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gremlinsteve 01-30-2013 05:19 PM

srt8 front and rear diff question
ive got a 2013 wk2, trailhawk edition. one of the nicest vehicles ive owned in my opinion.
a question i have is this. she has the hemi so what i have found is the current gearing should be the 3.45 correct?
with knowing that i found that the srt8 cherokee uses the same size rp at 215 and 230 correct? im not sure on axle spline count ect.

has any one researched the possible swap to the str8 diffs and there 3.70 gear ratio? with the addition of the 32.5 inch tire i am leaning towards the rpm at 65 would remain within a couple of rpm of the current and stock setup.

any one have input of whether these diffs are indeed the same and will swap in or am i treading into unknown waters.


Jeep_addicted 01-31-2013 10:29 AM

Re: srt8 front and rear diff question
All the current wheel and tire combos from jeep are geared from the same O.D. so I am note sure that messing with the diffs with help and there is not current way to adjust the speedometer.

Maybe when a tuner comes out but for now there is no way to change the reading do if you go oversized your reading will not be accurate.

ColdCase 01-31-2013 11:05 AM

Re: srt8 front and rear diff question
Axle also ratio depends on ELSD or not. You can find axle radios here:

Jeep Grand Cherokee WK2 - Maintenance information and schedules

5.7s have 3:45, 6.4s have 3.70. Dunno if they are swappable, don't think anyone sells the gears without the housing anyway (about $1500 each end). You may be able to get gears from a salvage yard.

Part of the reason the 6.4 and 5.7 use a different ratio is they also have a different transmission with different ratios.

Dunno about the rear, but you do have to pull the entire front diff assembly out of the chassis to split it and work on gearing, a 2-3 hour job each way.

kkreit01 01-31-2013 02:45 PM

Re: srt8 front and rear diff question
I also don't think that jump would be worth the hassle nor money. I know the previous Durangos/Apens used to have 3.92s if they came with the tow package. That's what we should get as well. That's my biggest complaint. That would be worth the jump to 3.92s. I don't think 3.70 would make that big of difference -- even if it's possible.

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