Need new 12 bolt posi unit - Chevelle Tech
Transmission & Driveline Transmissions and Differentials

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post #1 of 33 (permalink) Old Mar 4th, 20, 8:55 AM Thread Starter
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Talking Need new 12 bolt posi unit

Hello. Would like some feedback on what you guys like on posi units. My 67' set-up is 496/640ft/lbs tq/ 620hp @ 4100 rpm. Super t-10 and factory 12 bolt. I just pulled the cover last night to find what I thought I'd find; welded gears, teeth broke off, lots of wear and tear and some other miscellaneous hillbilly mods. Car will be street driven, some "playing around" with Nitto 555 G2 tires.

I just spent some pretty decent coinage on trailing arms (adjustable upper and lower), shock tower brace, sway bar, coil overs,etc. Don't really want to cut corners on the 12 bolt but it would be nice not to bust my wallet. Also, do I need new axles? Thanks
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post #2 of 33 (permalink) Old Mar 4th, 20, 9:31 AM
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John
 
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Re: Need new 12 bolt posi unit

Lots of good reviews about the True Trac posi unit. No discs to wear out, and good on the street. I have one, but not installed yet. I'd put a good set of axles in it. Mosers or whatever name brand you like. Some may suggest an axle without c clips being a good upgrade, however, that gives you 2 options, c clip eliminators, which tend to leak sooner or later, or cutting ur housing ends off and welding on the Ford ends. This would mean removing the housing from the car, finding a jig, ect, ect...Or, some may even suggest buying a Moser housing that already has the end welded on it. So it can be as simple as installing a new True Track and aftermarket axles, all the way to replacing the housing...Since your only street driven, and no track time, I'd go with the True Trac and Moser axles at the minimum. If on a tight budget, Quick Performance sells a Yukon Posi with gears and bearings for 550 or so I think.
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post #3 of 33 (permalink) Old Mar 4th, 20, 10:34 AM
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Freddie
 
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Re: Need new 12 bolt posi unit

Eaton Posi or Eaton Truetrac. If you have the money then look at the Wavetrac. Check your axles where the bearings run on them. If they are worn or pitted then replace them. If you are going to the drag strip with sticky tires then replace them.


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post #4 of 33 (permalink) Old Mar 4th, 20, 7:56 PM
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Lew
 
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Re: Need new 12 bolt posi unit

If you do axles some of these posi units come in the 33 spline versions so you might as well do that while you are there changing axles.
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post #5 of 33 (permalink) Old Mar 4th, 20, 8:43 PM
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Eric
 
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Re: Need new 12 bolt posi unit

I have an Eaton True Trac in my Moser 12 bolt. Great unit and it holds up to my 468's mid 11 second passes
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post #6 of 33 (permalink) Old Mar 4th, 20, 11:16 PM
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Re: Need new 12 bolt posi unit

True Trac / Worm Gears in my S60 since 2013 and no Springs etc. to wear out



Great on the Street and super at the Track
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67 Chevelle Malibu SS Cdn
Born 283 / PG / A51
468/TH400 2,500 stall/ S60 3.70 Gs
Prev Best on M/T ET S/S #3454 street Tires/Dress 2018/05/20
60' = 1.664
1/8 = 7.532 et / 91 mph
1/4 = 11.814 et / 115 mph
NEW Best with 3,500+ Stall TC 2019/09/08
60' = 1.547
1/8 = 7.311 et / 91.76 mph
1/4 = 11.595 et / 114.28 mph


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post #7 of 33 (permalink) Old Mar 5th, 20, 8:34 AM Thread Starter
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Talking Re: Need new 12 bolt posi unit

It's settled. Eaton true trac with Moser axles, and new seals, bearings etc. Thanks guys for the input.
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post #8 of 33 (permalink) Old Mar 8th, 20, 3:48 PM
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Rick
 
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Re: Need new 12 bolt posi unit

Before you start buying parts, give these guys a call.
https://www.drivetrainspecialists.com/
This is what I bought from them in a brand new housing:
1/4" tubes welded to a new nodular center section
eaton true trac
4.10
large axles
ford ends
larger ford truck drum brakes
larger yoke
much larger main saddles
No mater which way you go, there is a particular break in sequence for longevity. You will need an infrared thermometer.
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post #9 of 33 (permalink) Old Mar 9th, 20, 9:04 AM
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Re: Need new 12 bolt posi unit

Quote:
Originally Posted by big gear head View Post
Eaton Posi or Eaton Truetrac. If you have the money then look at the Wavetrac. Check your axles where the bearings run on them. If they are worn or pitted then replace them. If you are going to the drag strip with sticky tires then replace them.
Wavetrac is by far the most robust of the torque biasing type differentials (including the truetrac) but they are only available in 35-spline axles for the 12-bolt rear axle and you have to install 3.15" diameter bearing housing ends (big Ford).
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USAF Retired (1968-1988)
UTC Aerospace Systems, Space Systems International - Retired (1989-2014)
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post #10 of 33 (permalink) Old Mar 13th, 20, 9:25 AM Thread Starter
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Talking Re: Need new 12 bolt posi unit - UPDATE!!

