GM G80 locker axle transplant on Sprinter along with 4x4 conversion

Figured I'd share a work in progress. I am just getting started and value input!

With a few minor differences I am playing along with Luthj converting my van to 4wd. I was salivating over the ARB front locker he installed, but after consideration decided I'd try something different, and it is a unique enough project I reckon it deserves to be it's own topic. The ARB air locker with compressor is just too much $$ on top of the rest of the 4wd conversion, and to me a rear locker is more useful. It turns out I can accomplish this much more cheaply, though it will take significantly more work hours.

Since the 4wd part of the project is based on GMT 800 series front end, and GM 8 bolt wheels, this was my starting point looking for rear axle options.

I went into it somewhat naively not knowing all the permutations of GM 8 bolt rear axles and quickly found a GM 14 bolt 9.5" rear on a 2003 Chevy Silverado in a u pull junk yard with proper 3.73 gear ratio, has a G80 gov lock, and looked in very good shape except for a little too easy preload and a bit too much backlash. I opened the rear cover while still on the vehicle and the ring gear looks very good, so I figure it will probably be fine with pinion preload and backlash reset. I pulled it and brought it home for $138

Note: the gov lock isn't the greatest, but for the price it's something at least to start with, and the GM diffs can all be upgraded with other options. So I'll go with it for now and see how it performs.

So, the naive aspect was I did not know that there are multiple versions of 14 bolt GM rear axles. The biggest differences are:

9.5" ring gear, semi floating axle. GM 2500 series. This one has a different sized diff case and different rear cover which can be identified by it's rounder shape. It is not quite as heavy duty as the full floaters, but should be plenty adequate for the Sprinter. It is a pretty large increase in ring and pinion size, and the axles and tubes are heavier.

10.5 ring gear, full floating axle. GM 2500 HD series identified by larger diff housing, more angular diff cover, full floating axle bearing protruding through wheel center with bolted on cap, and pinion mounted into a bearing/hub assembly that bolts into the diff housing

11.5" ring gear full floating axle GM 2500HD-3500 series has all the same attributes as the 10.5 except the pinion gear does not have the additional hub which mounts to the housing, rather having bearings mount directly into the diff housing

Some of them apparently started having ABS sensors in 2006, but back to around the beginning of the GMT800 series, the rear ABS function was based only on rear axle speed, not independent wheel speeds for each rear wheel. This was accomplished with a speed sensor at the output shaft of T case or transmission.

There is a kit for adding wheel sensors and tone rings on the 10.5 axle: But these rings do not have a number of teeth that easily multiplies/divides in order to manipulate for inputting into the Sprinter's ESP computer. The ideal would be to have a set cut with with 44 teeth.

Likewise, another aspect like with Luthj's 4wd conversion is if you use a GM rear that does have independent sensors, they are 55 tooth (vs T1N's 44 tooth so frequency needs to be corrected before signal is sent to Sprinter ESP/ABS system. This is more mathematically desirable that the kit above since 55 is divisible by the integer 11, not a repeating decimal. We both are already using an arduino based circuit to correct the front wheel speed frequencies from the 55 tooth rings, so it would be do-able to use the same circuit for rear wheels, but if 44 tooth tone rings could be used, so much the better.

Another problem looking at more recent GM axles is that somewhere around 2011 wheel bolt circle diameter went from 156mm to 180mm.

So after realizing I may have set myself up for failure with the 9.5" axle I purchased, I sought options to add sensors to play well with the Sprinter.
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I considered three options for adding tone rings and sensors (listed from worst to best):

1: Add a tone ring on the neck of the pinion dust cover/slinger and mount the sensor to a bracket on the diff case. Split this signal into two and feed each to the Sprinter's ESP. This option has a problem though in terms of tone ring tooth count since axle ratio would need to be taken into account, and could present problems in optimizing the split signal to play well with T1N, like sending one signal when turning, the ESP might want to see faster wheel speed from the faster spinning wheel, or electrical mismatch due to splitting one signal to two. It would also be really good to cover the whole unit and even add a seal of sorts to keep debris out of the tone ring and sensor gap

2: Use sensor placement like in the kit referenced above, and add a split collar to attach tone ring to the wee bit of axle shaft protruding from the axle bearing before it tapers up to the wheel flange. This would be really tight. There is less than 1/2" of shaft to work with.

3: use something like the kit referenced above for the sensor mount and come up with a way to attach the tone ring to the axle's wheel flange. This is looking like the best option.

In the second two cases, 44 tooth tone rings can be custom cut to match the sprinters tooth count so no correction of signal frequency is necessary. Since I'll be using Luthj's front conversion frame for my 4wd conversion, and will have to have the laser cutting done anyway, we'll add custom cut tone rings and perhaps some needed spacers to the laser cutting order.

This is where I am with this now, I'll add some pics soon and will update progress as I go.
I would use 3500 parts. You need to ensure that the axle ratings of the donor are equal to or better than that of the Sprinter.
Thanks, potentially good call. I should have noted the door tag rear axle weight. Can go back and check soon. Internet info is not excellent regarding axle weight for this 9.5" variant, but some info points at 5000-5500lb. Sprinter's is 5360.

