Tires - Diminishing Returns? - JeepForum.com
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post #1 of 12 Old 05-18-2019, 01:36 AM Thread Starter
ghosted3
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Tires - Diminishing Returns?

I recently bought an 84 CJ7 with the straight 6 and 5sp manual. I am planning on doing most of the common stuff in the coming month or 2 like suspension lift, bigger tires, re-gearing front and back and some things on the interior. My main question / concern is that since the motor isn't very strong, is there a point (even with re-gearing) when the tires become too large? I am looking to build everything around 35s, 37s tops. Thanks in advance for anyone who offers feedback, it is much appreciated.

Corry

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post #2 of 12 Old 05-18-2019, 02:56 AM
HackFabrication
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Depends on how hard you are on the Jeep. And what sort of final performance you expect. Going to big tires creates a whole new set of potential problems.

The factory Dana 30 front axle and rear AMC 20 in your 84 CJ7, have a number of weak areas. The light duty T5 transmission is another area of concern. Increasing tire diameter is going to increase 'wear and tear' on those items. Toss in some mud, or any sort of 'high spin' scenario, and things are going to break.

Going to 35" tires will require swapping to 4.10 gearing with the 5 speed. Or you're not going to have use of the overdrive 5th gear. With 4.56 gearing even better for certain types of driving. You'll definitely want to consider upgrading to 1 piece axle shafts in the rear AMC 20. I really wouldn't recommend going any larger than 35's with the stock axles. Personally, I wouldn't go any larger than 33's. My CJ5 is running a 2.5" suspension lift and 32" tires.

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post #3 of 12 Old 05-19-2019, 10:42 AM
ddawg16
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Hack touched on some good points. I have the same jeep.....but quite a few mods...

The first question.....where do you live (helps to put that in your profile....it gives us an idea of what works best...don't need city...just state). Next, what are you going to do with the jeep. Third, what is your budget? Forth, what is your mechanical level?

The good points....your 4.2 is a tough engine with plenty of torque for rock crawling or mall crawling. Also, the D300 is one of the better xfer cases to be had....keep it. The other good point....lots of parts available for the jeep.

Bad points....

the DuraSpark and BBD carb are your weak points. With proper attention, they can be made to operate well. Biggest issues are vac leaks. There are plenty of us here to walk you through those problems.

The rear AMC20 is a good rear end....but it's main weakness is the 2-piece axle. Replacing them with 1-piece like Moser's takes care of that. The other weakness is the axle tubes. But not an issue as long as you don't slam the pumpkin on a huge rock. I've heard of bent tubes but have never seen one. Of course, you can truss the axle and solve that issue.

Front D30? For a mall crawler/daily driver, it's fine. Mild off roading with 33's...it's fine. But it is a D30. Note, a D30 and D45 use the same outers and axles. It's just the housing on a D45 that is beefier.
You didn't mention lockers which implies you're making a mall crawler. Take into consideration, going over 3.7 gears requires a different carrier. If you are planning to do any off-roading...now is the time to put in lockers. If you decide to do it later, then you are out of pocket for labor to set up the gears again. You can't just swap in a locker without redoing the gear adjustments. Typical going rate is $250-300 per axle....just for labor. I've done it a couple of times.....it's time consuming.

Lifts...two options....spring lift or SOA (Spring Over Axle). SOA is your cheapest because you can use stock wrangler springs. This will give you about 5.5" of lift and the best ride. If you buy a cheap spring lift, after you drive it you will understand why it was cheap. Avoid a body lift. It just looks dorky and causes other issues with clutch alignment and fan shroud.

An SOA will fit 35's or 37's....but you will have to trim some metal off your rear wheel well if you plan to rock crawl.

Engines.....should you decide you want more power, lots of options. Toss in a 4.0 out of a newer Cherokee....or 4.3 V6 out of a S10 Blazer....if you get the auto as well, Novak makes a nice adapter so you can keep your D300. The Chevy LS1's are also great swaps....I would also get the 4L60 that typically goes with it.....it's a lot tougher than your T5.

So, answer those questions above, and then we can help you spend your money.


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post #4 of 12 Old 05-19-2019, 07:58 PM Thread Starter
ghosted3
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Here we go, I am from Illinois, in the central area about center between Springfield and St. Louis Mo.. My CJ7 is going to be roughly 75% fun 25% DD, and of the regular driving that will be within a 1 mile radius of my house (daughter is looking forward to going to school with the top off). I am looking for more of mudding and trails over rock climbing, but with the ability to do some rocks if needed. My mechanic skills are fairly basic, but I also know when a project should be handed off to a mechanic instead of trying to do something myself.
I do plan on adding lockers, but I was not aware (still new to all this and am researching as much as I can) that it is best to install those when regearing, so I will make sure to try to get those knocked out at the same time. As of this moment I have about 8k sitting off to the side for the project, and working a lot of overtime at work so more will be coming soon.
My original plan was lift, tires, regear, seats and harnesses, winch, lockers (which will now be done sooner), then after I play with it a bit, drive shaft, axles, and then a couple of body mods, unless I am forgetting something. If there is a better or more practical order to go in please let me know, thanks.

