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Unread 08-18-2014, 11:24 PM   #1
Tyler-98-W68
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2012 MK Compass 
 
Join Date: May 2009
Location: Canada
Posts: 89
My locking differential Project

Thought I would share my progress on what is (to my knowledge) the first attempt at getting a locking differential installed in an MK.

Reason:

As I've explained before the BLD function of the MK's works well offroad but with limited torque available sometimes the BLD causes the vehicle to bog out and lose forward momentum. If a mechanical device in the differential could transfer torque across the rear axle without as much loss in torque from the brakes being used I feel the MK's would gain a lot more capability offroad.

Complications:

I have looked high and low for information on the rear diff in our MK's and while Aroundincirlces found a place that lists out rear diff being a Chrysler 8.25"
http://www.ringpinion.com/b2c/DiffLi...&DriveType=4WD

Looking at the specifications I can't see it as really fitting, otherwise someone would have done it already!

I"ve also never been able to track down any interior pictures of the MK diff, as I will need to take the diff apart to measure all the spider gears pinion ect.

Here's what I have found so far, the mitusibish outlander (The newest ones) use the same differential as MK's I've established that by looking at ebay auctions for them and the diff is exactly the same as ours. The main difference being is gearing.

Since I have a FDII compass, the rear gear ratio is 8:1, which is incredibly low and I think this may ultimately limit my chances at getting a locker or something put it.

What I've done so far:

Purchased a used differential out of a 2009 Patriot FDII with 37000kms on it. Basically the same mileage. Still waiting for it to be shipped out to me.

I have a mechanic friend who works at a Subaru and he hooked me up with the service manual on how to disassemble the rear diff, so I will post a few pictures of what it looks like:




As you can see it looks like a "normal" differential I just need to determine the size by measuring and the splines, if it turns out to be a 8.25" ring gear and say 27 splines, we are in luck as there are many options for that type of axle.

Diff has arrived!













Things to note, damn thing is a lot bigger off the vehicle and what pictures would suggest.

In the last picture you can see what I believe is the driveline vent, which apparently is higher on FDII modules. It looks like nothing more than a small rubber tube, that in theory could be extended and relocated to an ever higher position to increase water fording capability.

I have a couple emails out to a few companies regarding information on lockers and or LSD's hopefully I get some positive feedback soon.





23 Splines is what I count, so until I get the diff ripped apart I have this info to go on for now.

So I measured the ring gear and it came out at exactly 6 inches. I suppose I might have to take the carrier out too, however that is far above my mechanical skills to try that so someone else will have to do that if it will be necessary.

















Some more pics though:





Picture of the roll pin we couldn't punch out"







The final piece of the puzzleepper:epper:epper:







Cross Pin diameter = 0.587"

Spider Gear Hole diameter = 0.592"

I'm hoping for good news


PS other diff was a Dana 44

I have been in contact with Lokka and they had requested the specs which I have outlined above, so hopefully now I can get something made up, and be the first MK with a locking Diff!

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Unread 08-19-2014, 12:00 PM   #2
937Comanche
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You cite the 27-spline 8.25. This diff was last used almost 20 years ago and was replaced with the 29-spline version. There are more off-road oriented lockers available for the 29-spline version with offerings for the 27-spline versions being more scarce.

The new KL uses a reported 7.2" ring gear diff. Using a real locker on something like that might proof risky just as it is on the D30. On the D30A the aluminum diff. housing is prone to cracking, especially when locked. The MK's housing material be another area of concern.
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Unread 08-19-2014, 12:50 PM   #3
Tyler-98-W68
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Yes, the 27 spline 8.25" was the diff that came up from 2 online shops stating that they indeed had lockers for the Compass and Patriot, but obviously as you can see that's wrong, I contacted them, and the one company Lokka showed interest in actually making something. This diff is super tiny 6" ring gear, compared to everything else out there its just really small. So fingers crossed I can get something made up.
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Unread 08-19-2014, 01:00 PM   #4
Tyler-98-W68
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As for the strength of the MK diff, I have my doubts for sure, I will be extra careful if/when I get this installed just so that I don't break other parts, in reality as long as the diff holds up, I could handle replacing axles if they broke or anything else along up the drivetrain, its all a trial run since no one has tried this before.
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Unread 08-19-2014, 01:51 PM   #5
937Comanche
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A word of caution about Lokka: Although Lokka was originally the manufacturer of the Aussie locker for Torq Masters they no longer are. First Lokka started using Chinese-sourced metal and the failure rate increased. In spite of that they then also moved production to China and the corresponding failure rate caused Torq Masters to relocate both production and metal sourcing for the Aussie Locker to the U.S. Lokka's website touts "Australian design" and such but is purposefully very vague about the origin of their parts. It appears to be an effort to cash in on the Aussie name without really providing the same level of product.

