GM Axle transplant, 4x4 adding a locker rear axle

mountainhick

Active member
With a few minor differences I am playing along with Midwestdrifter converting my van to 4wd. I was salivating over the ARB 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. To me a rear locker is more useful, and 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 which fit proper 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: https://www.artecindustries.com/abs_kit_14b 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 MWD'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.

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. Next post...
 
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mountainhick

Active member
Re: GM Axle transplant, adding a locker rear axle

I considered three options for adding tone rings and sensors:

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 aproblem 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. 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 MWD'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.
 
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Midwestdrifter

Engineer In Residence
Re: GM Axle transplant, adding a locker rear axle

Sticking with the sprinters sensors and 44 tooth rings is worth it I think. Especially if you can fit a tone wheel somewhere near the hub. The sprinters sensor needs a small gap, so the runout on the tone wheel needs to be less than 15 thousands I think. It should be easy to do with machined parts. Pretty Sure I could do that with hand tools, but it would take a bit of fiddling to get right.
 

99sport

Well-known member
Re: GM Axle transplant, adding a locker rear axle

If I am interpreting option number 1 correctly (measuring the speed at the pinion / input to the diff) you would need a tone ring with 44 teeth multiplied by your axle ratio. I have a 3.727 ratio and 44x3.727=163.988, which might be close enough to 164 for the ESP to not notice the difference. I have no idea what would happen when you go around a turn and the ESP sees the difference in speed at the front wheels and not the back, but I suspect it might not like that.

Regarding splitting the signal, it might be easier to just install 2 sensors reading the same tone ring, although I suspect the cornering issue will force you to measure speed at the wheels anyway


I considered three options for adding tone rings and sensors:

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 would require custom cutting 44 tooth tone wheels, and could have presented problems in optimizing the split signal to play well with T1N. 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 all cases, the ideal is to cut custom 44 tooth tone rings. Since I'll be using MWD'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.
 

mountainhick

Active member
Re: GM Axle transplant, adding a locker rear axle

If I am interpreting option number 1 correctly (measuring the speed at the pinion / input to the diff) you would need a tone ring with 44 teeth multiplied by your axle ratio. I have a 3.727 ratio and 44x3.727=163.988, which might be close enough to 164 for the ESP to not notice the difference. I have no idea what would happen when you go around a turn and the ESP sees the difference in speed at the front wheels and not the back, but I suspect it might not like that.

Regarding splitting the signal, it might be easier to just install 2 sensors reading the same tone ring, although I suspect the cornering issue will force you to measure speed at the wheels anyway

Yes, correct, that tone ring would need electronic mathematical correction, and it could be better to use a different tooth count that is better mathematical match with less error. And yes, there could be error with the ESP expecting to see differing wheel speeds cornering. That is partly what I was referring to as problem with the split signal playing well with the ESP

Thanks, I edited the previous post

And sorry it may be a little confusing that I listed the options in order of worst to best in terms of potential feasibility. #3 is what I am actually going for. I took detailed measurements yesterday and will be making a mock model today.
 
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mountainhick

Active member
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/lather 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 tubes 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 thye 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 with axle c clip in place ensuring proper position so the axle shaft can be removed, so there is clearance from the brake shoes/parts, and a good distance from the back plate where the sensor will come through/
 

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mountainhick

Active member
I had some challenges over whether to do this with this used 9.5" axle I pulled, with a couple recommendations for the 10.5 full floater. Looks like I am heading back to doing the deed with this one

What I found looking for 10.5s: for the sure thing full meal deal with sensors, means 2009-2010 model year. These are going on average for $1000-1500 on the used market with one available locally at $895. This is flat out a no go for me based on price.

To add tone rings AKA the artec kit, to 10.5" years 99-2006, bearing axle hubs need to be machined and tone rings press fit. This means pretty close to the same machine shop charges for turning tube ends square in my design for 9.5" modelled above in this thread, I would prefer to laser cut 44 tooth rings anyway rather than use arduino for correction from 52 or 60 tooth rings, and adding sensors is exactly the same proposition regardless of 10.5 vs 9.5. So costs and amount of work in either case is a wash.

And, trying to find a 10.5 axle at a good price to restart the whole dang process, then having essentially the same amount of work to do on it as this 9.5 that I already have... well...

Two things remain questions regarding the ring and pinion in this 9.5" :

I checked a couple of the diff ring/pinion aspects on my 9.5". Backlash is actually in spec at .008.

