Nothing Special’s guide to differentials
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G80 (aka Gov-Loc aka Eaton MLocker)
(edit: after a little more digging I found that G80 is the GM order code for this diff, Gov-Loc is the informal name they are often called by, and MLocker is what the manufacturer, Eaton, calls it.)
I don’t know a lot about G80 diffs either, so take this for what it’s worth. I know they are made by Eaton, and as far as I know were only available in GM vehicles from the factory and are only available for GM axles. They work like an open diff most of the time, freely allowing one tire to go slower and the other to go faster so you can corner with no tendency to scuff tires. But when the speed differential between the two sides gets too high a centrifugal governor engages some type of clutch to lock the two sides together.
This could be the best of all worlds, but I’ve heard that they are prone to breaking. That, along with my understanding that they’re only available for GM axles, make me less interested in them. So sorry that I don’t have more info on them. And again, I only know what I’ve read about them, so take this for what it’s worth.
(edit: after a little more digging I found that G80 is the GM order code for this diff, Gov-Loc is the informal name they are often called by, and MLocker is what the manufacturer, Eaton, calls it.)
I don’t know a lot about G80 diffs either, so take this for what it’s worth. I know they are made by Eaton, and as far as I know were only available in GM vehicles from the factory and are only available for GM axles. They work like an open diff most of the time, freely allowing one tire to go slower and the other to go faster so you can corner with no tendency to scuff tires. But when the speed differential between the two sides gets too high a centrifugal governor engages some type of clutch to lock the two sides together.
This could be the best of all worlds, but I’ve heard that they are prone to breaking. That, along with my understanding that they’re only available for GM axles, make me less interested in them. So sorry that I don’t have more info on them. And again, I only know what I’ve read about them, so take this for what it’s worth.
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Front differentials
As I said at the start, most of what I’ve written so far applies to rear axles. You can also put limited slips or lockers in a front axle. But should you?
I had an automatic locker in the front axle of a daily driver ’95 F-150 for one winter. The first time I drove in in the snow, I went to change lanes on the freeway. As the left front tire hit the ridge of snow between lanes the truck suddenly pulled so hard to the left that the truck had jumped over 10 feet before I could catch it! I thought I was more ready for it when I went to change lanes again, and that time it only jumped over about 6 feet. I shifted into 2WD and never used 4WD on the road again until I removed the locker and went back to an open diff.
I’d experienced the torque steer of an automatic locker in a rear axle before, so why was this so much worse? Physics. Torque steer from a locker in a rear axle is due to pushing the vehicle from one side, like pushing a grocery cart from one end of the handle. But it’s really not even that bad because, unlike a grocery cart, a truck has front tires that are trying to keep you going straight rather than a grocery carts casters that don’t care which direction they go.
But in a front axle, not only does driving only one tire give you torque steer from pushing on one side of the truck, it also tries to turn the steering wheel. It’s like if you jack up both front tires and unlock the steering. If you grab a front tire and try to turn it to the right or left you can, and the steering wheel will spin as you do. Normally with both front tires driving the right tire is trying to turn the steering wheel to the left. But at the same time the left front tire is trying to turn the steering wheel to the right and the two perfectly balance out.
With an automatic locker, when I hit snow with one front tire that balance was suddenly upset, and the steering wheel turned in my hands before I could react to it.
My opinion:
I’ve heard others say that clutch-type limited slips or Truetracs are fine in a front axle. They might be right. But the physics tells me that any differential that can put more torque to one tire than the other can give this unbalanced steering force. Yes an automatic locker will do that the most abruptly, going from balanced to zero on one side instantly. But for me, in any vehicle that might be driven in 4WD on snowy roads at higher speeds, it’s not worth it, and I’d never have anything but an open diff in that situation.
I’d make the same call for a vehicle that would be driven at higher speeds on less slippery surfaces, like in the desert. The risks of the changes in steering balance at higher speeds aren’t worth it to me, although I could maybe see using a Truetrac in that situation.
For a rockcrawler or mud truck I could see using an automatic locker. In my one year experience with an automatic locker in the front of my F-150 I found the low speed handling quirks to be pretty bad, but livable. So in rocks or mud, where positive drive of both tires is important, I could see it being worth the quirks.
