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i gotta question, i can't tell what type of tranny i have i know it's a 5 speed manual with an extornally mounted clutch slave cylinder but i don't know if it's a T4, T5, AX 4 OR AX 5, it doesn't have 4 wheel drive, is there any way to id what it is? also could the 2.8 v6 with the 5speed manual tranny handle 235/75/R15 tires, i currently have 225/75/R15 and got a nice set of 235s in my back yard, also would they rub anywhere?

 

Redwolf

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With the 2.8V6 it is almost certainly an AX5. 

 

The 235 tires will be less than 1/2" wider and a little over 1/2" taller (little over 1/4" more from the center to the tread). Not much difference to speak of, and nothing the engine or transmission will worry about.

 

There is a possibility you might just barely rub the lower control arms at full lock steering.

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With the 2.8V6 it is almost certainly an AX5. 

 

The 235 tires will be less than 1/2" wider and a little over 1/2" taller (little over 1/4" more from the center to the tread). Not much difference to speak of, and nothing the engine or transmission will worry about.

 

There is a possibility you might just barely rub the lower control arms at full lock steering.

sweet, would there be any ride difference maybe a little more clearance, i wonder how it's look  :hmm:  :idea:

 

Redwolf

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my 88 manche is running 235/75r15 maxxis bighorns and i love them no rub whatsoever and its stock hight

sweet, well i guess i'm gonna have to borrow my old man's tires since he has 235/75/R15s on his wrangler, kinda curious as to how that'd look,

 

Redwolf

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Since you know it's a 5 speed, then you can eliminate the AX-4.  The AX-4 is the AX-5 minus the 5th gear.

 

I saw a rumor once about the T-5 being used in the XJ/MJ, but never saw proof of it.  Until I see otherwise, with definitive proof, the AX-4/5 were the ONLY manual transmissions used behind the 2.5/2.8 in the XJ/MJ.

 

When changing tire size, you want to look at the percentage change, not necessarily the amount in inches.  235/75R15s are ~4.4% bigger than the 225/75R15s.  Remember this is going to throw your speedo off a tiny bit, so if you speed already, you may want to back off a bit.  Say if your speedo was dead on with the 225s(which it isn't) at 60 mph, you'd actually be going 62.6 with the 235s.  Doesn't seem like much, but still a consideration.

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Since you know it's a 5 speed, then you can eliminate the AX-4.  The AX-4 is the AX-5 minus the 5th gear.

 

I saw a rumor once about the T-5 being used in the XJ/MJ, but never saw proof of it.  Until I see otherwise, with definitive proof, the AX-4/5 were the ONLY manual transmissions used behind the 2.5/2.8 in the XJ/MJ.

 

When changing tire size, you want to look at the percentage change, not necessarily the amount in inches.  235/75R15s are ~4.4% bigger than the 225/75R15s.  Remember this is going to throw your speedo off a tiny bit, so if you speed already, you may want to back off a bit.  Say if your speedo was dead on with the 225s(which it isn't) at 60 mph, you'd actually be going 62.6 with the 235s.  Doesn't seem like much, but still a consideration.

i learned the speedin issue from my dad when he had a cop gun him before, could my MJ bein stock hight with 235/75/R15s cause it to do 5 over or is that the speedo off from 27 years of never bein touched?

 

Redwolf

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The speedos weren't really accurate from the factory, especially since the speedo gear was based on axle ratio, and not which tire size was put on the vehicle.  XJs and MJs came with at least 4 different size tires, and they all used the same gear.

 

But yes, it could be off by that much for many different reasons combined.

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The speedos weren't really accurate from the factory, especially since the speedo gear was based on axle ratio, and not which tire size was put on the vehicle.  XJs and MJs came with at least 4 different size tires, and they all used the same gear.