Good luck.
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Unread 08-19-2014, 01:52 PM   #6
Tyler-98-W68
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Edited
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Unread 08-21-2014, 09:22 AM   #7
tjkj2002
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Quote:
Originally Posted by 937Comanche View Post
. On the D30A the aluminum diff. housing is prone to cracking, especially when locked.
Got it backwards,the KJ's D30A housing is less prone to cracking with a DTT or ARB installed.
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Unread 08-22-2014, 08:20 AM   #8
937Comanche
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The DTT ( Detroit Truetrac)is not a locker but an LSD. An unconventional one but still an LSD. Under most circumstances only one wheel is powered. The DTT just tries to make sure it is the wheel with more traction as opposed to the one with less traction as happens with an open diff. It does not prevent spinning in low traction especially if both sides have equally low traction. ( Read on to see where spinning is bad of the D30a.) Although a good improvement, especially in the front, it is not replacement for a locker if you need a locker. And as for the ARB...being selectable makes that a tougher call. The thought might be that having the front locked would spread the pressure more equally. However it actually increases the forces when one side is in a bind and the other is not. It is a well proven point that such situations increase your chance of breaking an axle shaft, u-joint,or diff parts, especially on a front axles. Many recommendations list a smaller maximum tire size for a locked axle versus an open or LSD one for this reason. Even so I am sure you are aware that in most cases it is not wheel bind that shatters the D30a but sudden shock forces. Most commonly it is when you have a spinning tire suddenly grab traction. The thought might be "well if you are locked the tire won't be spinning in the first place." While this may be true for those who wheel high-traction but misnamed "slick rock" or wheel mostly what would pass for roads in many parts of the world if you actually wheel you know that you can and do get both tires spinning on a locked axle. Then you are just as likely to pop that case if you suddenly get traction with an ARB as without. An ARB would also do nothing to prevent the shock if both wheels were off the ground, say when crowning a ledge, and then both suddenly return to earth & grab traction.

From what I have seen in the KJ world the very few ARB's there are out there are open 99.9999% of the time. The KJ is unfortunately another one of those jeeps were most of them that get modified for looks and "bragging rights" only and never actually get used. The more money the owner can dump in one, say with an ARB, the bigger their, um, swagger is around the KJ boards. This whole "expo vehicle" theme is right up that alley. I think that if ARB-equipped KJ owners actually used their ARB's they would find that it would help about as much as all of those "diff. collars" that people swore were the answer....until they were proven to do nothing except maybe keep the parts from scattering after the housing grenaded anyway. Do you remember that farce?
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Unread 08-22-2014, 08:59 AM   #9
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All I can say is...major props to you for doing something unique!
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Unread 08-26-2014, 09:51 AM   #10
tjkj2002
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Quote:
Originally Posted by 937Comanche View Post
The DTT ( Detroit Truetrac)is not a locker but an LSD. An unconventional one but still an LSD. Under most circumstances only one wheel is powered. The DTT just tries to make sure it is the wheel with more traction as opposed to the one with less traction as happens with an open diff. It does not prevent spinning in low traction especially if both sides have equally low traction. ( Read on to see where spinning is bad of the D30a.) Although a good improvement, especially in the front, it is not replacement for a locker if you need a locker. And as for the ARB...being selectable makes that a tougher call. The thought might be that having the front locked would spread the pressure more equally. However it actually increases the forces when one side is in a bind and the other is not. It is a well proven point that such situations increase your chance of breaking an axle shaft, u-joint,or diff parts, especially on a front axles. Many recommendations list a smaller maximum tire size for a locked axle versus an open or LSD one for this reason. Even so I am sure you are aware that in most cases it is not wheel bind that shatters the D30a but sudden shock forces. Most commonly it is when you have a spinning tire suddenly grab traction. The thought might be "well if you are locked the tire won't be spinning in the first place." While this may be true for those who wheel high-traction but misnamed "slick rock" or wheel mostly what would pass for roads in many parts of the world if you actually wheel you know that you can and do get both tires spinning on a locked axle. Then you are just as likely to pop that case if you suddenly get traction with an ARB as without. An ARB would also do nothing to prevent the shock if both wheels were off the ground, say when crowning a ledge, and then both suddenly return to earth & grab traction.

From what I have seen in the KJ world the very few ARB's there are out there are open 99.9999% of the time. The KJ is unfortunately another one of those jeeps were most of them that get modified for looks and "bragging rights" only and never actually get used. The more money the owner can dump in one, say with an ARB, the bigger their, um, swagger is around the KJ boards. This whole "expo vehicle" theme is right up that alley. I think that if ARB-equipped KJ owners actually used their ARB's they would find that it would help about as much as all of those "diff. collars" that people swore were the answer....until they were proven to do nothing except maybe keep the parts from scattering after the housing grenaded anyway. Do you remember that farce?


DDT front and ARB rear,no collar and no broken front diff ever,and yes it got wheeled hard..................





Did blow a CV axle apart though,diff unharmed and went on to live under a KJ CRD that is still going and heavily used in Moab.


Which lead to this.........

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