Likewise in a mud truck I could see using a spool for the strength and traction in spite of the handling issues. I wouldn’t do that in a rock crawler that has to turn more often than a mud truck. But I could see using a welded diff in the front of a low-buck rock crawler.
The exception to me “open front diff only” rule would be a selectable locker. It IS an open diff when unlocked, which it would be all of the time unless it was needed. And I’d only use it at slow speeds where there’s time to react to changing steering balance. I would readily put a selectable locker in the front of a vehicle for any use except for one thing: cost. Still, eventually I hope to have them in both my rockcrawling Bronco and my daily driver pickup.
As I said at the start, most of what I’ve written so far applies to rear axles. You can also put limited slips or lockers in a front axle. But should you?
I had an automatic locker in the front axle of a daily driver ’95 F-150 for one winter. The first time I drove in in the snow, I went to change lanes on the freeway. As the left front tire hit the ridge of snow between lanes the truck suddenly pulled so hard to the left that the truck had jumped over 10 feet before I could catch it! I thought I was more ready for it when I went to change lanes again, and that time it only jumped over about 6 feet. I shifted into 2WD and never used 4WD on the road again until I removed the locker and went back to an open diff.
I’d experienced the torque steer of an automatic locker in a rear axle before, so why was this so much worse? Physics. Torque steer from a locker in a rear axle is due to pushing the vehicle from one side, like pushing a grocery cart from one end of the handle. But it’s really not even that bad because, unlike a grocery cart, a truck has front tires that are trying to keep you going straight rather than a grocery carts casters that don’t care which direction they go.
But in a front axle, not only does driving only one tire give you torque steer from pushing on one side of the truck, it also tries to turn the steering wheel. It’s like if you jack up both front tires and unlock the steering. If you grab a front tire and try to turn it to the right or left you can, and the steering wheel will spin as you do. Normally with both front tires driving the right tire is trying to turn the steering wheel to the left. But at the same time the left front tire is trying to turn the steering wheel to the right and the two perfectly balance out.
With an automatic locker, when I hit snow with one front tire that balance was suddenly upset, and the steering wheel turned in my hands before I could react to it.
My opinion:
I’ve heard others say that clutch-type limited slips or Truetracs are fine in a front axle. They might be right. But the physics tells me that any differential that can put more torque to one tire than the other can give this unbalanced steering force. Yes an automatic locker will do that the most abruptly, going from balanced to zero on one side instantly. But for me, in any vehicle that might be driven in 4WD on snowy roads at higher speeds, it’s not worth it, and I’d never have anything but an open diff in that situation.
I’d make the same call for a vehicle that would be driven at higher speeds on less slippery surfaces, like in the desert. The risks of the changes in steering balance at higher speeds aren’t worth it to me, although I could maybe see using a Truetrac in that situation.
For a rockcrawler or mud truck I could see using an automatic locker. In my one year experience with an automatic locker in the front of my F-150 I found the low speed handling quirks to be pretty bad, but livable. So in rocks or mud, where positive drive of both tires is important, I could see it being worth the quirks.
Likewise in a mud truck I could see using a spool for the strength and traction in spite of the handling issues. I wouldn’t do that in a rock crawler that has to turn more often than a mud truck. But I could see using a welded diff in the front of a low-buck rock crawler.
The exception to me “open front diff only” rule would be a selectable locker. It IS an open diff when unlocked, which it would be all of the time unless it was needed. And I’d only use it at slow speeds where there’s time to react to changing steering balance. I would readily put a selectable locker in the front of a vehicle for any use except for one thing: cost. Still, eventually I hope to have them in both my rockcrawling Bronco and my daily driver pickup.
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Lead Driver
Joined: Feb 2013
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From: Roseville, MN
Had a gov lock diff in my 1995 blazer. They are speed governed by a flyweight in the diff but still use clutchpack. Pulled someone out in reverse and it distroyed the flyweights and cam gear. I'd by a lockright and install in the open diff since it will be better than a limited slip.
I ordered new an f150 back in 1993 with front and rear limited slip option. Limited slip,worked,great in the front axle,although you can feel it straighten up the steering when in the dirt (trying to pull back to center). If,they would have made,the same option available in the superduties, i would have bought it again in a heartbeat! As you said though, a locker may have a distinctly different outcome.
