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post #1 of (permalink) Old 03-29-2001, 01:44 PM
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Buying new tranny --is overdrive worth it?

My situation in short is this: trying to sell both my CJ's to buy a wrangler and build it. Entire drivetrain will come out, if necessary, and replaced. Waggy axles are going underneath, 35" tires, the tranny will eventually end up going, so I'd like to regear and do it all at once. I'll keep the NP231 if it will mate to the tranny choice easily, or I'll swap to anything else, I'm completely open here. The axles havn't been purchased yet, so front drop side isn't important.

I've been trying to figure out if I should go with an overdrive tranny or not. I'll be putting a lot of miles on the vehicle, so my gas mileage and highway driveability are big concerns. Everything is potentially changing, gears, tire size, tranny and engine. (many more decisions and Q's to come your way soon, but this is my biggest choice and the one I think I need to start with.) Considering my need to drive it daily and distances (65+ mph), should I:

sm or np series with 1:1 final drive
or
NV4500 with .74 final drive

35" tires @65 mph...
the 1:1 final with 3.31 gives me 2070 rpm
and .74 final with 4.56 gives me 2100 rpm

The NV seems like it would be nicer to drive on a daily basis, plus the advantage of deeper 4.56 gears, and I know I'm sick of a 3 speed, but will it make enough difference that I should pay out the extra cash?

The deep first gears I can get in either sm or np series of transmissions will help offset the 3.31 gears but aren't exactly what I'd like to have off-road. But for the added cost of the NV, I might be able to get a dual tcase setup?? (no idea on cost, I've only seen pics and read some threads talking about them)

Any input and especially experience anybody can give me will help out a ton. Thanks to the original jeepgod for the previous help... but I just can't decide what to go with, so I thought I'd finally post. My project start date is nearing so its time I got down and dirty and decided what I'm looking for. Hope I managed to explain my dilema and not confuse myself as well as all you.
Thanks again
Brian

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post #2 of (permalink) Old 03-29-2001, 02:02 PM
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Re: Buying new tranny --is overdrive worth it?

If I had it to do over again I would not have gone with the NV4500. T18 all the way. Deeper 1st, no need for an OD in a Jeep. If you need 5th in a Jeep with 35" tires then you are going too fast. I got it because I thought it was the thing to do.




Jason

<font color=green>----------------</font color=green>
<font color=green>[]llll[] '90 YJ</font color=green>
<font color=yellow>Barbie</font color=yellow> <font color=green>drives</font color=green> <font color=yellow>Wrangler</font color=yellow>, <font color=green>I got a YJ</font color=green>
post #3 of (permalink) Old 03-29-2001, 02:57 PM
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Re: Buying new tranny --is overdrive worth it?

I would have to disagree. I love having the overdrive for two reasons. First eventhough my Jeep gets trailered alot now I still drive it to the nearby trails, and in the summer I still like to drive it around town. The fifth is nice to have with the deeper gears. Second when I'm in 4 low on the trail and there is a short section of easy trail and can just shift up to 5th and move faster instead of stopping and putting it in 4 hi. The only reason i wouldn't do a five or six speed if I was to build another Jeep is b/c of cost.

Tim Springer
1980 CJ7
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post #4 of (permalink) Old 03-29-2001, 05:39 PM
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Re: Buying new tranny --is overdrive worth it?

I'm for the O/D. I drive mine too and it really comes in handy. While I only have the T-5 I wouldn't do w/o it anymore. If you want deep gears and drive it anywhere, I'd keep looking at the 4500. (man I wish I could afford one!!!!!)


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post #5 of (permalink) Old 03-29-2001, 05:49 PM
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Re: Buying new tranny --is overdrive worth it?

O/D for me too!!! SCRAM

The moment you are born you start to die so buy A Jeep and play hard!!!!!

It's All Out or Nothing At All!!!!!!!
post #6 of (permalink) Old 03-29-2001, 05:50 PM
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Re: Buying new tranny --is overdrive worth it?

Brian-

Think about what can be done with the transfer case, like a Tera gear swap, in combination with the granny 1st of the the tranny you select to get your low gearing. This will allow you to keep the tall (numerically smaller) gears in the pumpkins for your best gas mileage.

Good Luck!
Kriss

post #7 of (permalink) Old 03-29-2001, 06:14 PM
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Re: Buying new tranny --is overdrive worth it?

I like the idea of the low tcase gearing, but cost is a major concern, and if I end up going NV4500, then I've got some money to save other places. (until my money tree reaches maturity anyway) Then again, if I low gear the tcase, it would be to offset the high axle gears I'd use with a sm/np tranny and that would be less in the beginning. So cost would come closer to the same ballpark.

So is my thought process correct anyway? 1:1 final drive and 3.31 gears will produce the same rpm as .74:1 and 4.56 gears so my gas mileage will be the same. If so, then my choices for the same highway driveability are sm/np tranny and low geared tcase to match or NV4500 and stock tcase. after the low tcase gears, both setups will be similar, around 70 depending, but I'll still be able to upgrade the tcase gears in the NV setup later on if I'd find the money. So that gives and edge to the NV over a np or sm tranny setup.

I'm sure I can use a sm or np tranny and save a ton, even with a low geared tcase, so my biggest question still remains.... Is it worth it to have a 5th gear? And is my logic to the tranny and gear selection correct? eg. 3.31 with 1:1, 4.56 with .74:1.
Thanks for the input so far. Please keep it coming!!
Brian



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post #8 of (permalink) Old 03-29-2001, 06:20 PM
 
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Re: Buying new tranny --is overdrive worth it?

How about this....T18, Dana 18 w/Warn OD, offset axle from a qtrack waggie in the rear, passenger side front axle...pumpkins are lined up, you got OD, you got granny low and a good twinstick low range Tcase.

Now the trick is finding the T-18 and Warn OD.

'79 CJ-7
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post #9 of (permalink) Old 03-29-2001, 06:25 PM
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Re: Buying new tranny --is overdrive worth it?

OHH OHH Brian, I got a T18 [img]/wwwthreads_images/icons/wink.gif[/img] The OD will run at least $400

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post #10 of (permalink) Old 03-29-2001, 06:26 PM
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Re: Buying new tranny --is overdrive worth it?

In order to perform well both on-road and off-road the OD is probably the best solution. You could run 3.31,3.54, or 3.73 ratios with a 1:1 and a 4:1 t-case, but those gears are eventually going to cause problems with u-joints and possibly ring and pinion damage. In my opinion putting all your mechanical advantage upstream like that is a bad idea. All that multiplied torque will be hitting a mechanical log jam at the high speed gears. I run an SM420 with 1:1 4th with 5.38 gears. I can get 50-55, but my poor little Chevy yells at me when I do. Sometimes I really want the OD but I rarely drive my CJ on-road except to/from trails. I trailer to anything that is far away or requires freeway speeds.

I sort of like the security of having a trailer anyway. If I break the crap out of the CJ all I have to do is get it on the trailer and I can get home.

I am a "Sheetmetal Darwinist"
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