transmission and regearing

I have a 99XJ 4.0, AW4, 3.5" RE lift, 31x10.5, with stock 3.55 gears. My rig does great with factory gearing, except on hills, it is a dog. I am wanting to regear this summer and possibly go with 33" tires. I talked to a local transmission shop, and told them what differentials I had and that i wanted to go with 4.56 gears, and the guy there told me if i regeared I would ruin my transmission, because it wasnt strong enough to handle a regear with bigger tires. The way I see it is that I am working my transmission and engine harder trying to push the bigger tires, and if I regear, I should be able to get back to near factory performance. Any thoughts on this?

targetslayer said:

I have a 99XJ 4.0, AW4, 3.5" RE lift, 31x10.5, with stock 3.55 gears. My rig does great with factory gearing, except on hills, it is a dog. I am wanting to regear this summer and possibly go with 33" tires. I talked to a local transmission shop, and told them what differentials I had and that i wanted to go with 4.56 gears, and the guy there told me if i regeared I would ruin my transmission, because it wasnt strong enough to handle a regear with bigger tires. The way I see it is that I am working my transmission and engine harder trying to push the bigger tires, and if I regear, I should be able to get back to near factory performance. Any thoughts on this?

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Hmm only downside I can even think of is the gears themselves are smaller but 4;56 than say 5:13"s are plenty strong..in my mind youd be doing more damage to the tranny with 33"s and 3:55"s but I'm new to most this

My opinion is to go to another shop that knows what they are talking about....
Heat is what kills the AW4 or the wrong fluid. Many on this board have the set up you want,me included, I,m on 33/4:10,s and have over 200,000 miles on this combo. A cooler and routine maintenance have gotten it this far.
You should be fine......

Never, ever go back to that transmission shop.

Of course they're dead wrong, for the reasons already stated. Consider going to 4.88's if you're going to run 33's, that is generally accepted as the best ratio, a search will more than bear out this opinion. I've run 33's with both 4.56 and 4.88 and prefer the 4.88.

X3...

The guy is wrong.

I have wheeled the dog p!ss out of my rig on 33's with 4:56 gears for over a hundred thousand miles with no tranny issues at all. Find a new tranny shop.

Thanks for the input. I appreciate the responses. I had a funny feeling this guy was full of it.

Goatman said:

Never, ever go back to that transmission shop.

Of course they're dead wrong, for the reasons already stated. Consider going to 4.88's if you're going to run 33's, that is generally accepted as the best ratio, a search will more than bear out this opinion. I've run 33's with both 4.56 and 4.88 and prefer the 4.88.

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I'm currently on 33"s n 3.55"s but I'm trying to pickup axles with 4.88"s glad u think that's good way go!

the only things deeper gears will increase the stress on (compared to the same setup with stock gears) are axle shafts and components outboard. Your guy is completely wrong, as others have stated.

the straight up math says that 33's and 4.56 are the closest to stock, gearing, however the extra weight of the larger tires, extra rolling resistance, extra wind resistance from extra lift and are not taken into account when you just do a ratio of the old tire size and old gearing against the new tire size and new gearing. I do not believe that you will regret the 4.88's.


i love my xj with the aw4 4.88 and just 31's... I still cruise on the freeway... Not 80MPH but still very comfy 70-75 MPH.

targetslayer said:

Thanks for the input. I appreciate the responses. I had a funny feeling this guy was full of it.

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oddly enough... he was not wanting to take your money.

most people get worked the other way around.

Now the rest of the story. The initial transmission shop, that told me I would ruin my transmission, has never called me back. Transmission shop #2 wants $1000 for labor, I supply all the parts. Transmission shop #3 has not called me back. Does anybody know of a good trustworthy transmission shop in the Dallas/Fort Worth Texas area?

I would suggest joining the Red River Chapter of Naxja. They would be the folks to ask about reputable shops in your area.

Here ya go:
http://www.naxja.org/forum/forumdisplay.php?f=192

I run P285s (32.8") tires and 4.56 gears behind an AW4 that in turn is sitting behing a Supercharged engine.

Go ahead, ask me if I am the least bit concerned about the Transmission...

No, no I am not. The Supra guys are pushing better than 500hp through the Toyota version of this transmission with absolutely Zero Issues.

What you do need to do is properly maintain the oil and that includes managing the temperature. My transmission Aux Cooler is mounted inside of my front skid with a 650cfm puller fan on top of it. The fan is controlled by a Thermostat that brings the fan on at 185F and shuts it off at 165F.

As to why I mounted it there, I was chasing an engine temperature issue (What? A Heep with Engine Temp Issues? Say it isn't so...) and discovered a solid 5F reduction of temperature by remoting the cooler away from in front of the radiator. The cooler itself is off of a Ford Full Size Bronco and is a Ford Factory Stacked Plate unit.

At least I understand why the Jeep Factory Cooler sits below the radiator out of the air stream.

And, I can tell you that with the 4.56/33 combination you will be taking slightly better than 10% of the load off of the transmission. This I know as I had to slow my Speedometer/Odometer down by 10.2% to get them to be accurate.

If fact, you run shorter gears just for that reason. You can make up for a lack of HP with gears. It is not just about being able to go slow.

Consider this:
My 1948 CJ-2a has a whopping 60hp. On a good day. At Sea Level. It also has the stock 5.13 gears in it. Should I be worried about the transmission? It has ran for only 64 years with this combination.

That transmission shop is staffed by Fools. The AW4 is one of the best transmissions made and the only real difference between the Toyota version and ours is one clutch disk in the OD pack. There is a good thread on the AW4 here, check it out and be assured.