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  #1  
Old 11-08-2000, 12:26 PM
RedSandDog
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Default \"Boxing\" frame on pre \'76 CJ

Kinda' have three related questions: How common is it to "box" the frame on pre '76 frames, how hard is it to do and how much benefit is there?

I am keeping my 258 and will gear it down to about 90 to 1 crawl ratio, so I can go play on the rocks near Phoenix. Won't be a high H.P. application, but I don't like thing to break.

If you have some expereince doing this, let me know how it went. thanx

'74 CJ-5, 258, NP435, D44 w/LockRite
(OK, well the np435 is in the garage next to the Jeep)
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  #2  
Old 11-08-2000, 03:13 PM
**DONOTDELETE**
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Default Re: \"Boxing\" frame on pre \'76 CJ

I don't know how common it is to box it, but I'll throw in my thoughts...If the frame is thrashed (rusted out, etc.) boxing it will only prolong it's misery, not solve it. If, however, the frame is in good shape, adding additional support would be a good thing...For some. There are some who believe that a flexy frame is good, because they get extra articulation from frame flex. Even for these people, reinforcing critical areas (engine mounts, suspension mounts) would be a good idea. I fall into the "I'd rather let my suspension be the suspension and my frame be rigid" group of people, and I'd want my frame to be as rigid as possible...so boxing it sounds like a good idea. The only problem with boxing it is that you then get collection of all sorts of moisture, mud, and crap inside, that you can try to keep cleaned out...but it will eventually rust, even if you've got it painted. This is a longer term worry... If I were building an ideal frame, I'd avoid boxing it...you can then run stuff inside the framerails with ease (fuel lines, brake lines, air compressor lines) and you can still reinforce critical areas and add extra frame beef...you can use larger channel and go outside the existing frame, use smaller channel inside the frame, or use plating on the outside or inside of the frame. Hey, how many semi's have you seen that have C-channel frame? And how many with boxed frame (I've never seen a boxed semi-frame). The benefits of strengthening it are that you'll never have to worry about it again...it'll be good if you do it right. Difficulty? Well, to do it right, you'll have to be stripped down to the frame.

Once again, at the very least, you oughta reinforce the frame in the area of the motor mounts and suspension (spring and shock) mounts...in addition, you probably should reinforce the areas where there are body mounts, and areas where the frame bends. On something as tightly packed as a jeep, you're pretty much down to reinforcing everything...

As far as as the 90:1 goes...
NP435 tranny, so it's about 6.5:1, right?
What are you running for a t-case?
What size tires are you going to run?
Assuming that you want to be able to drive it on the street, I'd try to figure out what size tires you're going to run, and then do some calculations to figure out what kind of axle gearing would be acceptable on the road. From there, you can multiply your axle gearing by your first gear...Divide 90 by that number, and you'll know what t-case low range you'll want...unless you've already got a particular t-case picked out...

So if you're gonna run 4:11's, you'd need a t-case with a low range of about 3.35...which means either a teralow conversion, or an ATLAS II. Even with 4.56's, you still need a 3:1 low range... Running a D20 t-case, you'd need something like 7:1 axle gearing to get 90:1 crawl ratio...so you're gonna need some low t-case gears. I could be wrong on the NP435 1st gear...is it 6.5:1 or 7:1? That'll change the figures a bit.

Is your D44 the stock D44? I'd search some old posts for durability reports on the D44 with fewer splines. And what are you running for a front axle? 90:1 through a D30 with tires over 32-33" will spell doom according to many of our resident experts (EXPERts because they've EXPERienced blowing up D30's with low gears and big tires...small shafts, small pinion, small u-joints...big problem).

And before anyone sees and chews you out for it...fill out that profile!


