this rear axle stuff is confusing, but I have to go posi

[Slowguy]

I read the numbers off my rear axle today. Here's what I found:

Axle stamp is HA 08 29W

casting number "looks" like: 8896888 with an N directly above that.

The center portion also has casted into it a "gm14" and an "H156"

Can anyone tell me what I have, and if it's not posi, what they think I might need to turn it into one? I'm mating this with an ls engine and a 4l80e trans.

[weim55]

There's always a possibility the guts have been changed out in that housing at some point. Show a picture of the differential cover then take the cover off and shoot a picture of the inside. On the ring gear you will also see a part number, the gear count and the manufacture date.

Steve weim55 Colorado

[Slowguy]

Does this shed any light?

[Slowguy]

Another

[LockDoc]

-
Here are the charts.

http://67-72chevytrucks.com/vboard/s...d.php?t=578793

It looks like the HA is a 3.73 non-posi. Don't pay any attention to the C14 on the chart, it should read C10. The 11:41 also indicates a 3.73

LockDoc

[Slowguy]

Is 3.73 a good ratio for the 4l80e trans?...but I guess that wouldn’t matter if I convert to limited slip?

[LockDoc]

Originally Posted by Slowguy

Is 3.73 a good ratio for the 4l80e trans?...but I guess that wouldn’t matter if I convert to limited slip?

Yes, the 3.73 should work good for you. I run a 3.73 with my LS1/4l60e combo and it works good.....

LockDoc

[Mike C]

Originally Posted by LockDoc

Yes, the 3.73 should work good for you. I run a 3.73 with my LS1/4l60e combo and it works good.....

LockDoc

As LockDoc says, it will work, but the 2.48 first gear combined with the 3.73 gives you a 9.25 overall first gear ratio while his 4L60E with its 3.06 first gear gives him an 11.41 overall first gear ratio. IMO, the 4L80E really needs 4.10 gears to maximize low speed performance, but it suffers on the highway because it only has .75 overdrive instead of .70 of the 4L60E.

The one feature of newer vehicles that makes them performer so well is the much better chosen and implemented gear ratios and transmission speeds. They accelerate like 60's muscle cars and cruise like 70's sedans with 2.56 gears.

[LockDoc]

Originally Posted by Mike C

As LockDoc says, it will work, but the 2.48 first gear combined with the 3.73 gives you a 9.25 overall first gear ratio while his 4L60E with its 3.06 first gear gives him an 11.41 overall first gear ratio. IMO, the 4L80E really needs 4.10 gears to maximize low speed performance, but it suffers on the highway because it only has .75 overdrive instead of .70 of the 4L60E.

The one feature of newer vehicles that makes them performer so well is the much better chosen and implemented gear ratios and transmission speeds. They accelerate like 60's muscle cars and cruise like 70's sedans with 2.56 gears.

I was hesitant to answer his question not knowing anything about the 4l80 trans. That difference would pretty much make the 3.73 a no-go for that transmission. I originally had a 3.08 behind the 4l60e in my Panel Truck and that did not work for me. It made the transmission overheat when it was in OD. Thanks for the clarification. I will keep that in mind in the future.

LockDoc

[truckster]

There are alternatives to the posi, such as the Tru Trac.

What is your intended use for the truck, and what are you hoping to get by adding traction?

[Mike C]

Originally Posted by LockDoc

I was hesitant to answer his question not knowing anything about the 4l80 trans. That difference would pretty much make the 3.73 a no-go for that transmission. I originally had a 3.08 behind the 4l60e in my Panel Truck and that did not work for me. It made the transmission overheat when it was in OD. Thanks for the clarification. I will keep that in mind in the future.

LockDoc

I was not implying you were wrong just that he might want to think about his final application. You were absolutely right that it would work, and it would be a BIG improvement over a 3 speed trans. The 4L80E has the same first 3 gears as a TH400 plus a .75 overdrive. The big drawback to the 4L80 IMO is the expensive electronic controller required to run it.

These trucks came with 3.08 and the TH400 so the 3.73 would be a big improvement compared to the 6.776 ratio in first gear that application has!

[AJC]

You can reuse your gears when converting to a limited slip. But that is up to you.

[Slowguy]

I started watching some YouTube videos. It doesn’t look “terribly” difficult. Looks like it may take some patience to get it near perfect. I’d imagine it would be much easier that my rear end is out of the truck and be placed on a bench?

Looks like the most important part is setting the tolerances with shims? I found this video but the most important parts got left out by corrupted video....as the author says.

https://youtu.be/y4HhJ5WyRp4

Mike c...so if I were to change gears to 4.11, I’d need to change both the larger gear and the on that hooks to the driveshaft?