 

But yes, it could be off by that much for many different reasons combined.

wow, is there a way to currect it without takin it to a shop for one of those idiots to mess anything up cause acorddin to my parents and my friends i do 5 over the posted speed limit so i'm actually doin 10 over cause i generally speed 5 over anyhow  :yes: but i'd love to do it myself just like everything else i've done, the only thing i'm not gonna do myself to my MJ is the body work, i'm gonna get the inside and outside restored one day,

 

Redwolf

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Since you know it's a 5 speed, then you can eliminate the AX-4.  The AX-4 is the AX-5 minus the 5th gear.

 

I saw a rumor once about the T-5 being used in the XJ/MJ, but never saw proof of it.  Until I see otherwise, with definitive proof, the AX-4/5 were the ONLY manual transmissions used behind the 2.5/2.8 in the XJ/MJ.

 

When changing tire size, you want to look at the percentage change, not necessarily the amount in inches.  235/75R15s are ~4.4% bigger than the 225/75R15s.  Remember this is going to throw your speedo off a tiny bit, so if you speed already, you may want to back off a bit.  Say if your speedo was dead on with the 225s(which it isn't) at 60 mph, you'd actually be going 62.6 with the 235s.  Doesn't seem like much, but still a consideration.

4.4% wider. But the diameter and circumference are only 2.1% larger. So assuming the tires measure what they are supposed to and the speedometer is accurate, with the speedometer reading 60 you would be going 61.3.

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The speedos weren't really accurate from the factory, especially since the speedo gear was based on axle ratio, and not which tire size was put on the vehicle.  XJs and MJs came with at least 4 different size tires, and they all used the same gear.

 

But yes, it could be off by that much for many different reasons combined.

 

Umm, no.

 

Both my 87 MJs came from the factory with 3.55 gears (2.5/AX4 and 4.0/AW4). The 2.5 came with 205/75R15 and the 4.0 came with 225/75R15. And they came with different speedometer gears to make them as accurate as possible with that tire size. The difference is only 1 tooth, but still different.

 

Correction: the difference is two teeth.

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Since you know it's a 5 speed, then you can eliminate the AX-4.  The AX-4 is the AX-5 minus the 5th gear.

 

I saw a rumor once about the T-5 being used in the XJ/MJ, but never saw proof of it.  Until I see otherwise, with definitive proof, the AX-4/5 were the ONLY manual transmissions used behind the 2.5/2.8 in the XJ/MJ.

 

When changing tire size, you want to look at the percentage change, not necessarily the amount in inches.  235/75R15s are ~4.4% bigger than the 225/75R15s.  Remember this is going to throw your speedo off a tiny bit, so if you speed already, you may want to back off a bit.  Say if your speedo was dead on with the 225s(which it isn't) at 60 mph, you'd actually be going 62.6 with the 235s.  Doesn't seem like much, but still a consideration.

i learned the speedin issue from my dad when he had a cop gun him before, could my MJ bein stock hight with 235/75/R15s cause it to do 5 over or is that the speedo off from 27 years of never bein touched?

 

Vehicle height has nothing to do with it. Your speedometer is driven by a gear that's turned by the output shaft of the transfer case (or transmission, if you have 2WD). The number of teeth on the speedometer drive gear has to be matched to the tire size and rear axle gear ratio to calibrate the speedometer. It doesn't really have any idea how fast you're going -- it's only reading driveshaft revolutions.

 

So ... put on larger tires, and the vehicle travels farther for each revolution. That means you're going faster than the speedometer thinks you're going.

 

The difference between 225/75-15s and 235/75-15s isn't much. It's about 1 percent. Call it 2 percent to be safe, and that translates to traveling 2 MPH faster than you think at 100 MPH, and 1 MPH faster at 50 MPH.

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The speedos weren't really accurate from the factory, especially since the speedo gear was based on axle ratio, and not which tire size was put on the vehicle.  XJs and MJs came with at least 4 different size tires, and they all used the same gear.

 

No, they didn't.

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Since you know it's a 5 speed, then you can eliminate the AX-4.  The AX-4 is the AX-5 minus the 5th gear.

