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Old 10-24-2018, 10:53 AM   #1
Slowguy
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this rear axle stuff is confusing, but I have to go posi

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.
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Old 10-24-2018, 11:38 AM   #2
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Re: this rear axle stuff is confusing, but I have to go posi

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.

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Old 10-24-2018, 05:42 PM   #3
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Re: this rear axle stuff is confusing, but I have to go posi

Does this shed any light?
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Old 10-24-2018, 05:44 PM   #4
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Re: this rear axle stuff is confusing, but I have to go posi

Another
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Old 10-24-2018, 06:58 PM   #5
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Re: this rear axle stuff is confusing, but I have to go posi

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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

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Old 10-24-2018, 07:02 PM   #6
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Re: this rear axle stuff is confusing, but I have to go posi

Is 3.73 a good ratio for the 4l80e trans?...but I guess that wouldn’t matter if I convert to limited slip?
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Old 10-24-2018, 07:09 PM   #7
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Re: this rear axle stuff is confusing, but I have to go posi

Quote:
Originally Posted by Slowguy View Post
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.....

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Old 10-24-2018, 08:19 PM   #8
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Re: this rear axle stuff is confusing, but I have to go posi

Quote:
Originally Posted by LockDoc View Post
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.
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Old 10-24-2018, 08:31 PM   #9
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Re: this rear axle stuff is confusing, but I have to go posi

You can reuse your gears when converting to a limited slip. But that is up to you.
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Old 10-24-2018, 09:09 PM   #10
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Re: this rear axle stuff is confusing, but I have to go posi

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?
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Old 10-24-2018, 09:28 PM   #11
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Re: this rear axle stuff is confusing, but I have to go posi

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

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Old 10-25-2018, 12:37 AM   #12
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Re: this rear axle stuff is confusing, but I have to go posi

Quote:
Originally Posted by Mike C View Post
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.

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Old 10-25-2018, 01:05 AM   #13
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Re: this rear axle stuff is confusing, but I have to go posi

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?
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Old 10-25-2018, 07:48 AM   #14
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Re: this rear axle stuff is confusing, but I have to go posi

Quote:
Originally Posted by LockDoc View Post
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!
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Old 10-25-2018, 08:51 AM   #15
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Re: this rear axle stuff is confusing, but I have to go posi

I'm not really into burnouts; as many are. I'm the guy that hates to see hard earned money needlessly sprayed all over the side of my car and painting on the asphalt.

I am going to turbo this truck. So it will have at least 500-550 to the wheels...with the boost at a minimum. It could have much more if the truck could apply it to the road. I don't want racing slicks. I want normal performance tires. Probably only 275 or so in the rear.

I think it would be very important at this power level to have both wheels apply torque to the ground simultaneously or I'll just be driving around spinning one wheel everywhere I go. It probably won't do much but I'd imagine adding the rear gas tank, battery, and the air compressors near or over the rear axle will help with traction as well.

I'd call it a hopped up daily driver. Cam is light to keep the power a little lower in the band but tons of power up top when i want it. The 4l80 should be a good dd from what I've read.
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Old 10-25-2018, 09:31 AM   #16
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Re: this rear axle stuff is confusing, but I have to go posi

It will be. And turbo cars don't like a lot of gear. You will be happy with the 3.73 most likely. It may even want LESS gear than that, but the 3.7 are a good start. BUT the carrier break is at 3.73 and up on a truck 12 bolt. So if you wanted to run 3.42 that would require a different carrier.

If you want new car driving characteristics on the highway with the 4L80, the 3.42 gives you a 2.565 final drive and a overall first gear of 8.48 which may be better for the turbo. Additional load helps build more boost faster.

Everything should have a limited slip IMO. No matter how little power it makes. All I can say is learn as much as you can about the power characteristics of your motor and what the final goal is. Nothing hurts more than buying things twice.

And at those power levels, you are starting to reach the limits of the truck 12 bolt. Depending on if it is going to spend anytime with sticky tires at the strip, a custom axle housing might be a good idea. A Dana 60 with Big Ford housing ends and custom axles with 3.54 gears would be slick.

