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? About tires

D

DrShaggford

NAXJA Forum User
Location
Joliet IL
94 xj sport auto tranny 3" lift ,RE extended slip yoke 33x12.5 tires.

Finally got my 33s on the jeep yesterday and ive been having some odd behavior.

When im on the highway and driving up hills that my jeep normally would downshift for and lose speed it now seems to do the opposite. It doesn't downshift and I loose hardly any speed.

Fromy understanding shouldn't it be acting in the opposite manner?

I have an 8.25 rearend that I haven't opened the pumpkin on yet but I believe its the stock 3.55 gears.

Any input would be greatly appreciated. Im not concerned but im completely boggled on this one.
 
Did you change your wheels or just the tires? What size tires did you have before? How do the weights of the new tires and/or wheels compare to the old?
 
I'm guessing it's because you're already in that lower gear that it used to downshift into as your transmission is probably not getting the opportunity to shift into overdrive when you're charging up a hill. I bet you'll find that if you ease off the throttle while going uphill, it will now try to upshift on you instead. This is why a lot of folks that are running stock gears with larger tires just drive in "3" instead of "D".
 
Just took another trip on the highway and on a hill I tried letying off the gas a bit and it didnt upshift or downshift. On a flat on the highway I hammered down a bit and it downshifted just fine so thst makes me think that I am,in overdrive. There is no way I can be in 2nd or 3rd for that matter doing 65mph at just a hair over 2k rpm.


Sent from my SGH-T959 using Tapatalk
 
DrShaggford said:
There is no way I can be in 2nd or 3rd for that matter doing 65mph at just a hair over 2k rpm.


Sent from my SGH-T959 using Tapatalk
Click to expand...


With that size tire I will say you can in 3rd gear. Did you change the speedometer drive gear?

Is the 8.25 filled with 3.55 gears or another ratio? You need to verify that before any meaningful diagnostic could proceed.
 
DrShaggford said:
There is no way I can be in 2nd or 3rd for that matter doing 65mph at just a hair over 2k rpm.
Click to expand...

With my AW4 33/12.50x15 and 3.55 8.25 I do about 1,600 RPM in 4th gear at 65 MPH.

Sounds like you are in third gear to me.
 
Make sure you have a tranny cooler. If you haven't dropped the pan and changed the filter and half the fluid lately, do that. as long as you keep the aw4 cool, you really can't kill it. I run 32s on the stock 3.55s with a tranny cooler and it's all good. Go faster and you'll feel when it shifts into overdrive.
 
I have a tranny cooler wating to go in....i want to wait untill I pick up a tranny temp guage so I can install both at once.i will be regearing but I want to grab an sye and lift another 2-3 in first. And no I have not changed the speedo gear because when these tires are done I want to drop down to a 32x10.5. My soeed is gps verified though.
 
I haven't changed the speedo gear in the above jeep either. Not sure it makes a difference?? Does the AW4 read from the speedo? If so, it's about 5mph off at 60 mph according to GPS.
 
mjma said:
I haven't changed the speedo gear in the above jeep either. Not sure it makes a difference?? Does the AW4 read from the speedo? If so, it's about 5mph off at 60 mph according to GPS.
Click to expand...


Yes. The AW4 TCM (computer) does read the speed to determine when to change the gears both up and down. That is the reason I asked the question earlier.

GPS verified is all well and good but only to the driver. The GPS does not communicate with the TCM to say what the actual speed is. The TCM make its descision based on the information it receives whether that information it is accurate or in-accurate.
 
So since changing the speedo gear seems to be important does anyone know where to pick them up cheap....i just can't see spending $80 on something that will most likely be temporary. Also on my trip home I matched my speed to rpm...i was doing 69mph at 2000rpm in 4th gear I don't recall the rpm at 60 in 3rd though.
 
I ran my XJ on 4.10 gears and 30" tires using the OEM speedo drive gear for about a year. I knew the MPH and AW4 shift patterens would be out of wack and learned to live with it.

Now I have gone the other way. I have 4.10 gears and 30" tires and using the speedo sender for 4.10 gears and 32" tires and the MPH and shift patterns are still out of wack. To change or not to change the speedo is your call.

Oh,... by-the-way driving on flat road is OK. The hills is what causes the AW4 to throw a fit when using OEM speed sensor and gears with larger tires.
 
I got a new speedo gear for my MJ back in like 2000 or 2001!!!! It was my first jeep!! I don't think it cost me more than 10-15 bucks from the stealership. Are they still available??

I never knew they had any input on the tranny though!! I have the proper gear in my big XJ on Qs with 4.88s and it drives totally normal (it's a 99 and on long highway drives gets between 20 and 25 mpg!!, abouth 20 or just below when driving back roads and small amount of highway).....never drivin it with the wrong speedo gear though.
 
Last edited:
Years back they used to be about $15-$20 at the dealership, think that's what I paid back in '01. Now they cost a small fortune, for new OEM ones from Mopar anyway. There's deals to be found out there, they're just tougher to come by than they used to be.
 
Just out of curiosity is there a reason they are plastic or would I be able to have one made at a machine shop....the reason I ask os cause I know someone that could fab it for free but I don't know if its plastoc for safety reasons.

Sent from my SGH-T959 using Tapatalk
 
Spend $45, run the correct speedo gear for now, sell it for half that when you need to buy another to correct for different gears or tire size. That's almost too easy.
 
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