*Edit* For the lockers, would lunchbox lockers be good for someone who is looking for the "middle ground" area of mudding / trails and maybe light rock crawling, or would the air lockers still be the best thing to do?

Corry

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1984 CJ7 project

Last edited by ghosted3; 05-19-2019 at 08:13 PM.
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post #5 of 12 Old 05-19-2019, 09:05 PM Thread Starter
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Sorry I forgot to ask, is it better to run a wheel spacer if needed, or an offset wheel, or a combo of the 2? Thanks again for the feedback.

Corry
Hillsboro, Illinois
1984 CJ7 project
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post #6 of 12 Old 05-19-2019, 09:44 PM
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Living just up the road from you, so we play in the same terrain, 35's on a 4" lift with some fender trimming, 1 piece rear shafts and chromo fronts after you get tired of replacing the stock ones is a good setup. dad has one setup the way you want to be, his is a 4spd (t-4) running 4.88's and does good on short on road trips and works well off road. lunchbox lockers will work, but by the time you buy a new carrier for the gear change and the lunchbox locker, you are very close to the cost of a good limited slip or locker. i think air lockers/selectables are overkil for what you are wanting to do. The 6 cyl isn't the best for a bog, but works real well for trails. no need for wheel spacers, with factory wide track axles and a stock offset wheel, there is no need with a 35-36 12.50 tire.

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post #7 of 12 Old 05-19-2019, 11:01 PM
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I'm not a fan of wheel spacers. I agree with Fourtrail....or, buy a set of black steel wheels with the offset you want. Be aware....a lot of offset may look good...but after awhile, you get tired of the stuff they toss up.

For lockers...maybe a full Detroit in the rear and maybe a Detroit TrueTrac in the front. The TrueTrac is a form of limited slip but does not require the friction additive. They are basically bullet proof.

If your daughter is going to drive it....I think I'd be inclined to stay with 33's. 35's will give you only 1" more of actual ground clearance. And stick with the 4.2....no reason to give her more power than she needs. Your T5 will last a lot longer.


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post #8 of 12 Old 05-20-2019, 10:38 AM
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Quote:
Originally Posted by ghosted3 View Post
I am looking for more of mudding and trails over rock climbing, but with the ability to do some rocks if needed.
I see a short lifespan for the Dana 30 front end with large tires. Running mud is all about wheel spin. Yes, you can upgrade the front to larger u-joints and better shafts. But you still have a light duty front axle. Add in the effects of spinning larger tires, and then gaining traction, you will hear stuff snap. Hopefully, it will just be a lockout hub. More likely, it will be something more dramatic.

Crawling rocks is a different story. It's about going slow. Or banging into boulders and bouncing over them. Lots of shock on the drivetrain. You are going to have to compromise if you intend to run both.

Honestly, from what you've posted, go with a nice set of 33's and either 4.10 or 4.56 gears. 4" lift is more than adequate for what you've said is your intended terrain. One piece axles in the rear, weld the tubes. If you want lockers, put them in when you get the axles re-geared. It'll be less labor cost, as they've got everything apart at that point.

If you're mind set on 36"+ tires, you might as well go with a 1 ton conversion. Better axles, bigger brakes, more gearing options, etc. But then your weak link is the transmission. And the 4.2 I6 is a decent engine, but if you're turning 36-37" tires, you're going to want a V8. Especially if you're playing in deep mud.

Slapping on bigger tires, creates a lot of 'issues' that need to be addressed. And those issues equate to a large amount of money, even if you can do most of the work yourself. Trust me, I've got the receipts to prove it....

JMHO. It's your CJ, and your bank account....
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post #9 of 12 Old 05-20-2019, 02:34 PM
LumpyGrits
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Anything over 33" with stock axles becomes a guessing game of what breaks and when.
I did the mods to mine from lessons learned......
LG

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post #10 of 12 Old 05-21-2019, 02:09 AM Thread Starter
ghosted3
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Thanks again for the help, its much appreciated.

Corry

Corry
Hillsboro, Illinois
1984 CJ7 project
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post #11 of 12 Old 05-21-2019, 07:15 PM
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35’s, 258, T-5, D300, Dana 44 with Detroit in back, and true trak in front. Does fine but I never really get after it in the rocks. My weakpoint would be the tranny for sure. Also did the nutter and replaced the BBD with a Motorcraft 2150. Nutter and Motorcraft are really enjoyable.
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post #12 of 12 Old 05-21-2019, 07:41 PM
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I agree with all the folks above.
@LumpyGrits makes a great point, and it generally sums up my approach. I built around 33" tires, upgrading as things broke. If I was wheeling hard enough to want/need 35+, I would not put them on a D20.

I'm running a 304, T-18, D30 (welded), D20 (old Detroit) w/ 1 piece axles, and 4.10 gears
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