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Old 07-02-2012, 08:41 AM
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regearing required to run 33s with 3.7L

Hey guys,

Im trying to get some information on regearing my 07 wk 3.7L so I can run 33" tires. So far I know that the lowest I can go is 3.73 ratio most likely from a wk or xk. Or can I get the ring an pinion from another site as long as its made for a dana 44 axle? Any help or insight on this is greatly appreciated.
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Old 07-08-2012, 07:26 PM
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Re: regearing required to run 33s with 3.7L

there are a few people running 33's on their 3.7 with stock gears and no problems. look into getting the hypertech max programmer to recalculate tire size.

my next set of tires will be 33's, no plan to regear for the time being.
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Old 07-08-2012, 08:49 PM
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Re: regearing required to run 33s with 3.7L

from what Ive heard adding that big of a tire with our current gearing and engine size will put a huge strain on the engine and transmission and cause a severe loss of power and a very short life of the axles and transmission. Another forum had a guy that swapped the rear gearing for 3.73 and put a new front differential from a commander in that had 3.73 ratio. Then he used the hypertech programer to set up the transmission to recognize the new ratio and tire size.
Im trying to find out now if our rear axle is a dana44 or the chrysler 8.25".
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Old 07-09-2012, 01:45 PM
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Re: regearing required to run 33s with 3.7L

You've got the corporate 8.25. The Dana was only used in the SRT8. You'll find no problems getting the rear R&P in the aftermarket in different ratios, its the front thats not available. So you are stuck with stock ratios, either 3.55 or 3.73.

I've been running 33s with the 3.7L for over 40,000 miles and have had zero issues that you mention with the axles/trans. Yes, there is a slight loss of power and I would definitely not characterize it as "severe." I've even added armor and a rack and have no severe power loss issues. If you are that concerned about power loss, then you need to be looking at trading your Jeep in for a hemi.
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Old 07-09-2012, 02:06 PM
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Re: regearing required to run 33s with 3.7L

Thanks Mr. Boh, do you happen to know if the pinion flange is different on the 06-07's for the corporate 8.25?
Im trying to gain as much insight on this before I continue with any purchases or modding so Im basically going by what others have told me. But since you are actually running the set up, how bad is your gas mileage now and do you have any whining coming from the transmission? Did you use a hypertech programmer to set the wheel size and speedo recalibration?

I have already found a used front differential that is 3.73 ratio, and after calculating the cost of a new ring & pinion and other parts and tools ill need for a ratio change for the rear i could spend 50 more dollars and just get a used rear axle i found with 3.73 ratio. Do you think it would be worth it to swap them out or is it just a waste of money? Im wondering how big of a difference it would make just by the ratio change
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Old 07-09-2012, 03:19 PM
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Re: regearing required to run 33s with 3.7L

Sorry, can't answer your question on the pinion flange. My plan was to always swap 2005 to 2005 so that I wouldn't have to worry about any design change issues (if any). After all my mods...lift, tires, armor, rack, I'm down about 2 mpg on the highway. No whining from the trans. Don't have the Hypertech so my speedo is still off. However, I do plan on getting it soon as going up the mountains in WV is painful....the new gears and add hp will be welcomed.

As far as swapping the R&P or R&Ring the front diff and rear axle, I guess I would have to ask if you are doing the work yourself and if so how comfortable you are doing it. To me, R&Ring an axle is easier (assuming nothing has to be done to it) than shimming up a new R&P set. But that's just me.
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Old 07-09-2012, 05:44 PM
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Re: regearing required to run 33s with 3.7L

I do the work myself on my jeep and Ive never done a ring and pinion change so im really not wanting to mess up my daily driver and would prefer to just put in a different axle. Would you happen to know what the gear ratio change actually does? will it increase torque to push the bigger tires and ease engine strain? Thanks for the help
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Old 07-09-2012, 09:37 PM
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Re: regearing required to run 33s with 3.7L

im assuming the other forum you read about the gear swap was jeep forum...if so, talk to aj (ajeepzj) he also has 33's on his 3.7. there are a few others out there but the only other one i can think of off the top of my head is on here, nick (gcl06), he has a superlift on 33's...
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Old 07-09-2012, 10:41 PM
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Quote:
Originally Posted by Mr. Boh View Post
The Dana was only used in the SRT8.
Also in at least some 2wd wks...


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Old 07-09-2012, 11:50 PM
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I plan on running 33's on. 2wd but I have a 4.7
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Old 07-10-2012, 08:56 AM
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Re: regearing required to run 33s with 3.7L

Quote:
Originally Posted by guitarguy2186 View Post
Would you happen to know what the gear ratio change actually does? will it increase torque to push the bigger tires and ease engine strain? Thanks for the help
Regearing increases the RPMs at highway speeds. It should also help with not having to downshift when going up hills. So you might loose a nominal amount of MPGs at highway speeds.
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Old 07-10-2012, 09:39 AM
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Re: regearing required to run 33s with 3.7L

Hmm Im thinking it will just be easier to get they hypertech programmer to set the new tire size and if I run into problems I will change the gear ratio then. Thanks for all the help guys.
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