M220 e-Locker Differential Deep Dive Overview - skip if you're TLDR prone...

[mpeugeot]

Yeah, what I meant was you tear into those for a living, not like one of us who just take things apart to see what's in them. I'm pretty good at the tear down, not so much at the rebuild.

Hope you get a M190 and 210. Really interested in what you find on the M190 and whether it's worth putting more money into it.

Absolutely want to see an M190 deep dive before I go in there!

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[mpeugeot]

That is very cool. I have the rear locker in my 4.27 rear axle on my Outer Banks, non-sasquatch. No front locker. It works very nicely. I can switch it on from the dash, or the computer turns it on in Sand mode.

Is the one you picture the same locker, or are there different lockers in different Bronco axle configurations? The Sasquatch uses 4.7 axles front and rear lockers, the Badlands non-sas 4.46 gearing.

I have a Torsen style LSD that I want to install in my 4.27 M190. I doubt that I need anything beefier for non-rock crawling, baja type running for the axle.

I like sand mode, but Baja and Rock Crawl modes are fun too. Baja has to be the most fun off-road mode for me.

 

[Yetibronco21]

Thanks for doing this for us. Looking forward to what ARB may have on the works

 

[Rocketeer Rick]

I have a Torsen style LSD that I want to install in my 4.27 M190. I doubt that I need anything beefier for non-rock crawling, baja type running for the axle.

Just out of curiosity, who is making a unit for the 190? I think the tricky part of install is, as I mentioned before, where do you get the 4.27:1 gears that are bolt-on. I haven't seen that yet either.

 

[lakesinai]

Just out of curiosity, who is making a unit for the 190? I think the tricky part of install is, as I mentioned before, where do you get the 4.27:1 gears that are bolt-on. I haven't seen that yet either.

Not sure of your question. The 4.27 are standard in the non-sas OBX with the Locker & auto transfer case, otherwise it has the 3.73 axle.

 

[Rocketeer Rick]

Not sure of your question. The 4.27 are standard in the non-sas OBX with the Locker & auto transfer case, otherwise it has the 3.73 axle.

Ah, well, when you go to install a replacement differential into the M190 (or at least the Ford version), you have to install a new ring & pinion gear set as well. You have to do this because in the Ford-spec version of the axle, Dana welded the ring gear to the diff housing. Normally, you would unbolt the ring gear and transfer it to the new diff. But with it welded on, that is not possible.

So you need to replace the ring gear with a version that will bolt on. They always come in sets, matched to the pinion gear. You still need the ratio to be the 4.27:1 ratio that the vehicle came with. The catch is, as I noted previously, the ratios that Ford picked for the Bronco are unusual. Common ratios include 3.73, 4.10, 4.56, 5.13, etc. These are what the aftermarket commonly produces. Sometimes you'll see a 4.30 or 3.90 thrown in the mix. But 4.27:1 is not normal, and thus not made in a bolt form that I've seen yet.

So, without the bolt-on R&P, you can't install the aftermarket diff. This problem is solvable on the trucks w/ 3.73 gears, because (apparently) you can borrow the R&P from the Wrangler parts bin. But as I pointed out, you can't use Ford factory parts here because they get welded on. A replacement ring & pinion set from the dealer will also have the open diff welded to it already...

 

[andrusoid]

This is actually the first thread I've started here. In case anyone is interested, I put together this look at workings of the M220 e-locking differential. I got my hands on a sample part through work for development purposes. I thought it would be interesting to show it in depth, going through a tear-down of the assembly.

So here’s the differential as it stands complete, as you might remove it from the axle (bearings removed):

The wiring connection goes into the axle casing above and to the right of the differential, there’s a pass-through connector that it plugs into from the inside.

At the “top” of the assembly (in our business, we consider the flange-end of the unit to be the bottom) sits the locking solenoid. This is an electromagnet and has a sliding armature inside it that will push on a dog clutch mechanism inside the diff casing when activated.

