Check your cabs!

[shelbyluvv]

I just got done checking over Betty and finding all the spot welds and joints I need to remove for the conversion. While I was out there I pulled the seal down on the top corners of the back window. I have 1/2" long cracks in the rear of the cab going from the top window corners into the roof. This is the 2nd MJ I have seen with these cracks.

 

Check your trucks before it is too late and they get out of hand!

 

EDIT: I don't know if it matters but both have been long beds.

[MancheKid86]

booked it down the stairs to check,

all good :banana:

 

THANK YOU!!!!!! :bowdown: :bowdown: :yes: :yes: :D :thumbsup:

you just found my water leak, p/o painted the truck from red to white and didnt put the window seal in all the way :doh:

 

thanks again :cheers:

[Dave Stark]

Mine is a short bed & all four corners have this issue, when i get into the bodywork portion of my build they will be getting my attention...

 

 

 

 

[comanche13]

wow i have never seen that before how would you go about fixing that?

[MancheKid86]

grind er down, get rid of the brittle metal,

and either put good stuff in, or bondo

[Dave Stark]

grind er down, get rid of the brittle metal,

and either put good stuff in, or bondo

 

 

Not really, stop drill to relieve the stress, then weld it up.

[wannabeMJ]

mine is a long bed 86 and no crack for me............

[comanche09]

Wow, my 88 and 89 does not have any cracks. 89 was a hardcore wheeling rig.

[mvusse]

Just checked my severely abused and rusted 87 trail rig. No cracks.

[jpnjim]

Just found some stress cracks like that (tho not as bad as Raoden83's! :eek: ) in the door-jam of my (98) 2dr XJ last week.

 

The MJ's are fine tho. :cheers:

[Comanche County]

good tip!

[man-coche]

I just done a search for cab cracks when I saw what I have, and found this post. I have then on my short bed 89 pioneer. They are from the window courners out and are caused by presure. I live about 10,800ft in the highlands of Guatemala, and the air presuse changes every time I go to the Capital. I have found the stress factor of air presure is about 3 times as much here in the highlands and all metal wood, and plastic expands. I don't know about any of the others that have these cracks, but this is what I have found to be the cause with mine.

[reece146]

I really doubt the cracks are due to air pressure changes. Are you travelling on a lot of gravel and/or uneven roads?

 

These cracks are most likely due to a lack of torsional rigidity AND the truck being flexed out semi-regularly enough to have twist occur down the centerline of the truck. General unpaved road vibration can cause it too.

 

To fix them, drill a hole at the end of the crack. This will act as a stress relief so the crack doesn't go any farther down this path. Then weld the cracks up. Some say drilling the hole is not necessary since the welding process changes the metallurgy anyway but what does it "cost" to run a 1/8" drill bit through the end of the crack? Nothing, just do it.

 

If you spend a lot of time with your unibody Jeep twisted up think about doing some stiffening to reduce the impart of torsional flex.

 

2¢

[flint54]

"lack of torsional rigidity"....Exactly the words that came to mind as I looked at the images.

 

(either that, or the driver has some real serious digestive issues.....)

 

Seems to me that in order to get this much flex this high on the body, there must be

other weaknesses down lower. Imagine pinning LF and RR to the ground and quickly lifting

RF and LR, and then reversing, repeatedly. Real hard on sheet metal.

 

You could weld it, but you can't solve it, short of a roll cage.

[SW86]

i check for this constantly. i go hardcore offroad looking for places to get flex non-stop and (knock on wood) i havent had an issue

[reece146]

Seems to me that in order to get this much flex this high on the body, there must be

other weaknesses down lower.

 

It's more of a geometry thing. Think of a square cardboard box. Try to squish one edge of the box such that one of the faces change from a square to a rhombus, it's pretty hard.

 

Now cut a big hole in the same face and do the same thing... it collapses.

 

If you only apply enough force to load the box but not to collapse it, say a million times, rips in the cardboard will appear at the corners of the hole you have cut due to cardboard fatigue. Same thing happens in the metal of the cab of any vehicle.

