Author Topic: '78 C10 Bonanza Rear End Swap  (Read 1796 times)

Offline munztead

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'78 C10 Bonanza Rear End Swap
« on: August 18, 2014, 06:03:57 PM »
Back in Dec, I bought a 78' C10 Bonanza with 5.3 Vortec (LM7) out of a '03 Tahoe, and a 4L60 auto trans. Recently, found the right rear axle seal leaking so decided I'd pull the rear end apart and change the wheel bearings and seals. I removed the differential cover and center pin retaining bolt, but the center pin barely moved. I banged on that thing for about three hours with a 2lb hammer and brass punch, and only managed to move it about 3/4''.
I noticed the pin was pretty beat up where it appeared to ride in the spider gear, so I believe it was run without oil for a while and caused some burs on the pin.
Anyway, I want to replace the rear end, but needed some advice. I found the numbers on the ring gear and it looks like the rear end is actually and 84. Here are the numbers: 15 41 4 84.
My question is, what rear end should I be looking for? Should I stick with the 2.73:1 ratio, or am I free to look at other gears? Also, what years are compatible with this engine and trans?
Just using the truck as a daily driver and to haul my boat.

Thanks everybody!!!

Offline bake74

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Re: '78 C10 Bonanza Rear End Swap
« Reply #1 on: August 18, 2014, 07:30:20 PM »
     Compatibility with engine/trans is what gear ratio you want unless you have some monster engine/trans combo that could put too much torque on the rear end.  Which is not the case.
     So on your C-10 you probably have the 12 bolt, maybe the 10 bolt.  Is it cheaper for you to find a whole rear end or rebuild the one you have ?  As long as the case and axles did not get damaged, the rebuild kits with new gears are common, again it comes down to which you can find and which is cheaper. 
     With a used axle though, you will need to verify that it is in good shape, or you could be rebuilding that one.
#1: The easiest and most obvious solution to any problem is 99% of the time correct.
#2: There is no such thing as impossible, it just takes longer.
  74 k10, 77k10    Tom

Offline munztead

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Re: '78 C10 Bonanza Rear End Swap
« Reply #2 on: August 19, 2014, 09:36:01 AM »
Bake, Thanks for the reply.
I have a 10 bolt, and it's probably going to be cheaper and less time to find a used replacement, and I don't have the equipment to cut out the existing pin. I'm pretty sure the existing axle is bent anyway, and I had planned on replacing the wheel bearings, seals and rebuilding the brakes.

I'm going to remove the dif cover at the salvage yard prior to removal to ensure the center pin is free.

I need to do some research to figure out which gear ratio would be best.
Thanks again!

Offline fitz

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Re: '78 C10 Bonanza Rear End Swap
« Reply #3 on: August 19, 2014, 02:30:13 PM »
With your 4 speed auto I would think about running 3.73's in it.
Like Bake pointed out, its worth looking into rebuilding you rear end.
The newest one you can use is from a 1991 Blazer/Suburban, that's still 23 years old.
I'd guess you could get a Eaton limited slip,3.73 gears, and install kit for around $750. Add  a few hundred for labor, and you have a nice 10 bolt for about $1,000.