The "pulling back to center" with the locker in the front was annoying (I'm sure it was stronger than with a limited slip), but even so it was tolerable. The dangerous situation was when one tire lost traction at higher speed(like when it hit snow or ice with the other tire still on pavement). Then it pulled toward the tire with no traction. I'm sure a limited slip would do this to some extent as well. I don't know if it would be horribly dangerous (like a locker) or not though.
Laughing Gas
Joined: Nov 2012
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From: Bismarck, ND
I had Sure-Grips in both front and rear of my '74 Powerwagon, 4.10 gears, part time hubs (Warn) and a divorced gear driven part time transfer case (did not bolt to the trans tail shaft for those of you confused by the term "divorced").
I only did snow/ice a couple times a year then (lived in AZ then), would take this hunting deer/elk in N. AZ country.
Most of the time the front diff was fine. I very, very rarely had the hubs locked on pavement, and would drive slower those times. In loose traction, you could definitely feel the torque steer if you got on it, but carefully feathering the gas pedal made it barely noticeable. Truck was heavy, especially front end, cast iron big block 440, gobs of torque. I always felt it was controllable, but was quite used to the rig in about any kind of off road conditions. But, if you unconsciously hammered the gas pedal, it would definitely try to swap ends on you.
I had front and rear Sure Grips in my '90 Wrangler as well. This was an entirely different animal driven with the front engaged. Snow and ice was squirrelly as hell, would swap ends on you in the blink of an eye if you got on it. I wouldn't let most people drive it on snow/ice. Other terrain, dirt, sand, rocks, Jeep trails, it was usually fine. Would definitely try to torque steer you, but not as quick to get out of hand as snow/ice.
Several guys in my Jeep club put in the ARB air lockers, and I really liked them in about any condition. I think if I was going to build a do-all general purpose rig like a CJ again, I'd go with the front and rear ARB air lockers. Really gives you the best of all worlds, ability to lock/unlock one or both diff's, depending on terrain demands.
I only did snow/ice a couple times a year then (lived in AZ then), would take this hunting deer/elk in N. AZ country.
Most of the time the front diff was fine. I very, very rarely had the hubs locked on pavement, and would drive slower those times. In loose traction, you could definitely feel the torque steer if you got on it, but carefully feathering the gas pedal made it barely noticeable. Truck was heavy, especially front end, cast iron big block 440, gobs of torque. I always felt it was controllable, but was quite used to the rig in about any kind of off road conditions. But, if you unconsciously hammered the gas pedal, it would definitely try to swap ends on you.
I had front and rear Sure Grips in my '90 Wrangler as well. This was an entirely different animal driven with the front engaged. Snow and ice was squirrelly as hell, would swap ends on you in the blink of an eye if you got on it. I wouldn't let most people drive it on snow/ice. Other terrain, dirt, sand, rocks, Jeep trails, it was usually fine. Would definitely try to torque steer you, but not as quick to get out of hand as snow/ice.
Several guys in my Jeep club put in the ARB air lockers, and I really liked them in about any condition. I think if I was going to build a do-all general purpose rig like a CJ again, I'd go with the front and rear ARB air lockers. Really gives you the best of all worlds, ability to lock/unlock one or both diff's, depending on terrain demands.
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From: Roseville, MN
I wasn't familiar with "Sure-Grip" so I did a very quick Google search on it. It seems to be simply Chrysler's name for a clutch-type limited slip (like TractionLock for Ford or Positraction for Eaton / GM).
Your experience is about what I'd expect, but it's good to hear it from someone with experience rather than just going by theory. I'd still like to hear people's experience driving on snow with a TrueTrac in front. But at least for now I'm going to stick with my rule of never driving in 4WD on snowy or icy roads with anything other than an open diff (or an unlocked selectable) in the front axle.
Your experience is about what I'd expect, but it's good to hear it from someone with experience rather than just going by theory. I'd still like to hear people's experience driving on snow with a TrueTrac in front. But at least for now I'm going to stick with my rule of never driving in 4WD on snowy or icy roads with anything other than an open diff (or an unlocked selectable) in the front axle.