 

I agree that some form of a roll hoop could help, provided it is designed properly and doesn't just cause other problems of course.

[Jeep Driver]

I really doubt the cracks are due to air pressure changes. Are you travelling on a lot of gravel and/or uneven roads?

 

These cracks are most likely due to a lack of torsional rigidity AND the truck being flexed out semi-regularly enough to have twist occur down the centerline of the truck. General unpaved road vibration can cause it too.

 

To fix them, drill a hole at the end of the crack. This will act as a stress relief so the crack doesn't go any farther down this path. Then weld the cracks up. Some say drilling the hole is not necessary since the welding process changes the metallurgy anyway but what does it "cost" to run a 1/8" drill bit through the end of the crack? Nothing, just do it.

 

If you spend a lot of time with your unibody Jeep twisted up think about doing some stiffening to reduce the impart of torsional flex.

 

2¢

 

 

You got it. And yes drilling the hole is the way to stop the crack from growing, it's the only way to stop it, the weld is the repair of the damage and not the fix for the cracking.

 

The cab in it entirety is the frame......that's what uni-body is. You stress the 'frame' you stress the entire cab.

[man-coche]

I really doubt the cracks are due to air pressure changes. Are you travelling on a lot of gravel and/or uneven roads?

 

These cracks are most likely due to a lack of torsional rigidity AND the truck being flexed out semi-regularly enough to have twist occur down the centerline of the truck. General unpaved road vibration can cause it too.

 

To fix them, drill a hole at the end of the crack. This will act as a stress relief so the crack doesn't go any farther down this path. Then weld the cracks up. Some say drilling the hole is not necessary since the welding process changes the metallurgy anyway but what does it "cost" to run a 1/8" drill bit through the end of the crack? Nothing, just do it.

 

If you spend a lot of time with your unibody Jeep twisted up think about doing some stiffening to reduce the impart of torsional flex.

 

2¢

 

Although the air presure changes may not be the resulting factor, :brows: I know and have seen it is a contributing factor. I mean when you're going down a level hwy and you see in your rearview mirror your back window flexing in and out only being held by the welt and sylicone. :eek: I mean when I am in the higher altitudes the exsiting cracks are alittle wider open than when I came from the city. :shake:

 

:wrench: But I am on the repaire, as you are right on with drilling a hole at the end of the crack to stop it from spreading.

 

And yes the roads here are mainly coble stone type and uneven blacktop at times in the city, but good and flate for the most part on the hwys, yet like wheeling offroad everywhere eise.

[dakal]

thanks for the tip. i'm ok

[reece146]

Although the air presure changes may not be the resulting factor, :brows: I know and have seen it is a contributing factor. I mean when you're going down a level hwy and you see in your rearview mirror your back window flexing in and out only being held by the welt and sylicone. :eek: I mean when I am in the higher altitudes the exsiting cracks are alittle wider open than when I came from the city. :shake:

 

:wrench: But I am on the repaire, as you are right on with drilling a hole at the end of the crack to stop it from spreading.

 

And yes the roads here are mainly coble stone type and uneven blacktop at times in the city, but good and flate for the most part on the hwys, yet like wheeling offroad everywhere eise.

 

You are driving a truck, not an aircraft - your cabin is not pressurized.

 

The pressure inside the cab is the same as outside of the cab with the exception of high and low pressure areas caused by the aerodynamics of the vehicle at speed.

 

I'd speculate the things you are seeing are due to other factors (poor roads causing accelerated metal fatigue) and the cab is already "worn out".

[Pete M]

could be a manufacturing defect too. ford had a similar issue with their truck door window corners a few years back.

[Exgrayxj]

:(

Saw this and went to look at mine...never noticed it before, but left and right both have about 1/4" cracks showing above the rubber trim at the top...damn, I thought the seam below the window swelling with rust was my only problem in that area! :doh:

[xjrev10]

My 88 2wd has cracks on both bottom corners of the rear window. No wheeling with this one obviously.