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Rusty Pseudo-frame?


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So I have been searching for a while for a used MJ, and I have had to be patient because I fairly firmly want a 91 or 92 MJ with a 4.0L, AW4, 4wd, and A/C. (I woulds take a 5-speed too!)

 

So I found one locally, and it is in pretty good shape despite my location in the rust belt.

 

The truck has some small issues that I can fix slowly over time, but it also has one issue that scares me a bit: The unit-body is not very rusty except in a one foot section of the Pseudo-frame rail on the passenger side just under the passenger seat. Both sides of the rail have holes. None of the holes are very large (maybe quarter size at most), but they are there, and there are more on the inside of the rail than out side. Oddly there are no holes through the bottom of the Pseudo-frame in this area. I think I could patch it, but maybe its not worth the trouble. Please give opinions and or information if you have it. Is this a fatal rust spot for an MJ?

 

Also I have a MIG welder, and I am not afraid to use it, but i am not sure if there is a good way to fix/patch this?

 

thanks!

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First of all, your looking for a '91 or a '92 MJ......and Yes, their somewhat rare, And if you found one, I don't think your going to find 2 in the same parking lot.

 

What I've seen, is the uni-frame seams to rust out on the right side, just before the spring bracket, more likely from the heat from the cat/muffler super heating and then the cooling of the metal. An '88 I'm parting out now, the "frame" section is totally gone, and it's not worth the repair, thus......a parts vehicle. Plus the body panels, door bottoms and floor are.......well, just not all there.

 

You write......"one issue that scares me a bit".....I wouldn't let it scare you at all, from what you describe, you have very little rust issue, of course......once you start cleaning it up I'm sure you would find additional rust :roll:

 

But still........You would not have a major project to get the frame rail repaired.

 

As far as additional info........try to find a FSM, that includes the "Body" or if your can, find the book "M.R.278" which was published in 1985 "Jeep Comanche" Workshop manual 'Bodywork', that will give you the details you need to see how the floor frame and sub frame were constructed. That would give you a better idea on how to make the repair, and tie it into the existing sub frame.

 

Also.......one of my favored sites........http://www.autobodystore.com/......where there is a wealth of information there, and an open form for any questions.

 

Just one thing.......Patching the frame is one thing......doing a proper repair, and adding additional steel to support and repair the rusted section would be the better of the two. Do a proper repair, and you'll get many more years from you "rare" find :D

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i have heard from ear that a "legal" frame repair has to be done with an arc welder. i don't really care if you use a mig. its your truck I'm not so sure that it makes a difference (someone will correct me).

 

it's nice that our trucks don't have frames :brows:

 

gotta love unibody.

 

and yes, if that law is accurate, this is aa viable loophole.

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I will try and get some pics of the rusted area. its a pretty nice truck otherwise, and if I buy it I do want to fix it properly.

 

Can you even arc weld thin gauge metal that these trucks are built out of? I was under the impression that MIG was best for the Unit-body? Eh what do I know any ways?

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ARC is different than MIG.

 

As I use it, ARC creates more heat faster, so penetrates better. I use it for thicker applications. Think Lincoln Buzz box. Generally use flux rods where shielding gas isn't required. All but the most expansive units do not use gas.

 

MIG offers finer controls and finer wire allowing better thin metal welding applications. Although you certainly could by a balls out HD unit that will weld everything a ARC can, generally they are used for thinner welding applications. Can be run with or with out shielding gas in all but the very cheapest units.

 

CW

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A couple things about this thread...

 

1) Stop calling it a god-damn unibody! It's not! A unibody is what you see in a crappy sub-compact car. A UNIFRAME is what we have. It is different in that we still have clearly defined 'frame-rails', which just so happen to have the cab welded to them.

 

2) Welding process DOES NOT MATTER when welding mild steel. Stick, MIG, Flux-core, TIG, gas, whatever. It'll all work and when used by a competent person who chooses the correct filler it will produce a near identical result. Most el-cheapo MIGs can produce enough heat to get proper penetration on the frame rails, as they really aren't very think (most of it is about 16ga, I believe). I'd personally use a MIG welder as I have one, I know how to use it, and it's faster/easier than most of the other avaliable methods. If anybody told me I had to do the repair with an ARC/stick I would either look them in the eye and tell them to get bent, or tell them I did as they would not be able to verify otherwise.

 

And as a side note, prep is king on the uniframe. It's dip-galvanized from the factory, and you'll get mad zinc contamination if you don't prep it well. If you burn through multiple layers (where there is seams, etc) you may get some unavoidable contamination. That will suck.

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A couple things about this thread...

 

1) Stop calling it a god-damn unibody! It's not! A unibody is what you see in a crappy sub-compact car. A UNIFRAME is what we have. It is different in that we still have clearly defined 'frame-rails', which just so happen to have the cab welded to them.

 

what the heck do you think a unibody is

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