I tried looking but came up empty handed. What is the differences between a 12 bolt car rearend vs a 12 bolt truck rearend? The reason I'm asking is because I see the 12 bolt truck rears for alot less money. Wondering what the differences are so I know if its worth picking up or not.
Housing is wider in most applications. Ring gear carrier is different. I once put a 12 passenger car 4:10 r&p into a 12 bolt van rear. It was a challange.
The truck units are cheaper and easier to find. But I was told that the 10 bolt truck units are stronger. I can only tell you that Iv'e never broken the truck 12 bolts that I have had. They did get a bit sloppy after 200K+ miles, but never broken.
I was told that pinion bearings were different size on early ones but that could just be BS as I had no way of checking. I would say that the axles may differ as the bolt pattern would be different.
I am totally naive to all this. What exactly does that mean? I saw 12 bolt truck rear for $50.00 that's what really started my questioning. So educate me as much as possible cause I really don't understand it all.
GM truck rears have 12 spline axels and that limits the availability of limited slips to about none.If you dont need the posi they are fine. The wheel bolt pattern is different or so I seem to remember.I pulled mine in favor of the 9 inch.
If you want to change ratios, better check and see what ratios are available before you decide to buy. Car 12 bolts are so high because of restoration needs and needing proper date codes.
Gears for truck rear are as easy to come by as gears for a car. It depends on your carrier as to what gear you can choose for instance the 6 cylinder '65 Chevy C-10 3 speed with the 12 bolt had a 3.08, the 3.08 carrier will not handle a 4.54 gear. Does that make sense? GM used two different carriers one for air plane gears and the other for tractor gears, they were interchangable in the housings and what you wanted or want is the eaton steel carrier if you are after all out performance and are going to throw the meat to it on a regular basis.
So am I better off just saving my money and buying a car 12 bolt? Any reason I should buy the truck one? Is the expense of making it work not worth it?
Any particular reason you need a 12 bolt? A 8 1/2" 10 bolt has the same sized pinion as a car 12 bolt and is a LOT easier to find parts for. I understand if a it's got to be a 12 bolt, that's what I'm building for my Anglia. They aren't too hard to find in a wrecking yard (out of the bigger cars), but they have to be cut down for a lot of applications.
i agree the 10 bolts are easier to find parts for. i had one in my apache project. that being said...... i ended up swapping it out for a 9 inch. you can probably snag a good running 9 inch for $100 if you look hard enough. i got my 31 spline 3.50 unit for $120. and parts are at a SURPLUS. almost infinite gear ratios, axle shaft options, etc etc etc. and the ease of switching the 3rd member to change gear is insane. the strength is pretty remarkable. its safe to say ill be running a 9 inch in any project i take on now
To be honest, I don't really know. I see everyone installing them in Chevelles etc and thought maybe if I could build one cheap enough I should follow suit. I don't really know all that I am doing so I sometimes have to follow the crowd.
FYI There are type 2 type, type3, and type 4, 2-bolt rears and they all carry different differential ratios. Check on Hemmings.
An article I am reviewing right now says "All original 12-bolt Positraction rearends used 30-spline C-clip or C-type rear axles in varying lengths, depending on the suspension width."
Car and truck 12 bolts are different. Ring gear size is different, axles are different, and covers are different. I do believe the truck rears have a good selection of parts available, but not as strong as car units due to pinion placement.
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