hello, curious about whats going to break first

[metalman]

hello, I'm finally making some headway on my wifes project, and although I've built tons of cars, I'm still sort of new to jeeps, so I was looking for what anyone thought was the weak link in this.

90 xj,
-4.7 stroker, MS, probably a 75 dry nitrous shot, cammed for the low end
-ax-15 freshly rebuilt, stock clutch
-np231 with wide chain swap and 6 pinion planetary and JB sye
-front hp d30 w/o vac disconnect, wj knuckles, brakes, stub shafts, hubs for 5on5 lug, high steer
-rear 8.25 29 spline, wj rear brakes, 5on5 lug, moser axles
-RC 6.5 inch short arm kit, prothane bumps
-33" tires, nothing very aggressive tread wise.
-For the Drive shafts, I'd like to stick with factory shafts pulled from something else, but if they start blowing up I'll go aftermarket.
-I still haven't settled on a ring and pinion ratio yet, probably 3.55 or 3.73, we aren't very interested in rock crawling, and although not a highway cruiser, I'd swap in a 4:1 before I'd sacrafice mileage anymore.
-Down the road, it will probably get a hydro boost, and if she really likes the jeep after all this airlockers front and rear and a 2lo kit and long arms for the front, probably better shocks.
-for the frame, I was going to get a full set of stiffners, better bumpers to tie the frame in better, replace the rockers and connect them to the frame rails, some steering bracing, and beef up the shock mounts, I wasn't planning on getting serious enough for a cage.

basically my idea with this has been to maximize the number of stock parts used so that replacements are cheap and plentiful, I hate having a one off part break and being stuck buying another for too much $$$, or worse having to convert to something else because the needed part is no longer made/available (my chevelle needed a new spindle after a disc conversion, and I found out it was a custom part, I had to toss the entire front end because they didn't support their original suspension design). I was also looking to keep the vehicle somewhat tame so that my wife can still reasonably drive it around, after all it is her project.

My question is what is the weak links in all this are, or better yet what you guys think the first couple of things to break will be? Not just wheeling it, but driving it in general. I already have most of the major parts, I'm fairly committed to the engine trans and axles, I'd just like to build the details as right as possible the first time so I don't break anything more than I have too and avoid getting stranded as much as possible.

Thanks for any replies, I've done a good bit of searching, and Ive found info in the individual parts and building them up, but I have had a hard time nailing down where the weak link would be because most of the builds I've found good documentation on are much more aggressive.

 

[dick.breakey]

i dont have much to add haha, but im just curious what the nitrous is for haha. never seen it on a rig of these sorts. im all for it, cause i love the go go juice, but im just curious whats your reason for it.

 

[WrenchMonkey]

As far as breakage, if you're planning to juice it offroad, I'd worry about the stockish D30 shafts. I hope you'd be carrying spares, anyway.

-I still haven't settled on a ring and pinion ratio yet, probably 3.55 or 3.73, we aren't very interested in rock crawling, and although not a highway cruiser, I'd swap in a 4:1 before I'd sacrafice mileage anymore....

This part is a little counter-intuitive, but bear with me:

On street cars, shallower gears usually give better gas milage. Once you bolt on a set of 33s, however, things change.

The larger diameter effectively raises the gear ratio (lower numerically) and the extra mass makes it harder for the engine to spin em.

410s or 456s will compensate for both, and actually increase both your performance and efficiency by keeping the engine in its power band.


Sounds like a helluva build, good luck and keep us posted!

Robert

 

[metalman]

as for the nitrous, it doesn't hurt gas mileage because when you aren't using it, its not there, i personally think its a very underrated option for a street vehicle because of that, even though oddly it usually has a "racy" reputation to most people.

Its also much cheaper than turbo or supercharging options, plus it doesn't add to heat buildup under the hood, which is a problem for jeeps in general anyways, and packaging on it is the smallest by far, virtually nothing. its also better for the low end where a truck or jeep will actually use it, even a small shot makes for a huge increase it torque at any rpm, turbos need a good bit of rpm, even superchargers need some, nitrous is all in even at idle.