The solenoid itself is easy to remove, in fact, the Ford service manual for the axle shows that you remove the solenoid when you replace the differential. It will lift off of the top end once the journal bearing is removed; the bearing is basically the retainer for it. With the solenoid removed, there is a thrust washer and we’d call an “apply plate” remaining underneath where it sat. You can see those below:

The apply plate snaps onto the differential’s locking plate with little spring tabs. The apply plate looks like this:

Its just a .06” thick steel stamping, but it serves the purpose of connecting the solenoid (which is fixed from rotation inside the axle – otherwise the wiring would wrap up) and the lock plate inside the diff which, of course, spins at road speed. The plastic thrust washer that sits above it provides a low friction sliding surface to translate the motion of the solenoid armature to the apply plate.

So, if we take off those parts, we’re left with just the differential itself. Fundamentally, it’s a basic open differential design. However, it has 4 pinion gears (sometimes called “spider” gears) to connect the output gears to the casing. Typical open diffs have 2 pinion gears, so using 4 effectively doubles the strength of the gearing itself by spreading out the load across twice as many teeth at any given moment. So that’s a nice feature.

It might be nice functionally, but doing that adds a bit of complication (read: cost) to the design. For starters, the differential’s casing has to be made from 2 pieces for assembly purposes. Most open diff casings are 1-piece (and thus dirt cheap to make), and all the gears can be loaded through the holes in the sides.

In this design, the casing is split through the ring gear flange and relies on the ring gear bolts to hold it all together when assembled. This is the end cap piece after removal:

Removing that exposes the bevel gearing:

And the by lifting out the flange-end output gear, you can see the 4 pinions riding on their cross pins.

Having 4 pinions requires a more complicated cross pin – you can see it has one full-length pin, and two “half” pins, which are guided in a cross-drilled hole through the full pin. So, you can see where the part and assembly costs are increased.

If we further remove the cross pins (BTW, the half pins are retained with a spirol pin that’s driven into the casing from the flange end, you can see the holes they go in near the “1” and “3” marked on the casing), you can see into the housing with the remaining output gear in place. Removing these pins is a pain in the butt, which I am not detailing here. Here we see inside the casing with the pinions removed:

This gear is part of the lock device, but the lock plate that is operated by the solenoid is underneath it:

Also visible in this photo is the return spring, which holds the lock plate away from side gear when not in use. This is just a simple wave spring.
And then, finally, removing the lock plate from the assembly leaves an empty diff housing.

Note the five slots in the end of the housing, these are important in a couple of ways, which I’ll return to. The lock mechanism itself is about as dirt-simple as it could be. It uses what is called a “face clutch”, which has sort of like spline teeth that run radially outward instead of being parallel along the sides of a shaft. These “dog” teeth allow a lot of contact surface when engaged, with the benefit of only having slide a few millimeters to achieve a full engagement.

You could do the same thing with a sliding collar over a conventional spline, but it would have to translate over a greater length to have good strength. The picture to the left shows the face clutch in the relaxed position, to the right is engaged.

The actual teeth on the face clutch have a slight angle to them, so that they can drop into engagement easily when commanded. They also allow the spring to quickly pop them back out when the lock is turned off.

Of course, making it easier to pop out adds a concern about coming out when you don’t want it to. This is where the slots I referred to before have a role.

The slots work in conjunction with the protrusions, or what I call “towers” on the back side of the lock plate. The primary function of these towers is to create a torque flow path from the casing to the lock plate, and then on to the output gear when the lock is used. Normally, torque in a differential flow from the ring gear to the casing, then through the cross pin to pinion gears. The pinion gears transfer it to the output gears, and on out to the axle shafts.

However, when you lock the unit, you create an alternate torque flow, where it flows from the case to the lock plate, and to one output gear. It then is transferred to the other output gear through the pinions. The towers engage in the slots in the casing to allow that transfer, like a kind of keyway.

The towers and slots have a secondary function, which prevents the lock plate from accidentally popping out of engagement with the lock output gear. Note the shape of the towers – they have a 15-degree taper to the sides, which is match by a taper in the slots.

This is a rather clever bit of engineering - by having a taper angle to them, when any torque is applied to the differential at all in the locked mode, the tapers act as a sort of wedge cam. The load on the taper forces the lock plate to thrust into the mating clutch face on the gear; it can’t back out until the load is removed.

This also means that the solenoid doesn’t have to try to prevent unintended disengagement. It’s held in place mechanically.

Here is more detail of the components – to the right, gears laid out after removal from the housing. Below is all of the assembly’s parts spread out.

