10-bolt to 12-bolt rear differential, r u sure?

[john8662]

Alright, I've been junky vehicle looking and found a place that had several 70 & 80s type stuff, which would have what I was looking for a 73-80 12-bolt differential for a 2WD 1/2 ton truck with the 5x5 bolt pattern.

I took one home that supposedly had a posi in it (nope, figures) but had what I would call the "BIG BRAKES" on it, larger than the other 12-bolt truck rear end near it.

It followed me home, I pulled it's pan to find a good gear ratio (3.73) which matches what I have in the truck right now with the 10-bolt.

Anyways, I'm still having second thoughts about this thing on whether it's really that much better than the 10-bolt is/was.

So, one big question, since these things are supposed to be a "bolt-in" replacement for the 10, how bolt-in are we talking here? I mean, I want the driveshaft length to align just like it did with the 10. I don't want to have to shorten or lengthen another one, this last one (for racing) cost me a pretty penny that I'd like to keep and use.

I struck out 100% on the 14-Bolt SF with 5x5 (out of a 454ss pickup) those things are impossible to put your hands on, and I need a little stonger solution, like now.

Thanks!

[DmaxMaverick]

I switched my '85 to the 12 bolt from a '78. Best thing I did, and it saved me a bunch of money. Rebuilding the 10 bolt every 18 months got old. I even replaced the housing once, thinking maybe I had one that wasn't true. Changed the ratio to 4.10. Nope, nothing changed. 18 months was it. I now have over 200K on the 12 bolt, and not a peep out of it. And, I've been running the same Auburn L/S as before (same series, different model, they're not interchangeable). Also didn't have to mod the shaft. Did need a "special" U-Joint, though. Although, I could have changed the pinion yoke (12 bolt didn't leak, and I wasn't about to upset that). U-joints are cheaper, by a long shot, but they haven't been a problem. The brake backing plates were a match between them, also.

I still have a 10 bolt housing and axles (6 lug), if you want them. Free to any taker. Nothing more than a boat anchor to me.

[john8662]

So a different size u-joint is all. I wonder where I can find the right yoke for the axle I have, I don't mind replacing the seals on it now, because I'm debating taking it over to my favorite Differential Dude and having him go through it and throw in an Eaton Clutch-Style Posi. I also want C-Clip elminators in this one, cause if it breaks I don't want to lose a wheel, been there done that.

Thanks for the info Greg! Lemme know bout the yoke stuff...

[DmaxMaverick]

It's been several years. At the time, I had the option of changing the yoke. It was over $100 (including the pinion--not compatible), and the U-joints were only $2 more than what I was using. Couldn't make the math work. I haven't had to replace the U-joint (still on the original "special"). Then, TRW and Moog both had a replacement yoke. The housing/pinion series and U-joint series was all that was needed to size it. Don't know about now. The U-joint is a Neepco, I think (like I said, been several years). I still have the original box around here, somewhere. Your 12 bolt yoke may be different, depending on what it came out of. The original 12 bolt yoke on mine has forged caps, instead of the stamped straps. Interesting, though. Haven't seen one before, nor since. Not on a light duty, anyway. IIRC, it was originally an 8 bolt axle. I was able to get 6 bolt axles that fit right in from TRW. Thinking back, I didn't (and don't) know of early SF heavy duties. In any case, still better than the 10 bolt, not matter what flavor.

Consider the Auburn L/S carrier. They're a favorite on the track, and has put up well with my abuse. You just have to be choosy with the lube and additive. I've had the best results (by far) with GM 85-90 diff gear lube (in those stupid 23 oz. bottles), and 2 bottles of GM L/S additive. Anything else didn't last more than about 10K miles, and chattered after 5K. Synthetic was good, but the L/S didn't work (too slippery for a cone clutch). If you are mostly on the track with this truck, the Eaton (not the Gov-Loc) or Detroit would be a good choice, not so good for a DD.

The C-clip eliminators are an excellent idea. Hope you never have to put them to use!

[DA BIG ONE]

What I've read is that the 12 bolt parts into the 10 bolt solve the 10 bolts weak issues. I have a link about this, I'll find it and post here.

http://www.chevyhiperformance.com/te...all/index.html

[john8662]

Ok, so I'll get to doing some research on finding a replacement yoke since that should be more common for swaps now.

I need a yoke because I just noticed that mine is missing the straps or caps (don't know what it had), I would prefer the cast caps verses the straps for strength.

For the posi I'm currently running the Eaton and it does pretty good on the street, but not so much DD driving with a stack through the hood, not to say I haven't done it though. Working on exhaust system that goes downward, almost finished. But, the truck is primarily strip use.

I need to also wait till Wednesday because i've got a friend delivering another 12-bolt differential that I traded some stuff for, so I need to look at it and see what parts it has to offer.

Thanks, will update!

J

[DmaxMaverick]

What I've read is that the 12 bolt parts into the 10 bolt solve the 10 bolts weak issues. I have a link about this, I'll find it and post here.

http://www.chevyhiperformance.com/te...all/index.html

Not really sure what those guys are trying to do. The axles I have are not interchangeable. Not even a little. Believe me, I tried to stuff the 12 bolt carrier into my 10 bolt housing. Wouldn't work without some serious machine work, and then, even doubtful. And, their simple math isn't making much sense, either. I'd have to see it to believe it. Even then, my parts still won't fit.

