple of different measurements - the number of bolts and a diametric measurement. Does the number of bolts refer to the differential cover or the number of bolts actually holding down the ring gear? And what is the other measurement? I've seen 7.5, 8.5, 8.6 and others. Also, there are apparently small and large spline shafts that come into play, as well. And what would the right measurements be for my 56 P/U? Just looking to pick the brain of those of you who've been doing this longer than I... Thanks for your wisdom!
stock 56 rears I just completed a custom build of my stock rearend in my 56 1/2ton chevy. And have learned alot about these rears. If you are going to change the ring & pinion in the STOCK rearend on a 56 chevy 1/2ton pickup....there is only one choose, and that is a 3.38 to 1 ring and pinion set. That are a couple of places to purchase...Classic Parts, Tom's Differentials, Yukon Gears and maybe a couple of other venders I'm not aware of. The rear end in the 55.2, 56 and 57 is unique, it has 10 bolts holding the carrier in the housing and the cover is also 10 bolts, but the ring gear is held on with 12 bolts. GM calls it a model H033. It is similiar to the 55 thru ??63?? passenger car rearend, but it is not the same. Most or the internal parts, spider & side gears are obsolete from GM. The axle and pinion are both 17 splined. U-joint yoke is the same as the passenger car item. Tom's Differentials is a wealth of information. "tomsdifferentials.com" Ask Tom about the 30 spline replacement axles and late model spider/side gears. Good Luck Just Plain Ray
Ray, thanks for the info i would rather have a 3.38 then 3.90's.Do you know about the 3/4 tons and 1 tons rears?I was told you are out of luck with the chevys but the gmcs you can get sets for. Cliff
Thanks for the thorough reply. One more question that I think you may have answered, but here goes... I have found a 3.3.6 gear set from a 62 Impala. What are the chances that I can do a swap of the pumpkin and use my stock drive shaft and axles? Thanks, Jon
I think the short answer is it won't fit. The truck axleshafts are retained with a C-clip inside the differential, the axle bearings are flat rollers. The car axleshafts are ball bearings which have a retaining plate located at the brake backing plate and do not use the C-clips. I don't think the car differential and the C-clips will work together. And the truck axle housing will not accommodate the car ball bearings and the associated retaining plates. As far a 3/4 and 1 ton trucks go I am totally clueless. I've only "studied" the 1/2 ton Chevys as thats what I own. Regards, Ray
Okay, this makes sense. I don't like the answer, but it makes sense. Digging a little deeper... why couldn't I just swap out the ring and pinion gears between the two rear ends? Are the pinion shaft bearings the same? Any other issues that would be show-stoppers?
