TCUCV
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So I've heard our trucks don't have a detroit locker in the rear but just a posi track system?
Anyone else run inti this?
Anyone else run inti this?
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No Detroit locker in rear?
- Thread starter TCUCV
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Negative. The CUCV chevy trucks came with a Detroit locker in the rear. The CUCV blazer had a gov-lock which is hybrid of a posi/locker unit (crap).
buzzinhalfdozzen
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X2. Gov-loc = junk
bushhawg73
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The best way to answer the question is to pull the cover and take a look. I just did and my M1008 has the Detroit locker. It was time to change the diff oil anyway and now I know for sure.
It could have anything under it once it's in civvy hands. Mine no longer has original gears. Not everyone changes out the lockers/carriers when they change gears. Most of the confusion comes from the fact the 1009's use a Gov-lok which is a totally different animal than a Detroit locker, and the contact maintenance trucks indeed use a limited slip (but it's in the front).
Not an expert but this is what I know regarding how the Chevy's were equipped when Uncle Sam owned them:
m1009 blazer had 10 bolt 3.07 ratio rears, open front, gov-lok rear.
Everything else 4.56 ratio with one ton driveline.
m1008 Dana 60 open front, 14 bolt rear with detroit locker
m1010 Dana 60 open? front, 14 bolt rear with Detroit locker.
m1028 Dana 60 front with trac-lok limited slip, rear depends on which revision. Can be either 14 bolt or Dana 70 dually rear with Detroit locker
m1031 Dana 60 front with trac-lok limited slip, 14 bolt rear with Detroit locker
Another oddball driveline difference between CUCV's
Anything with a PTO driven generator (some M1028's? and all m1031's) used the NP205 transfer case instead of the NP208.
NONE of the above should be considered written in stone - there are exceptions, especially when it comes to National Guard trucks. If a part from another CUCV interchanged, they may or may not have used it. There are trucks out there "owned" by small Nat Guard units that are literally cobbled together from spare parts. The Army isn't as organized as some people think it is.
My point is: The only way to know for sure what's in your diffs is to pull the covers and look for yourself. Anything 25+ years old that's had multiple owners is bound to have a few hidden surprises.
TCUCV
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Supposedly my mechanic told me that its not a Detroit locker but a posi-trac system...I'm going to be checking it out personally next week. Do the Detroit lockers have their logo on them? How can I tell the difference? I guess it's possible someone could have taken the Detroit locker out before I got to the truck but I was the first civilian to get this particular truck. I will update sometime next week...
91W350
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I am betting it has the Detroit, back up and to the right in a slow tight circle with light braking, then drop it in drive. A lot of times the Detroits will bang, kick the truck sideways a little and make the drive shaft ring. They do not always do it, but if you catch it loading up to ratchet or lock and change the rotation, they can really ring the shaft. Occasionally you will feel an unlock kick when slowing down, almost feels like you skipped a tooth on the ring gear. Glen
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Genuine Detroit or not Detroit? I have wondered about this myself. Have a '77 Chevy C20 w/14bolt corporate and had Detroit Locker installed back in the early 90's. It's basically a solid axle while you accelerate and only unlocks when free wheeling or in a turn. And it does sound-off fairly often and with gusto. But it's never missed a beat and I've never been stuck in this vehicle either at work or while off-roading. Had it installed by a pro off road shop in Pomona off Garey Ave, forgot their name.
My point is--- these guys told me, at the time, that too many sales-types use the name Detroit Locker for a bunch of different manufacturer's locking units. Not going to try an list them here but I will say this; my M1008 rear axle acts quite a bit different than my KNOWN Detroit Locker in the '77 Chevy. The 1008 is a smoother transition when locking up at slow speed and rarely ever gives that big, loud, Detroit KA-LANK! However, the Chevy's locker is really pronounced and noticeable when it locks up--- all this at slow speed--- and sometimes at highway speeds it will, if you give it just the right bit of pedel, make that lock/unlock sound that you just can't miss. Had my M1008 for a year now and hve yet to hear/feel that same sound. So, I've begun to wonder whether these trucks have identical locking units, perhaps the 1008's is an updated version--- but until I pull both trucks rear axle covers at the same time the mystery will remain...
