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post #1 of 26 Old 07-10-2020, 09:56 AM Thread Starter
tamersinger
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looking at a yj

Currently rig-less right now but my wife and I are looking at changing that.

a good buddy of mine has a 90s yj 4.0 for sale with some mods and I was wanting to pick the hive brain about thoughts on that and my upgrades I may do.

its got a 4.0 5 speed with a rubi t-case and 8.8 with 4.10s and an arb locker, 2" lift on 31s and a fuel cell behind the rear seat

I plan on trimming the fenders(or running tube fenders) and re-gearing to 4.88s or 5.13 to and run 35s.

I want to run a arb in the front 30 and probably upgrade the shafts but not sure about 30-splines.

M8000-s on the front.

budget is around 6000 after purchase of the jeep.

this is not a daily driver (it will be my 3rd behind the commuter and tow rig) I just want something that is light small and capable and setup like the jp shrink ray (something I could do the ultimate adventure in would be nice)


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post #2 of 26 Old 07-10-2020, 04:41 PM
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I'm not a fan of fuel cells behind the seat but lots of people do it so you should evaluate if that is what you want or not. Are you sure it's a 4.0 or is it really a 4.2 with a carb? 8.8 is good, ARB is good, 4.10 is probably plenty for 35's. The 2" lift is kind of irrelevant if you're going to run 35's since you have to replace it anyway.

If you're on a budget, a lunchbox locker in the front will do really well with 35's but a selectable locker is definitely the way to go if you can afford it. I can tell you that my Spartan locker and Yukon shafts in my D30 held up but my 4.88 gears did not. Granted I've got a V8 and I did give it a little extra throttle to bump over a rock. I got over the rock but when the tire came down, the ring gear broke a few teeth and gear setup was perfect. So I'm not sure 30 splines axles are really worth the investment considering the what my weak link was.


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post #3 of 26 Old 07-10-2020, 06:00 PM Thread Starter
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I'm not a fan of fuel cells behind the seat but lots of people do it so you should evaluate if that is what you want or not. Are you sure it's a 4.0 or is it really a 4.2 with a carb? 8.8 is good, ARB is good, 4.10 is probably plenty for 35's. The 2" lift is kind of irrelevant if you're going to run 35's since you have to replace it anyway.

If you're on a budget, a lunchbox locker in the front will do really well with 35's but a selectable locker is definitely the way to go if you can afford it. I can tell you that my Spartan locker and Yukon shafts in my D30 held up but my 4.88 gears did not. Granted I've got a V8 and I did give it a little extra throttle to bump over a rock. I got over the rock but when the tire came down, the ring gear broke a few teeth and gear setup was perfect. So I'm not sure 30 splines axles are really worth the investment considering the what my weak link was.
I am going to keep the 2" lift and trim the tub/fenders to fit the 35s

will the 30 hold up to the 35s though, I have seen much varied opinions on this.


it is a 4.0.

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post #4 of 26 Old 07-10-2020, 06:14 PM
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Most people who say the D30 won't hold up are usually running low pinion axles like on TJ's or maybe the JK guys. Weight and driving style will play the biggest factor in any axles life. You can run a YJ on D44s with 35s for many many years....then someone will come along with a fully loaded and armored YJ with the same axles and tires and break something after only a couple trips.

When I broke my ring gear, I was on a rock trail that I've seen guys on 40s struggle with so the reality is that I was pushing well beyond what my Jeep was comfortable doing. Pretty sure I've seen a Jeep broken on that trail every time I've gone and most are running 37+ tires.


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post #5 of 26 Old 07-10-2020, 08:18 PM
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2” lift with 35s doesn’t seem like a good option. Why not set the rig up with appropriate suspension instead of cutting the body? You can upgrade the suspension and still stay within budget.

Regear is solid idea. My rig has 4.56 gears, 35s, and the ax15/4.0 combo. 4.56s suck for 35s. I like your idea of 5.13s in the high pinion 30.

I also have an XJ with 5.13s in the front HP30 and a Spartan Locker. Run the Rubicon Trail many times with no issues.
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post #6 of 26 Old 07-10-2020, 08:48 PM Thread Starter
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To be honest I dont want it tall at all I would maybe go up to some 3.5 springs to prepare for bigger tires in the future but low and light is the idea, it's not a dd and it already had body damage so why not.

