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-   -   2.5L Re-Gear (http://www.wranglerforum.com/f282/2-5l-re-gear-247139.html)

Bielzebub 06-04-2013 01:53 PM

2.5L Re-Gear
 
I did a search and really didn't find the information that I am looking for, so I figured what the heck, make a new thread! Honestly, if I could have found this elsewhere, I wouldn't bother with making a new thread.

Currently I am running stock axles on my '99 2.5L with 29" tires, P235/75R15s to be exact, and I figured out that I can run 31's with no rub. I was wondering if I need to re-gear to ensure that my poor little 2.5L can keep those 31's rolling up hills on the highway. I already have trouble maintaining 65 mph going up hills, so I am afraid that increasing to 31's will absolutely kill my up hill speed, though I still want to do it because, well, it's a jeep and 31's look cooler on a jeep than the 29's do! Thanks for any help!

Jerry Bransford 06-04-2013 02:50 PM

I wouldn't pay the typical $1200-1300 to regear just for 31" tires. I'd wait until/if you go to 33" when a regear to 4.88 from your existing 4.11 will make better economic sense.

XwXCHADWICKYXwX 06-04-2013 05:24 PM

I have 33s and haven't re-geared from the stock 4.10s so 31s should be no problem.

Bielzebub 06-05-2013 07:21 AM

I am not sure 100% where I got the link, somewhere in this forum, but when I did a VIN look-up it showed that I had 3.73 axle ratio. Does that sound right? Also I am not sure what a 175MM rear axle and a 186MM Front axle means. It's a Dana 30, but that's all I am understanding.

Another question to add, what is the half shift? To explain better, when I am going up hills the jeep seems to slow down a little bit, then I press on the gas a little harder, and it drops down like a half shift. If I smash the gas to the floor, then it does a full downshift. BTW, this is on the 30RH tranny. I am not sure what this is or what this means.

Jerry Bransford 06-05-2013 09:54 AM

Yep the automatic version of the 2.5L came with 3.73 gearing. Your front axle is a Dana30, your rear axle is a Dana 35c.

That "half-shift" is just the automatic transmission's torque converter unlocking which very slightly raises the engine rpms. It locks once you reach cruising speed to help with mpg & to help the transmission run a bit cooler. Giving it a bit of gas will unlock the torque converter to give slightly higher engine rpms for a little more power, giving it even more gas will cause it to downshift to 2nd (passing) gear. All modern automatics work in pretty much the same way.

Bielzebub 06-05-2013 12:06 PM

Awesome. I wasn't aware of that! Thanks, Jerry!

So I guess going back to the original question: going from the 29's to the 31's I shouldn't need to re-gear and it won't affect my power enough to notice anything?

Jerry Bransford 06-05-2013 12:08 PM

An automatic makes slight tire size/axle gear ratio mismatches more easily handled. I wouldn't worry about it until you get to a larger tire size.

Bielzebub 06-05-2013 12:16 PM

Excellent. Thanks again, Jerry! You have been more than helpful!

Bielzebub 06-05-2013 12:31 PM

Last stupid question... Currently I have P235/75R15s on it, which if I am reading right is about a 28.5" tire. I am a little confused when it comes to looking at tire sizes. I know that I can go into a dealer and say I want 31's and they will tell me what they have, but I am thinking that it would be cheaper for me to buy them online then have my maint shop mount and balance them for free. What is the conversion on this and how do I understand it? I have tried reading about it, but it's very confusing to me. Thanks again!

Jerry Bransford 06-05-2013 12:38 PM

No need to stick with a metric size designation, you can just look directly for a 31x10.50x15 tire. :)

Bielzebub 06-05-2013 01:30 PM

Awesome! Again, you have been more than helpful! Thanks again!

Bielzebub 06-06-2013 07:23 AM

One more question. Alright, 2...

Occasionally when I shift from reverse after backing out the garage into drive it seems to have some hesitation wanting to go into gear. It does go into forward, but it seems like it's trying to think about what it's doing before it actually shifts. This is only when going from reverse to drive. I didn't know if this was normal or not.

Second question: Occasionally after backing down my semi-steep driveway into the flat street, the engine starts to sputter when I get to the bottom and stop to put it in drive. It has died on me once or twice, but normally doesn't. Is this because the fuel is shifting to the back of the tank and not hitting where the fuel pump is or do you think it may be something else?

erickpl 06-06-2013 10:48 AM

When was the last time you changed transmission fluid? If you bought it used, I'd make fluid changes a priority. Jeep TJ - Jeep Wrangler TJ Web Site of Stu Olson has a maintenance section that lists fluid amounts and types you'd need on your 99. If you're an automatic, Redline MTL-90 would be a great choice. I use MT-90 in my manual 97 (with 2.5L engine also).

For your second question, it COULD be part of that, but you may have fuel line/fuel injector issues that you want to clean out. Perhaps run a bottle or two of STP fuel treatment through it just to help clean things up a bit.

Jeff City has a few good hills there (ran cross country there a few times), so I can imagine you could have a pretty steep driveway.

Jerry Bransford 06-06-2013 10:57 AM

Quote:

Originally Posted by erickpl (Post 3831868)
When was the last time you changed transmission fluid? If you bought it used, I'd make fluid changes a priority. Jeep TJ - Jeep Wrangler TJ Web Site of Stu Olson has a maintenance section that lists fluid amounts and types you'd need on your 99. If you're an automatic, Redline MTL-90 would be a great choice.

With an automatic, he can only use ATF+3 or ATF+4. For manual transmissions, Redline makes MTL and MT-90 but not an MTL-90. :)

Bielzebub 06-07-2013 07:47 AM

Quote:

Originally Posted by erickpl (Post 3831868)
When was the last time you changed transmission fluid? If you bought it used, I'd make fluid changes a priority. Jeep TJ - Jeep Wrangler TJ Web Site of Stu Olson has a maintenance section that lists fluid amounts and types you'd need on your 99. If you're an automatic, Redline MTL-90 would be a great choice. I use MT-90 in my manual 97 (with 2.5L engine also).

For your second question, it COULD be part of that, but you may have fuel line/fuel injector issues that you want to clean out. Perhaps run a bottle or two of STP fuel treatment through it just to help clean things up a bit.

Jeff City has a few good hills there (ran cross country there a few times), so I can imagine you could have a pretty steep driveway.

Sweet, thanks for the info!

Yeah, I used to run CC back in the day, tore the crap out of Oak Hills Country Club, about $40k worth of damage after a week of rain. Everyone ran in 1" spikes just to get traction.

I will run a bottle of STP through and see if that helps out as well as a tranny flush. How difficult is that?


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