 

I saw a rumor once about the T-5 being used in the XJ/MJ, but never saw proof of it.  Until I see otherwise, with definitive proof, the AX-4/5 were the ONLY manual transmissions used behind the 2.5/2.8 in the XJ/MJ.

 

When changing tire size, you want to look at the percentage change, not necessarily the amount in inches.  235/75R15s are ~4.4% bigger than the 225/75R15s.  Remember this is going to throw your speedo off a tiny bit, so if you speed already, you may want to back off a bit.  Say if your speedo was dead on with the 225s(which it isn't) at 60 mph, you'd actually be going 62.6 with the 235s.  Doesn't seem like much, but still a consideration.

i learned the speedin issue from my dad when he had a cop gun him before, could my MJ bein stock hight with 235/75/R15s cause it to do 5 over or is that the speedo off from 27 years of never bein touched?

 

Vehicle height has nothing to do with it. Your speedometer is driven by a gear that's turned by the output shaft of the transfer case (or transmission, if you have 2WD). The number of teeth on the speedometer drive gear has to be matched to the tire size and rear axle gear ratio to calibrate the speedometer. It doesn't really have any idea how fast you're going -- it's only reading driveshaft revolutions.

 

So ... put on larger tires, and the vehicle travels farther for each revolution. That means you're going faster than the speedometer thinks you're going.

 

The difference between 225/75-15s and 235/75-15s isn't much. It's about 1 percent. Call it 2 percent to be safe, and that translates to traveling 2 MPH faster than you think at 100 MPH, and 1 MPH faster at 50 MPH.

now i'm confused, i know that larger tires "adds" a little bit more of speed by 1MPH or so but how can i figure this whole speedo thing out, i don't know my gears, all i know bout my MJ is it's an 86, it has a 2.8 v6 out of a 93 GMC sonoma (only cause the old motor had a crack in the block), it has a 5 speed tranny, it's 2wd and i have a 7'8" bed (i messured it  :D), and i'm rollin on 225/75/R15s and apparently i speed 5MPH when my speedo reads 25 i do 30,

 

Redwolf

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The speedos weren't really accurate from the factory, especially since the speedo gear was based on axle ratio, and not which tire size was put on the vehicle.  XJs and MJs came with at least 4 different size tires, and they all used the same gear.

 

No, they didn't.

 

 

The speedos weren't really accurate from the factory, especially since the speedo gear was based on axle ratio, and not which tire size was put on the vehicle.  XJs and MJs came with at least 4 different size tires, and they all used the same gear.

 

But yes, it could be off by that much for many different reasons combined.

 

Umm, no.

 

Both my 87 MJs came from the factory with 3.55 gears (2.5/AX4 and 4.0/AW4). The 2.5 came with 205/75R15 and the 4.0 came with 225/75R15. And they came with different speedometer gears to make them as accurate as possible with that tire size. The difference is only 1 tooth, but still different.

 

 

I stand corrected, gentlemen.

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From another 2.8 guy, don't get bigger tires until you have a bigger engine. I dropped down to 205's on mine. Does fine on and offroad with smaller tires, they're Firestone Destination A/Ts, look good, run good, and you still "feel" like you have a little bit of power in your engine. Just my .02

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From another 2.8 guy, don't get bigger tires until you have a bigger engine. I dropped down to 205's on mine. Does fine on and offroad with smaller tires, they're Firestone Destination A/Ts, look good, run good, and you still "feel" like you have a little bit of power in your engine. Just my .02

i thought bout droppin down to the 205 but i saw one the other day with those and it just didn't look right to me, plus my dad has so almost new 235s out in the back yard so i was thinkin bout gettin those slapped on when my 225 are done, just a thought though, also how do ya like the firestone destination ATs, i've been lookin at those and the MTs both look really agressive  :D  :yes:  :banana:  :jump:

 

Redwolf

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Since you know it's a 5 speed, then you can eliminate the AX-4.  The AX-4 is the AX-5 minus the 5th gear.

