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Old 01-26-2011, 02:29 AM   #1
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Swapping 98 auto trans for 08 4speed with o/d

I came across a 2008 4 speed o/d auto trans with transfer case adaptor an torque convertor. I know I jumped others on this field , now I'm getting serious. Any help with how and who can install, when I'm done does anyone need a 98 auto trans . I'm located in socal, thanks

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Old 01-26-2011, 08:15 AM   #2
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First of all, why are you doing this swap? I dont see any benefits at all to the OD tranny. The three speed auto you have now is the most desirable tranny of the two, actually the most desirable period. The 4spd is also computer controlled so you have to have the computer to go along with it as well as configuring the wiring. It's not a simple swap and go and I cant think of the benefits, if any. Maybe if you explained the reason for the swap I could learn something?

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Old 01-26-2011, 09:01 AM   #3
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My thinking is to bring my Rpm down a notch, most of my driving is highway and it's at least a hour to wheeling , if I can get just a bit better gas milage, I will be happy,
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Old 01-26-2011, 09:04 AM   #4
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It may not help the mileage at all and will actually make it worse if you lug the engine. The 4.0 is happier and more efficient with a higher RPM. IF you did get a little better MPG, I doubt it would offset the cost of the swap.
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Old 01-26-2011, 09:41 AM   #5
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Having had the same transmission you have now and now running the same transmission you wish you had, my best advice is to stay with the 3-speed which is a much better transmission. The 4-speed drops the rpms so much in overdrive that unless you regear the axles to an extra low ratio, the engine tends to lug way too much. I wish I had my old 3-speed automatic back.

But it would be a nearly impossible swap to make anyway since due to the electronics and the interfacing between the engine computer and transmission computer, not to mention a whole new engine wiring harness and engine computer would be needed. And even then, due to the different types of ignition systems used I doubt you could get it working.

The 3-speed you have is a superb transmission with a reputation for being nearly bulletproof. I miss mine... a lot.
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Old 01-26-2011, 09:53 AM   #6
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@ 70 mph it's 3000 rpm my other car Xterra @ 70 mph is 2000 rpm. A total of 7 mpg difference , this difference may not seem much to you but it means alot to me if only if I get half that, and yes if I drive back roads it takes longer to get where I'm going wheeling , means less time to wheel but still have to fill up at same place anyway, it's a keeper so I'm trying to build it up to where I believe I can have the best of both worlds, your opinion is appreciated and seems to be alot of peoples , if that trans not good then what auto with o/d do you recommend, in the long haul I believe a o/d will pay for itself,
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Old 01-26-2011, 09:58 AM   #7
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So if I have an 06, keeping the OD off would be to my advantage?
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Old 01-26-2011, 10:05 AM   #8
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@ 70 mph it's 3000 rpm my other car Xterra @ 70 mph is 2000 rpm.
2000 rpms is fine for a car or Xterra, they are both aerodynamic and pushing relatively small diameter tires, but not for a Jeep that would be lugging at such a low rpm. Don't confuse your Jeep with a car, they are completely different vehicles and run differently. No one buys Jeeps because of their fuel economy and you cannot try to run your Jeep at car-like rpms trying to achieve car-like fuel economy.
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Old 01-26-2011, 10:07 AM   #9
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Thanks for that info, that was my main concern, I'll lay that harebrained idea to rest, my trans been rebuilt once allready , guess I'll save the money n braincells n go for flatfenders n bigger tires 33 from 31 , Regear to 4:10 from 3:73, would I need to upgrade brakes?
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Old 01-26-2011, 10:38 AM   #10
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So if I have an 06, keeping the OD off would be to my advantage?
You can probably leave your OD on. As the axles are most likely geared to compensate for the OD gearing a little.

I would also like to add to Jerry's point.

Our inline 6 4.0L is nothing like all these newer V6's. The 4.0L was built for higher rpms at a steady pace and OD that lowers the RPM won't do much other than take it out of it's power-band and there for it's best power:efficiency zone. Or called lugging the engine. Our jeep's should go a couple hundred thousand miles at ~3000 rpms
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Old 01-26-2011, 10:45 AM   #11
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You can probably leave your OD on. As the axles are most likely geared to compensate for the OD gearing a little.
No, they are not geared any differently to compensate for the 4-speed automatic... 3.73 is as deep as they go for the non-Rubicons. And if you actually had a 4-speed automatic, you'd realize that you live with pushing that overdrive button mostly off and rarely back on all day.
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Old 01-26-2011, 10:52 AM   #12
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I came across a 2008 4 speed o/d auto trans with transfer case adaptor an torque convertor. I know I jumped others on this field , now I'm getting serious. Any help with how and who can install, when I'm done does anyone need a 98 auto trans . I'm located in socal, thanks
well, the 2008 tranny is a 42RLE that is heavily integrated into the PCM. The 2008 is OBD3, but your TJ is OBD2 and the wiring is completely different. Also, the bellhousing pattern is different between the TJ 4.0L and the JK 3.8L....I doubt the inputs are the same either.

I wouldn't even think of this swap, and I've researched the 42RLE wiring quite a bit myself. the 42RLE is a P.O.S. tranny IMO, i've got one. worst tranny ever put in a Jeep.

