Technical Early Bronco Axle Question

I've got a 69 Bronco out behind the shop that I've had since the early 70's. It was totaled due to an engine fire with about 10K miles on it and I bought it from the plant that owned it.

In looking at old threads where the large bearing vs small bearing rear axles are discussed, I didn't find anything that said whether there was some relation between the engine and the axle it used. So that's what I'm wondering, Did the v8 ones use the big bearing axle, and the 6 cyl use the small brg one, or was it just random? This one has the remains of a 302 in it.

I'm gonna drag the thing out and strip out the axle for a future project regardless, but was just curious if there's any way to know short of crawling under it.

 

Pretty sure 76-77 was large bearing, all earlier were small.

 

How to positively identify: Small bearing brake backing plates bolts are 3/8 fine thread with 9/16 socket size to take the nuts off. Bronco's. Large bearing brake backing plate bolts are 7/16 fine thread with 11/16 socket size to remove the nuts, found on years 1966 to 1977.
Read this very informative Bronco 9 in. thread:
http://www.jalopyjournal.com/forum/threads/scored-a-9-inch-out-of-an-early-bronco.683875/

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A sma bearing will have 3/8 bolts that hold the bearing in. The large will have 1/2". My 67 is a small, my 70 is the large...

 

The bearing size had nothing to do with the engine that was in the vehicle. It was all about the amount of weight the rear suspension was rated for. The big bearing was for larger weight capacities. The small bearing - lighter. Of course after 40 to 50 years, rear ends due tend to get swapped, so there are exceptions to every rule.

 

The standard suspension had a GVWR of 3900 lb with the small bearing axle. The optional heavy duty suspension had a GVWR of 4700 with overload leafs and the big bearing axle. The vin tag on the glove box door should list the GVWR.
Suspension package was independent of engine choice.

The vin tag will also have the axle code. 2780 lb is small bearing, 3300 lb is big bearing. These codes are for '69. They changed some for different years. The V8 had 3.50 gears standard, 4.11 optional. The six had 4.11 standard, 4.57 optional.

 

Thanks for all the replies. Won't know for sure until I pull it out, but I'm guessing its likely a small bearing 3.50 ratio since the Bronco was originally bought for use by security guards patrolling several miles of roads winding around thru a munitions plant. Not much need there for anything optional in the way of HD suspension or deep axle ratios. After sitting for 40+ yrs, getting it cleaned up and rebuilt as necessary oughta keep me occupied for a while anyway.

 

I disagree I think it had to do with axle spline count on the Bronco rear. I have an early 31 spine Bronco rear and it is big bearing.

 

None of the early ('66-'77) Bronco's had 31 spline from the factory. Must have been upgraded by a previous owner.