Speed costs money, how fast do you want to go as they say.
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Old 10-25-2018, 09:54 AM   #17
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Re: this rear axle stuff is confusing, but I have to go posi

I know all too well about purchasing what I don't need or will end up not wanting and then it sits on a shelf. I've already done a little of that on this build. It's why I ask so many questions and spend days searching. LOTS of info to read but sometimes difficult to find EXACTLY what you are doing that someone has already done. 67 c10, with a 3.73 ratio, lq4 engine with a custom tune boosting to about 500 hp, 4l80e trans with a 3200 stall circle d converter, a transgo shift kit, and an elgin 1839p cam....see what I mean? That's more variables then just searching "ls swap 67 c10". Then on top of that, you get many opinions and what has worked well for "person 1", then "person 2" says something completely opposite (and that opposite opinion obviously worked well for person 2). So all that just adds to my confusion.

Unfortunately, what usually ends up happening, is exactly as you described. I end up buying what I think may work, I don't like it but it gave me a perspective to know what or how I want to change it, and I purchase a new option.

I just know I want posi. I'd like the first gear not to crawl like I've read many stock c10 are from factory, and I'd like to cruise down the road at 70 mph somewhere in the 2-3k range. This build is like many others I've done....I go all it, without ever even spending time driving the original vehicle. I bet I have a total of 10 miles driving the original truck. I can tell you, in comparison to any vehicle 1980 or newer, it was super unstable-feeling and sounded like it was fully revved at about 60. It would clunk and felt like it would sway off the road with any sudden movements.
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Old 10-25-2018, 11:31 AM   #18
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Re: this rear axle stuff is confusing, but I have to go posi

You should start sorting out the chassis before you quadruple the power output IMO. My 69 is super predicatable, rides smooth and stops hard with OEM disc on ECE conversion spindles.

Google may be a better asset for information for other boards that have similar driveline setups to yours even if they are in a different vehicle.

Here's just one example of a well-built Chevelle.

https://ls1tech.com/forums/conversio...gle-turbo.html
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Old 10-25-2018, 12:21 PM   #19
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Re: this rear axle stuff is confusing, but I have to go posi

Thanks for the link. I'll read through it this evening. I think (hope) I have most of the chassis figured out.

I am giving it an adjustable ride height with four 2600# bags that will be controlled by an accuair e level control. I like the idea of it always maintaining the height automatically and even help with cornering.

Shock relocation for front and rear. Adjustable panhard bar. front and rear sway bar kits, new ps components with hydroboost, new front disk kit and drop spindles, ss braided brake lines, front lower control arms cupped and welded for bags, i'll have to go with a custom or modified drive shaft (i think...haven't gotten far enough to start researching yet), better distributed weight (as i mentioned earlier), all the ball joints and tie rod components brand new, new rear drums and pads, new control arm bars, rear c notches, and I'll soon order the shocks when I settle my ride height and can measure the exact type i need.

All this is stuff I already have and is ready to start assembling once the frame is finished being prepared. Other than going to a completely custom system like PB, I've covered just about everything on the frame. Now I need to get the rearend figured out before I can get it back it the frame and have the thing rolling soon.

...and the engine is setup for more than the power i'm actually aiming for. I could always do even less boost. Heck, I could even do it stock and it would probably be double the output from the original, stock 327

Last edited by Slowguy; 10-25-2018 at 12:24 PM. Reason: adding
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Old 10-25-2018, 08:06 PM   #20
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Re: this rear axle stuff is confusing, but I have to go posi

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/
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Old 10-25-2018, 08:40 PM   #21
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Re: this rear axle stuff is confusing, but I have to go posi

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.
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Old 10-27-2018, 07:17 PM   #22
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Re: this rear axle stuff is confusing, but I have to go posi

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/
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Old 10-28-2018, 08:53 AM   #23
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Re: this rear axle stuff is confusing, but I have to go posi

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.
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Last edited by Mike C; 10-28-2018 at 10:46 AM.
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Old 10-28-2018, 03:33 PM   #24
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Re: this rear axle stuff is confusing, but I have to go posi

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.
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Old 10-28-2018, 08:38 PM   #25
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Re: this rear axle stuff is confusing, but I have to go posi

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.
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