At the bottom of the page, we have the solenoid up close. The brown ring on the underside of it is the armature I mentioned above. It slides inside of the solenoid when activated, moving a total of about 3mm from the relaxed to engaged positions. As I mentioned before, the solenoid itself is not a rotating part. It has a retaining bracket that is held in place by the bearing cap bolts, which in turn keys onto the pin you can see in the 7:00 position in the photo at the bottom right. The solenoid has a molded bushing on its inside diameter, which allows it to ride on the differential casing while the casing spins inside it. Note that the plastic bushing on this particular part was damaged in shipping (Ford's service part group could do a better job packaging)...

I am not going to get into details of how the computer controls work for this, as that’s above my pay grade. But on a high level, the control module sends about 5 amps or so to the coil to activate the lock. It holds that current for a minute or so to make sure it has time to engage, then cuts the current down to maybe 2 amps to help hold the lock, but without drawing enough power to overheat the coil. When you (or the ECU) decide to disengage, it cuts the power, and the return spring pops the lock plate out of mesh just as soon as it isn’t torque bound. Overall, this whole system is pretty simple from an engineering perspective - very effective and reliable. There is little to fail. For the lock to physically break, you’d have to either shear the dog teeth off or the towers off.

I’ve run through the math; those features both have about a 30% safety factor above the shear strength of the axle shaft itself. And that, BTW, assumes that only 40% of the dog teeth actually carry significant load, and that only 3 of the 5 towers are pulling their weight. Past that, the electromagnet can’t really fail unless a wire is cut. The solenoid mechanism really must work if current is applied the to the coil, there’s little choice from a physics perspective. The only other failure mode is then if the ECU that operates takes a dump. But that could be field fixed by rewiring the solenoid to a simple switch and relay.

Then consider that a design like this will essentially drop into the existing axle packaging. Aside from a wiring port, there are no extra pieces of hardware required, no plumbing to run, no servos or shift motors to mount to make it work. That’s why most truck manufacturers have adopted this or something similar. The locking differential in the F-150 is essentially the same design, though there are differences in how it’s packaged.

Although the M220 axle is made by Dana, I think that this e-locker is sourced from GKN. The tapered tower design is their patent feature. Ford also buys the F-150 lockers from GKN as well. Dana uses Eaton e-lockers in their aftermarket Jeep axle assemblies, so it could be that Ford directed them use the GKN design here. The Eaton design has a similar operating principle but relies on sliding pins into a lock plate instead of the face clutch as I recall. There are a lot of different variations on the theme out there, but hopefully this gives a good overview of how they work.

Thanks for that. Looks as the face clutch is way better than the sliding pin design.

 

[lakesinai]

Ah, well, when you go to install a replacement differential into the M190 (or at least the Ford version), you have to install a new ring & pinion gear set as well. You have to do this because in the Ford-spec version of the axle, Dana welded the ring gear to the diff housing. Normally, you would unbolt the ring gear and transfer it to the new diff. But with it welded on, that is not possible.

So you need to replace the ring gear with a version that will bolt on. They always come in sets, matched to the pinion gear. You still need the ratio to be the 4.27:1 ratio that the vehicle came with. The catch is, as I noted previously, the ratios that Ford picked for the Bronco are unusual. Common ratios include 3.73, 4.10, 4.56, 5.13, etc. These are what the aftermarket commonly produces. Sometimes you'll see a 4.30 or 3.90 thrown in the mix. But 4.27:1 is not normal, and thus not made in a bolt form that I've seen yet.

So, without the bolt-on R&P, you can't install the aftermarket diff. This problem is solvable on the trucks w/ 3.73 gears, because (apparently) you can borrow the R&P from the Wrangler parts bin. But as I pointed out, you can't use Ford factory parts here because they get welded on. A replacement ring & pinion set from the dealer will also have the open diff welded to it already...

I have to say I'm very glad that I'm quite satisfied with the stock rear locker I have for beach driving, and that I don't have enough expertise or knowledge to want something better! But I enjoy reading y'all's expertise on what's possible!

 

[Winger57]

In the end is thus a feasible upgrade for those trim levels not equipped with a front locker?

 

[Dusty]

This is actually the first thread I've started here. In case anyone is interested, I put together this look at workings of the M220 e-locking differential. I got my hands on a sample part through work for development purposes. I thought it would be interesting to show it in depth, going through a tear-down of the assembly.

