TJ can not maintain 75 mph in overdrive
- Thread starter matkal
- Start date
OP
The thing about a regear is at some point I want to go to 33s. That has to come after a lift and all the associated issues with that. Ugh. I don’t want to regear twice. I may have to rethink my strategy about the gearing.
My mechanic is very reasonable, it shouldn’t cost all that much.
My mechanic is very reasonable, it shouldn’t cost all that much.
This is your setup now: 3.73, 31s, 75mph. Looking at my spreadsheet, obviously gears 1 and 2 make no sense at 75, but 3 and 4 do because you may have to downshift on occasion.
With 4.56s and the 31s it's not a bad RPM at 75.
Changing the tires to 33s it is still way better than you current setup. From current setup, you will pick up about 25 ft-lbs of torque and about 20 horsepower and the torque will multiply times 4.56 instead of 3.73.
Now most of the experts will not like the 4.56 solution, I do because I want the lower RPM cruising around. Performance will be better at 5.13, but the RPMs are higher. Below is the 5.13 case with 33s:
With your 31s, 5.13 will put you at right about 3000 RPM.
Although, I must protest again: 75 mph? if you really want to do that, put 29s on it with a 2 in lowering kit and you should be OK. 33s and a lift kit won't help....
With 4.56s and the 31s it's not a bad RPM at 75.
Changing the tires to 33s it is still way better than you current setup. From current setup, you will pick up about 25 ft-lbs of torque and about 20 horsepower and the torque will multiply times 4.56 instead of 3.73.
Now most of the experts will not like the 4.56 solution, I do because I want the lower RPM cruising around. Performance will be better at 5.13, but the RPMs are higher. Below is the 5.13 case with 33s:
With your 31s, 5.13 will put you at right about 3000 RPM.
Although, I must protest again: 75 mph? if you really want to do that, put 29s on it with a 2 in lowering kit and you should be OK. 33s and a lift kit won't help....
OP
Thank you for the spreadsheet and for taking the time! So 4.56 will work well for both 31 and 33 inch tires, that’s good news and definitely is making me rethink how I’m going to progress with my TJ.
As far as 75mph goes it’s a semi arbitrary number. Meaning I rarely drive on roads with a 70 or 75mph speed limit such as driving to work once in a while and driving to northern Michigan where all our wheeling is. I do not like driving 75 but I don’t like being a rolling roadblock either. I will be reconsidering taking interstates and stick to the state hwys which are definitely more comfortable in the Jeep.
I’m still going to try to track down the loss of power because if it’s something that will strand me somewhere I will fix it.
Thank you again for helping me to put this in perspective
As far as 75mph goes it’s a semi arbitrary number. Meaning I rarely drive on roads with a 70 or 75mph speed limit such as driving to work once in a while and driving to northern Michigan where all our wheeling is. I do not like driving 75 but I don’t like being a rolling roadblock either. I will be reconsidering taking interstates and stick to the state hwys which are definitely more comfortable in the Jeep.
I’m still going to try to track down the loss of power because if it’s something that will strand me somewhere I will fix it.
Thank you again for helping me to put this in perspective
deadbeat son
TJ Addict
Why go from 4.56 to 5.13? What’s wrong with 4.88?
OP - good luck figuring out your issue. These things are such a PITA to figure out sometimes. I had a similar problem with a classic Range Rover one time; it was a plugged injector. Sorry that didn’t end up being the situation for you.
My 2006 will give similar symptoms when the exhaust flange bolts vibrate loose driving rough wash board roads allowing the exhaust gas mixture to leak out before the O2 sensors. It only seems to take a little gap to mess up the computer, everything is fine heading out Jeep runs great and on the way home after the bolts loosen I’ll see my fuel ratio get really rich maintaining speed and along with the super rich fuel mix some loss of performance most times it throws a code eventually, but less noticeable running the stroker engine due to the added hp I’m guessing.
Red locktite won’t stand the heat and there’s not much room to work, I carry a little short 17mm socket wrench and check it from time to time.
Red locktite won’t stand the heat and there’s not much room to work, I carry a little short 17mm socket wrench and check it from time to time.