 

I saw a rumor once about the T-5 being used in the XJ/MJ, but never saw proof of it.  Until I see otherwise, with definitive proof, the AX-4/5 were the ONLY manual transmissions used behind the 2.5/2.8 in the XJ/MJ.

 

When changing tire size, you want to look at the percentage change, not necessarily the amount in inches.  235/75R15s are ~4.4% bigger than the 225/75R15s.  Remember this is going to throw your speedo off a tiny bit, so if you speed already, you may want to back off a bit.  Say if your speedo was dead on with the 225s(which it isn't) at 60 mph, you'd actually be going 62.6 with the 235s.  Doesn't seem like much, but still a consideration.

i learned the speedin issue from my dad when he had a cop gun him before, could my MJ bein stock hight with 235/75/R15s cause it to do 5 over or is that the speedo off from 27 years of never bein touched?

 

Vehicle height has nothing to do with it. Your speedometer is driven by a gear that's turned by the output shaft of the transfer case (or transmission, if you have 2WD). The number of teeth on the speedometer drive gear has to be matched to the tire size and rear axle gear ratio to calibrate the speedometer. It doesn't really have any idea how fast you're going -- it's only reading driveshaft revolutions.

 

So ... put on larger tires, and the vehicle travels farther for each revolution. That means you're going faster than the speedometer thinks you're going.

 

The difference between 225/75-15s and 235/75-15s isn't much. It's about 1 percent. Call it 2 percent to be safe, and that translates to traveling 2 MPH faster than you think at 100 MPH, and 1 MPH faster at 50 MPH.

now i'm confused, i know that larger tires "adds" a little bit more of speed by 1MPH or so but how can i figure this whole speedo thing out, i don't know my gears, all i know bout my MJ is it's an 86, it has a 2.8 v6 out of a 93 GMC sonoma (only cause the old motor had a crack in the block), it has a 5 speed tranny, it's 2wd and i have a 7'8" bed (i messured it  :D), and i'm rollin on 225/75/R15s and apparently i speed 5MPH when my speedo reads 25 i do 30,

 

Redwolf

 

First off, you NEED to know what your axle ratio is. It's probably 3.73 with the 2.8L V6, but it might be 4.10. But you need to find out. Once you have that, there are charts on the Internet that tell you which speedo drive gear to use for each combination of tire size and axle ratio.

 

The second thing is that you should understand that the wrong speedo gear doesn't make the speedometer read high (or low) by the same amount at all speeds. It's a proportion. The same applies to tires. The difference gets larger as the speed increases. The way I calculate the difference due to tires is the most accurate way there is. Most tire manufacturers publish the number of revolutions per mile for each tire model and size. Comparing those numbers tells you what percentage of difference there is.

 

I don't have access to 1986 specifications, but I'll take a guess that the original tires on your truck were probably 215/75-15s. According to the tire charts I used when I compiled my tire/gear/speed spreadsheet many years ago (I think I used Cooper Discovere tires, but I don't remember), a 215/75-15 turns 754 revolutions per mile. That's all you need at this point. If you know the axle and transmission gear ratios you can calculate (accurately) the engine RPM for any road speed in any gear, but for just comparing the effect of different tire sizes, all you need is the (tire) revolutions per mile.

 

From the same data, I get 730 revolutions per mile for 225/75-15 tires, and 722 revolutions per mile for 235/75-15s.

 

To calculate the percentage of any change, you take the difference between two values, divide the difference by the original value, and multiply by 100. So, to go from 215s to 235s we get:

 

(754 - 722)/754 x 100 = 4.24 percent.

 

So whatever your speedometer should be reading with 215/75 tires, your actual speed will be 4.24 percent faster. At 10 MPH, that's 10.4 MPH. At 30 MPH, it's 31.3 MPH. At 50 MPH, it's 52.1 MPH.

 

The number I threw at you a few posts above was based on starting with 225/75-15 tires. For those, the numbers are:

 

(730 - 722)/730 x 100 = 1.10 percent.

