Topic: GEARS & TIRES

[mbolan]

I'm new to the Jeep world. We just bought a 91 Wrangler with a 2.5 4 cyl and a supposed to be ax5 tranny (more to come on the tranny later) for my son. It has a few issues but it seems like a pretty good deal and I'm a pretty decent wrench so I'm not afraid of diggin in. It has 33s on the corners and I'm guessing about a 2.5" lift. The 1st thing I want to ask about is the lack of power. It runs great up to about 55mph (the speedo is off because of the tires) then hits a wall. No bucking or surging just no more power with a lot of accelorator pedal left. You can hold the pedal half way down or floor it and its still going to get about 55mph and thats it. I searched this forum a little for similiar posts and have found some pretty good stuff on gearing. It looks like our jeep has 3.55s or something close to it. Is my power problem gearing? Until I read the posts about gearing I was thinking I had a stopped up catalytic converter. I also checked the fuel pressure and it stays steady at 30psi when idling or maxed out at 55mph. I'm thinking its a little low but probably not the causing the lack of power.

[Jeffy]

It's probably the gearing.  With stock gearing and 33's you'll will need to keep the RPM's high.  Over 3000 RPM to get any headway.  Also, I would suspect that the Jeep has at least 3" if not 4" of lift.  2.5" is awfully small for 33's.  Have any pictures?

To get it to go faster you'll have to probably rev the engine close to 4000 RPM so when you shift you're solidly in the 3000's.  Because of the tires, you're not getting into the meaty part of the powerband.

Check the ID tags on the diffs.  They should read 4.10 on the front and 4.11 on the rear.  3.55 was not offered on the 2.5L's so unless someone swapped them from a 4.0L to get the 4.10/4.11's it should be 4.10/4.11 for the manual and 3.73 for the auto.

[mbolan]

I'll snap some pics and get them posted later when I get home.  I jacked the rear wheels up and counted rotation of the drive shaft and it looked to be somewhere in the 3.55 range. So I'll double check that and look at the ID tags when I get home also.  There's a good chance that something has been changed in the gearing and trans. That was the more to come part I was talking about getting to later. The tranny only has 4 working gears. 5th gear is gone as in it acts like its in neutral. Just looking at the trans without digging in it looks like an ax5 and the shifter definately has a 5th gear location but it has a 4 speed shift pattern knob on it. So maybe the tranny was changed or the linkage is messed up or maybe its just broken. I'm not familiar with the ax5 trannys yet but i've rebuilt some muncies before and they're not too hard to rebuild if its required. Ya I know its a project but he price was right and it looks cool. Now we just need to make go right.

[oldjeep]

I'll snap some pics and get them posted later when I get home.  I jacked the rear wheels up and counted rotation of the drive shaft and it looked to be somewhere in the 3.55 range. So I'll double check that and look at the ID tags when I get home also.  There's a good chance that something has been changed in the gearing and trans. That was the more to come part I was talking about getting to later. The tranny only has 4 working gears. 5th gear is gone as in it acts like its in neutral. Just looking at the trans without digging in it looks like an ax5 and the shifter definately has a 5th gear location but it has a 4 speed shift pattern knob on it. So maybe the tranny was changed or the linkage is messed up or maybe its just broken. I'm not familiar with the ax5 trannys yet but i've rebuilt some muncies before and they're not too hard to rebuild if its required. Ya I know its a project but he price was right and it looks cool. Now we just need to make go right.

Could be an AX4 out of a cherokee.  Looks the same, just has no 5th gear.

[mbolan]

Yup it might be. Is the the 5th gear in the ax5 an overdrive gear? If so and I have an ax4 with a 1:1 4th its going to make a gear change harder to swallow.

[Jeffy]

Most likely you broke the clip that holds the 5th gear in place.

When choosing gears you're supposed to use 1:1 in all calculations.  5th is always OD and should not be considered when setting the RPM.

[mbolan]

I confirmed the rear end ratio by rotation again and by the ID tag. Its got 3.55 gears in it. So I'm guessing its been changed at some point in its 20 year life. I would'nt be suprised if the original 5 speeds been swapped with a 4speed since they put a 4 speed hift knob on it. Although I hope its just a broken clip in the tranny. So I guess a gear change is required to get this rig up to speed. As a side note I can shake the cat coverter and it rattles so maybe I have more than one problem with power. I also attached a couple of pics. What do ya think?