So here’s the differential as it stands complete, as you might remove it from the axle (bearings removed):

The wiring connection goes into the axle casing above and to the right of the differential, there’s a pass-through connector that it plugs into from the inside.

At the “top” of the assembly (in our business, we consider the flange-end of the unit to be the bottom) sits the locking solenoid. This is an electromagnet and has a sliding armature inside it that will push on a dog clutch mechanism inside the diff casing when activated.

The solenoid itself is easy to remove, in fact, the Ford service manual for the axle shows that you remove the solenoid when you replace the differential. It will lift off of the top end once the journal bearing is removed; the bearing is basically the retainer for it. With the solenoid removed, there is a thrust washer and we’d call an “apply plate” remaining underneath where it sat. You can see those below:

The apply plate snaps onto the differential’s locking plate with little spring tabs. The apply plate looks like this:

Its just a .06” thick steel stamping, but it serves the purpose of connecting the solenoid (which is fixed from rotation inside the axle – otherwise the wiring would wrap up) and the lock plate inside the diff which, of course, spins at road speed. The plastic thrust washer that sits above it provides a low friction sliding surface to translate the motion of the solenoid armature to the apply plate.

So, if we take off those parts, we’re left with just the differential itself. Fundamentally, it’s a basic open differential design. However, it has 4 pinion gears (sometimes called “spider” gears) to connect the output gears to the casing. Typical open diffs have 2 pinion gears, so using 4 effectively doubles the strength of the gearing itself by spreading out the load across twice as many teeth at any given moment. So that’s a nice feature.

It might be nice functionally, but doing that adds a bit of complication (read: cost) to the design. For starters, the differential’s casing has to be made from 2 pieces for assembly purposes. Most open diff casings are 1-piece (and thus dirt cheap to make), and all the gears can be loaded through the holes in the sides.

In this design, the casing is split through the ring gear flange and relies on the ring gear bolts to hold it all together when assembled. This is the end cap piece after removal:

Removing that exposes the bevel gearing:

And the by lifting out the flange-end output gear, you can see the 4 pinions riding on their cross pins.

Having 4 pinions requires a more complicated cross pin – you can see it has one full-length pin, and two “half” pins, which are guided in a cross-drilled hole through the full pin. So, you can see where the part and assembly costs are increased.

If we further remove the cross pins (BTW, the half pins are retained with a spirol pin that’s driven into the casing from the flange end, you can see the holes they go in near the “1” and “3” marked on the casing), you can see into the housing with the remaining output gear in place. Removing these pins is a pain in the butt, which I am not detailing here. Here we see inside the casing with the pinions removed:

This gear is part of the lock device, but the lock plate that is operated by the solenoid is underneath it:

Also visible in this photo is the return spring, which holds the lock plate away from side gear when not in use. This is just a simple wave spring.
And then, finally, removing the lock plate from the assembly leaves an empty diff housing.

Note the five slots in the end of the housing, these are important in a couple of ways, which I’ll return to. The lock mechanism itself is about as dirt-simple as it could be. It uses what is called a “face clutch”, which has sort of like spline teeth that run radially outward instead of being parallel along the sides of a shaft. These “dog” teeth allow a lot of contact surface when engaged, with the benefit of only having slide a few millimeters to achieve a full engagement.

You could do the same thing with a sliding collar over a conventional spline, but it would have to translate over a greater length to have good strength. The picture to the left shows the face clutch in the relaxed position, to the right is engaged.

The actual teeth on the face clutch have a slight angle to them, so that they can drop into engagement easily when commanded. They also allow the spring to quickly pop them back out when the lock is turned off.

Of course, making it easier to pop out adds a concern about coming out when you don’t want it to. This is where the slots I referred to before have a role.

The slots work in conjunction with the protrusions, or what I call “towers” on the back side of the lock plate. The primary function of these towers is to create a torque flow path from the casing to the lock plate, and then on to the output gear when the lock is used. Normally, torque in a differential flow from the ring gear to the casing, then through the cross pin to pinion gears. The pinion gears transfer it to the output gears, and on out to the axle shafts.