My point is--- these guys told me, at the time, that too many sales-types use the name Detroit Locker for a bunch of different manufacturer's locking units. Not going to try an list them here but I will say this; my M1008 rear axle acts quite a bit different than my KNOWN Detroit Locker in the '77 Chevy. The 1008 is a smoother transition when locking up at slow speed and rarely ever gives that big, loud, Detroit KA-LANK! However, the Chevy's locker is really pronounced and noticeable when it locks up--- all this at slow speed--- and sometimes at highway speeds it will, if you give it just the right bit of pedel, make that lock/unlock sound that you just can't miss. Had my M1008 for a year now and hve yet to hear/feel that same sound. So, I've begun to wonder whether these trucks have identical locking units, perhaps the 1008's is an updated version--- but until I pull both trucks rear axle covers at the same time the mystery will remain...
91W350
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I have never slipped a single wheel in either one of my M1008s. This one bangs a lot more frequently than the older one did. This truck has 40,000 miles and the old one was twice that when it got plowed by a Suburban. Frequently when accelerating in a turn I also get that friendly kick. I installed a Detroit in a Toyota axle and you could slip the clutch in a tight turn and listen to it click. I have not been able to do that in these Chevrolets, but the engine is much louder than the old Toy was. What always got me was how far the pinion can be rotated back and forth on a Detroit. Makes one think it surely must be broken. 
5ton4ever
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We used to jack up both rear wheels and turn one tire, it will turn only a little and then (lock) and engage the other side.
DrJekl
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Factory GM 14 bolt (civilian) rears has a Gov Loc in them as well. These are normally open axles that lock when you have one wheel spinning faster than the other.
A Posi-Trac is just another name for limited slip. Pontiac used Safe-t-trac, then you have trac-loc and others. A detroit locker is a kind of a posi I suppose as a posi and detroit are normally locked. Spin one tire the other goes the same direction where a normally open (gov-loc) axle one goes forward the other spins to the rear (both wheels up, not on the ground with your foot on the pedal). The detroit uses a spring compression type system while limited slip uses clutches. Same end result I suppose but a detroit is a beast when compared to a posi/limited slip.
I have seen some units come into FT Campbell that have had the good stuff removed. 10 bolts up front and semi float or open rears.
I think your guy is just using different terminology. If she is a D70 in the back then he could be correct.
A Posi-Trac is just another name for limited slip. Pontiac used Safe-t-trac, then you have trac-loc and others. A detroit locker is a kind of a posi I suppose as a posi and detroit are normally locked. Spin one tire the other goes the same direction where a normally open (gov-loc) axle one goes forward the other spins to the rear (both wheels up, not on the ground with your foot on the pedal). The detroit uses a spring compression type system while limited slip uses clutches. Same end result I suppose but a detroit is a beast when compared to a posi/limited slip.
I have seen some units come into FT Campbell that have had the good stuff removed. 10 bolts up front and semi float or open rears.
I think your guy is just using different terminology. If she is a D70 in the back then he could be correct.
DrJekl
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The DL is installed inside an open differential housing. If you look into the slots in the housing you can see what looks like a spring in there. Without a photo it is difficult to descibe but it is like a hocky puck with four studs on it that the spider gears ride on. You can see the body of the locker from the slots. An open carrier you can just see the spider gears, a Gov Lok uses a different carrier with only three internal spider gears while the open/detroit carrier has four.
If you have a 14 bolt full floater and both wheels spin the same direction when you jack up the rear wheels off the ground and spin a tire by hand then you have a DL in there if it is under a military truck. Call it a posi, locker, etc. but I'd bet on it being a Detroit.
