Information needed for 12 bolt axle swap

[6 2 Carl]

I blew out my spider gears in my rear-end on my 1987 C10 Suburban. The ring was also damaged. In addition the pinion seal was leaking and the whole axle may have been bent, since the passenger side tire always wears abnormally.

I am currently researching my options on the best way to get my truck back on the road. I have come up with several possible plans. They are listed in order from cheapest to most expensive.

1. Swap in a 12 bolt axle from a 1980 truck that is rusting away on our family farm. This option is free, but less than ideal since it has 3.08 gears and no posi. I want 3.42 gears and a posi.

2. Buy a used 10 bolt with 3.42 gears and hopefully a posi, from a wrecking yard. I am a little weary of this option, since I don't want rear-end to fail prematurely again in a couple of years.

3. Rebuild my 10 bolt and add a posi. I am shying away from this, since my axle may be bent

4. Rebuild the 12 bolt and add 3.42 gears and a posi. I think I want to go with this solution.

I have several questions about the 12 bolt swap:

Will it be a direct swap, or will I have to shorten my driveshaft?

Will the pinion angle be the same or will I have to add shims?

I want to try to rebuild the axle myself so I will need detailed instructions. Any links to online instructions on how to rebuild a 12 bolt will be really valuable.

Any advice on which posi I should use? Eaton, Auburn gear, or any others (maybe even a locker).

Were can I get my best deal on a rebuild kit, and what brand of gears and bearings should I use.

Any other options and advice will be appreciated.


Carl

[DmaxMaverick]

I did exactly what you are considering, on my '85 Blazer (same powertrain).

Originally, it had a 3.73 10 bolt with an Auburn L/S. After replacing the carrier and all the contents twice, I realized the need for a more robust rear end. I bought a 12 bolt housing (1978 M/Y, IIRC) from a wrecking yard (about $75, 8 years ago) and built it with the auburn L/S. It was a direct bolt-up with the exception of the U-joint. I had to get an aftermarket "adapter" U-joint. I could have replaced the pinion, but the U-joint was only about $2 more than the OEM, compared to about $150 for a pinion change. I've only replaced the joint once, so far.

Bottom line...Flawless since the change (and about 200K).

If you do go with an Auburn L/S, be sure to use mineral based lube and TWO bottles of the GM additive. The Auburns don't like synthetic lube.
My change intervals have been 25K.

Good luck.

Added on edit:
The 10 bolt axles, ring/pinion and carrier are not compatible with the 12 bolt housing. I had to buy new axles, and the complete carrier from Auburn, as well as the ring/pinion for the 12 bolt. The new(er) rear end is a 4.10 ratio. IMO, 3.08, even for stock tires, is too high. If you are running larger than 31" tires, 3.42 is too high. I run 33" tires.

[ 12-08-2003, 06:16 AM: Message edited by: DmaxMaverick ]

[deanstud]

Auburn is not rbuildable, the posi untit must be replaced. Eatons are rebuildable.

[DmaxMaverick]

Originally posted by deanstud:
Auburn is not rbuildable, the posi untit must be replaced. Eatons are rebuildable. That was true at one time, maybe around 1988 or so (my first 10 bolt replacement on the '85). I have since replaced several Auburn parts (on different vehicles), including the clutch ass'y (cone). Parts are available. Replacement is simple, as tollerances are not critical unless the R/P is replaced. Auburn machined parts are of close enough tollerance that I haven't had to re-shim any of them. The last one was about 6 years ago.

BTW:
Welcome to the forums!

[NH2112]

I think that if I was in the same situation I'd look for a 14-bolt semi-floater from a 3/4 ton, even though it'd require running different wheels on the rear. They have huge brakes, are tremendously strong and very plentiful, with ratios running from 3.42:1 to 4.10:1 and probably higher. Grab the driveshaft and center support bearing with it and it's a 100% bolt-in swap except for parking brake cables. You should be able to adjust them down enough to compensate for the slightly greater distance from the backing plate to the park brake lever.

[6 2 Carl]

An update on the project. I decided to rebuild the 12 bolt and put in 3.42 gears and an Eaton posi. When I put everything back together I found out I only had first and reverse in my transmission. I did not have time to deal with that problem, since I was just starting a new job. So I parked the Suburban and drove my grandfathers 88 K2500, until my Dodge that I ordered arrived in April.

Well just after Christmas, somebody hit my Dodge, and it was in the body shop for 3 weeks. I decided that this would be the perfect time to get the old sub going again. I had done a little research and discovered that a broken governor gear could be the cause of my problems. Sure enough it was the problem and a quick $20 fix.

I sure enjoy driving my truck again, and the funny thing is that during the 3 weeks that my Dodge was at the body shop, I didn't miss it at all. :D

I would much rather drive my Suburban around in the city. It is big enough to see around other cars, but it doesn't have the huge blind spots like my Ram. It is also much more "toss able" in traffic. With the quick downshifting automatic I can move in and out of lanes much quicker than my 6-speed Dodge. The Sub actually feels sporty when compared to my Ram, if you can call a diesel sub sporty.

I do have a vibration that starts around 60mph that wasn't there before. I think my driveshaft may be slightly bent. And since my steady bearing is pretty much shot, I think I am going to convert over to a 1 piece driveshaft. Hopefully that will cure the problem.

My water pump is starting to leak so I guess I will be changing that out, and while I am at it I might as well put in some DSG gears and a new balancer. Where would be the cheapest place to get the water pump and balancer?

All in all I am glad to have my Suburban running again, and it will be a great back up vehicle, especially since my Ram has already had a lift pump failure @ less than 30,000km :mad:

Carl

[DmaxMaverick]

....I do have a vibration that starts around 60mph that wasn't there before....Tires. If your truck sat for a while (which it has), the tires are probably not round or concentric any more. Very common. My '85 has that problem since I got my '01. It takes quite a few heat cycles of the rubber to get them to smooth out. It takes longer in the winter than summer. Some tires (brand X) never recover, higher quality tires seem to recover more quickly.

You may have drivetrain issues causing a vibration, but the tires will surely contribute to them. Rotate the tires, or swap on a known good set to be sure. Good luck.