[sharpxmen]

I confirmed the rear end ratio by rotation again and by the ID tag. Its got 3.55 gears in it. So I'm guessing its been changed at some point in its 20 year life. I would'nt be suprised if the original 5 speeds been swapped with a 4speed since they put a 4 speed hift knob on it. Although I hope its just a broken clip in the tranny. So I guess a gear change is required to get this rig up to speed. As a side note I can shake the cat coverter and it rattles so maybe I have more than one problem with power. I also attached a couple of pics. What do ya think?

change the cat as soon as possible, it will eventually plug your exhaust - it happened to me (twice if you can believe that) and the last time i had to punch a hole in the cat to drive it home as it would die the moment i would accelerate.

EDIT: do you have 3.55 both front and rear? not sure if the 91 model came with 3.55s, i wonder if the whole drivetrain was replaced - Jeffy do you know if that's the case (did 91 had a 3.55)? or maybe it had an auto from factory but even then i thought they were 3.73s, you might be able to find out at a dealer if you give them your VIN

[Jeffy]

Can the transmission actually shift into 5th?  (right and up) If not then my guess is that it was originally an automatic and someone swapped in a manual.  Unlike XJ's, YJ's were never offered with a AX-4 and even in XJ's they are rare.  Personally, I'd consider swapping in a AX-15 or NV3550 if you're going to bother changing it out.  No point sticking with a 4-speed unless it's a SM420, SM465 or NV435.

If you want to at least get stock 4.10/4.11's then I suggest buying a complete set of axles rather then having the gears changed.  You'll end up with two spare axles for parts and you'll be able to swap the axles without having to deal with installing gears.  The other option is to look for someone selling some axles off a YJ that are geared lower already.  Maybe use it as a chance to upgrade to D44's.  You can regear to 4.88's and be OK even with a 4-speed.

Although it does look good with those wheels, tires and lift.

[drunkencityworker]

I would check to make sure the front axle is geared to match the back. They could have blown the original rear axle and just swapped in what they coul get there hands on since you coul rive in 2wd with out causing damage. If you happen to have 3.73 or 4.10 in the front you can get an 8.8 relativley cheap to match the front. And I ont believe in putting money in a dana35

As long as frame and body are fairly rust free. The rest is managable.

[mbolan]

It does shift into 5th gear spot but its just like being in neutral.  I have'nt checked the front ratio yet but I bet its the same because I had it 4wd and it seemed to roll fine. If it was different it would proably try to tear the drive shafts out. I had to manually apply vacuum to the front axle shift motor but it did lock in and the transfer case shifts fine. I have a pneumatic switch I'm going to mount on the dash to engage the front axles. I'll jump on the cat hopefully this weekend since its a logical upgrade even if its not the problem. I'll take Jeffy's advice and start looking for bargain dana 40 stuff (if there is such a thing). I was really hoping to only stick in new gears. I see dana 35 gears for about $200 a set + $100 for the install kits. So about $600 total. I suspect its going to cost more to convert and I'm not really in a big hurry. This is actually a project for my son who is just now getting his permit. Of course I will probably have to ocassionally test drive it for him. What do you typically see dana 45 stuff sell for?

[sma97tj]

i would go with an 8.8 before a dana 44 marginly stronger and probaly a little cheaper to do look for an explorer 95-99 i think or even a ranger they also have 8.8s and most have 4.11  explorers could also have 3.73  with a limited slip

[st.chevrolet]

i would go with an 8.8 before a dana 44 marginly stronger and probaly a little cheaper to do look for an explorer 95-99 i think or even a ranger they also have 8.8s and most have 4.11  explorers could also have 3.73  with a limited slip

Ford Explorers  came with the following ratio's 3.08, 3.27, 3.55, 3.73, 4.10, 4.56. All Explorer axle shafts are
31 spline and the Explorer axle is rated @ 3200#. The Ranger axle came with the same ratio's with the
addition of  3.45's but the axle shafts are 28 spline and the axle is rated @  2750#. The 2002 Ranger FX4
Ranger came with 4.10 only and 31 spline shafts.  Explorer axle's from 95 and up have disc brakes.

[Jeffy]

Ford Explorers  came with the following ratio's 3.08, 3.27, 3.55, 3.73, 4.10, 4.56. All Explorer axle shafts are 31 spline
and the Explorer axle is rated  (at)  3200#. The Ranger axle came with the same ratio's with the addition of  3.45's but the axle shafts are 28 spline and the axle is rated  (at)  2750#. The 2002 Ranger FX4 Ranger came with 4.10 only and 31 spline shafts.  Explorer axle from 95 and up have disc brakes

Hmm, I don't think Explorers came with 4.56's.  That should have been limited to the Ranger XLT.

[st.chevrolet]

Hmm, I don't think Explorers came with 4.56's.  That should have been limited to the Ranger XLT.

You could be right, but it is listed under Explorer on the Ranger Station.