Eaton Truetrac Issue

[tk-mpl]

I am installing a new posi carrier in my 68 C10 that I bought months ago and having some issues. The carrier seems to be a little different...

[mechanicalman]

Originally Posted by tk-mpl

I am installing a new posi carrier in my 68 C10 that I bought months ago and having some issues. The carrier seems to be a little different...

What gear ratio was on the old carrier, and what gear ratio are you putting on the new one?

[Ironangel]

Need to know what axle housing you have.(Show the cover if you can) And as mentioned, the gear ratio of the ring & pinion that came out of the old unit? Are you reusing the gears?..."More info needed"...Appears to be an open 12-bolt on the right, and the wrong carrier on the left if that's the old ring gear sitting on it? Not to confuse the situation, but was there a spacer under the ring gear on the old carrier? If so, and if that spacer is the same thickness as the offset shown in the pic, then your probably good to go...Just need more info to be sure.

[Bigdav160]

Looks like the difference between a 3 series and 4 series case or a 2 series on the right and a 3 series on the left. What ratio are you running?

[special-K]

Originally Posted by Bigdav160

Looks like the difference between a 3 series and 4 series case or a 2 series on the right and a 3 series on the left. What ratio are you running?

My thoughts, too...different series.

[tk-mpl]

It is a 12 bolt open diff. . It has 3:73 gears that I am reusing. I hope it's the right one cause as I said I bought it way back in June I think..

[Lee H]

Assume you still have the packaging, time to verify the part number and it's compatibility with 373s.

[tk-mpl]

That's the bad part... . I sent the number on the box away with a copy of the invoice, which I can't find the original, to get a rebate that I never got..

[Bigdav160]

Are you sure of the gear ratio?

Looking at the application guide shows the case break for a 4 series at 3.73 and up

edit, it shows truetrac case fitting 3.73 and 4.10. Perhaps you have one for a 4.56 and up?

As a general rule, as the gear ratio goes lower the pinion gets smaller so the ring gear surface moves closer to the center of the case

[tk-mpl]

I will count the teeth and check just to verify..

[tk-mpl]

Ok... . Found the invoice, it was in my Belair folder.. . It is a 913A315 for a 3:73-4.88 30 spline.

[tk-mpl]

Ring gear-43
Pinion-14
Thats 3:07 gears right??

Can I just get a set of 3:73 gears to make this work??

[Bigdav160]

Yes, and some shims

[tk-mpl]

Ordered a set of 3:73 gears to repair my stupid mistake...

[special-K]

Aww... You'll like the 3.73s better anyway. Did yourself a favor

[tk-mpl]

Well got it all together.. Had to play around a lot with shims to get the right backlash. . Was either 0.014" or 0.005" backlash.. Spec is 0.006"- 0.10" it's a little on the tight side, but I'm hoping it'll be OK..

[mechanicalman]

Originally Posted by tk-mpl

Well got it all together.. Had to play around a lot with shims to get the right backlash. . Was either 0.014" or 0.005" backlash.. Spec is 0.006"- 0.10" it's a little on the tight side, but I'm hoping it'll be OK..

Be careful breaking it in with it on the tight side. Some diffs actually give you a .005-.010" spec.

Living in Alaska I 'm thinking that it's going to run cooler anyway?

What viscosity oil do you run up there?

Good luck! Can't wait to hear how you like that diff.

[tk-mpl]

Does anyone know the rotating torque of the pinion and carrier together.?

[mechanicalman]

Originally Posted by tk-mpl

Does anyone know the rotating torque of the pinion and carrier together.?

No, I don't. But I found this on the internet:

"Used pinion bearings should resist rotation at the rate of 10 to 15 inch-lbs. (not foot-lbs.) of torque; new bearings are a little tighter and should check in at 20 to 24 inch-lbs. of pre-load".
http://www.ehow.com/list_7566691_12-...que-specs.html

I can't find any specs on side bearing pre-load except Richmond Gear says to add .005" shims to both sides, I suppose after you set up the gears with 0 pre-load. Drop-out diffs are easier to spec out. You might find the spec and how to check in in a GM manual.

I've never used a rotating torque spec on any of the hundreds of diffs I repaired in my career, I always went by feel. You would need a very sensitive inch pound torque wrench that I always had but never used for that.

There are a couple ways to do the job, the best way is to set the bearing pre-load on the pinion by itself, mark the nut to the shaft then remove it to set the side bearing pre-load then after setting the side bearing pre-load by itself, re-install the pinion bearing and tighten the nut to the mark. This is the method I use when replacing pinion seals, even with the side bearing still in I just do it by feel (this method eliminates the drag of a new pinion seal in the equation).

The other ways is to add the two values together and set it to the high side of the specs to account for gear drag. If you use the "add shims" method to set the side bearing pre-load, you would have to check the drag on the pinion before you actually tighten it to get an idea how much to add to the drag after tightening the pinion bearings as you have already accounted for side bearing and gear mesh drag.

Clear as mud? Hopefully someone else will chime in with the GM spec.

[tk-mpl]

I did the Pinion preload by feel because I didn't have a in/lb torque wrench at the time. . I have one now, but the carrier is in now and I am NOT taking it out AGAIN... Feels pretty good to me..

[Ironangel]

12-Bolt Truck Pinion Preload is 13 -15 (inch pounds) New...6-7 (inch pounds) Used. Ring Gear Backlash is 6-10/1000"...Next time you open and dismantle a rear end, it's important to take readings and document the preloads and shim locations and thicknesses as well as the carrier bearing cap direction and locations. I have Randy Lyman's (Randy's Ring & Pinon) manual and remember a formula used for the combined rotating resistance reading of the carrier and pinion but cant seem to find where I read that in the manual. It's a rather insignificant reading as long as your backlash and pinion preload is correct because the GM 12-Bolts use "outside shims" for the backlash adjustment...I remember my final total rotating reading was 23 inch pounds with the correct 13 inch pounds of pinion preload and 0.007" backlash...Just for giggles and grins, what is your total reading in inch pounds? Pattern on the coast side looks good, what does the drive side look like?

[tk-mpl]

The total rotating torque is about 25in/lbs and here's a pic of the drive side..

[tk-mpl]

Oops, wouldn't work from my phone.

[Ironangel]

You should be alright...The pattern dont look to bad either...You should be alright as long as your not nailin hole shots behind 400+ HP with slicks...Make sure you break the new gear set in properly and go easy on it for the first 200 miles and change the gear lube at 500 miles...Any good dino (non-synthetic) 80w-90 gear lube with 4oz. of Posi additive will do fine. Get out and place your hand on the diff cover after the first 20 miles to check the temp. If it's too hot to hold your hand on the cover, let her cool down for about 20 minutes and take another 20 mile run and check it again, allowing it to cool down. The phosphate coating on new gear sets is impregnated with a wear agent to aid in meshing and tempering the tooth surfaces...Keeping the new gear sets cool is critical and is why changing that lube out after 500 miles is equally important. "Oil is cheap insurance, new gear sets aint" Good job!

[tk-mpl]

Thanks for the advice. I was going to keep an eye on it and change the oil after I put some miles on it. You are totally right, fluid is cheap.. Now just have to wait for summer...