Moneyless, Will weld for jeep accessories.
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  #3  
Old 11-08-2000, 03:52 PM
**DONOTDELETE**
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Default Re: \"Boxing\" frame on pre \'76 CJ

I agree with Farmjeep on the frame boxing. I have a spare frame and I am working on boxing the areas around all of the suspension mounts only. The engine area is already boxed. I am simply welding steel plate inside the existing channel. I place a piece of cardboard against the inside and run a hammer down where the edges of the channel is. Makes a great template for cutting your steel.

If you want to run 90:1 you're going to need 4.27's in the R&P and the TeraLow kit in the t-case if you stick with the Dana 20(6.69 first x 3.15 t-case x 4.27 r&p).

The Dana 44 you have should be fine. The switch to the 30 spline, flanged axles happened in 1971.

'75 CJ5,258 w/Howell EFI,T18a,4.27's,33's,On-board air,Warn 8274
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  #4  
Old 11-08-2000, 04:31 PM
RedSandDog
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Default Re: \"Boxing\" frame on pre \'76 CJ

Actually I will probably only go to 70 to 1, I thought I had a line on a 20 with a Terra Low in it, but he just (like 10 minutes ago) decided to keep it [img]/wwwthreads_images/icons/mad.gif[/img] so I guess I will try to track down a 300.

'74 CJ-5, 258, NP435, D44 w/LockRite
(OK, well the np435 is in the garage next to the Jeep)
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  #5  
Old 11-09-2000, 08:41 PM
utahjeepr
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Default Re: \"Boxing\" frame on pre \'76 CJ

Boxing the entire frame on an 72-75 CJ is not in your best interest unless you swap spring mounts and run a later model lift kit. NOBODY makes a decent set of springs for early CJs unless you get some customs from National Spring. I own a 72 with the same frame as yours. I am running a Chevy V-8 and 100:1. I mostly run hardcore trails, and have only had a problem cracking the frame right right behind the rear spring hanger for the front spring, exactly where the factory boxing ends. This makes sense due to the comparitive rigidity of the front end and the rest of the frame, combined with the stress applied by the suspension at this point. Increasing the boxing to extend about 9 inches rearward of the hanger solves the problem. The rear springs mounts are not really a problem , so I have left the rear alone.

I am a "Sheetmetal Darwinist"
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  #6  
Old 11-09-2000, 10:55 PM
**DONOTDELETE**
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Default Re: \"Boxing\" frame on pre \'76 CJ

Now these may be stupid questions, but at the very least, entertain yourselves with them.

1. Boxing the frame? Are you welding a piece over the edges of the C-Channel to form a box with 4 sides, or are you welding a plate to the inside of the c channel?
2. If boxing a fram allows mud and other goodies to get in there and cause rust, how about using cardboard and welding say a piece of 5/16" plate steel the entire length of the frame, inside of the C. [<--in there. That way, no mud or stuff could get in there, it would still strengthen the frame, and maybe a few other goo/bad things? Now you guys got me thinking!!!!

mike

If you cant DODGE it, JEEP it!
Big Mud Tires are from the Earth....they were put here for you...and for me...take advantage!!
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  #7  
Old 11-09-2000, 11:55 PM
**DONOTDELETE**
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Default Re: \"Boxing\" frame on pre \'76 CJ

If you did put a plate inside the C-channel you would have to take off all the body mounts that are riveted on since the rivets would not let the plate lay flat wouldn't you? If you did take them off what would be the best way to reattach them, bolts or welding them back on?

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  #8  
Old 11-10-2000, 10:30 AM
**DONOTDELETE**
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Default Re: \"Boxing\" frame on pre \'76 CJ

Putting a plate inside the channel would add very little to the strength of the frame. The idea behind boxing the frame is to add structural ridgity to prevent twisting. Adding a plate inside would still allow the upper and lower portions of the "C" to twist and wouldn't do anything to help prevent cracks in these portions. The lower leg of the "C" is where most cracks start in the older frames.
RemyDodge,
Depending on what year your CJ7 frame is it may be fully boxed already.

'75 CJ5,258 w/Howell EFI,T18a,4.27's,33's,On-board air,Warn 8274
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