Another reason is that thanks to the OBD non-compliant renix (renix has no scan port, so you can ditch the ECU), I can run MS and still pass cali smog as long as the factory vac system is present and the tailpipe is clean, and a nitrous system could sneak through or just get removed really quick. It sucks taking a turbo off and swapping over your entire intake and exhaust just so you can pass smog.

Last point, its a bit different, I haven't decided on it for sure, but since the jeep is for the wife, she would get a kick out of it just being there, even if she never uses it.

 

[metalman]

efficiency by keeping the engine in its power band.

I've been debating about this a bit, has anyone done a direct comparison between them? I can see how that would impact the mileage on a stock 4.0, but that was part of my thinking with the stroker, aside from the fact that building a 4.7 didn't cost me anymore than a 4.0, I was planning on camming it for down low, and the extra cubes should push the power band even lower, so I was hoping it would compensate and let me get away with a steeper ratio to offset some of the lost mileage on the stroker.

So would having a locked d30 with a strong motor and 33s be the weak link in the plan? Do you think upgraded 27 spline axles would hold, or would I have to jump to 30 spline? also, are the u joints or the shafts themselves the weak point?

 

[old_man]

My bet on first breakage is the drivers side D30 axle shaft if it is driven offroad.

 

[tbburg]

JP magazine did a build a few years ago, 33"s, lots of little mods, and a 50hp shot of nitrous. They had nothing but praise for it. The first thing they broke was the engine.
(Then again, the guys at JP are idiots. They were using the nitrous for passing on the highway.)

I wouldn't bother with the nitrous. it's not like you're going street racing. It definitely won't get used on the trail. If you absolutely have to have the pretty, pretty bottle, get a power-tank, paint it blue, and slap an "Nos" sticker on it. Then you'll have both a Nos sticker and on board air.

 

[redrider2911]

I wouldn't bother with the nitrous. it's not like you're going street racing. It definitely won't get used on the trail. If you absolutely have to have the pretty, pretty bottle, get a power-tank, paint it blue, and slap an "Nos" sticker on it. Then you'll have both a Nos sticker and on board air.

Agreed

 

[jrowell]

Agreed

X3 I like to go fast as much as the next guy, but I've never thought "wow, I could sure use a shot of NOS right now".

Stick with the stoker & regear to 410s. It should get around nicely.
that's my .02

 

[FlexdXJ]

I think 4.56 will be your best option gearing wise and like was said before, Don't do a nitrous kit.

 

[metalman]

Its the wifes call about the nitrous, this is about what makes her happy so that I can work on my other projects guilt free, although its grown on me quite a bit, and I'm all about trying to beat the cali smog system in case we move, I'm just turning wrenches on this one. Its not a key part of the plan, but in my experience it will find weak links in your drive train pretty fast, so thats more of why I was asking about it. I understand parts will break, but throwing that out there eliminates the "do this and keep your fingers crossed" advice, and keeps from finding out the hard way if she does want to spray it.

I'll probably start with 3.55 gears because thats what I've found a deal on, and if she decides to take it up a notch after that, throw 4.10s in when we do the arb lockers.

so the consensus seems to be the d30 shafts being the weak link. Assuming I upgrade to alloy 30 spline shafts with the lockers, what would be the next weakness?

 

[redrider2911]

I say the straps on the pinion yokes. Drill the holes out and replace them with u bolts. You said you found a deal on the 3.55 gears? Are you buying a set new because they come in alot of cherokees stock...

 

[WrenchMonkey]

Its the wifes call about the nitrous, this is about what makes her happy...

Man, I really need a wife like that. The only way nitrous would make my psycho happy is if I fed it into a bag over her head...


Having the D30 shafts as a weak link isn't the end of the world. Carry spares with the unibearings on em, and you can swap one in no time.

With alloy shafts, the weak link moves up to scarier stuff, like ring-n-pinion gears...

