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Project Locking Differential for MK's (Currently unsuccessful)

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61K views 156 replies 28 participants last post by  Silvr_Pat  
#1 · (Edited)
I figured I'd start a new thread to highlight the progress and the successful attempt (or failure) to get some sort of locking differential made up for my Compass.

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/DiffL.../b2c/DiffList.aspx?SearchMode=Make&MakeID=7&ModelID=514&Side=Rear&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.

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Cross Pin diameter = 0.587"

Spider Gear Hole diameter = 0.592"

As you can see it looks like a "normal" differential

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#8 ·
The diff should be here early next week I hope. Unfortunately I had surgery on my foot a few weeks back so my mobility is reduced but by the time the diff gets here I should be able to walk without too much trouble, it's not a huge issue as I have someone to work on my diff anyways.

Doing some thinking and pretending for a second that there is lockers available, i'm torn at what I want to do.

ARB air locker is at the top of my list for a few reasons:

It's a totally seamless operation functioning like an open diff until needing to lock it up.

Problem is i'm looking at nearly $1500 to get the locker, air compressor and everything else needed to make it work. It seems rather complex and there could be things that go wrong with it.

Powertrax No Slip

I"ve looked a lot at these and watched videos, it seems that they are rather street friendly and will unlock going around corners on the street. I could get one for around $500 so money wise it's attractive.

Looking at it from a traction control perspective I cant see any issues with the operation of the BLD or traction control since both tires will always be spinning at the same rate (except when turning) in reality the BLD will only be functioning on the front axle.

The downside to this is that I live in a climate where we have snow for 5-6 months out of the year and i'm thinking I might notice some extra back end slip going around corners while doing city driving on slippery roads, I might not have any problems as the traction control will probably compensate for that, and the fact that the rear end isn't going to be getting power all the time anyways unless I lock it in 4x4.

First things first though I have to determine whether a locker will actually work. The last ditch effort may be to weld it, but that creates it's own set of problems, mainly i'm not sure the back end components are strong enough to survive being locked while driving on the street. I could see the CV axles snapping like twigs, but I don't really know for sure.

Anyways I"ll post again when I have some more updates.
 
#10 ·
Diff has arrived!

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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 companines regarding information on lockers and or LSD's hopefully I get some positive feedback soon.
 
#14 ·
Haha, it just showed up today i'm still not super mobile yet, I should have it open by the end of the week. So someone had just reposted that service manual in a thread, turns out there is complete pics on how to disassemble it.

By no means an accurate measurement but i'm going to venture a guess that the ring gear is 6.5-6.75"

Looking online a dana 28 diff, which was a front diff for the older rangers is 6.625" 23 spline Powertrax lists a lockrite for it, unfortunately they are less street friendly that the powertrax no slip lockers they sell.

I really hope something can be done, I would be 100% happy and content with my Compass at that point. I might even be finished modding it too.

If I was able to get a locker put in, I was thinking about putting one in my factory diff and possibly selling it to another member to offset the costs of the whole project:)
 
#15 ·
Tyler, thanks for the time/money/effort. I hope something turns up, it would great to have.

I think a Wavetrac would be interesting. Supposedly like a Torsen or Trutrac LSD, but fully locks (or close to it) automatically when a wheel is off the ground. Also has a Lifetime guarantee.

http://www.wavetrac.net/technical.htm

They don't make one specifically for the MK, but they do cover a lot of passenger cars so maybe there's something close that could be adapted.

http://www.wavetrac.net/application.htm
 
#18 ·
The evo diff while similar is different as a member here pointed out there is no spot for the ecc clutch to attach at the front of the diff like it does on the patriot. So I'm not sure if it would actually work. Sandstone that wavetrac diff looks ideal. I will email then today and see what they have to say.
 
#21 ·
Well I emailed wavetrac and they got back to me very quickly.

