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Old 10-23-2019, 01:05 AM   #1
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Rear Locker for Express

Hey y'all,

First time poster! Before I go on any further: this is a question about how to add a locker to a 2WD van. It's technically not a 4x4 question, but I checked the threads in this section and this seems most appropriate.

That out of the way, I got a 2006 Chevrolet Express 3500 Passenger Extended 6.0 LQ4 4L80E about a year ago and have been absolutely loving this thing. It had some nice basic things like electric windows/power doors/cruise control, rear AC. It was a fleet vehicle to getting folks to the local airport, I grabbed it for $3700 with 204K miles on it. It turned out to be worth it because this one was maintained flawlessly, and that LS and transmission combination is second to none.

I took it and made it nicer, here's an incomplete list:
- Weldtec 5" lift w/ Kumho Road Venture 33s
- Underglow and interior LED lighting
- Android w/ component audio + amp and sub
- Some light sound deadening
- Backup camera
- PA system, a light bar, the essentials
- A fantastically overbuilt roof rack with a wind deflector
- Xtra Duty tow bar, front tow hooks, fullsize spare
- Recovery strap, D rings, traction boards, valvestem tool and lots of spares

Mostly I have just been going through the car and doing major maintenance while taking this puppy on roadtrips (obviously). I haven't owned the car for a year and I'm already at 221K (and I don't even commute for a job).

The one thing that I notice is, no matter how much I wanted to avoid ripping into the rear end, I just get stuck all the time and everywhere. Just yesterday I realized how much I love this darn thing and now on a path of getting it a locker. This finally bring me to my question.

What are my options?

It sounds like GM offered the option G80 which was a centripetal-style bidirectional auto-locker that used a weight to trigger the clutch lockup. If nothing else works, this is what I might have to go for.

However, I might also have Detroit Locker or ARB locker options, but I cannot seem to confirm this. Based on my research, I have a Dana Super 70 with a 12 bolt housing, that much is identified with a factory sticker and I am including a photo.

Based on further unconfirmed research, it sounds like this is the biggest rear end available in these vans and my ring gear should be 10.75" (some sources say 10.5"). However, when it comes to the spline count, I'm getting no consistent answers. 32, 32, 35, even 37 comes up.

Is there a way to identify this without cracking the housing and sliding out an axle? Asking because it's got fresh fluid in there, and I'd rather avoid a night of getting dirty.





Thanks for any guidance in advance!
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Old 10-23-2019, 01:07 AM   #2
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Oh and some photos of my thang:













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Old 10-23-2019, 05:37 AM   #3
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Nice looking van. Great you are getting out.

Last time I looked at this, I thought they were 9.75" and 33. I am in no way sure and maybe you have a bigger axle. It was hard to find definitive information. The "STD" code means you have an open differential I believe. If you had a locker of some sort, it would be "LOC". I have a G80. What are the van RPO codes for the axle?

Looking at Napa online, I get what I put above:
https://www.napaonline.com/en/p/NDP8...wordInput=axle

The axle BOM is 2001079. This is a "70GM" as you mentioned. GMT 610 platform.
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Old 10-23-2019, 12:59 PM   #4
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Quote:
Originally Posted by marret View Post
Nice looking van. Great you are getting out.

Last time I looked at this, I thought they were 9.75" and 33. I am in no way sure and maybe you have a bigger axle. It was hard to find definitive information. The "STD" code means you have an open differential I believe. If you had a locker of some sort, it would be "LOC". I have a G80. What are the van RPO codes for the axle?

Looking at Napa online, I get what I put above:
https://www.napaonline.com/en/p/NDP8...wordInput=axle

The axle BOM is 2001079. This is a "70GM" as you mentioned. GMT 610 platform.
I checked my RPO codes, I definitely have an open differential. Not that I need to run the VIN for that:



I reached out to Yukon Axle and Gear with the same problem, here is what I heard back from Brian "Gus" Pyeatt:

Quote:
GM designed that with an oddball cross pin offset and staggered axle shafts. This prevents ANY aftermarket carrier from fitting with out also changing axle shafts etc.

The ONLY out of the box option for you is the factory G80 Gov-lock.
This is the second time hearing something like this about these rear-ends, so I'm inclined to give up the search and focus on sourcing the right G80 parts. Here is what GM microfische says about it all:

6 88982386 Differential Case
EXPRESS, SAVANA; W/ O LIMITED SLIP; 1 TON
$999.51 $618.15

6 88982481 Differential Case
EXPRESS, SAVANA; W/ O LIMITED SLIP; 1 TON; 9.75
$907.63 $689.34

6 88982489 Differential Case
EXPRESS, SAVANA; W/ LIMITED SLIP; 1 TON; 9.75
$1,008.60 $623.78

6 88982384 Differential Case
EXPRESS, SAVANA; W/ LIMITED SLIP
$1,017.94 $629.55

6 88982385 Differential Case
EXPRESS, SAVANA; W/ O LIMITED SLIP; 1 TON; 10.50
$1,358.93 $840.43

I'm going to go ahead and eliminate the 9.75" options due to the shear size of this honker, also via confirming by way of Dana 70GM/70S specs. Still, this is very confusing.
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Old 10-23-2019, 02:07 PM   #5
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Just got back from the local GM dealer where I got fantastic service. I confirmed the part I need from the diagram above.

According to them, I do in fact have the 10.5" ring gear and the part I need is the loaded posi-traction unit: 88982384. It retails for a grand but can be had for 600 or so from online dealer-networked suppliers.