Good luck.
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Old 01-26-2011, 11:13 AM   #13
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So is cursing at 70 mph and 2000 rpm bad? Because that's what I do a lot of on the way to work and back
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Old 01-26-2011, 11:16 AM   #14
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So is cursing at 70 mph and 2000 rpm bad? Because that's what I do a lot of on the way to work and back
2000 rpms at 70 mph says your Jeep needs to be regeared, at least to me it does. I would expect your engine is lugging a lot, especially at lower speeds but even at 70.
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Old 01-26-2011, 11:16 AM   #15
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No, they are not geared any differently to compensate for the 4-speed automatic... 3.73 is as deep as they go for the non-Rubicons. And if you actually had a 4-speed automatic, you'd realize that you live with pushing that overdrive button mostly off and rarely back on all day.
Since I have the 5-speed I don't have much knowledge on the options for the autos. Thanks for the correction, every time it happens I get smarter. I have 3.73's and use my overdrive gear regularly even with the 33's. Though it becomes useless at any incline. 4.88's gears here I come(with 35's).
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Old 01-26-2011, 11:30 AM   #16
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I have a bone stock LJ and 2000 or 2100 RPM is what I can set my cruise control at for 70 mph ( on a flat road with no wind). It has the stock 3.73 rear end. It doesnt seem like my engine is doing anything weird, just cruising. Enlighten me please
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Old 01-26-2011, 11:32 AM   #17
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I dunno what more I can say to enlighten you that wasn't already said above.
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Old 01-26-2011, 11:33 AM   #18
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I have a bone stock LJ and 2000 or 2100 RPM is what I can set my cruise control at for 70 mph ( on a flat road with no wind). It has the stock 3.73 rear end. It doesnt seem like my engine is doing anything weird, just cruising. Enlighten me please
I get about 2200rpm at 70mpg and I loose speed on the inclines and I have almost no passing ability. Then get about 2900+rpm in 4th gear at 70 and cann zip around everywhere. I feel 4.10's on my 33's would give me the sweet spot, but moving to 35's after a few other things and more chances to wheel I am getting 4.88's
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Just bought a True Hi9 rear and a D44 front, both with ARB's and 4.88 gears!! Check out the build!
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Old 01-26-2011, 12:21 PM   #19
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So is cursing at 70 mph and 2000 rpm bad? Because that's what I do a lot of on the way to work and back
2000rpms and 70mph was worthless to me. I hated it. I had to kick into 3rd every time a bug hit the windshield, or a gust of wind came up, or i wanted to pass somebody...etc.

FWIW, the 42RLE came grossly undergeared from the factory. it should have had 4.10s (or more like 4.27s) with 30s or 4.56s with 31s. 4.88s or even 5.13s for 33s, and 5.38s or 5.50s for 35s.

here's where I like mine:

^^4.88s & 33s.

After regearing I also saw an average 40-80° temp drop in the transmission fluid temperature....tranny stays in gear and isn't constantly locking/unlocking & downshifting. I finally put the trans cooler on...it barely moves above 120° now, even in stop and go traffic...I used to see 160-180, even 220°+ in the mountain switchbacks.
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Old 01-26-2011, 12:28 PM   #20
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I agree that with big tires, 2700-2750 rpms at 70 mph is absolutely ideal. I ran that way for years and wish my present Rubicon with its 4.88 gears, 35" tires, and 4-speed automatic ran those rpms but it doesn't. If I had the $$$, I would be at the local gear shop to have it regeared to 5.38 to achieve those rpms today. This morning.
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Old 01-26-2011, 12:59 PM   #21
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Just so people know 4.88 is the highest gears manufactures make for our standard rotation d30's.

PS: 5.13's are available for the JK's HP D30's
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Old 01-26-2011, 01:21 PM   #22
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So it looks like I could run lower gears and get better mileage while going faster and with bigger tires. Kinda counter intuitive
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Old 01-26-2011, 02:26 PM   #23
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When I drive out to the desert on the highway doing 70+ 3000 to 3200 rpm sure I get there faster. When I take the back roads doing stop n go average of 40 mph at average 1900 rpm it takes longer ni still have to fill up n put same amount of gas in, my point being if a crow flies is faster the early bird gets to play in the dirt, but if he flies with a tail wind he plays longer. For those that have sidetracked the question was how n who can do this swap? So far it's cons 5 pros zippy, but I still would like to know what type of o/d I should use?
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Old 01-26-2011, 03:13 PM   #24
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how n who can do this swap? So far it's cons 5 pros zippy, but I still would like to know what type of o/d I should use?
the swap just won't work. OBD3 vs OBDII, and completely different motors. complete waste of time to even mess with it.

if you want OD then look at an AW4 swap....which was an XJ transmission that was actually designed to be behind a 4.0L.
AW-4 Transmission Swap - 1
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Old 01-26-2011, 04:43 PM   #25
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That is some great info thank you,
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Old 02-05-2011, 08:04 PM   #26
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And you have the 3 speed auto with overdrive Unlimited Lj04?
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Old 02-06-2011, 12:43 PM   #27
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And you have the 3 speed auto with overdrive Unlimited Lj04?
To avoid confusion with the 2002 and older automatic transmission which is a true 3-speed without an Overdrive, the 2003 and newer is considered a 4-speed with that 4th gear being its Overdrive ratio.
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Old 02-06-2011, 01:12 PM   #28
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Thanks jerry

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