New to Forum- what rear diff in my 63 C10?

[63frankintruck]

Really excited about this forum. My first post. I just purchased a 63 long bed C10. Have do some pokinhg around the site but did not find a section for rear differential set swaps.
Read about 70 model not fitting, but 71 & 72 fitting but wider.
Can anyone clear all this up?
Also I was thinking it maybe an option to rebuild my original rear. If so(could I add a posi to it)? Currently the truck has 79 model 350 w/ powerglide. (Revs very high at 55 or 60 mph. 😒

[wilbur46]

Look through the FAQs
There is a list of codes for the ratios.
The codes are on the passengers side axle tube in the front.
Wire brush em, look em up.
W

[jchav62]

I think 3:73 was the most common ratio, some have a 4:10. As far as I know, they are pretty similar from 63-70...12 bolt. '71-'72 is a bolt on option if you are converting from 6 to 5 lug. Plenty of knowledgeable people on here. Someone will definitely chime in...

Welcome to the forums!!

JC62

[Captainfab]

Welcome to the forum

Your '63 C10 will have a 12 bolt with likely 3.73 gears. The best way to know what gears you have is to simply pull the rear cover and have a look. The tooth count of both the ring and pinion will be stamped into the edge of the ring gear. Then you will klow exactly what gears you have and what the condition is of the gears in your differential. Plus the differential is one of the most neglected parts of a vehicle. So more than likely the oil needs changed. You'll just need a cover gasket and 2qts of 75W90 gear oil.

The truck 12 bolt was used from '63-'82. The '63 to early '70 12 bolts are 62" wide. The late '70 to '82 12 bolts are 73.5" wide. The '63 and '64 12 bolts had 17 spline axles and spider gears and a longer panhard bar than the '65-'72's. The spider gears will need to be changed if upgrading to 5 x 5" conversion axles. The '71-'82 12 bolts will have the 5 x 5" wheel stud pattern.

[63frankintruck]

Thanks for all the replys! Will try to check out rear this weekend. Still wondering though… can I make my rear differential a posi? Guess I better make sure what differential I have first. Will let you all know As soon as I find out

[Captainfab]

Yes you can install a posi carrier. However you will then have to change your axles to 30 spline axles since that is all that is available in a aftermarket posi carrier. The 17 spline axles are obsolete and were discontinued long ago.

[63frankintruck]

Here's some pics of my rear differential. Can you guys help me ID what gears these are?