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  #1  
Old October 29th, 2020, 12:52 PM
douglas685 douglas685 is offline
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Default 4.10 Gears?

Hey guys, new member, I'm considering getting an m715 to restore. I'd like to be able to occasionally travel with it to go to various car shows, Cars and Coffee, that kind of thing. As we know, a factory m715 is effectively limited to around 50mph (if that) for highway use, as any faster will cook the NP200. NP205 swaps are a thing, but from what I can tell the prices are pretty steep, $1000-$2000 for a rebuilt one and quite a bit of fooling around to get it to fit. I also know that there are 4.54 gears which do allow a bit higher speeds but still are somewhat taxing on the NP200 above 55mph.

I've seen a few posts where people mention 4.10 gears, including one from 2018 where a group/company was wondering about interest in these. Did anyone ever make a 4.10 kit? Is is possible to do without a kit?

With 4.10 gears and factory size tires, I'm assuming 60mph isn't too far out of the question even with an NP200 (other than possibly deafening)? Btw I plan to keep the stock i6 engine and 4-speed.

Thanks!!
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Old October 30th, 2020, 08:31 AM
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As far as I know, 4.56's are it for R&P availability. I believe they are (were?) available from Full Size Jeep.

Welcome aboard, by the way.

50 mph isn't so bad if all you're going to do with your 715 is cruise around & enjoy the sensations of the stock powertrain. I really don't have any complaints about that powertrain in that type of usage, and I live 5000' up where the 230 is even farther behind the eight ball.

With an engine swap, I think it becomes a different story, however...
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Old October 30th, 2020, 03:04 PM
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Yeah I get that 50mph might be fine for most, however I'd really like at least 60mph as I do plan on highway driving. At 60mph in the right/slow lane, people will just pass you without too much of a care or complaint (especially if you are in an interesting-looking vehicle like an m715, they might even slow down to get a better look as they pass). However if you are driving 50mph in the slow lane and the speed limit is 70mph, you will get dang near run off the road. It almost seems unsafe to drive at those speeds on a highway for fear of getting run over by going so slowly. I would feel better at 60mph for sure.
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Old October 30th, 2020, 04:03 PM
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I'd pick slower highways.
Unless you're changing the gear ratios yourself- I don't think I could get a gear swap for under $1200 in my area. I found my NP205 on craigslist after about 8 months of consistent searching for $200 iirc, which me and a buddy swapped out ourselves. Much easier than a gear swap.
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Old October 30th, 2020, 05:10 PM
douglas685 douglas685 is offline
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It looks like BJ's offroad still has the 4.56 gearset, which based on my math with factory tires would make the engine spin at around 2,600rpm at 60mph. I might go slightly bigger on the tires, probably 35's or 36's but no bigger than that. It does look like the 4.10 gears are a unicorn, and other than doing a ton of work I'm guessing the 4.56 will have to do. My other thoughts, does this engine like running at 2,600rpm for long periods of time (say a couple hours for instance)? I'm guessing 2,600rpm is basically the limit for the NP200 for anything more than a quick burst, right? Any thoughts on sustaining 2,600rpm with some load at speed for the engine too? Would it be purring along or is that "working" this engine? (that was also my other concern with stock gearing and an np205, 3,333rpm at 60 seems like quite a lot).

https://www.bjsoffroad.com/M715-M725...ng_p_1012.html
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Old October 31st, 2020, 09:16 AM
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A lot of my driving is highway and regularly cruise for an 45mins to an hour with no problems yet. I generally keep my speed around 60ish and the engine is turning at about 2500 (I did get it up to 75 once). This is with 4.56s and 37" tires. Stock NP200 but 318cid engine. I've done this in the summer and haven't grenaded the TC yet. I do have a NP205 sitting on the shelf if I do destroy the 200, but so far so good. Speed limit here is 65 so its not too bad.
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Old October 31st, 2020, 09:46 AM
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Quote:
Originally Posted by eightydeuce View Post
A lot of my driving is highway and regularly cruise for an 45mins to an hour with no problems yet. I generally keep my speed around 60ish and the engine is turning at about 2500 (I did get it up to 75 once). This is with 4.56s and 37" tires. Stock NP200 but 318cid engine. I've done this in the summer and haven't grenaded the TC yet. I do have a NP205 sitting on the shelf if I do destroy the 200, but so far so good. Speed limit here is 65 so its not too bad.
You will likely be just fine at those speeds with the 200 and that gearing if my M37/43 experience is any indicator. Those trucks (M43 got totaled in a head-on, drivetrain transferred to an M37) had the same t-case with 4.89's and a Hercules turbodiesel. I regularly ran 65 and had no issues with t-case heating in years of driving, and I attribute that to the decreased t-case RPM from higher gearing.
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