Change carrier in 12 bolt to posi

[hooperca]

Hi all. I recently purchased a 67 C10 with the factory 3.73 12 bolt in it. I removed the back cover and everything appears to be in really good shape. I would like to put an Eaton posi unit in it. Can I change out the carrier using the existing gears? I've been told I wouldn't have to bother the pinion at all. Just make sure the backlash stays the same as it is currently. Thoughts on this? I really don't want to take a chance screwing up the gears but a posi sure would be nice! Thanks!!

[Frankie P.]

Yes you can. So long as you are able to get everything back together within specs for a used ring and pinion. Wear pattern on ring gear for example. I tried doing the same, but my ring and pinion were to worn out. Best of luck, cause it can become a pain.

[hooperca]

Thanks for the response! When you say back in spec for a used ring and pinion, what is there other than lash? On the wear pattern, I guess you could "paint" several teeth and look at that versus the existing wear pattern?

I hear you on the pain comment. The last thing I want to do is get into changing out the gears or, worse, putting in a new posi and destroying it when the gears go if they're not set perfect.

Maybe I'll just leave 'em alone - at least for now.

[Bigdav160]

Backlash and preload on the side bearings. The relationship to the pinion (depth) should not change by replacing the differential case.

Doing a pattern check is just to verify it's acceptable. They were rarely perfect from the factory.

[Rick Bollinger]

If you do the switch I am on the lookout for a carrier for 373. I have 308 gears now and going with a 700r4.
Rick

[Frankie P.]

What Bigday160 said. After setting my truetrac with old ring gear my carrier preload was off. Finally after getting it somewhat close and my backlash (with dial indicator) within spec, my pattern was extremely off..

So had to get a whole new set and got it to where it needed to be.

[TXgearhead67]

I have the same setup as you. I went with a Eaton posi and used my original 3.73 gears. I replaced all the bearings and seals while I was in there. Not to much trouble. Like previously said check your pattern. My biggest problem came from me buying a cheap chrome cover and broke the very bottom cover bolt. They were super cheap bolts and I knew better but got in a hurry.

[hooperca]

Bigdav160 or Frankie P - thanks for the input. Sorry, been out of town for a while.

How do you check carrier bearing preload? I assume the preload is set by the shims and think the shims also "control" the lash. But how do you check, or verify the preload.

Also, Frankie P, when you said you had to get a whole new set, did you mean gearset and everything? I really don't have the money, or stomach, for that right now.

Thanks Guys!!

[hooperca]

Originally Posted by TXgearhead67

I have the same setup as you. I went with a Eaton posi and used my original 3.73 gears. I replaced all the bearings and seals while I was in there. Not to much trouble. Like previously said check your pattern. My biggest problem came from me buying a cheap chrome cover and broke the very bottom cover bolt. They were super cheap bolts and I knew better but got in a hurry.

Mr Gearhead, how long has it been since you installed the Eaton. Are the gears holding up? Sorry to hear about your cover bolt. Soiuunds like you've had a little bit the luck I normally have.

Thanks to all! Love this site.

[Jrainman]

Originally Posted by hooperca

Bigdav160 or Frankie P - thanks for the input. Sorry, been out of town for a while.

How do you check carrier bearing preload? I assume the preload is set by the shims and think the shims also "control" the lash. But how do you check, or verify the preload.

Also, Frankie P, when you said you had to get a whole new set, did you mean gearset and everything? I really don't have the money, or stomach, for that right now.

Thanks Guys!!

To check the pre load you must use a torque wrench that mesures in Inch Pounds , the carrier bearing pre load is set by the Crush sleeve , it really is not that hard of a job to due, the problem is having the proper tools to do this , bearing removel will be diffucult unless you have or know someone who can press the bearing off for you , the other problem when doing this job is the cost of a torque wrench that messures in inch pounds they are not cheep ,again if you have one or know someone you can borrow from.

The carrier gear set most likly are ok so all you would need is carrier bearings and crush sleeve , seal and nut. so it is not expensive to due yourself you just need the proper tools , In my opinion you are doing half the job by not replacing (rebuilding everything ) and at some point you may need to go back in again . but again this is my personal opinion not saying what you are doing is wrong its just that the posi unit plus new bearings shim kit and seals was not a cheep purchase , another 60 -75 dollars at most and the job is 100%.

[TXgearhead67]

I haven’t drove it since the eaton swap. I feel like they’ll be fine though.

[BCOWANWHEELS]

I just did this swap. Measured backlash, removed carrier, took off ring gear, installed it on eaton posi, pulled carrier bearings off, pressed them on eaton, installed shims back where they came off of, put cover back on with permetex ultra black, put gm posi additive in diff, filled diff with 80w140 syn gear lube. Works perfect. Needed posi to get my boat out of ramp.

[7 Devils]

Follow the manufacturer instructions! So you don't end up with vibration/harmonics down the road. Break in procedure and correct lash are critical in initial setup for vibration free long life.
Also, carriers are gear specific i.e. 3 series usually covers 3.08 sets up to 3.90 sets.
Hope that helps.

Dan

[Frankie P.]

Good evening,
Yes I went with a new 3.73 gear set from US Gear. Stuff gets pricey quickly, hence why I did it’ myself and saved on the labor. And I also learned how to rebuild a rear end. If you go this route, prepare to test your patience. Google and old Chilton service manual helped a ton.

[BCOWANWHEELS]

The old gear set is far better than that china set you bought, same with bearings.

[7 Devils]

Many are not aware that a significant percentage of automotive parts labeled "Made in the USA" are cast/forged in China, among other places. They are "finished" (machined to final tolerance) in America and thus carry the Made in the USA tag.
I wish it weren't true but it is.

Dan.

[BCOWANWHEELS]

In 67-72 gm used us stuff, times was good then . 73 ON WAS RECYCLED STEEL

[7 Devils]

Agreed on time frame. I wish it was all still completely made here. In all honesty though the finishing process (done here) is the critical part.

Dan

[Frankie P.]

Bought what was recommended by a reputable gear shop owner. Couldn’t use my old stuff, so went with what was best for my build and budget.