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Discussion Starter #1
I'm planning to swap rear diff my compass trailhawk use trailhawk Cherokee 2.4 has the 50to1 crawl ratio if not Avid coming out straight axle swap
 

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I don't think you quite understand whats involved, the diff in the Cherokee is not where the gear reduction takes place. They have a 2-speed PTU in the transaxle whereas the Compass has a single-speed PTU.

If you could swap in the Cherokee rear diff with the locker that would be an upgrade but you would have to check that the ring/pinion ratio is exactly the same as the ratio in your front diff which is not a separate part, the front diff is part of the transaxle assembly.

Basically what you would need to do is swap in both the entire transaxle and rear diff from a properly equipped Cherokee with the "Active Drive Lock" drivetrain package, and then you would need to swap in their selec-terrain control panel and try to get all of that programmed and working in the various computers in the car. Even with AlfaOBD you could get hosed at that point, the Compass may not be able to be programmed to control an Active Drive II or Active Drive Lock system even if all the physical parts did bolt up.

If you really want a 2-speed PTU with real low range the only thing that makes sense is to just go buy a properly equipped Cherokee. By the time you cannibalize an entire Cherokee's drivetrain for your Compass you will be out way too much money for it to make any sense, and there is still a good chance the programming won't work out.

I do, however, think its viable to explore swapping in a Cherokee rear diff with the factory locker IF AND ONLY IF the ring and pinion ratio can be confirmed to match that of a person's front diff. The trailhawk guys are likely the only ones who stand a chance of that working out. Very maybably you could swap the ring and pinion in a lockable Cherokee rear diff with the ones from your stock rear diff, nobody has tried anything like that. If you can get lucky with the ratios or get them the same then I am guessing the electronic control for the locker is likely almost as simple as an ON/OFF 12v signal that you could rig up yourself and piggyback on the car with your own button somewhere.

Even still, way too much work to be worth the hassle today. 5-10 years from now these will be old enough and enough of them in the junk yards that someone might actually dig into something like this, only a crazy person who has recently won a mega-millions lottery could seriously consider trying a swap like this.

I'd suggest you digest that truth and avoid looking like a fool going around telling people how "someday soon you're gonna swap low range into your Compass". The worst kind of car-wannabe-guy is the kind who sits on a stock car talking about extreme advanced mods he thinks he is eventually going to do to it, but never will.
 

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A person could explore the vague possibility of swapping in the two-speed PTU also, but my guess is you'd be better off finding out how its shifted and running that with a piggy-back controller vs programming it into the Compass's computers. If its just an encoder motor and the PTU can be swapped without changing anything else then there is a chance, but only a small one, and you'll still have open diffs front and back.

Buying a properly equipped Cherokee is still the only thing that makes sense today until these things are and cheap and common enough to waste time and money with experiments like that.
 

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Discussion Starter #4
Thank you I not familiar with jeeps I come from honda seen so trans axel ok I was thinking swapping ecu 4x4 switch for snow mud rock drive shaft if need
 

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I have to come back and admit when I am wrong, I've been trying to study up more on the 4x4 system and it does sound like in the Cherokee Active Drive II system uses both a two-speed PTU and a two-speed RDM. I am a little confused about exactly how that works though and how it differs from our Compass Active Drive system despite both using a ZF9 transmission.

Animations I have seen of the Renegade lead me to believe our system uses a simple PTU that comes after the front differential, on the passenger side. So something like engine -> 9 Speed -> Front diff and from there sideshafts go out to the front wheels BUT between the front diff and the passenger-side front tire the PTU is jammed in there and forks off torque to send to the rear. I assume the FWD models just have a half-shaft where the PTU would be. A very simple, cheap, easy system for sure but highly limited in its capabilities.

The Cherokee would not be able to work that way and have 2 speeds, it would have to get into the two-speed PTU before the front diff (I would think), so power flow would be engine -> 2 speed PTU and then apparently the front diff is part of the PTU(?) and the rear propshaft is only driven at one speed but the Cherokee RDM has a second speed to match the low speed of the front diff/PTU combo?

Blah... I don't understand. The Compass and the Renegade and the Cherokee all have 2.4L engine options mated to a ZF9 but the casing and the way the two versions of the PTU hook up and take power must be significantly different somehow, or the animation I saw for the Renegade's system was highly inaccurate.

Anyways as far as this thread is concerned it makes me think you'd need the entire drivetrain from a Cherokee for sure, from the transaxle to the RDM. Without getting underneath and inspecting several variants we don't know if the transaxle casing varies from the Cherokee's with the low range to ours, it just seems likely that it would and I'm a bit concerned the mounts would be different as well.

I do see in the BCM configuration for AlfaOBD that you can set the drive type variant to single speed AWD, 2 speed AWD, or 2 speed with "Elocker", but just because you can set that doesn't mean it will actually pick it up and work. AlfaOBD has a lot of things that don't work or don't read right. For example, there is also an option to set the transmission variant but mine came from the factory set to "Jatco JF613E 4x4 2 speed PTU (DFN)/948 TE(COMPASS MP)" and we know that isn't correct!
 

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