Edit: This Sprinter is my cargo van converted to camper, and I am running 4260lb on the rear axle. I don't intend to run it as a unimog, rather lighter duty 4X4 use, though it would not be bad to have higher torque rating adding the low range, though the GM donor was 4x4 with low range anyway.

Edit #2, I called a dealership parts and service dept and asked for rear axle weight based on VIN. They only had GVW, not specifically rear axle. The donor GMC is 8600lb, Sprinter 8550, so we're in the same weight class.

Edit #3, Sprinter ring gear is 8.5", this axle has 9.5" Sprinter axle shaft is 26 spline with 5 bolt wheel flange. GM 9.5" 33 spline 8 bolt wheel flange

Honestly while a full float 10.5 would certainly be a HD upgrade, I am not too worried about this GM 9.5", but go ahead and tell me if I am an idiot (I know I can be at times)
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Alright! I made a model of the tone ring assembly and it will work. Still have a little dimensional tweaking to do

PIc 1- The mockup. Very simple, will amount to 4 parts. in this pic three of the 4; The larger flange mounts to the axle's wheel flange, the inner smaller ring is the tone ring itself. The tube is 3.5" ID, 4" OD DOM tubing machined/lathed square on the ends and welded into the flanges on a dead flat surface. This ensures concentricity and that the rings will be exactly perpendicular to the tube's axis. The DOM tube just fits over the axle housing tube and just inside the brake shoes and hardware


Pic 2: the mockup assembly roughly in place on the axle shaft. Note that there will be a laser cut spacer filling the space between the Lug bolt heads so the tone ring assembly can be bolted flush right into drilled tapped holes in the axle's wheel flange between the lugs... Also the outer flange on the mockup is oversized and the real part will be cut to the same diameter as the wheel flange


Pic 3, the axle and tone ring mockup in place in operating position with axle c clip in place. There is enough movement to install/remove c -clip for axle removal. There is clearance from the brake shoes/parts, and tone ring is a good distance from the back plate where the sensor will come through.



Engineer In Residence
So, the disc ring is the tone wheel? What is the purpose of the smaller inner disc?


Engineer In Residence
I think Len is referring to the later models that have ABS. You can get a GMT900 silverado 2500 semi-float axle for about 500-1500$ used, and it will have ABS sensors. There is an 09 2500 with 60k miles near me for ~$550. You would still need a frequency modifier unless you replaced the tone rings.
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luthj, I appreciate your input as always. What you have to say is duly noted and it is an echo of what I just did this week researching the entire local market for GM axles. I made the decision to work with this one with that in consideration.

I am however still open to discussion of specifics of what would make this such an upstream swim. So far, I don't see the problem. I'd really like to hear what Len's thinking from Len.


luthj hit it right on, you are doing a lot of custom work to an average axle that has limited aftermarket support, in addition the "gov-lock" locker for these axles aren't known for their function/reliability. used rear axles at picknpull yards are frequently less than $250, you can also search FB and CL classifieds to find a better fit that already has the tone ring, bigger brakes and full floating axles. both the 10.5 and 11.5 axles have excellent aftermarket support, and the factory g80 in the 11.5 is actually a pretty good differential. If it were me I'd also look at the ford sterling 10.25, it's an excellent axle that offers better ground clearance, has the tone ring, good brakes and good aftermarket support. I'd worry less about the wheel pattern, if anything you could swap to later outers up front an run the 180mm pattern, all the new trucks run that anyways so your choice of new take off wheels would be better..
Thanks @Len.Barron, the detailed info is really helpful, and this info is compelling enough to put this 9.5" on hold. While I don't shy away from doing the work to tune up the pinion and backlash and add the ABS wheel sensors and tone ring, these points are most pertinent to me:

-Aftermarket support if G80 turns out to be insufficient: (and rebuild-ability for the long haul)
-G80 in 11.5 "actually a pretty good differential" Can you elaborate on why the 11.5 G80 is better? Because it is larger, more rugged or is there something else mechanically different?

Sounds like this 9.5" is a bit of an odd duck compared to the 10.5 and 11.5

Re: "swapping outers", I already have 165mm wheels. So, that's a big minus related to going to 180mm.

Unfortunately right now there are no good u pull options locally. There are a few take offs with unknown diff guts for $550-ish, but I'd prefer to do the pull and save the cash.
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-G80 in 11.5 "actually a pretty good differential" Can you elaborate on why the 11.5 G80 is better? Because it is larger, more rugged or is there something else mechanically different?
yes the larger (11.5) differential allowed for the parts to be larger and more robust...even in the 10.5" configuration the factory locker isn't well thought of, most prefer to buy an open differential configuration then just install the Detroit locker as it is effectively a "lunchbox locker" for the 10.5" AAM diff. No one builds off the the 9.5, if you want a good axle in that general size you'd be better off starting with a full float Dana 60 or 70
Thanks again @Len.Barron Sincerely appreciated. I'll scrap this project, return this 9.5 and go for 11.5.

I looked into the Ford, looks like too much trouble due to incompatible wheel bolt circle diameter. Same as luthj, I am using a GMT 800 based front for the 4x4 conversion, and I already have the wheels so keeping it all with the 165mm GM wheels is a prerequisite.