However, when you lock the unit, you create an alternate torque flow, where it flows from the case to the lock plate, and to one output gear. It then is transferred to the other output gear through the pinions. The towers engage in the slots in the casing to allow that transfer, like a kind of keyway.

The towers and slots have a secondary function, which prevents the lock plate from accidentally popping out of engagement with the lock output gear. Note the shape of the towers – they have a 15-degree taper to the sides, which is match by a taper in the slots.

This is a rather clever bit of engineering - by having a taper angle to them, when any torque is applied to the differential at all in the locked mode, the tapers act as a sort of wedge cam. The load on the taper forces the lock plate to thrust into the mating clutch face on the gear; it can’t back out until the load is removed.

This also means that the solenoid doesn’t have to try to prevent unintended disengagement. It’s held in place mechanically.

Here is more detail of the components – to the right, gears laid out after removal from the housing. Below is all of the assembly’s parts spread out.

At the bottom of the page, we have the solenoid up close. The brown ring on the underside of it is the armature I mentioned above. It slides inside of the solenoid when activated, moving a total of about 3mm from the relaxed to engaged positions. As I mentioned before, the solenoid itself is not a rotating part. It has a retaining bracket that is held in place by the bearing cap bolts, which in turn keys onto the pin you can see in the 7:00 position in the photo at the bottom right. The solenoid has a molded bushing on its inside diameter, which allows it to ride on the differential casing while the casing spins inside it. Note that the plastic bushing on this particular part was damaged in shipping (Ford's service part group could do a better job packaging)...

I am not going to get into details of how the computer controls work for this, as that’s above my pay grade. But on a high level, the control module sends about 5 amps or so to the coil to activate the lock. It holds that current for a minute or so to make sure it has time to engage, then cuts the current down to maybe 2 amps to help hold the lock, but without drawing enough power to overheat the coil. When you (or the ECU) decide to disengage, it cuts the power, and the return spring pops the lock plate out of mesh just as soon as it isn’t torque bound. Overall, this whole system is pretty simple from an engineering perspective - very effective and reliable. There is little to fail. For the lock to physically break, you’d have to either shear the dog teeth off or the towers off.

I’ve run through the math; those features both have about a 30% safety factor above the shear strength of the axle shaft itself. And that, BTW, assumes that only 40% of the dog teeth actually carry significant load, and that only 3 of the 5 towers are pulling their weight. Past that, the electromagnet can’t really fail unless a wire is cut. The solenoid mechanism really must work if current is applied the to the coil, there’s little choice from a physics perspective. The only other failure mode is then if the ECU that operates takes a dump. But that could be field fixed by rewiring the solenoid to a simple switch and relay.

Then consider that a design like this will essentially drop into the existing axle packaging. Aside from a wiring port, there are no extra pieces of hardware required, no plumbing to run, no servos or shift motors to mount to make it work. That’s why most truck manufacturers have adopted this or something similar. The locking differential in the F-150 is essentially the same design, though there are differences in how it’s packaged.

Although the M220 axle is made by Dana, I think that this e-locker is sourced from GKN. The tapered tower design is their patent feature. Ford also buys the F-150 lockers from GKN as well. Dana uses Eaton e-lockers in their aftermarket Jeep axle assemblies, so it could be that Ford directed them use the GKN design here. The Eaton design has a similar operating principle but relies on sliding pins into a lock plate instead of the face clutch as I recall. There are a lot of different variations on the theme out there, but hopefully this gives a good overview of how they work.

Awesome deep dive! Tech like this is why forums>facebook for discussion groups. This will always be indexed and searchable. I'm sure I will refer back to it again and again. Big thanks for taking the time to do it.

 

[mpeugeot]

Ah, well, when you go to install a replacement differential into the M190 (or at least the Ford version), you have to install a new ring & pinion gear set as well. You have to do this because in the Ford-spec version of the axle, Dana welded the ring gear to the diff housing. Normally, you would unbolt the ring gear and transfer it to the new diff. But with it welded on, that is not possible.

So you need to replace the ring gear with a version that will bolt on. They always come in sets, matched to the pinion gear. You still need the ratio to be the 4.27:1 ratio that the vehicle came with. The catch is, as I noted previously, the ratios that Ford picked for the Bronco are unusual. Common ratios include 3.73, 4.10, 4.56, 5.13, etc. These are what the aftermarket commonly produces. Sometimes you'll see a 4.30 or 3.90 thrown in the mix. But 4.27:1 is not normal, and thus not made in a bolt form that I've seen yet.