There is a GM strike currently, so I will avoid ordering through that supply network just yet, but at least I know my next moves. Also have to figure out which axle minor service kit I will be needing along with this.

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Old 10-23-2019, 03:35 PM   #6
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Please, please, please do not buy a gov-lock! They are very failure prone (though less so in the bigger axles like yours.) Once the clutches get some wear on them, the engagement gets harder and harder, often remaining locked like a spool until you unload it by romping on the throttle in reverse. Eventually they explode, splitting the carrier in half, and even forcing their guts out of the cast iron differential housing.

Though I'm not well versed in your specific D70, I'd suggest sticking with a non-clutch based unit such as a Detroit locker if you don't drive on ice often, or a selectable locker like the ARB or Eaton E-locker. The Detroit Trutrac is popular around these parts, but it's more like a very good limited slip than a true locker as you can overpower it if you find yourself with one wheel in the air and good traction on the other. Depending on your use, that may still be a good choice.
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Old 10-23-2019, 04:46 PM   #7
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Originally Posted by TheLetterJ View Post
Please, please, please do not buy a gov-lock! They are very failure prone (though less so in the bigger axles like yours.) Once the clutches get some wear on them, the engagement gets harder and harder, often remaining locked like a spool until you unload it by romping on the throttle in reverse. Eventually they explode, splitting the carrier in half, and even forcing their guts out of the cast iron differential housing.

Though I'm not well versed in your specific D70, I'd suggest sticking with a non-clutch based unit such as a Detroit locker if you don't drive on ice often, or a selectable locker like the ARB or Eaton E-locker. The Detroit Trutrac is popular around these parts, but it's more like a very good limited slip than a true locker as you can overpower it if you find yourself with one wheel in the air and good traction on the other. Depending on your use, that may still be a good choice.
A couple of points:

1. I exhausted all possible options. Nothing fits my axle housing without non-trivial modifications like replacing axles. Trust me, I'd love to go for something like a Detroit Locker, alas, not in the cards, like I already outlined above.

2. The gov-lock stigma is almost always perpetuated by non gov-lock users.

3. On an axle this size, the drawbacks you outlined are minimized. I found that the people who actually had one of these vans with the G80 option had no issues.

However, when and if my housing does grenade, that would be a reason to do a full conversion to something that does have locker availability
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Old 10-23-2019, 06:48 PM   #8
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1) axleshafts are probably cheaper than you think. I paid ~$350 for custom 35 spline Dutchman shafts, don't let that stop you.

2) I have personally exploded not 1, but 2 govlocs. The 1/2 ton variant sent the cross pin through the housing and put a dent in my floor. The 14 bolt just let go and would not drive, cross pin (3 pin like your d70 looks to be) was intact, but the carrier had enough and parted ways with itself. I have personally rebuilt a handful of axles with failed govlocs (yes, mostly 10 bolts) and have been involved in the recovery of countless more.

3) You are correct that the chances of catastrophic failure in the larger axles is lower, but still a very real possibility when used hard (like an 8,000lb van carrying itself over an obstacle with the traction from only 1 wheel.) I'll put my money on a machined steel part over a cast iron chunk any day of the week.

P.S. That diagram certainly looks like a GM Corporate 14 bolt (10.5") and NOT a Dana axle, yet the picture of your van's axle is definitely a Dana axle. To my knowledge, the govloc was never used outside of the gm corporate axles. In other words, your parts guy may be wrong.
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Old 10-23-2019, 06:53 PM   #9
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Quote:
Originally Posted by TheLetterJ View Post
1) axleshafts are probably cheaper than you think. I paid ~$350 for custom 35 spline Dutchman shafts, don't let that stop you.
Thanks for this. This is definitely encouraging to hear.

Quote:
Originally Posted by TheLetterJ View Post
2) I have personally exploded not 1, but 2 govlocs. The 1/2 ton variant sent the cross pin through the housing and put a dent in my floor. The 14 bolt just let go and would not drive, cross pin (3 pin like your d70 looks to be) was intact, but the carrier had enough and parted ways with itself. I have personally rebuilt a handful of axles with failed govlocs (yes, mostly 10 bolts) and have been involved in the recovery of countless more.
Roger that. What kind of use are we talking here?

Quote:
Originally Posted by TheLetterJ View Post
3) You are correct that the chances of catastrophic failure in the larger axles is lower, but still a very real possibility when used hard (like an 8,000lb van carrying itself over an obstacle with the traction from only 1 wheel.) I'll put my money on a machined steel part over a cast iron chunk any day of the week.
This is probably true. 100% of my use cases have been snow, sand and mud. Both sides of axles loaded equally with weight, one side losing traction before the other. All things considered gentle-ish(?) applications.

Quote:
Originally Posted by TheLetterJ View Post
P.S. That diagram certainly looks like a GM Corporate 14 bolt (10.5") and NOT a Dana axle, yet the picture of your van's axle is definitely a Dana axle. To my knowledge, the govloc was never used outside of the gm corporate axles. In other words, your parts guy may be wrong.
Yeah, I know what you mean, that hasty bolt pattern markup is completely wrong, but the housing cover outline is spot on. GM has been known to reuse diagrams they deem similar enough. You've mentioned 14 bolt twice now, but I thought they did not come on this generation of vans.

Lucky you, does this mean you have actual aftermarket options?

I appreciate your help navigating all this!
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Old 10-23-2019, 07:08 PM   #10
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I didn't think they put the G80 in the Dana 70 either.

PS - Possible to blow up the Dana 70 too. Ask me how I know.
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