Do not go to 4.56 with the 42RLE….on any tire size that is a waste of money. Go to 5.13 on the 31’s. You will still be turning less rpm than the manuals running 4.88 and 33’s in 5th. Then you can get your 33’s and run lower rpm, although I don’t see what fun that would be. It will feel semi sluggish again after that transition but it would be worlds better than 4.56, which would be inadequate on both 31’s and 33’s.
for your “issue”, it’s hard to determine what your issue might be if anything. I, like the others, can promise you that 31’s and 3.73 will never produce a good driving combo on the highway with the 42RLE trans. Does it drive decently if you turn off overdrive? If it still doesn’t then, maybe you have something to look for.
to me it sounds like you have a gearing issue (we know you do) and you may not have other issues. If so, regear to 5.13 and don’t even think about 4.56 because no, that won’t cure much of anything, especially not for the cost. And you definitely do not need to regear twice to run two sets of tires, all you do is just regear to the lowest option and it will still work perfectly on the smaller tires. It’s not a drastic difference from one tire size to the next and I’d get you enjoy 5.13 with 31’s more than 33’s.
for your “issue”, it’s hard to determine what your issue might be if anything. I, like the others, can promise you that 31’s and 3.73 will never produce a good driving combo on the highway with the 42RLE trans. Does it drive decently if you turn off overdrive? If it still doesn’t then, maybe you have something to look for.
to me it sounds like you have a gearing issue (we know you do) and you may not have other issues. If so, regear to 5.13 and don’t even think about 4.56 because no, that won’t cure much of anything, especially not for the cost. And you definitely do not need to regear twice to run two sets of tires, all you do is just regear to the lowest option and it will still work perfectly on the smaller tires. It’s not a drastic difference from one tire size to the next and I’d get you enjoy 5.13 with 31’s more than 33’s.
You are full of it. I've run 31" tires on the 42RLE with 3.73 gears for longer than you've owned your TJ and done just fine. Averaged 16.5 about the last 10 or so years, how 'bout you? Probably can't do the math.
Full of it? Kindly, piss off. Every once in a while you do this ridiculous dance where you suggest folks using/recommending lower gears are out of their minds all because you’re so pleased with stock undergeared crap.
Please go try a few different gear setups besides stock and then come back and let me know what your updated views are about what performance really is. Until then, butt out. I’m smart enough to calculate mpg and gasp, even smart enough to change the speedo gear so that the new odometer readings reflect mpg accurately when calculated!
BTW - 2900 at 70 generates about 17 mpg on 33’s in my experience. Would you like to swing by and verify that math for me? Not sure if I calculated it right.
You are full of it. This guy has problems with his Jeep that prevents him from maintaining 75 in overdrive on the freeway which has nothing to do with the final drive ratio. That's all this thread is about sparky.
Full of what, real world experience? You’ve got someone trying to push 75 mph in a giant crate on wheels with at best 235 ft lbs of torque (at 3200 rpm) at 2150 rpm which is not where peak torque is, so even less. That is a recipe for anything but good performance.
If you actually read what I said, I asked him to clarify if disabling OD fixes the issue or at least improves it to try and narrow down whether he has a real “issue” or not. Instead, you were too busy nitpicking at advice about gear ratios when you’ve run one single ratio and have no real world experience with anything else. Save it.
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OP
It runs very well with OD off and as ill advised as it may be I’ve had it up to 80 in third.
As @pagrey alluded to, I went from being able to maintain 75 in OD to not being able to in a short period of time. My primary focus right now is finding out why because whatever issue has caused this there’s a pretty good chance it could leave me stranded.
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OP
I don't know what changed for you but running very well in OD off vs running poorly with OD on is pretty indicative of one thing: insufficient gearing.
Nothing wrong with 80 in third, that's like 3300 rpm, and it isn't ill advised at all. May burn some fuel but that's the end of the trouble it's causing.
Put a scanner on it and see what you find, if anything. Personally, your gear and tire combo should have never ran well at 75 in 4th to begin with. I've always had better rpm vs speed setups than that and it was still always terrible, and not able to hold 75 unless completely flat. And I for sure have no engine problems.
Well this is certainly one of the more standard answer shitfests I've seen in awhile. I hope this isn't a trend and folks actually start reading and listening to what the actual problem being described is.
It used to work, he didn't change the gearing higher and now it doesn't do what it used to do. Fucking gearing won't fix that. How hard is that to understand? (rhetorical since apparently it is impossible)
It used to work, he didn't change the gearing higher and now it doesn't do what it used to do. Fucking gearing won't fix that. How hard is that to understand? (rhetorical since apparently it is impossible)
I lost interest reading much of this but did anyone suggest starting with the basics and plugging in a cheap live time scanner and see if it’s pulling spark or if the fuel trims are going full lean/ rich so you can try and rule out ignition or fueling problems? The fact that something changed is the key here as mrblaine said.
OP
I talked to my mechanic this morning and am going to make an appointment for him to do exactly that.
OP
Thank you for the heads up.
How were the trans and the cats diagnosed?
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I had intermittent check engine light and codes leading up to the cats. When the shop replaced the cats, the first thing they asked when I came to pick it up was if the car was sluggish and hard to maintain high speed. It was. He then showed me a completely destroyed and dislodged cat in the pipe he removed. My sluggishness improved as did the high-end speed.
A couple of years later, I had a code related to the transmission. Once the torque converter was replaced, maintaining 70-80 on the freeway was easy and drove like it used to.
So, in both cases my issues were preceded with a check engine light.