If you have a 14 bolt full floater and both wheels spin the same direction when you jack up the rear wheels off the ground and spin a tire by hand then you have a DL in there if it is under a military truck. Call it a posi, locker, etc. but I'd bet on it being a Detroit.
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DrJekl
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Here we go.
The carrier on the ground is a 14 bolt 10.5" Gov Lock Carrier. Note the funky cone shape. More of a cast cone with no ribs on it. There are three spider gears in there and you can see the holes they ride in in the carrier under where the gear bolts on.
The other carrier is an open carrier with a detroit installed. If you look inside you can see some guts in there. Note the ribs cast into the carrier and the slots. Four spider gears in there and you have the four holes they ride in where the two halves of the carrier bolt together.
The carrier on the ground is a 14 bolt 10.5" Gov Lock Carrier. Note the funky cone shape. More of a cast cone with no ribs on it. There are three spider gears in there and you can see the holes they ride in in the carrier under where the gear bolts on.
The other carrier is an open carrier with a detroit installed. If you look inside you can see some guts in there. Note the ribs cast into the carrier and the slots. Four spider gears in there and you have the four holes they ride in where the two halves of the carrier bolt together.
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ODdave
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Or as said, Jack both rear wheels up. Leave truck in park, 2wd. turn one wheel SLOWLY, if it "locks" and you cannot turn it, its a Detroit.
Terracoma
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The M1028 parts truck I got from a GSA auction (small volunteer fire outfit) had an open Dana 60 up front...
I kept reading that the '28s had Trac-Loks, but my Dana 60 is definitely open. Hmm.
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The simplest answer for a your original question is still "pull the cover and look if you want to know 100% for sure what you have".
If it's impractical to remove the cover for whatever reason, here are some quick checks to get a general idea what's in your axle without the need for disassemby:
-Equipment required: One floor jack (apppropriately rated for weight of vehicle), two jack stands, one wheel chock.
-Time to complete task : about 5-10 minutes.
-Skill level: Easy
The basic operational check for a Detroit locker is to pull the vehicle forward into your shop bay or driveway. Turn off engine. Jack up *one* side tire off the ground with transmission in park or if manual trans equipped, left in gear. Do not leave the trans or t case in neutral, driveshaft needs to be held immobile for this check. Remember to leave parking brake off if checking the rear axle. To make this a little easier to explain, just picture everything from the hand right side of your truck, with only the right rear tire off the ground. You should be able to spin the tire forward (clockwise) and you will hear/feel a faint clicking from the diff - don't worry that's normal. Try spinning the wheel backward (counterclockwise) and you'll feel the locker engage with a solid "clunk"and you won't be able to move it more than a couple degrees of rotation. Note that there's some "slop" or backlash designed into a Detroit for it to work properly, so you can turn the wheel a little bit backwards, just not very much. Detroits work by letting the outside wheel overrun the inside wheel during a turn so with this method you're basically simulating that driving condition. When both wheels are turning at approximate the same speed, the locker stays locked . Locked is the default position for a Detroit locker so it's only active when it's UNlocking - that's what you're checking to see if it does.
Supposedly if you back the vehicle up a hill and try the above or make a long pause in reverse before shifting to park, the free/locked directions above will be swapped around because of the way the outside cams are being loaded against the center spider (essentially, your truck "thinks" it's making a turn, but while traveling in reverse) I can't confirm the reverse thing because in the few times I've checked mine, I never actually tried it like that, but it makes logical sense if you have a pretty good grasp of how a Detroit locker works. Important part is that the tire in the air is going to lock up turning one direction and spin freely in the other. A single wheel can spin faster than the ring gear, but never slower than the ring gear. With the truck in park the ring gear can't move so it's relative speed is zero and with the opposite tire on the ground, the other axle's relative speed is zero. If the tire off the ground locks up turning BOTH directions with the other side's wheel and driveshaft are both prevented from movement then it's NOT a Detroit locker, you've got something else. I mention this because a lot of people expect you can't spin the tire at all, truth is you can spin the tire by hand with very little effort (the locker unlocks) but you're only going to be able to turn it one direction. It is possible to break the teeth on just one side of a Detroit locker, so if you know for a fact your truck has a DL and you're just doing a function check because of some odd noise or driveability problem, repeat the whole process on the other side. Gov-locks are the opposite, default is unlocked and they only lock up when wheel speeds become significantly different, so none of the above applies. (This also is why Govloks have tendency to blow up if the driver is real throttle happy during slippery conditions)
So what if you don't seem to have a Detroit locker after doing the above quick test, what's next?
