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Building a Universal Modified

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jpet View Drop Down
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    Posted: 03 May 2013 at 7:02pm
Hi All,

I want to build a modified, but really "modified" is not exactly the correct word because I'm not modifying a jeep but putting one together with parts most of which are probably not even jeep parts.

Basically I want a guiltless MB that can cruise at highway speed safely, but has a crawl ratio that can hang with a stock CJ2A on the trail. Secondly, I want the flatty to look as stock as possible from the outside and identical to my stock MB (which is also in project mode).

Since I want it to be as efficient as possible on the highway, I want to use higher pumpkin gears. My CJ5 has 3.73 gears and it is able to do the interstate pretty good. I may want even higher gears than that though. The down side to that is, that I would not have the crawl ratio that matches a 2A so if I had the jeep in Colorado, I'd be running over the ,other jeeps on the trail.

My thought is to use my SM420 tranny to get a suitable crawl. A CJ2A has a crawl ratio of 37:1 in 1-low. The SM420 has a 7:1 first gear. Couple that to a dana 18 t/c I could actually have 2.14:1 differentials and still match a 2A crawl ratio. Now I know that that ratio does not exist for Dana 44 but you get the idea.

So far I have the SM420 and dana 18. I plan on adapting them together similar to what Metcalf did but with his suggestion of machining the adapter with a lip and seals. I also have a couple offset dana 44s but they currently have 5.38 gears. I also have several dana 25s but I would be limited to the ratios I can choose for those. What would my choices be? I figure I would put this all on a 3A frame and "modify" the frame to make it look MB. Engine is still undecided other than it being a GM so that I don't need an adapter for the SM420. I also am thinking fuel injection.

I have this idea that I can build one that could be driven to some of the jeep events the different FFCs are putting on and when I get there, I can jump right on the trail. With the 2As.

I'm open for suggestions other than, "if you want a jeep like that you should buy a TJ".

I plan to put my repro MB body on it so no jeeps are being sacrificed here. What do you think?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oilleaker1 Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2013 at 7:27pm
If you are going to maintain Interstate speed, you'll also need to change the steering and brakes to handle better. I've not seen a MB with your recipe , so this will be fun to follow. If you put a overdrive on it, would leaving it in low range get you at the desired crawl speed and then shift into OD up on the highway? Maybe you should just put the MB body on your fiberglass CJ5? The possibilities are endless. It will come down to your recipe for what you want. The idea of a 80 MPH MB, that looks stock blows my mind----LOL. John
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpet Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2013 at 7:43pm
I don't need 80, but a comfortable 65. My CJ5 can go 70 no problem but it does sound like it needs another gear and 14 mpg. I'm hoping for at least 17 mpg @ 55. When I bought my CJ5, that was my intent but it just seems like too nice of a jeep to do that to and it has a 350 which I have been told would be hard to keep cool in a flatty. The cj5 has the narrow frame but the spri gs are longer. It also has centered pumpkin.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote plowpusher Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2013 at 8:14pm
My thoughts would be....   Fuel injected 4.3 chevy ,SM 420,D18, Warn OD, Dana 44's (cj5 ) 3.55 gears 11 inch brakes and 700x16 tires
Saginaw power steering, box the frame maybe a 1"rough country lift for tire clearance in turns. It would look fairly stock except maybe for the steering box, have triple the hp be able to pull the 3.55 gears with the OD. With a fuel injection system have good drive ability at low speeds and on hills.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpet Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2013 at 8:17pm
What front axle would I have to have to get 3:55 gears?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote plowpusher Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2013 at 8:28pm
Dana 44 look in Petersons 4wd or JP mags there was an issue last summer about narrowing a bone yard axle, that didn't look at all hard really just need to be able to weld. go to one of there web sites and look in the tech section it is a pretty good write up. many late 70's 4x4 used 3.55 gears.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote plowpusher Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2013 at 8:39pm
Okay found the article go to the 4wd/Offroad magazine's web site, click on tech articles go to transmissions and driveline  on the right side of that page about 1/2 way down, click on that then scroll down to the article about narrowing your axle at home.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote F Bill Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2013 at 9:22pm
I wonder how a Suzuki or Toyota drivetrain would work out for you with the flatty tub and frame...
If you haven't checked out the tech FAQ section, go to:
http://www.thecj2apage.com/forums/tech-faq_forum57.html
for a lot of great stuff you need to know!!