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post #7 of 26 Old 07-11-2020, 06:16 AM
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Here's the gear ratio calculator. My advice is to be realistic and evaluate the gearing you want with the speeds you plan to run or might want to run. I know it's not a DD but if you do decide to drive on the road, you probably don't want the engine screaming down the road. When you input your tire size, don't put 35" as your tire size if you plan to run a 35" tire. The tire is never 35" anyway and when properly inflated, the tire has some squish to it so a 35" tire is going to effectively be more like a 33.5" tire if you measure from ground to center of the axle. At 75mph, I'm getting a 4.10 gear runs 2400rpms in 5th gear and a 5.13 gear runs 3000rpms.

http://www.grimmjeeper.com/gears.html

One thing to remember is that gear strength goes down as you go higher in numerical number. Maybe 4.88 or 5.13 is what you want but you are definitely pushing the limits of the D30. If you do everything yourself, figure somewhere in the ballpark of $500 on Chromo axles, $350 R&P plus master install kit, $250 luncbox locker or $1000 for ARB, $40 for CAD delete, and any other random things you decide you may need like high steer, bigger brakes, unit bearings, truss, etc. I did all of the work myself on my D30 and it's not cheap to build up an axle. I probably spent around $1500-$2000 on my HP D30 and now it collects rust in the driveway because no one is going to spend money on a used axle that needs gears. I certainly wasn't going to put new gears in it just to have them break again. This is the point where you really need to be realistic with yourself.... Are you a crawler or a pedal masher? Are 35's the biggest you'll ever go? Where is your weak link and how hard is it to get off the trail if that weak link fails?


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post #8 of 26 Old 07-11-2020, 06:29 AM
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35s: if you’re gonna trail it, 35s take 3-1/2” room over stock. If you do stuff to trail-worthy it you need another 2-3”. So basically you need room for flex PLUS the tires. You can buy almost an inch with 1-1/4” body mounts, and get at least 1-1/2” by modifying the perches. 5/8” from 5-1/4” lift shackles So at minimum you need about three more inches imho to make it work, and part of that will be cutting.

It sounds simple to skip all that and keep it “low” but actually it takes a lot of work and planning to be low COG. Trail performance either takes a ton of work or a ton of money- but the planning can’t be skipped.

[size=3]Shackles & D-rings are different things.
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post #9 of 26 Old 07-11-2020, 12:20 PM
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I'll piggyback on what @fishadventure is saying.

YES! You can technically put 35's under 2-3" or less of lift with fender modifications and get a nice low center of gravity. Will it be the capable offroad rig you're dreaming of? Most likely not... There is a really good reason that the "low CG" concept is predominantly in magazines and driveway pictures and not in hardcore offroad photos. Part of a good offroad rig depends on articulation and you just can't get very much articulation without much lift....or a complete and total redesign of the entire suspension system.

Here is a picture of what a 4.5" Rough Country lift looks like with 33's and a flat front fender. At full flex, the tires touch the fenders lightly. To get even these 33's to fit with 2" less lift would require large bumpstops or you'd have to remove the front fenders entirely and cut into the hood. You can do high line fenders and cut the hood but it's not exactly the easiest thing to do. How far are you prepared to go to avoid going to a bigger lift?
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post #10 of 26 Old 07-11-2020, 02:04 PM Thread Starter
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Quote:
Originally Posted by Waternut View Post
I'll piggyback on what @fishadventure is saying.

YES! You can technically put 35's under 2-3" or less of lift with fender modifications and get a nice low center of gravity. Will it be the capable offroad rig you're dreaming of? Most likely not... There is a really good reason that the "low CG" concept is predominantly in magazines and driveway pictures and not in hardcore offroad photos. Part of a good offroad rig depends on articulation and you just can't get very much articulation without much lift....or a complete and total redesign of the entire suspension system.

Here is a picture of what a 4.5" Rough Country lift looks like with 33's and a flat front fender. At full flex, the tires touch the fenders lightly. To get even these 33's to fit with 2" less lift would require large bumpstops or you'd have to remove the front fenders entirely and cut into the hood. You can do high line fenders and cut the hood but it's not exactly the easiest thing to do. How far are you prepared to go to avoid going to a bigger lift?
I know I don't really want to go to a 4", I also Don't think 37s are in my future for at least the next 3-4 years.

is there much difference in 3" springs with shackles on a yj vs 4". I just wonder what all additional I need to do from the 2" and if I need to consider a different rig for my 35s or bigger rule.

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post #11 of 26 Old 07-11-2020, 03:01 PM
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Originally Posted by tamersinger View Post
I know I don't really want to go to a 4", I also Don't think 37s are in my future for at least the next 3-4 years.

is there much difference in 3" springs with shackles on a yj vs 4". I just wonder what all additional I need to do from the 2" and if I need to consider a different rig for my 35s or bigger rule.
A lot of the actual lift difference probably is shackles but like anything, it's not quite that simple. You'll inevitably need longer shocks, longer sway bar links (should you choose to run them), drop pitman arm, etc. The biggest thing is you're going to want a slip yoke eliminator and a double cardan driveshaft for the rear. That will help get your driveshaft angle where you need it and you don't have to run the stupid transfer case drop which lowers your ground clearance.