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From: Roseville, MN
That video is pretty good. For people who want to look up certain things in it without having to watch the entire thing, here is an index:
I also think he overstates the driveability issues of an automatic locker when he talks about them not disengaging easily under a light vehicle. There's nothing in the design of a Detroit or any of the lunchbox lockers that would make them resist disengaging. I certainly haven't had any trouble with the Detroits in my CJ5 or Bronco or the LockRight in my F-150 not disengaging easily. But he is right that they don't engage or disengage with any finesse, and they do require you to "drive to the vehicle" and certainly aren't for everyone.
- 1:00 - Open differentials
- 3:40 - clutch-type limited slips (he just calls them "limited slip")
- 6:05 - gear-type limited slip (he calls them "Torsen")
- 10:30 - Selectable lockers, which he breaks down into air lockers (at 11:22), e-lockers (at 14:18) and manual lockers (at 17:50)
- 21:35 - automatic lockers (he calls them "Detroit lockers")
- 26:52 - spools
I also think he overstates the driveability issues of an automatic locker when he talks about them not disengaging easily under a light vehicle. There's nothing in the design of a Detroit or any of the lunchbox lockers that would make them resist disengaging. I certainly haven't had any trouble with the Detroits in my CJ5 or Bronco or the LockRight in my F-150 not disengaging easily. But he is right that they don't engage or disengage with any finesse, and they do require you to "drive to the vehicle" and certainly aren't for everyone.
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Thank you for the thorough write up!
I am in the selection phase of differential (and gear) replacement on my '07 F150. Its primary use is, like you, MN roads. But, I will be making a trip this November to the Baja 1000 to support a friend's race team and I want a very capable rig for whatever I have to drive over.
I was contemplating the Truetrac in the front as well as the back, but the possibility of ill behavior on the highway in the snow has me rethinking that idea. Also, after learning about the Torsen diff, I might want one of those.
If you have a strong opinion about diffs for a MN daily driver that will see some desert use once or twice a year, I'd appreciate it.
Off to read more.....
I am in the selection phase of differential (and gear) replacement on my '07 F150. Its primary use is, like you, MN roads. But, I will be making a trip this November to the Baja 1000 to support a friend's race team and I want a very capable rig for whatever I have to drive over.
I was contemplating the Truetrac in the front as well as the back, but the possibility of ill behavior on the highway in the snow has me rethinking that idea. Also, after learning about the Torsen diff, I might want one of those.
If you have a strong opinion about diffs for a MN daily driver that will see some desert use once or twice a year, I'd appreciate it.
Off to read more.....
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From: Roseville, MN
The TrueTrac and Torsen are pretty much the same thing. Gleason patented it and Eaton makes it on a license (although the patent has likely expired by now). There may be slight differences in bias, that might give noticeably different performance, but they work the same way.
As far as a TrueTrac / Torsen on MN winter highways, "they" say that it works fine (but who are they and what do they know?). Seriously, I know it would be less dramatic than an automatic locker (which I do have winter experience with and I strongly recommend against for that kind of use). But I also know that it would be less stable than an open diff. Sometime I'd kind of like to try one in the front, but I do think it would be a risk.
The one thing I can wholeheartedly recommend for a front axle (although still with no personal experience with it) is a selectable locker. It'd be open all the time on winter highways. When you need it, it would be a spool. I think for a lot of off-roading a TrueTrac might be easier to use, but a selectable is the only way to get really good on-road stability in 4WD and really good off-road traction.
As far as a TrueTrac / Torsen on MN winter highways, "they" say that it works fine (but who are they and what do they know?). Seriously, I know it would be less dramatic than an automatic locker (which I do have winter experience with and I strongly recommend against for that kind of use). But I also know that it would be less stable than an open diff. Sometime I'd kind of like to try one in the front, but I do think it would be a risk.
The one thing I can wholeheartedly recommend for a front axle (although still with no personal experience with it) is a selectable locker. It'd be open all the time on winter highways. When you need it, it would be a spool. I think for a lot of off-roading a TrueTrac might be easier to use, but a selectable is the only way to get really good on-road stability in 4WD and really good off-road traction.
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Thanks for your insight. I think I am going to go with the Truetrac in the rear and stick w/ the open diff in the front when I swap to 4.10 gears to compensate for the larger tires I put on. I think for the majority of what I will encounter, I'll be fine (knocking on wood).