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ok well before i start gettin into all that math, how do i find out my gear ratio, all i know bout my MJ is it has a 2.8 v6, 5 speed manual and it's 2WD, i have no info sticker on the doors, i only got the tire pressure info sticker in the glove box and the cadalatic converter sticker inside the door, i have no idea what axle i have, what type of tranny weather it be AX5, AX4 and so on,

 

Redwolf

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one tooth diff or not, still like to know if there's a way to calabrate my speedo, i'm currently rollin with 225/75/R15s and everyone i know says i do 5 over,

 

Redwolf

 

I corrected my original posts as the difference is two teeth. Since the speedometer gears are in the neighborhood of 30 teeth, one tooth more or less makes about a 3% difference. If (I'm assuming at high speed) you're off about 5mph with the 225 tires, then you have a speedometer gear for 205 tires. I run 235 on a truck that had originally 205 and when the speedometer reads 70 I'm actuallly going 75.

 

Besides changing the speedometer gear (about $60 for the gear, not too difficult to install) there is no calibration possible for the speedometer.

 

There should be a tag bolted to the diff cover with the ratio stamped in it. Even if the tag is still there it is probably not readable anymore because of 27 years of rust. Alternative way is to shift the transmission into neutral, jack up one rear tire and rotate it by hand 2 turns. If the drive shaft goes around three and a half turns you have  3.55 gears, three and three quarter turns is 3.73 and a bit over four is 4.10. My guess is that you have 4.10 gears, but Eagle seems to think 3.73 is more likely.

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It SHOULD have 4.10's Your transmission is an AX5. If its a 5spd it can not be an ax4 because an ax4 is a 4spd. Hence, the "4" in ax4. Simple way to check your axle gearing is to jack the rear end up, put the trans in neutral. Spin your tires 2 full revolutions, and count how many revolutions your drive shaft makes. Thats your axle gear ratio.

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one tooth diff or not, still like to know if there's a way to calabrate my speedo, i'm currently rollin with 225/75/R15s and everyone i know says i do 5 over,

 

Redwolf

 

I corrected my original posts as the difference is two teeth. Since the speedometer gears are in the neighborhood of 30 teeth, one tooth more or less makes about a 3% difference. If (I'm assuming at high speed) you're off about 5mph with the 225 tires, then you have a speedometer gear for 205 tires. I run 235 on a truck that had originally 205 and when the speedometer reads 70 I'm actuallly going 75.

 

Besides changing the speedometer gear (about $60 for the gear, not too difficult to install) there is no calibration possible for the speedometer.

 

There should be a tag bolted to the diff cover with the ratio stamped in it. Even if the tag is still there it is probably not readable anymore because of 27 years of rust. Alternative way is to shift the transmission into neutral, jack up one rear tire and rotate it by hand 2 turns. If the drive shaft goes around three and a half turns you have  3.55 gears, three and three quarter turns is 3.73 and a bit over four is 4.10. My guess is that you have 4.10 gears, but Eagle seems to think 3.73 is more likely.

 

 

It SHOULD have 4.10's Your transmission is an AX5. If its a 5spd it can not be an ax4 because an ax4 is a 4spd. Hence, the "4" in ax4. Simple way to check your axle gearing is to jack the rear end up, put the trans in neutral. Spin your tires 2 full revolutions, and count how many revolutions your drive shaft makes. Thats your axle gear ratio.

alright, what happens if i end up havin open diffs instead of a limited slip? could that mean i have a different gearin or same math involved, and i was readin my haynes manual and it mentioned a T5 and T4 tranny, along with the AX4 and 5, what's the difference between the two?

 

Redwolf

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one tooth diff or not, still like to know if there's a way to calabrate my speedo, i'm currently rollin with 225/75/R15s and everyone i know says i do 5 over,

 

Redwolf

 

I corrected my original posts as the difference is two teeth. Since the speedometer gears are in the neighborhood of 30 teeth, one tooth more or less makes about a 3% difference. If (I'm assuming at high speed) you're off about 5mph with the 225 tires, then you have a speedometer gear for 205 tires. I run 235 on a truck that had originally 205 and when the speedometer reads 70 I'm actuallly going 75.