35's used to be kind of a big milestone really. In the days of YJ's, TJ's, and XJ's, a 35" tire was a really big tire and it took a lot of work to fit those. Trucks and Jeeps made in the last 10 years can usually fit 35's with minimal effort and often no lift at all because everything has gotten so big. JK's basically come with a 32-33" tire as stock depending on the model (yes the most stripped down JK comes with 29's but it looks stupid because it's the same suspension on other JK's that come with bigger tires). Meanwhile, most Jeeps in the 80-90's came with 27-28" tires stock. So a YJ going to 35's is similar to a JK trying to go to 40's. It's not quite an apples to apples comparison but in both cases, you're going to need some body trimming, a big lift, axle upgrades and/or axle swap, new gears, new driveshafts, steering geometry correction, etc etc.


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post #12 of 26 Old 07-11-2020, 03:11 PM Thread Starter
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Originally Posted by Waternut View Post
A lot of the actual lift difference probably is shackles but like anything, it's not quite that simple. You'll inevitably need longer shocks, longer sway bar links (should you choose to run them), drop pitman arm, etc. The biggest thing is you're going to want a slip yoke eliminator and a double cardan driveshaft for the rear. That will help get your driveshaft angle where you need it and you don't have to run the stupid transfer case drop which lowers your ground clearance.

35's used to be kind of a big milestone really. In the days of YJ's, TJ's, and XJ's, a 35" tire was a really big tire and it took a lot of work to fit those. Trucks and Jeeps made in the last 10 years can usually fit 35's with minimal effort and often no lift at all because everything has gotten so big. JK's basically come with a 32-33" tire as stock depending on the model (yes the most stripped down JK comes with 29's but it looks stupid because it's the same suspension on other JK's that come with bigger tires). Meanwhile, most Jeeps in the 80-90's came with 27-28" tires stock. So a YJ going to 35's is similar to a JK trying to go to 40's. It's not quite an apples to apples comparison but in both cases, you're going to need some body trimming, a big lift, axle upgrades and/or axle swap, new gears, new driveshafts, steering geometry correction, etc etc.
rubicon t-case doesn't have a slip-yoke. also the cad has been deleted with a tj shaft.

but the driveshaft shocks and what not.

I am looking at better name brand kits right now and have my eye on any of the re extreme duty kits.

I think as long as low range has enough crawl for 35s I can ignore the gearing for now at least till I find a suitable 44 front.

coming from the world of samurais I am used to no power but lots of gearing option. my last ride was an 88 samurai with 4.10 locked toyota axles and a 6.5 tcase on 33s.

I just want more room like my old rubicion had.

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post #13 of 26 Old 07-11-2020, 03:34 PM
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rubicon t-case doesn't have a slip-yoke. also the cad has been deleted with a tj shaft.

but the driveshaft shocks and what not.

I am looking at better name brand kits right now and have my eye on any of the re extreme duty kits.

I think as long as low range has enough crawl for 35s I can ignore the gearing for now at least till I find a suitable 44 front.

coming from the world of samurais I am used to no power but lots of gearing option. my last ride was an 88 samurai with 4.10 locked toyota axles and a 6.5 tcase on 33s.

I just want more room like my old rubicion had.
Oh yeah.... forgot about the rubi transfer case. A 4 cyl with the stock 2.72:1 transfer case typically has enough power and a decent crawl ratio with 35's so the 4.0 will have absolutely no trouble with a 4:1 transfer case. With the 241OR, 4.10 gears, and 35's you're looking at about 1mph at idle in 1st gear, 2mph in 2nd gear, etc. At redline in first gear in low range, you still won't even hit 10mph. To put it another way... when you're in low range and 4th gear, it's basically the same as 1st in HI. I kind of suspect you'll be using 2nd and 3rd more than 1st when you're offroad.


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post #14 of 26 Old 07-11-2020, 03:37 PM Thread Starter
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Oh yeah.... forgot about the rubi transfer case. A 4 cyl with the stock 2.72:1 transfer case typically has enough power and a decent crawl ratio with 35's so the 4.0 will have absolutely no trouble with a 4:1 transfer case. With the 241OR, 4.10 gears, and 35's you're looking at about 1mph at idle in 1st gear, 2mph in 2nd gear, etc. At redline in first gear in low range, you still won't even hit 10mph. To put it another way... when you're in low range and 4th gear, it's basically the same as 1st in HI. I kind of suspect you'll be using 2nd and 3rd more than 1st when you're offroad.
so now that gearing is taken care of I need to find some flexy springs and some good shocks. figure out steering and a rear driveshaft.

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post #15 of 26 Old 07-11-2020, 07:05 PM
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In answer to a couple of posts above, 4” springs are going to ride hard. I don’t like tall arched springs myself. And don’t worry about the tj shaft problem- it’s fairly inexpensive to upgrade to the factory-type vacuum CAD and two-part axle.

You can probably do the little mods I posted above along with 2-1/2 OME springs or other 3” springs but wise fender cutting and appropriate flares will probably make it actually work out.

[size=3]Shackles & D-rings are different things.
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