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Post Options Post Options   Thanks (0) Thanks(0)   Quote all4jpn Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2013 at 9:29pm
there are quite a few build on pirate4x4 like that....one recent to the top one is a F.I. 2.5l wrangler drivetrain with a flatty body....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike S Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2013 at 11:19pm
I may be wrong, but a 4.3L with an SM420 and 3.XX gearing will not have the crawl ratio you want. The 4.3 has the sauce to spin the rear to 65mph, so I doubt you want an overdrive - maybe an "underdrive" for a low crawl ratio in all the LR gears, not just first. You could also get a lower geared transfer case from Herm and have fun on any trail.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpet Quote  Post ReplyReply Direct Link To This Post Posted: 04 May 2013 at 6:03am
A stock CJ2A has a 37:1 crawl ratio:

5.38 (pumpkin gears)
2.46 (TC low)
2.79 (T-90 1st gear)

This rig, with 3.55 differentials would have a 61.5:1 crawl ratio:
3:55 (diffs)
2.46 (TC)
7.05 (SM420 granny low)


Edited by jpet - 04 May 2013 at 8:23am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpet Quote  Post ReplyReply Direct Link To This Post Posted: 04 May 2013 at 6:17am
In 2nd gear, the rig would have a 31:1 crawl,

A stock 2A with 29" diameter wheels would only be able to go 64 mph at maximum rom (4000)   The same vehicle with 3.55 diffs would go 97 @ 4000 rpm and @ 65 mph would be doing 2680 rpm.

Actually, 3.55 is still too low but I think that is the highest ratio available.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bkwudz Quote  Post ReplyReply Direct Link To This Post Posted: 04 May 2013 at 6:54am
Sounds like a cool project, mine with, carbed 4.3, th350 and 3:73's will cruise at 55-65 all day long.   
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Post Options Post Options   Thanks (0) Thanks(0)   Quote plowpusher Quote  Post ReplyReply Direct Link To This Post Posted: 04 May 2013 at 11:27am
Actually many early-mid 80's gm's had Dana 44 fronts with 3.08:1 ratios in a feeble attempt at getting millage with higher gears, but the engines didn't have enough torque to pull them. Even the army diesel blazers had 3.08s because of the low rpm potential of the engine. The sm420 is such a game changer with that granny gear but you still have to remember where the engine will make good torque sometimes lugging an engine with high gearing will hurt efficiency. I guess I would look to see what gear options gm had available with the 4.3. I know a CJ2a is quite a bit lighter than an s10 pickup or blazer.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike S Quote  Post ReplyReply Direct Link To This Post Posted: 04 May 2013 at 11:57am
I am certain that you can make this work. My comment was prompted by my own preference for tractable LR performance off-road in any gear. The Willys is so lightweight that the 4.3L should be fine with just about any gearing. On the road an overdrive would be 'overkill', I think.

Sounds like a fun project.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote willys54wagon Quote  Post ReplyReply Direct Link To This Post Posted: 04 May 2013 at 12:14pm

So what is the sweet spot (best torque?)for a 4.3 tbi in terms of rpm?

Two jeeps on the road, one is close and the rest are dreams.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpet Quote  Post ReplyReply Direct Link To This Post Posted: 04 May 2013 at 12:48pm
Yeah, I'm thinking with the SM420, I'll have a much better selection but I know a 61:1 crawl ratio is way lower than I need to be.

If I get a ring & pinion set for a d-44 will it work in any year d-44?

Originally posted by willys54wagon willys54wagon wrote:

So what is the sweet spot (best torque?)for a 4.3 tbi in terms of rpm?


Yeah?

Edited by jpet - 04 May 2013 at 12:56pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote plowpusher Quote  Post ReplyReply Direct Link To This Post Posted: 04 May 2013 at 4:23pm
4.3 Chevy 180-200 hp @ 4600 rpm  torque 260 ft/lb @ 2800 rpm

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