EDIT: UPDATE; Gear contact is looking better. I added more pigment and thickened my marking compound... see attachments

I measured pinion preload it is way under spec, 1 in lb.

spec is:
Pinion Preload New: 15 to 22 in-lbs
Pinion Preload Reused: 7 to 9 in-lbs

Whaddya think, crank the crush a bit and call it good?
 

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mountainhick

Active member
Cranked preload, got it to 8-10 in-lb. As it is reused I am going to leave it there.

I think I am set with the innards.Now to the tone ring assembly. I got one quote on the DOM tubing at ~$30, a piece long enough to chuck in a lathe and my local machinist says around $40 to square, part and finish 2 pcs. All I will need are the laser cut disks, then mount sensors and do the welding bits to get it to play with the Sprinter mounting.


This is a go!
 

mountainhick

Active member
WOW! Many things in my life have been going quite poorly lately. Today I am a happy man. I finished the setup on this diff:

Spec:
Pinion Preload New: 15 to 22 in-lbs
Pinion Preload Reused: 7 to 9 in-lbs

My final preload 10-12in lbs


Spec:
Ring Gear Backlash: .006" to .010"

My final backlash .007"

Contact pattern PERFECT!
 

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mountainhick

Active member
Well, it's been a while. I came down with a bad case of Leukemia last October. I am not out of the woods, still having blood transfusions for anemia and getting over fungal pneumonia (bothe due to te cancer) but regained a little bit of energy. The Sprinter has been up on blocks since last September. I only hope I can get it back on the ground and mobile soon!

So, today, finally I got back to this project.

I had the flat parts laser cut when I had the frame assembly cut for the 4WD project. The center is 3.5" ID DOM pipe I had my local guy lathe square.

Here is the spacer which provides level surface for tone ring assembly to sit on.

spacer-1.jpg

And in place on the wheel flange

spacer-2.jpg

Here is a tone ring assembly freshly welded and set in place on the spacer. Now I need to drill and tap holes, clean everything, paint and bolt together.

tone ring-1.jpg
 
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vanski

If it’s winter, I’m probably skiing..
as I’m sure you’re well aware, great things are happening in Leukemia treatment. My buddy had/has it.. his body took the bone marrow transplant but then the L came back. Now he’s been on some kind of drug which has enabled his body to kill it or at least keep it at levels which are not of concern. Very minute. Which is kind of crazy because for the longest time L was like being pregnant; you either are or are not pregnant...

Congrats on getting back to the project! I can only imagine how nice it must be..
 

mountainhick

Active member
BTW, the Sprinter tone ring count is 54 teeth, not 44 as previously discussed. The GM count is 55. This is close enough that no electronic frequency adjustment is needed. Since I'll be using a GM front end, I made the rear the same at 55.
 

mountainhick

Active member
Some progress. I ran into problems aligning things and drilling into the axle flanges. The axle metal is hardened, and I don;t have good drill bits for this application. Also broke a tap inside a drilled hole.

So plan B, rather than bolting all together, I turned a wood spacer on my lathe to be sure everything is concentric, and welded all together. The problem with this is that if I ever need to replace a lug bolt, I'll have to grind through 4 welds to remove the tone ring assembly. In retrospect it would have been good to cut clearance holes like on the spacer (post #12 above) but larger diameter in order for the lug bolts to have an opening to be removed. Live and learn when prototyping.

Clamped with spacer ready to weld.

axleassmbly-1.jpg


fully assembled, being painted:

axleassmbly-2.jpg
 
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tbuyan

'04 3500 140" low roof cargo w/dually delete
I too have longed for a locking diff, but lately a "yeah but" has me wondering: As I understand it, the function of the steering angle sensor is to reassure the computer that it's OK that the wheels are not all rotating at the same speed when the van is negotiating a turn. So, is the converse not also true? Does the computer expect the steering angle sensor signal to be "straight ahead" if all wheels are rotating at the same speed? That is, if the rear axle is locked (both rear wheels rotating at the same speed), and you turn the steering wheel (steering angle sensor signal not "straight ahead") will the computer not expect to see different wheel speeds left and right? And if so, what happens? Put another way, what happens if the rear wheels are rotating at the same speed but the front wheels are not pointed straight ahead and are rotating at different speeds?
 

BrennWagon

He’s just this guy, you know?
I think the question is if turning off the stability control with the dash switch will have any effect on how the computer interprets the wheel speed signals. If it does, lockers shouldn’t present much problem. I recall someone who put a T1N engine and drive train in another vehicle mounted the tone wheel and sensor(s) to the drive shaft, so it may be no issue whatsoever
 

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