Robert

 

[redrider2911]

And I know you are really only asking whats going to break first but at 6.5 inches you should really run long arms or at least drop brackets. It sounds like this is going to be driven around town alot and on trips and I can tell you right now she is not going to like how rough it will ride.

 

[boomhauer]

Man, I really need a wife like that. The only way nitrous would make my psycho happy is if I fed it into a bag over her head...
Robert

Thanks Robert, i now have spewed coffee all over my keyboard! -B:roflmao:

 

[metalman]

sorry, double post.

 

[metalman]

I say the straps on the pinion yokes. Drill the holes out and replace them with u bolts. You said you found a deal on the 3.55 gears? Are you buying a set new because they come in alot of cherokees stock...

The 3.55 gears are because thats what I can find a pair of non-vac front and 29 spline 8.25 rear axles in, when I buy aftermarket gears I'll get 4.10s most likely, but for the price jump getting 4.10 axles from a yard I could just buy aftermarket anyways. Right now it has the 35 rear, so I'm waiting until I can get a 8.25 under it to put in the stroker and do the major work on the frame and such, but it isn't getting driven much or hard until then.

Its already running around with the 6.5 lift, it isn't a daily driver, just trips to the beach and its rarely more than 10 miles from the house. She doesn't mind the ride, but it'll be getting some drop brackets anyways.

thanks for the tip on the front yokes, I hadn't run across that. I'd thought about girdles because I've used them before, but I've also read they can have clearance issues on jeeps. I still debate about eventually upgrading to 30 spline front shafts with the locker. Unfortunately I'd be committed to one path or the other, and although the warranties on the shafts inspire confidence, breaking the RP doesn't. I have heard of people breaking 4.56s with the 30 spline shafts, have many people broken the 4.10s with them? I know in theory the 4.10 would be stronger, but are the gears breaking themselves or is it housing flex causing it?

Thanks for the responses, I know some of these questions are probably on the basic side of things, and searching perviously has helped a lot, but the variety in peoples builds has surprised me, and it is appreciated to have someone offer up direct advice like this.

Man, I really need a wife like that. The only way nitrous would make my psycho happy is if I fed it into a bag over her head...

I am lucky, I had to show her your post, she got a kick out of it, shes pretty high strung, but very good to me. We've been together for a few years now, and I've always been working on something, to her its just part of who I am, and with job related stress being on the high side some times, it keeps me sane. I think for her its a way to connect to my interests, but in her own way with it being a jeep. She's always wanted one, and I'm more into cars. In return, we usually watch her movies, so its give and take.

 

[tbburg]

I'll probably start with 3.55 gears because thats what I've found a deal on, and if she decides to take it up a notch after that, throw 4.10s in when we do the arb lockers.

I really wouldn't do the 3.55s. I put a set of Goodyear MTRs/Wrangler Moab wheels(Brand new TJ Rubicon take-offs) on my XJ and drove it around a little. It was a dog. That's about equivalent to a 32" tire. My jeep did NOT like those.(Neither did I, but that's another story) If you're going to go to 33"s, seriously consider at least 4.10 gears.(4.10s are the stock gears for the Rubicon)
On a related note: If you jump up to 4.10 gears, with open carriers, then later decide to go with any full-case locker, you can do the axles one at a time. You won't have to match the gearing, because it's already done. You don't have to pay to have the axle gears set up again(they just re-set back-lash when they change a carrier)

PS: If the lady thinks a stock XJ is down on power, 33"s and 3.55 gears are going to require a lot more then a 75hp shot of laughing gas to make her happy.

 

[metalman]

Right now its got 3.07s and 31" tires on a renix motor, so its not exactly a speed machine, but she's fine with it, 3.55s probably won't be permanent, and it will be an improvement either way, plus it'll have the 4.7 in it by then, so it should get around okay. If first is too steep now, she's got it in 4lo anyways and then its fine.

 

[WrenchMonkey]

307s?

Oh, AX15, I missed that.

That change my answers about the gear ratios a bit...

And the next weak link with the alloys! :gag:

Robert