Tyler, thank you for your inquiry, but unfortunately we do not have a unit available for your vehicle and there is no planned production for a Wavetrac application for that car at this time. Usually for us to start making a new production we would need enough interest to make a batch of 30-50 units if that information helps at all, we have not had any other inquiries on a diff for that vehicle that I am aware of.

So....do I buy 30 diffs and then resell them to everyone, too bad that's not cost effective in the least.

I'm not too deterred though since I highly doubt anything would be a ready to install product for our jeeps anyways.
 
#23 ·
So i'm typing this out in disbelief and I still can't quite believe it myself................a while back I emailed a company.

http://lokka.com/site/

I used their application guide and while they list a Compass as a option when filling out the form, it comes up with no fitment.

Last night I got this email:

Hi Tyler,
Thank-you for your enquiry about LOKKA automatic differential locker.

Have you tried the LOKKA 'Wizard' ?
Yes, there is a model LOKKA to suit your vehicle.
Use the 'Lokka Wizard':
Jeep
Compass
2012
Canada

The result is JEE-RO-152
Cost is $259 including shipping to your door.

If you wish to purchase, use the 'LOKKA Wizard', or if you have any further questions, please email.

Are you kidding me:pepper::pepper::pepper: Either they have existed the entire time or the made something up for me:notworthy:

I know its not a selectable locker which would have been the best idea, however the thought of zero modification to make this work is extremely appealing. If it turns out this actually works and a selectable locker does in fact exist I will have my existing factory diff I could add it too since I will have a spare laying around.

I will update with more info as I get it:D
 
#24 ·
No, Lokka still has it wrong stating it's a Chrysler 8.25" 29 spline rear axle. They have confused the Compass for the Liberty. That axle is a solid axle, found on XJ's and Liberty's...heck I think it's been used for decades on all sorts of cars and trucks. Yea, I found this little nugget about the 8.25" axle. Note the 29 splines was a change in 1997 (bolded below). So far as I can see...they never made an 8.25" IRS (independent rear suspension) rear axle.

Chrysler 8 1/4" Rear Axle

Chrysler Corporation's Spicer 8.25" rear was one of two differential types used in M-bodies, with the other being the weaker 7.25" unit. The 8.25" rear axle first appeared around 1969 in Plymouth Belvederes, Satellites and Dodge Coronets. The measurement refers to the size of the ring gear. This gear, which is turned by the pinion gear, changes the direction of the power being transmitted to it. The pinion gear is turned by the driveshaft. From 1973 on, the 8.25" rear was used in virtually every rear wheel drive car model produced by Chrysler through 1989 and in trucks and Jeeps through the 1990s. Some truck versions were designated as 8 3/8" or 8.375", but many internal parts interchanged with the 8.25" unit. It should be noted that all 8.25" rear axle assemblies DO NOT necessarily interchange across all models due to different widths.

Built by the Dana Corporation, the housing is cast iron with tubular steel axle tubes pressed and welded in to form a complete carrier and tube assembly. The gear assembly is accessed by removing an inspection cover having 10 bolts. 8.25" axles use either the "7260" or "7290" style U-joints. All 8.25" rears had 3" axle tubes with large bolt pattern (5 X 4.5" bolt circle) axles. Units with a 2.45:1 gear ratio have a special case that will not accept any other gear ratio. The axles are retained by a c-clip on either side. All axles were 27 spline until 1997 when they were upgraded to 29 spline.

Although the consensus among many Mopar enthusiasts is that a Sure-Grip (limited slip) equiped 8.25" rear is good for up to 500 crank horsepower, it fares much better in street applications than the strip, and in lighter cars than heavy cars. Open 8.25" differentials are more prone to fail at higher horsepower levels than Sure-Grip units. The 8.25" axle has considerable aftermarket support since it was so widely used in the 1970s for performance use.
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#25 ·
I totally agree with you, when I emailed them a ways back I explained I had a jeep compass with a cvt with IRS and a rear ratio of 8:135:1. So maybe they did their homework this time? Who knows just waiting to hear back on what they have to say to the million questions I have.
 
#26 ·
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