KJ 8.25in differential questions

Hi all,

So after some 4 wheeling in the Jeep it was clear to be that the limited slip was urerly useless.
This led me to a wild search for a rear locker.
Keeping budget, import duties and shipping in mind, I landed on a Powertrax No Slip locker. A lunch box locker.


And this is where my issue started.
What I missed while looking at the Powertrax drop in locker was that it wouldn't fit the lsd carrier. Somehow I missed that it's open differential.

I have the locker after alot of money, so now I need to make a plan to get it in.
I'm thinking of swapping the internal carrier with an open one in order to fit the locker.

So to get to my question. Can it be done?
I've been searching and reading and can't really find an answer. I went to a few breaker yards locally to try and find another KJ diff with perhaps an open differential. No luck, all have lsd.
I have however found a KK differential, which I believe is open.
My current KJ diff if the Corporate 8.25, DSA: Anti-spin, according to the Vin. The KK diff I'm looking at is Corporate 8.25, DS8: conventional differential
Can the internals be swapped out and will this locker fit in the KK carrier?

Thanks for the assistance

I believe the KK and KJ rears are both 29 spline Chrysler 8.25 diffs and the internals should be interchangeable. The spring perches, control arm mounts, etc. on the axles are not the same, so unfortunately you cannot swap a whole rear end over from a KK, which would be easier than swapping gears. Setting up gears with the right spacing pattern and backlash is hard and either requires specialized tools or a specialist to do. It is probably more money than you want to spend. Keep looking for a KJ rear end with an open diff- they’ve got to be out there. Then you don’t have to mess with ring & pinion gears and spend a ton more money.

Yes 29 spline & the only good reasonably priced locker IMHO for the rear 8.25... should be an Eaton DTT (Detroit true trac) Part Number: DTL-912A553
Best to have a diff shop install it correctly with warranty.
Of course ARB air locker would be better but is $$.

PowerTrax ,

sorry for ya
I realize budget in mind you went that way
But in the long run a DTT is so much better and no strange noises when driving, rounding corners etc

LibertyTC said:

Yes 29 spline & the only good reasonably priced locker IMHO for the rear 8.25... should be an Eaton DTT (Detroit true trac) Part Number: DTL-912A553
Best to have a diff shop install it correctly with warranty.
Of course ARB air locker would be better but is $$.

Click to expand...

Really does depend on what he wants it for ...easier trails, forest roads yeah the dtt will be the best but if its alot of off camber stuff and hard trails and budget is the issue the powertrax will be better the noises will **** and cornering will he different but nothing you cant adjust too...now me personally powertrax rear and dtt up front I think that's my best combo for what I do,especially with ifs being such a weak point for the kj,I think a full time locker locker would be alot of stress up front

lfhoward said:

I believe the KK and KJ rears are both 29 spline Chrysler 8.25 diffs and the internals should be interchangeable. The spring perches, control arm mounts, etc. on the axles are not the same, so unfortunately you cannot swap a whole rear end over from a KK, which would be easier than swapping gears. Setting up gears with the right spacing pattern and backlash is hard and either requires specialized tools or a specialist to do. It is probably more money than you want to spend. Keep looking for a KJ rear end with an open diff- they’ve got to be out there. Then you don’t have to mess with ring & pinion gears and spend a ton more money.

Click to expand...

Thanks for the reply.

Getting a correct KJ diff would be first price, but seems to be a problem.
I was actually just going to replace the "basket" or carrier and plan to bolt the current ring gear to it. I was also thinking about the pre-load on the pinion, so the plan is to leave it in place and use the old ring gear with it.
If I bolt the current ring gear to a new carrier out of the KK, would pre-load still be an issue?

Need some educating here.

My understanding is that ring and pinion gears are matched sets. You’d definitely want to use your old ring gear on a new carrier, and you’re right that if you don’t take out the pinion the preload would still be fine. But the new carrier may be slightly different than the one you have now, meaning it could need to be shimmed a little to the right or left to get the correct backlash. You’d want to paint the gears and turn them some to verify the contact pattern, and verify the backlash with a gauge.

