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Old 04-18-2013, 11:50 AM   #1
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1998 TJ can't go over 65mph

Hi everyone, new member and new Jeep owner. I just bought a '98 TJ 4.0L 5 speed. Jeep has 200K mi. on it but appears well kept and runs good. The only problem I notice is that at 5th gear I can't go 65mph or higher. tires are 35x13.50x15 not sure what gears it has. Is there anything I can do to be able to drive at least 65MPH consistently?.
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Old 04-18-2013, 12:00 PM   #2
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Check your speed against a GPS. You may be going faster than you think if the PO didn't change the speedo gear out for the tires.

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Old 04-18-2013, 12:04 PM   #3
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Check the tag on your rear axle. Solid chance you need a regear.
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Old 04-18-2013, 12:07 PM   #4
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Like indicated above, if the speedometer gear was not changed, with the larger than stock tires, the speedometer is going to be reading slow.

Depending on what differential gearing it has, it may not even be able to get up to speed with 35s, though it should go a lot faster that 65. (I can get over 90 with my 33's .....yea , yea let's not turn this into a what's safe speed thread)
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Old 04-18-2013, 12:07 PM   #5
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1998 tj

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Originally Posted by BigDeaner View Post
Check the tag on your rear axle. Solid chance you need a regear.
There is no tag on rear axle. I don't think it's a speedo error because sometimes big rigs passes me when I'm doing 60mph.
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Old 04-18-2013, 12:09 PM   #6
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I was doing 73 MPH the other day going home (verified by GPS), my speedo indicated about 62MPH, and oh yeah I had trucks passing me. Jus sayin'.
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Old 04-18-2013, 12:11 PM   #7
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There is no tag on rear axle.
Really? Do you have a pic of the pumpkin? Would help to identify and need to know this first. As Deaner mentioned... solid chance you need a regear.
Can you do over 65 in 4th?
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Old 04-18-2013, 12:13 PM   #8
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Hi everyone, new member and new Jeep owner. I just bought a '98 TJ 4.0L 5 speed. Jeep has 200K mi. on it but appears well kept and runs good. The only problem I notice is that at 5th gear I can't go 65mph or higher. tires are 35x13.50x15 not sure what gears it has. Is there anything I can do to be able to drive at least 65MPH consistently?.
Thanks
You need to regear to 4.88. If you have a D35 rear I would suggest installing a 8.8 or D44 axle.
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Old 04-18-2013, 12:16 PM   #9
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You need to regear to 4.88. If you have a D35 rear I would suggest installing a 8.8 or D44 axle.
Not sure that's a must, as I am running 4.10 gears with 35/12.50/15's and I have the 4 banger. Regearing to 4.88's is in my future plans though as she is very sluggish but does eventually get there and can sustain speeds over 65 without big uphils.
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Old 04-18-2013, 12:49 PM   #10
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Really? Do you have a pic of the pumpkin? Would help to identify and need to know this first. As Deaner mentioned... solid chance you need a regear.
Can you do over 65 in 4th?
I read that if you have a rubber plug in the rear diff, that you have a Dana 35?. If I do have a Dana 35 would that be sufficient enough gearing to run 35's?.
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Old 04-18-2013, 12:49 PM   #11
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Not sure that's a must, as I am running 4.10 gears with 35/12.50/15's and I have the 4 banger. Regearing to 4.88's is in my future plans though as she is very sluggish but does eventually get there and can sustain speeds over 65 without big uphils.
The OP is complaining he can't get past 65 mph, I would certainly consider regearing a "must" as that is the only realistic option that will fix the problem he is complaining about.

For 35" tires, 5-speed transmission, and 4.0L engine, 4.88 is the optimal ratio.