[Mike C]

Yes, you would need to change both. Gears are a matched set and broken in together on a machine. They then need to be setup in the housing at the same relationship they were run on the machine.

Those dimensions are pinion depth of distance from axle centerline to the pinion head. Then backlash, which is how much the ring gear moves in relation to the pinion when assembled.

It's not rocket science, but it is fairly precise. It requires a few special tools as well. If you really want to know how to do it, get a Factory Service Manual. Honestly, if you are going to work on your truck at all, you need a factory service manual and overhaul manual.

You can find some books on differentials as well, and they are worth the money.

Here is just one on Amazon:
https://www.amazon.com/Chevy-Differe...al+repair+book

[Slowguy]

So can I use this with the original 3.73 with a 4l80e and I should be ok?

https://www.summitracing.com/parts/d...a315/overview/

[Mike C]

Yes. And the TruTrac is a great choice. I had one in my Impala SS and I still have one in the front Dana 30 on my M38A1.

[Slowguy]

Does this look like the correct kit to go along with my same ring gear and pinion with the trutrac? I’d like to replace as much as possible while I’m in there.

https://www.strangeengineering.net/p...tion-kit.html/

[Mike C]

It does. Somebody, I think Yukon, makes what they call "Super shims" that interlock holding the smaller inside shims in place that are easier to drive it when setting preload.

Edit: that's a pretty good price with Timken bearings. But the super shims make the assembly easier so you may want to go with that kit and buy the other shims separately. They run around $23 I think.

[Slowguy]

Mike c....thank you for answering all my questions. It really helps. Do you think I need to do anything with the yoke now (hope I’ve got the terminology correct. I’ve rebuilt an engine but never opened a rear end until now!) I assume something custom will be necessary to get power from the output of the 4l80 to the original 12 bolt?

I haven’t researched the options for this yet as I felt it would probably be a bit before I got the engine/trans mounted and connected to the rear. As A note, I do have two original driveshafts. Both trucks were manual trans and I also have the original shaft from the 2001 2500 hd donor truck.

[Mike C]

If you are going to have a driveshaft built and you are planning big power, a 1350 yoke would be a nice upgrade. I would if it were mine. Then get a 1350 output yoke for your trans for the new shaft.

But you are getting close to the limits on the truck 12 bolt as I mentioned before. A Ford 9 inch or Dana 60 (I prefer the 60) starts to look like a good upgrade at the 500 hp range.

I would not shorten/modify either of the OEM driveshafts but have a custom shop build me one. A good shop will ask a lot of questions because length, diamter, wall thickness, and ends all matter.

[Slowguy]

I think for the time being I’d like to use the 2500 donor truck driveshaft...if that’s a possibility as the cheapest option? It would already fit directly into the 4l80e and I’d need to install the yoke onto the posi 12 bike I’m building now. Hopefully the yoke from the donor rearend fits the 12 bolt? I’ve never removed a yoke but it looks like a bolt and a spline.

I ordered all the stuff we discussed including the trutrac, locking shims, and the rebuild kit from strang. The yoke selection will be the last peice of the puzzle.

[Mike C]

There are some differences with the yokes. Most 12 bolts will have a 1310 u-joint size, but big block 1/2 ton trucks will have 1330.

The 1330 is same diameter cap as the 1310 with a wider cross. The 1350 has the wider cross of the 1330 as well as a larger cap diameter. Most likely the donor truck has 1350 joints already I would think. But you can measure cap diameter and cross length and Google will let you cross reference those things.

So yes, you can use the 2500 driveshaft after it has been shortened and balanced. I am assuming it is a one piece shaft. I know you can buy 1310-1330 conversion joints but I’m not sure if you can get a 1310-1350 conversion joint. Meaning you may have to buy the yoke for the rear or a different end for the 2500 driveshaft.

[Slowguy]

Should I replace the outer axle bearings at the same time since it appears the axle can easily be pulled out at this time?

[Slowguy]

I'm getting close to getting my body parts back for assembly on the frame. I thought I had my wheel combo figured out but now I've changed my mind again. I need to go with 5 lug axles in the rear. Can anyone tell me what axle I would need to match the stock axles I have in there now? 12 bolt stock 67 axle 3.73 and I changed out the dif to a tru trac as was talked about in earlier part of this thread.

[gmc684x4]

I have looked a bit into 14 bolts companies do make a 6 bolt hub to fit the rear spindle need to turn down the axle hub a bit
Give you a full floater gm diff that can take a lot of abuse

Lots of great advice on 4l80e and gear ratios i have a non posi 3.73 diff 4 series posi i might drive it as is at first see how i like the highway rpms before I drop in the posi might look for a set of 3.42s not looking to build this into a burn out truck getting to old to get caught doing donuts on main Street