Thread: what rear end do I have

Tweet

Hi gang, We have a 1955 Chevy Bel Air. Don't know what rear end or the ratio it is. Please help! It is a 10 bolt, casting #3725888 E126GM7, stamped #BB0514. Hope someone can help. As always - THANKS!

If there's not a tag on it you'll need to raise the rear wheels off the ground, mark reference points on the driveshaft and tire, and spin the wheel/tire while counting the revolutions of the driveshaft. One turn of the tire will yield some odd number of turns on the driveshaft, like 3 3/4 would tell you it's a 3.73 to one. I'd look at doing ten turns of the tire to yield the most accurate numbers - ten turns giving 37 1/3 turns tells you 3.73, 41 and change tells you 4.11's, or almost 31 points to 3.08's.

Be aware that the '55 rear isn't as strong as the '57 and later ones. The pinion shaft is smaller and easier to break. Of course, in over half a century, the original pumpkin might have been swapped out.

The internet search is a friend.............
You threw me a curve saying "10 bolt". In GM speak that usually refers to the rear ends that started production in '65 and went on for a couple decades. It refers to the 10 bolts that hold on the back cover of the differential housing. Your '55 originally has an enclosed/welded housing with a drop in carrier (the "pumpkin"), which is probably where you got those numbers, though they might have 10 bolts holding the carrier in, they're not what most people mean when they say "10 bolt", at least in GM rear end speak.

All that out of the way, looks like the BB decodes to a 3.36 ratio. But as suggested above, over the years changes could happen so it's worth a manual check.