To tell a limited slip from an open diff, if the vehicle is in park with only one wheel off the ground, you aren't going to be able to spin the tire either direction without putting the truck in neutral so the driveshaft can rotate freely. To differrentiate an open diff from a limited slip the usual method is to jack the whole axle off the ground so both tires are off the ground and then spin one tire by hand while watching the other side. With an open diff the wheels will rotate opposite directions (one fwd, one reverse), with almost all limited slips the clutches will drag enough so that both wheels will be rotating the same direction. There are a couple oddball types of limited slips where this won't be true, but it's generally a pretty reliable indicator. If the vehicle has a spooled or welded rear you wont be able to spin the tire either direction if the opposite side tire is still on the ground regardless of whether the truck is in gear or neutral. A spool is 100% locked, 100% of the time.
If you do the limited slip vs open test first (both tires off ground), and both tires turn the same direction that still doesn't mean for sure that the vehicle in question is equipped with a limited slip. A really mangled open diff with damaged spider gears, a detroit locker, and a welded/spooled rear will all also spin both tires the same direction. You can narrow it down further by lowering one wheel to the ground - spool wont spin at all regardless of whether transmission is in park or neutral - Limited slip will only let tire spin when transmission is in netral and will usually be pretty hard to turn - Detroit locker will do it's thing but only one dierction as described above with trans in Park.
Hope that clears up all the confusion.
-Matt
If it's impractical to remove the cover for whatever reason, here are some quick checks to get a general idea what's in your axle without the need for disassemby:
-Equipment required: One floor jack (apppropriately rated for weight of vehicle), two jack stands, one wheel chock.
-Time to complete task : about 5-10 minutes.
-Skill level: Easy
The basic operational check for a Detroit locker is to pull the vehicle forward into your shop bay or driveway. Turn off engine. Jack up *one* side tire off the ground with transmission in park or if manual trans equipped, left in gear. Do not leave the trans or t case in neutral, driveshaft needs to be held immobile for this check. Remember to leave parking brake off if checking the rear axle. To make this a little easier to explain, just picture everything from the hand right side of your truck, with only the right rear tire off the ground. You should be able to spin the tire forward (clockwise) and you will hear/feel a faint clicking from the diff - don't worry that's normal. Try spinning the wheel backward (counterclockwise) and you'll feel the locker engage with a solid "clunk"and you won't be able to move it more than a couple degrees of rotation. Note that there's some "slop" or backlash designed into a Detroit for it to work properly, so you can turn the wheel a little bit backwards, just not very much. Detroits work by letting the outside wheel overrun the inside wheel during a turn so with this method you're basically simulating that driving condition. When both wheels are turning at approximate the same speed, the locker stays locked . Locked is the default position for a Detroit locker so it's only active when it's UNlocking - that's what you're checking to see if it does.