So, without the bolt-on R&P, you can't install the aftermarket diff. This problem is solvable on the trucks w/ 3.73 gears, because (apparently) you can borrow the R&P from the Wrangler parts bin. But as I pointed out, you can't use Ford factory parts here because they get welded on. A replacement ring & pinion set from the dealer will also have the open diff welded to it already...

You can use a 4.30, as it's close enough, but I would prefer a 4.27. Now, Ford did state that they were going to have a 5.13 R&P (which I would consider) for the M190/220, which would be interesting. I have a set of 4.27 gears, but they may not work in the M190 (as I would need to see what I am up against). I would like to find a M190 in the junkyard a year or two down the line for a reasonable price to see what can and can't be done to it.

 

[VoltageDrop]

This is a great post, thanks for doing it.

I have a non-sas Base and have always thought that some day I would find a 4.46 with locking diff from a junkyard or salvage Badlands and just do a full axle swap. But this part you wrote makes it sounds like it wouldn't be as simple as just routing 12V to engage it:

" But on a high level, the control module sends about 5 amps or so to the coil to activate the lock. It holds that current for a minute or so to make sure it has time to engage, then cuts the current down to maybe 2 amps to help hold the lock, but without drawing enough power to overheat the coil. When you (or the ECU) decide to disengage, it cuts the power, and the return spring pops the lock plate out of mesh just as soon as it isn’t torque bound. "

I have an OEM F250 10.5" electric locker I'm putting in my 69 Bronco axle and guys have tested those coils overnight at 12V and they don't get hot, even without oil splashing around them. I bet it would be fine but it also wouldn't be hard to make a little circuit to do it properly. Some other systems will probably need to know your axle is locked so there might be other considerations if powering the locker directly. You wouldn't want to accidentally use trail turn assist with the rear locker engaged

 

[Rocketeer Rick]

You can use a 4.30, as it's close enough, but I would prefer a 4.27. Now, Ford did state that they were going to have a 5.13 R&P (which I would consider) for the M190/220, which would be interesting. I have a set of 4.27 gears, but they may not work in the M190 (as I would need to see what I am up against). I would like to find a M190 in the junkyard a year or two down the line for a reasonable price to see what can and can't be done to it.

You could probably use a 4.30, but that's barely close enough. I'd be happier is it was a little closer. But even then, I don't see where there is a 4.30:1 available for the M190 either. What are the 4.27 gears you have from? I'd be interested to see what people are finding and what will ultimately work.

 

[tjdeerslayer37]

this seems to be a far better design than the eaton E-lockers i have messed with. those have a set of 6 pins that are shot into a mating plate but only have about 1/16" of engagement on the pins. that makes it very easy for them to pop out and round off the pins making the locker useless.

 

[Winger57]

Ah, well, when you go to install a replacement differential into the M190 (or at least the Ford version), you have to install a new ring & pinion gear set as well. You have to do this because in the Ford-spec version of the axle, Dana welded the ring gear to the diff housing. Normally, you would unbolt the ring gear and transfer it to the new diff. But with it welded on, that is not possible.

So you need to replace the ring gear with a version that will bolt on. They always come in sets, matched to the pinion gear. You still need the ratio to be the 4.27:1 ratio that the vehicle came with. The catch is, as I noted previously, the ratios that Ford picked for the Bronco are unusual. Common ratios include 3.73, 4.10, 4.56, 5.13, etc. These are what the aftermarket commonly produces. Sometimes you'll see a 4.30 or 3.90 thrown in the mix. But 4.27:1 is not normal, and thus not made in a bolt form that I've seen yet.

So, without the bolt-on R&P, you can't install the aftermarket diff. This problem is solvable on the trucks w/ 3.73 gears, because (apparently) you can borrow the R&P from the Wrangler parts bin. But as I pointed out, you can't use Ford factory parts here because they get welded on. A replacement ring & pinion set from the dealer will also have the open diff welded to it already...

Genius! Proprietary Ratios and welding the ring gears seems pretty well aimed at adding a level of expense and difficulty at the average do it yourself mechanic. I wonder was this Ford directed or vendor?

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