65 C10 differential swap questions

[Bills65C10]

Hello fellow C10 lovers. I am new to this forum and am still learning to navigate the site. I still haven't learned how to even post a picture yet, but I am in need of some educated and experienced advise on which way to go on my truck. I can not afford to learn by trial and error. Besides, I'm want to drive my truck......sooner than later.

So, here goes. I've owned a few C10's in my day, but never one this old. It needs updated in a bad way. I have purchased an entire front suspension from a 83 C10 donor truck. I was able to get everything from the firewall forward. I want to convert it to power disk brakes, power steering and convert to 5 lug. I am going to do a static drop for now, so drop spindles and drop springs are in the works. I have a couple questions at this point of collecting parts.

1) What is the best rear end to run in this truck for a better hwy friendly gear ratio? I want between a 308 and a 355 gear ratio with the limited slip I think. I'm going to put a V8 in it eventually I'm sure, but this 230, 6 will have to work for now. So I'm not worried about not having any low end in it right now.
2) What year differentials are the best to run? I know after 70 they are wider, so how does that effect the "trail" of the truck when I'm using a 83 front suspension? I also would like it to bolt up to the stock trailing arms if possible.

My goal is for this to be somewhat of a daily driver. So,an updated drive train is a must. But I want it to be updated in the smartest most logical way. The expertise and combined knowledge on this forum is invaluable, so all input and advise is greatly appreciated.

Thanks,
Bill

I think I figured out how to post a pic. This my truck before I purchased it, but it still looks the same. I'm still gathering parts at this point.

[PGSigns]

The best way to get to 5 lug and a 3.08 gear would be a 71 or 71 rear. The wider rear was don the match the wider front when the went to disc so you will be fine with it.
Jimmy

[Captainfab]

Welcome to the forum

That is correct. The '71 and '72 12 bolt will be the only direct bolt in differential to your truck that will have the 5 x 5" wheel stud pattern. But the odds of finding one with the gear ratio you want and a posi is going to be very difficult and $$$$$ when you do. The '73 and up will require cutting and welding to install.

Of course you could always install different gears and the conversion axles in your current 12 bolt. A taller tire will help lower the rpm's with your current gear ratio. Have you considered an OD trans?

[Bills65C10]

Originally Posted by Captainfab

Welcome to the forum

That is correct. The '71 and '72 12 bolt will be the only direct bolt in differential to your truck that will have the 5 x 5" wheel stud pattern. But the odds of finding one with the gear ratio you want and a posi is going to be very difficult and $$$$$ when you do. The '73 and up will require cutting and welding to install.

Of course you could always install different gears and the conversion axles in your current 12 bolt. A taller tire will help lower the rpm's with your current gear ratio. Have you considered an OD trans?

Thanks for the reply. I never even thought of a taller tire. That's so simple. I have picked up a set of later model C10 rallies that should help. I had been leaning toward changing axles and ring gear and pinion, but wasn't sure about it not being as wide as the front suspension. Wasn't sure how that changes the geometry of the truck or if it effects tire wear. So, I will have to cut down a 73-87 rear end then? I've also read where people use Camero and Trans Am rear ends. Sorry about the stupid questions, but I really want to get this right the first time.

[Captainfab]

There's no need to go to the expense of narrowing a '73-'87 differential. With a '73-'87 differential the original spring perches and shock mounts need to be cut off and trailing arm mounts welded on at the correct pinion angle. Plus a panhard bar mount needs to be either welded to the passenger side axle tube or an aftermarket one that mounts to the passenger side trailing arm.

[Bills65C10]

Thanks very much Captfab. You wouldn't believe how hard this kind of info is to find. I guess I just wasn't asking the right people. The C10's I've had in the past were all 73-87. I never had one this old, but this 65 is by far my favorite truck. I see you sell adapter plates for the brake booster and steering box, so when I get that far, I'll be back in touch with you.

Thanks again

[chevy_mike]

Lots of good info about axles but another option would be to add an overdrive transmission. For an auto, a 700R4 would work great, a manual a T5 or AX15 swap would be great as well.

Since it sounds like you want a posi and 5 lug axles, the easiest (not cheapest) would be to have a new set of gears, posi unit and 5 lug axles installed into your current housing. This would require zero fab work and most shops who do this work could have it done in a day. If you are not ever looking to install an overdrive transmission, I would recommend 3.08 gears. 3.55 would be perfect with an overdrive.

[Bills65C10]

Thanks for the advice on my rear differential questions. Just to update y'all, I was able to score a 72 C10 rear end. Literally the only one I've seen for sale. It has a 307 gear ratio, but is an open carrier. So, not exactly what I wanted, but close enough. I can always add the LTD slip later.

That being said. The install opened up a whole new set of issues. U-joint, pinion yoke issues, wheel cylinders didn't fit, parking brake differences, etc. The damn trailing arm split right in two. We welded the trailing arm back together and are working through the other issues. So, It's all good. I have the front suspension to install next. It's all back from powder coat and I had the machine shop install new lower ball joints and a-arm bushings. Lots to do!

Thanks again for all your help.

Bill