Supposedly if you back the vehicle up a hill and try the above or make a long pause in reverse before shifting to park, the free/locked directions above will be swapped around because of the way the outside cams are being loaded against the center spider (essentially, your truck "thinks" it's making a turn, but while traveling in reverse) I can't confirm the reverse thing because in the few times I've checked mine, I never actually tried it like that, but it makes logical sense if you have a pretty good grasp of how a Detroit locker works. Important part is that the tire in the air is going to lock up turning one direction and spin freely in the other. A single wheel can spin faster than the ring gear, but never slower than the ring gear. With the truck in park the ring gear can't move so it's relative speed is zero and with the opposite tire on the ground, the other axle's relative speed is zero. If the tire off the ground locks up turning BOTH directions with the other side's wheel and driveshaft are both prevented from movement then it's NOT a Detroit locker, you've got something else. I mention this because a lot of people expect you can't spin the tire at all, truth is you can spin the tire by hand with very little effort (the locker unlocks) but you're only going to be able to turn it one direction. It is possible to break the teeth on just one side of a Detroit locker, so if you know for a fact your truck has a DL and you're just doing a function check because of some odd noise or driveability problem, repeat the whole process on the other side. Gov-locks are the opposite, default is unlocked and they only lock up when wheel speeds become significantly different, so none of the above applies. (This also is why Govloks have tendency to blow up if the driver is real throttle happy during slippery conditions)
So what if you don't seem to have a Detroit locker after doing the above quick test, what's next?
To tell a limited slip from an open diff, if the vehicle is in park with only one wheel off the ground, you aren't going to be able to spin the tire either direction without putting the truck in neutral so the driveshaft can rotate freely. To differrentiate an open diff from a limited slip the usual method is to jack the whole axle off the ground so both tires are off the ground and then spin one tire by hand while watching the other side. With an open diff the wheels will rotate opposite directions (one fwd, one reverse), with almost all limited slips the clutches will drag enough so that both wheels will be rotating the same direction. There are a couple oddball types of limited slips where this won't be true, but it's generally a pretty reliable indicator. If the vehicle has a spooled or welded rear you wont be able to spin the tire either direction if the opposite side tire is still on the ground regardless of whether the truck is in gear or neutral. A spool is 100% locked, 100% of the time.
If you do the limited slip vs open test first (both tires off ground), and both tires turn the same direction that still doesn't mean for sure that the vehicle in question is equipped with a limited slip. A really mangled open diff with damaged spider gears, a detroit locker, and a welded/spooled rear will all also spin both tires the same direction. You can narrow it down further by lowering one wheel to the ground - spool wont spin at all regardless of whether transmission is in park or neutral - Limited slip will only let tire spin when transmission is in netral and will usually be pretty hard to turn - Detroit locker will do it's thing but only one dierction as described above with trans in Park.
Hope that clears up all the confusion.
-Matt
Pirate 4x4 has a pretty rude and crude forum so visit at your own risk, but if you want a *perfect* comparison picture of some 14 bolt carrier/locker visual differences go to 14 bolt gov lock - Pirate4x4.Com Bulletin Board and skip down to post 12.
DrJekl
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Matt,
Those pics are better than mine. I took those a while back. Not the best but it is all I have on the computer. I may steal those from Pirate for future reference.
Those pics are better than mine. I took those a while back. Not the best but it is all I have on the computer. I may steal those from Pirate for future reference.
TCUCV
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Well first off thanks for all the helpfull responses! When I first bought the truck I know for sure the rear had some sort of locker in the rear b/c when I would go around turns I would get a little chirp from the rear tires. I'm waiting to hear from my mechanic sometime soon and I will take a picture of what is in there. Again thanks for the comments and I will be in touch
TCUCV
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I wasn't able to look inside the rear end b/c of work, but I do know my locker or posi trac system isn't broke neccessarily. My mechanic said that sometimes rear end would lock into place and other times is wouldn't. My dad had a very similar problem with his corvette and told me to drive around in a circle to my left about 10-15 times, then drive around in a circle to my right about 10-15 times. This is a way to test the "clutches" in the rear end to lock it into place. So far my rear end seems to be working fine, I guess I'll really know when I'm trying to climb a rock in Uwharrie at the end of the month.