Hopefully this thread isn't dead yet. Well, my buddy and I pulled the 12 bolt out of car last night because we have to "beef up" some brackets for the rear coil overs. Here's what we found: the 12 bolt is a 68' not 67', I think about one inch longer than 67? The rear-end is an open carrier. The spider gears are welded together and someone had installed washers in the chunk to make some mods to how the springs respond. We also found an assortment of miscellaneous teeth, bolts, washers, nuts and toggle bolts. Anyway, everything will be replaced except the housing.

My buddy said "hey, I've got a 12 bolt with disc brakes and 3.73 gears, BUT it is out of a chevy s10 truck. I'm like well won't we have to shorten it? He said yes, and the $650 disc brake kit you just ordered won't work either. I'm thinking well, I'm running a four speed and 3.73's well not be a good "all around" driver set-up. I was going to run 3.08's or 3.42's. In Atlanta traffic, running 90 mph, that 496 will be screaming. Here's where I screwed up; I should have gone through the drive train before I did body and paint. I would have done a mini-tub and built a custom rear end.

Anyway, I told my friend: Why don't we use the housing we have instead of starting over and adding extra fab and mods to the equation. SO, I need the whole enchilada. So with the housing on a jig, any and everything goes. I want to build this 12 bolt to withstand some abuse. I like the true trac unit and moser axles. I need some help with beefing up the gear count and c clip eliminators. Also is the "Ford ends" something you weld on? I've never built a 12 bolt.......THANKS!
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post #11 of 33 (permalink) Old Mar 13th, 20, 10:17 AM
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Freddie
 
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Re: Need new 12 bolt posi unit

C clip eliminators usually don't work well on the street, and most won't work with disc brakes. If you want to get rid of the c clips then the Ford stile ends is the way to go. You MUST order the axles to work with the Ford bearings. They will not work with standard type axles. The Moser 7900FM ends will work with your disc brakes. Yes, they must be welded on using a housing fixture. Also, if you want to brace the axle tubes then check out the LPW ultimate cover with the axle tube brace kit. https://www.lpwracing.com/Ultimate_GM/Ultimate_GM.html
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post #12 of 33 (permalink) Old Mar 13th, 20, 11:36 AM
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Greg.
 
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Re: Need new 12 bolt posi unit

I ordered my S60 from Strange with Big Ford Ends H1135 / 11" Drum Brakes / 1/2" Studs / 1350 Pinion Yoke / S/T 35 Spline Axles
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67 Chevelle Malibu SS Cdn
Born 283 / PG / A51
468/TH400 2,500 stall/ S60 3.70 Gs
Prev Best on M/T ET S/S #3454 street Tires/Dress 2018/05/20
60' = 1.664
1/8 = 7.532 et / 91 mph
1/4 = 11.814 et / 115 mph
NEW Best with 3,500+ Stall TC 2019/09/08
60' = 1.547
1/8 = 7.311 et / 91.76 mph
1/4 = 11.595 et / 114.28 mph


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post #13 of 33 (permalink) Old Mar 13th, 20, 11:43 AM
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Bill
 
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Re: Need new 12 bolt posi unit

You didn't mention if your 12 bolt is a posi unit. I rebuilt my factory posi unit but went with 400 pound springs and carbon fiber clutches. Grabs good and no chatter going around corners. Pretty easy job except getting the springs plates in.

Update - Missed your last post where you stated open carrier with welded spiders. left my initial post for those needing to rebuild their original posi
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post #14 of 33 (permalink) Old Mar 13th, 20, 1:09 PM Thread Starter
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Re: Need new 12 bolt posi unit

Ok, I'm all schooled up now. Just kidding, but I do have more knowledge now. Going with Eaton Truetrac, 33 spline. Running 3.31 gears. Puts me at 2713 rpm's @ 65 mph. Thought about running 3.55's. My friend talked me out of it, probably so he can be faster. He said I'd be looking for another gear with 3.55's. My 4 speed also has 2.64 1st gear. Picking out axles now. I am not doing c clips. Thanks
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post #15 of 33 (permalink) Old Mar 13th, 20, 1:55 PM
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Re: Need new 12 bolt posi unit - UPDATE!!

Quote:
Originally Posted by FAT SACK View Post
In Atlanta traffic, running 90 mph, that 496 will be screaming.
What part of Atlanta do you live in where 90 MPH is possible???? Maybe you are talking aboout 3AM blasts on the interstate but latley it seems high speed travel down here is more like 35 MPH.
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