LibertyTC said:

Yes 29 spline & the only good reasonably priced locker IMHO for the rear 8.25... should be an Eaton DTT (Detroit true trac) Part Number: DTL-912A553
Best to have a diff shop install it correctly with warranty.
Of course ARB air locker would be better but is $$.

Click to expand...

I'm jumping in on this thread to try to get some clarification on the locker options..
I've been reading all I could find in the forum, and what i understand is that for the front Dana 30a your only option is to replace the carrier. As Iunderstand it, there isn't a lunch box locker that fits into the carrier?
DTT and ARB are what's recommended mostly, but i'm wondering if the DTT ( I assume that would be part number 912A585) fits in the house wouldn't the Detroit Locker (Part number 162SL60B) also fit?
And the same for the rear diff. The DTT 912A553 fits, and therefore should the Detroit Locker 187C179A also fit?

I wouldn't mind go with lunch boxes as I use the Jeep mostly in the woods and on trails, but it doesn't seems to be possible in the Dana 30a or in the carrier with Trac-Lok.

Am I all confused, or did I get at least some of it right? ;-)

And one other thing I was wondering about:
Would it be possible to fit a carrier from a Dana 30 into the differential house of the 30a?
In that case it would be possible to get a lunch box that fits.
The DTT seems to be the same for the 30 and 30a, as read the Eaton application guide ...

A 30 and a 30a are two different horses
LOTS of places will tell you or have posted on their site the same parts numbers but they are not

tommudd said:

A 30 and a 30a are two different horses
LOTS of places will tell you or have posted on their site the same parts numbers but they are not

Click to expand...

Thats what I thought...
But do I have the part numbers for the DTT's right?
912A585 for the front
912A553 for the rear

Reviving my old thread.

Does anyone know the wall thickness of the diff carrier? The internals.

This is on a 2005 3.7 V6.

As stated in the opening post, the locker does not fit the current carrier. The current spider gear is about 7.5cm (if I remember correctly) and the new locker gear is about 8.5cm.
So the plan (and experiment) would be to machine out some internal material to open up the inside of the carrier. Then the locker would fit.

So, without opening the diff again, I was hoping someone knows the thickness or, has a part lying around to measure.

It would obviously make the carrier thinner, but I don't think it will be an issue, as the part there the axle goes in will not be affected, therefor not affecting it's working function.
Can it be done?

In my area there are dozens of kj's in the wrecking yards. I think it would be far easier and cheaper to go pull a carrier from one. In fact I have one in my driveway that'll soon go to the to be with it's friends.

Thinking about installing an ARB air locker in the Libby. I know they have models that will fit, but do you guys think the differential will be able to hold up to it? Asking because I'm planning on re-gearing to 4.10's and while that work is getting done might as well get rear lockers.

tommudd said:

A 30 and a 30a are two different horses
LOTS of places will tell you or have posted on their site the same parts numbers but they are not

Click to expand...

Tom, as far as I can tell, the ring and pinion for a Dana 30A are different from a standard Dana 30. However, the differential case/carrier are the same between the two. There is not a Liberty specific Detroit Truetrac, for the Dana 30A, as an example.

65Corvair said:

Tom, as far as I can tell, the ring and pinion for a Dana 30A are different from a standard Dana 30. However, the differential case/carrier are the same between the two. There is not a Liberty specific Detroit Truetrac, for the Dana 30A, as an example.

Click to expand...

I believe you to be correct. Eaton lists the same part for both the kj (30a) and jk (30) if I'm remembering correctly. The pinion, however is not interchangeable and as we all know ring and pinions are matched sets.

oh dear , oh well glad Im getting out

tommudd said:

oh dear , oh well glad Im getting out

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What are you getting out of?

tommudd said:

oh dear , oh well glad Im getting out

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Please don't go.

tommudd said:

oh dear , oh well glad Im getting out

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This can’t be your last post!!! Are you selling your KJ’s and driving off into the sunset in a vintage 911 Carrera? Hope you will be back.