small GM 14-bolt


Junior Member
I have an '83 k10 shortbox mounted on a '79 drivetrain. My problem is this:

My stock 10&12 bolt axrles have 3.08 gears, and I want 3.42 to 3.73 gears. I can either buy new ring & pinion gears or use one of the small 14 bolt semi-floating rear axles. I can get one of these 9-1/2" rearends for dirt cheap, it has 3.42 gears, and just change the front ring & pinion. Does anyone know how much beefier the 14 bolt would be compared to the 12?


mike reeh

Senior Member
i would assume considerably stronger, but if cheapness is your game, you have to factor in new wheels and stuff too for 8 lug 14bolt, among other things...



Senior Member
Fairbanks AK
OR, an idea I have kicked around before is get the 14 bolt 9.5" ring gear axel off of a late model light duty 3/4 ton with the six lug wheels and hang on to your wheels and tires that you have now. If you can't get one of these, I'd stick to the 12 bolt so that you are running the same wheels and bolt pattern front and rear. Stinks to have to carry 2 different spare tires around.


Junior Member
Don't even bother with the 9-1/2" "14 bolt". It's junk. One thing to remember, you get exactly what you pay for.

Best way to solve the problem is to purchase a fairly beat 3/4 ton Chevy 4x4 with a 3" axle tube Dana 44 and a full floating 14 Bolt and swap them in. I did this after going through 2 expensive rear diffs in my Blazer. Used a Detroit in the rear, and it resolved all breakage and traction problems. If you run anything larger than a 31" tire, if you don't go to this set-up your wasting your money.

I suggest using smaller 11 inch rear drums if you can find them - frequently these are on 1 ton rated Chevy Vans. The 13 inch drums are too much brake for the Blazer and result in rear brake lockup.

You will have to have rear driveshaft work done, and may also have to change your proportioning valve as it should be matched to the rear cylinder sizes. You can try using a used one provided the donor system is clean, but if the bleed pin is the least bit stiff get a new one ($60+). This is a safety item so don't compromise just to save a few bucks.

Try to make sure the donor vehicle has good tires and wheels (preferably 16" as 16.5 tires are beginning to become dated) as you will probably have to change these. Another route is to find 15" 8 lug rims that won't hit your front disc brakes. Yes, you may spend about $1200 doing this but for the 1.5 times the cost of a decent complete 12 bolt rebuild, it's fixed once and for all. The only thing better is to run a Dana 60 in the front, but these are choice axles that easily command $1,000 by themselves. Want the best? Boyce Truck Parts in Odgen, UT has Dana 60s and GM 14 Bolts with 4.56 Gears (other ratios and lockers are higher) all rebuilt and ready to go at your door for about $3200.

Hope this helps.

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