 

Besides changing the speedometer gear (about $60 for the gear, not too difficult to install) there is no calibration possible for the speedometer.

 

There should be a tag bolted to the diff cover with the ratio stamped in it. Even if the tag is still there it is probably not readable anymore because of 27 years of rust. Alternative way is to shift the transmission into neutral, jack up one rear tire and rotate it by hand 2 turns. If the drive shaft goes around three and a half turns you have  3.55 gears, three and three quarter turns is 3.73 and a bit over four is 4.10. My guess is that you have 4.10 gears, but Eagle seems to think 3.73 is more likely.

 

 

>It SHOULD have 4.10's Your transmission is an AX5. If its a 5spd it can not be an ax4 because an ax4 is a 4spd. Hence, the "4" in ax4. Simple way to check your axle gearing is to jack the rear end up, put the trans in neutral. Spin your tires 2 full revolutions, and count how many revolutions your drive shaft makes. Thats your axle gear ratio.

alright, what happens if i end up havin open diffs instead of a limited slip? could that mean i have a different gearin or same math involved, and i was readin my haynes manual and it mentioned a T5 and T4 tranny, along with the AX4 and 5, what's the difference between the two?

 

Redwolf

 

Open diff or limited slip has no effect on gear ratio. Limited slip is basically a clutch system between the spider gears to force power to the other wheel when one wheel is on ice or in mud.

 

Haynes is not an authority on anything. But there is a rumor Jeep may have used T4 and T5 transmissions instead of the AX4 and AX5 when supply was running low in early Cherokees and Comanches. I have never seen one yet, though.

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one tooth diff or not, still like to know if there's a way to calabrate my speedo, i'm currently rollin with 225/75/R15s and everyone i know says i do 5 over,

 

Redwolf

 

I corrected my original posts as the difference is two teeth. Since the speedometer gears are in the neighborhood of 30 teeth, one tooth more or less makes about a 3% difference. If (I'm assuming at high speed) you're off about 5mph with the 225 tires, then you have a speedometer gear for 205 tires. I run 235 on a truck that had originally 205 and when the speedometer reads 70 I'm actuallly going 75.

 

Besides changing the speedometer gear (about $60 for the gear, not too difficult to install) there is no calibration possible for the speedometer.

 

There should be a tag bolted to the diff cover with the ratio stamped in it. Even if the tag is still there it is probably not readable anymore because of 27 years of rust. Alternative way is to shift the transmission into neutral, jack up one rear tire and rotate it by hand 2 turns. If the drive shaft goes around three and a half turns you have  3.55 gears, three and three quarter turns is 3.73 and a bit over four is 4.10. My guess is that you have 4.10 gears, but Eagle seems to think 3.73 is more likely.

 

 

>It SHOULD have 4.10's Your transmission is an AX5. If its a 5spd it can not be an ax4 because an ax4 is a 4spd. Hence, the "4" in ax4. Simple way to check your axle gearing is to jack the rear end up, put the trans in neutral. Spin your tires 2 full revolutions, and count how many revolutions your drive shaft makes. Thats your axle gear

ratio.

alright, what happens if i end up havin open diffs instead of a limited slip? could that mean i have a different gearin or same math involved, and i was readin my haynes manual and it mentioned a T5 and T4 tranny, along with the AX4 and 5, what's the difference between the two?

 

Redwolf

Open diff or limited slip has no effect on gear ratio. Limited slip is basically a clutch system between the spider gears to force power to the other wheel when one wheel is on ice or in mud.

 

Haynes is not an authority on anything. But there is a rumor Jeep may have used T4 and T5 transmissions instead of the AX4 and AX5 when supply was running low in early Cherokees and Comanches. I have never seen one yet, though.

 

i didn't know that, that's nice to know, and i guess the next time i drop my tranny i outta take a pic of it for yall cause it kinda looks like the AX5 but at the same time kinda looks like the T5 in the haynes manual,

 

Redwolf

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