[DA BIG ONE]

Not really sure what those guys are trying to do. The axles I have are not interchangeable. Not even a little. Believe me, I tried to stuff the 12 bolt carrier into my 10 bolt housing. Wouldn't work without some serious machine work, and then, even doubtful. And, their simple math isn't making much sense, either. I'd have to see it to believe it. Even then, my parts still won't fit.

I had read many articles like the one in link posted but never tried the converting to 12 bolt r/p in 10 bolt myself.

Guess anything can appear on net! Sorry, about that!

[john8662]

I've heard of using the 12-bolt axles in the 10-bolt differential with some modification to the axles. To me this didn't make sense because the 12-bolt axles are 30-spline 1.31" spline diameter, and the later 88+ 10-bolts came with 30-spline 1.31" diameter axles to replace the previous weak 28-spline 1.28" diameter axles. But, this only applies to the 8.5/8.6 version of the 10-bolt for trucks.

I could upgrade the current 10-bolt to near that of the 12, that's a hold up of mine too. But this doesn't address other weaknesses in the differential.

[DmaxMaverick]

I don't know. It could be some guy had a combination in hand that just happened to work, and assumed all 10 bolts are compatible with all 12 bolt parts. Back when I did mine (about 92/3/4?), that was not an option with everything I tried. The '85 10 bolt axle wasn't compatible with anything but 10 bolt parts. I spent a lot of time in the junk yard mixing and matching, looking for a solution. I didn't want to replace the housing again, but had to, to get what I needed. The article could be somewhat correct, with some car axles working. I have noticed much less axle failure with the later 10 bolts, so John is probably right about the improvements. I don't know otherwise, so I'll take his word for it.

[cowboywildbill]

I had a simular swap a few years ago.It was in a chevy truck. At the trans end, I swapped a different tranny and had to use a fine spline yoke and it had smaller or larger caps, I can't remember which. I bought the two u-joints one that was like the originial on the drive shaft and the one for the yoke. I was lucky because the the diameter of the caps were the only difference between the two. So I put the correct size caps from the other u-joint on the other joint. In other words two caps fit the yoke and two caps fit the drive shaft. I was fortunate the the u-joint had the same size pins and all of the caps and bearings fit. Just a thought.

[SimonUK]

Did the conversion a few months back when when my 10 bolt turned its internals into shrapnel. You need the neapco 3-3130 conversion u/joint. I'm assuming you kept the smaller u/j u bolts when you pulled the 12 bolt.

The axle is a straight bolt in swap, took me about 2 hours but that included new brake shoes and making cunifer brake pipes and fitting the new u/j to the propshaft.

There are a couple of threads relating in this forum, just do a search under my user name.

The next step is to swap out my front for the dana that came with the 12 bolt rear

Simon.

[john8662]

The 12 bolt I have has a 1310 series joint requirement, the truck's driveshaft has the 3011 series joint and according to a local driveline/joint shop said that the 12-bolt was going to require driveshaft modification to fit the truck.

A conversion joint as mention is offered, no replacement yoke is offered for the series joint that the truck previously used. There is however a 1310 series yoke for the 10 bolt, oh boy.

I think I will build the 12-bolt and keep it for spare. In the mean time, I think I may just snag some 30-spline axles for the current 10-bolt and swap carrier input gears to accept the 30-spline shafts, install 3.42 gears in place of the 3.73.

[DmaxMaverick]

Measure from the axle center to the U-joint center to determine whether you need a driveshaft mod or not. Take into consideration how much you have in the slip yoke for some variation. Also, the spring perch angle may be different, depending on application, so keep that in mind.

I have a pair of good 10 bolt axles (free to good home). They are 6 lug, and I'm not sure of the spline count. If you are interested, I can check them tomorrow. Just as good in your barn as mine, so to speak. You can have the housing, too, but I don't think shipping will be worth it. I still have 1995 K1500 chassis parts, engine (350), tranny (4L60E-like new), and TC (241) available, BTW.

[Rytari]

i have 12 bolt originally under my blazer.

all are saying change a 14 bolt but i still have kept my original axles.


i have 4.56 gears and lock-right in my 12b. i broke one ring last summer.. new richmond lassted almost 3 weeks before toothferry came.

i dont know if it its a big problem or not, but 12 bolts (10 also) are known to loose some tooths from the ring, one good reason is weak housing, when you are rotating tires w good traction pinion pushes ring away and when housing is too weak whitstand, backlash increases and you will loose some tooths.



i made this axle truss in to my axle for support. pipe structure on top holds the axle not to bend when jumping and bolted ring will hold housing (carrier side bearings mostly) in place when torque stretches it.


the ring is laser cutted 15mm thick steel. atleast now i havnt broke anything from it.

[john8662]

Toothfairy, now that's funny!

I know what you mean though, the difference now is that when the tooth fairy comes now days, you don't get money, you get to pay.

So far all I've broke in the 10-bolt is one axle and one spider gear in the posi carrier (hardened spider gears, better than what's in an open). The 3.73 gears were setup by the Axle Dude to be "set tight" for racing I'm told, not as great for a Daily Driver. I can see the wear pattern, there is certainly more contact area the way he set it up.

But, that was last year, now I'm sporting even more power than when it was last Dyno'ed and have increased traction dramatically.

I like your girdle for the rear diff, I've heard that the cases aren't rigid enough too. I've also heard that the lower yet numerically higher numbered gear ratios lend to being weaker (ring gear wise) which makes sense.

I'm swapping to 3.42 in the very near future tho and 1" taller tire (already installed).

J