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Joined: Jun 2015
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From: Littleton, CO
A Truetrac is going to perform just like a factory equipped clutch style LSD on snowy highways. Which is to say "virtually invisible".
The Truetrac offroad will actually work- unlike that factory equipped clutch style LSD.
The Truetrac offroad will actually work- unlike that factory equipped clutch style LSD.
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From: Roseville, MN
A clutch-type tries to stick the two sides together, regardless of what you are trying to do. How well it does that depends on how tight the clutches are set up. At the extreme loose end it will act just like an open diff. At the extreme tight end (which you can't actually get to) it will act just like a spool. My beef with clutch-type limited slips in the rear is that there is no "sweet spot" where it's tight enough for me without being too tight. In fact it's just the opposite. The 197K mile LSD in my F-250 is way too worn out to be at all useful, but it's still tight enough that it will scrub a worn back tire when coasting around a corner on packed snow. That makes the back end tend to slide out and required me to get new tires sooner than I otherwise would have needed to.
It'll do the same thing in the front, but with more weight on the tires it likely won't be as big of an issue.
TrueTracs don't try to lock the sides together, so they will exhibit none of this problem.
But the other issue is the torque steer. No matter how you do it, if you send unequal torque to the two front tires you will get torque steer, and the only diff that always sends equal torque to both sides is an open diff. An automatic locker will be the worst, because it will go back and forth between even to both, all to one, or all to the other, depending on whether you are turning or going straight and what traction each front tire has. As I said before, this is scary dangerous at highway speeds.
Limited slips, whether clutch- or gear-type, will also give torque steer. Clutch-types will do it differently if you are turning or going straight (gear-types won't do that), and both will do it as one or the other tire loses traction.
Whether this torque steer is dangerous or not I can't say. I know it wouldn't be as violent as an automatic locker, but I also know that it wouldn't be virtually invisible (unless the limited slip wasn't doing anything, like a worn out clutch-type).
Some time I would like to try a TrueTrac in a front axle in the snow so I can see what it's really like. But until I either experience it myself, or at least hear from someone who has real-world experience driving a TrueTrac on snowy freeways, I'm going to stick with the advice I'm giving, that I'd never recommend anything other than an open diff (or an unlocked selectable) in a front axle when driving on a snow covered highway.
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Truetrac in the front
After initially deciding to keep the open diff in the front, I did more searching of the innertube and came across this YouTube video:
https://youtu.be/HlP9Du8sVFc
He is a fella that lives in Northern MN. He said that the only time that the front Truetrac really noticeable is under hard acceleration while turning from a stop. You can see our exchange in the comments.
Since I am going to put new gears in the front, I think I will put the Truetrac in while it is open.
Bob, we'll have to get together for a test drive in the future.
https://youtu.be/HlP9Du8sVFc
He is a fella that lives in Northern MN. He said that the only time that the front Truetrac really noticeable is under hard acceleration while turning from a stop. You can see our exchange in the comments.
Since I am going to put new gears in the front, I think I will put the Truetrac in while it is open.
Bob, we'll have to get together for a test drive in the future.
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From: Roseville, MN
Good to hear from someone who's actually driven a front TrueTrac on the highway! As you asked him in the comments, my biggest concern would be lane changes where the tire tracks are mostly clear but there's a snow berm between lanes (as you know, a very common thing in MN after it snows but before the plows get finished). That's where the LockRight in my F-150 scared me. Driving on evenly icy roads like he showed in the video wasn't too bad. You could definitely feel it pull in different directions, but nothing you couldn't catch (at least in a longer wheelbase pickup, a CJ5 might be a different story).
I definitely want to try a TrueTrac in front sometime. I think it would be great for almost everything I (or most others) do with 4WD, as long as it doesn't have bad manners on snowy freeways.
I definitely want to try a TrueTrac in front sometime. I think it would be great for almost everything I (or most others) do with 4WD, as long as it doesn't have bad manners on snowy freeways.
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From: Littleton, CO
My Explorer is equipped with TTs front and back. Drive it on the freeway in dry, wet and snow.
It drives like........ normal.
Now that's when driving normal. If you want to switch off normal and have some fun, the TTs will help you have fun.
It drives like........ normal.
Now that's when driving normal. If you want to switch off normal and have some fun, the TTs will help you have fun.