Big Sarge, your SE came with a Dana 35 rear axle so unless you have beefed it up with stronger axle shafts or entirely replaced the Dana 35, I'd regear to 4.88 but I'd drop down to 33" tires. 35" tires are just too big for a Dana 35 axle to remain reliable. For the SE with its 2.5L 4-banger engine, it needs slightly higher RPMs than the 4.0L does so 4.88 is the preferred ratio for 33" tires.
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Old 04-18-2013, 01:03 PM   #12
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Guys....
before telling him he needs better axles etc, maybe find out what he actually wants to do with the Jeep?....
If it's just driving around town, no rock crawling etc, re-gearing might be all he needs to do.
Offroad is another story entirely, but until you ask, who knows.
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Old 04-18-2013, 01:04 PM   #13
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I read that if you have a rubber plug in the rear diff, that you have a Dana 35?. If I do have a Dana 35 would that be sufficient enough gearing to run 35's?.
You need to check and see WHAT gearing your D35 has.
There is a metal tag on the upper left of the pumpkin with this info stamped into it. Not all D35s were created equal. I would encourage you to crawl under there, scrape the grit off the tag and determine this.
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Old 04-18-2013, 01:06 PM   #14
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Guys....
maybe find out what he actually wants to do with the Jeep?....
I was under the impression he wants to do this: "Is there anything I can do to be able to drive at least 65MPH consistently?"
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Old 04-18-2013, 01:08 PM   #15
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Check the back axle may need a regear. :/ Good Luck
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Old 04-18-2013, 01:08 PM   #16
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I read that if you have a rubber plug in the rear diff, that you have a Dana 35?. If I do have a Dana 35 would that be sufficient enough gearing to run 35's?.
A Dana 35 as the factory built it just isn't strong enough to remain reliable with 35" tires. The Dana 35 can be strengthened with stronger hardened aftermarket axle shafts which are made by several aftermarket manufacturers which would allow it to hold up to 35" tires for most uses. Stock, it's just not strong enough to be reliable with 35" tires... especially if it is offroaded.
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Old 04-18-2013, 01:09 PM   #17
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Jerry is correct.
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Old 04-18-2013, 01:13 PM   #18
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I was under the impression he wants to do this: "Is there anything I can do to be able to drive at least 65MPH consistently?"
LOL yep

I was unaware that it was a requirement to have a D44 or 8.8 in order to do this....
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Old 04-18-2013, 01:34 PM   #19
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LOL yep

I was unaware that it was a requirement to have a D44 or 8.8 in order to do this....
I used the term "suggest." The OP can certainly regear the D35 if he feels the stock axle's attributes are commensurate with his intended uses.
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Old 04-18-2013, 01:39 PM   #20
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I was unaware that it was a requirement to have a D44 or 8.8 in order to do this....
No, not a requirement IF he is running stock tires.
He is not. Did you read his post? He's running 35s.
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Old 04-18-2013, 03:37 PM   #21
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Thanks for your input guys. I'll check what gears I have maybe this weekend, was planning on changing fluids anyway.
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Old 04-18-2013, 03:40 PM   #22
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By the way would 4.88 gears fit in a Dana 35 carrier?.
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Old 04-18-2013, 03:48 PM   #23
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By the way would 4.88 gears fit in a Dana 35 carrier?.
Yes. Those are the biggest that will fit
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Old 04-18-2013, 04:03 PM   #24
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Yes. Those are the biggest that will fit
I may be off here, but if he has 3.07 or 3.21 now, he would be capped to 3.55? I think the carrier break is at 3.55/3.73 for normal sized ring gears.
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Old 04-18-2013, 04:21 PM   #25
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I may be off here, but if he has 3.07 or 3.21 now, he would be capped to 3.55? I think the carrier break is at 3.55/3.73 for normal sized ring gears.
Replacing the carrier to go to a lower ratio like 4.88 adds no labor cost to the job and only a $60-80 cost per carrier overall when replacing the carrier. So the ratio is not capped by a carrier that was installed for 3.07 or 3.55.
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Old 04-18-2013, 04:39 PM   #26
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I may be off here, but if he has 3.07 or 3.21 now, he would be capped to 3.55? I think the carrier break is at 3.55/3.73 for normal sized ring gears.
Yeah sorry. Jerry explained it better. As usual. Haha
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Old 04-18-2013, 04:41 PM   #27
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You don't have enough power to pull more than that in 5th gear unless you re-gear. Just leave it in 4th on the highway. It will give you close to the same final drive ratio as 4.88's in 5th.
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Old 04-18-2013, 05:04 PM   #28
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Lot's of ideas of fixing the problem. My question is, and I may get slammed for asking, why do you want to go over 65? Our maximum speed here is 110km/hr which is about the same as your 65m/hr. And that speed in only on divided highways.
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Old 04-18-2013, 05:28 PM   #29
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No, not a requirement IF he is running stock tires.
He is not. Did you read his post? He's running 35s.
Yes I did read his post, but he left out details, such as.....is he using it to go to the mall?....or actual offroading?....

D35 will push 35" tires to the mall & back no problem....
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Old 04-18-2013, 07:20 PM   #30
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Thanks for your input guys. I'll check what gears I have maybe this weekend, was planning on changing fluids anyway.
I have a 99 that came with the Dana 35 and if you have a 4.0l 5 speed with Dana 35 most likely you have 3.73 gears. I had the same prob with my jeep running 33 inch tires so I replaced my axles completely and installed a d 44 in front and a g2 rock jock 60 rear with 4.88 I'm still running the 33's but I can no go 65+ with no problem if you intend to keep running the 35s I would req upgrading the rear end to at least a d44 You'll be much less likely to break anything

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