When you weld metal is pulled away from the surrounding area towards the bead, creating "stress points". That big crack looks like its in that stress point area next to the panhard bar drop mount. Years of bashing the front end to and fro probably torques that spot and viola, you get a little crevase formed in the weak spot.
I had that same crack on my 91. Noticed after a run my steering wheel was a little off center & changed when I turned from stop to stop. A welder buddy of mine welded & plated it while I held the steering cranked to close up the gap. Been fine ever since.
Jon, there is a small crack coming from the lower left steeringbox bolt hole, but the big crack is on the under side of the frame kinda like the stress is from the drag link mount
Also pics that describe the EXACT same location as yours.
Like I said, this is a common stress point and a poor design IMO (one of the few). The steering box is only supported by the outer frame rail. There are spacers on the inside that locate the box properly, but there is no support from the inner frame. It is under constant flex and the metal simply fatuiges over time.
I had the same cracks in mine, and also on the inside around all the steering box bolt holes. This is extrememly common and I have seen at least 10 80 series with the same issues. Other cracks apear around the panhard rod bracket, this can actually crack so bad it falls off the chassis. Also wear the radius arms attach via brackets to the diff housing, these can crack at the welds so bad that diff oil runs out of them. I'm sure most of you have those cracked and dont know about it.
Don't feel special.
I have two 93 RHD HDJ81's and they have bioth had fracracks around the steering miounts and panhard pillar mounts.
They do not fully weld around the spigot tubes that are fitted through the frame rails for the steering box mounts. Thsi eventually results in cracking from the weld area due to the repeated stresses on this area. Fully welding in the spigot tubes stops this from becoming a major problem. I have a fereind who had to install a steel plate in this area as his frame was so badly cracked before it was noticed.
The panhard tower also has the cracking problem. The harder you wheel things the bigger the stresses on the tower. Remember it is the only thing in the front of the vehicle that is keeping the front axle centered under the frame and must resist all the side loading on the front end.
The best thing to do is get a competent welder to grind out the area of cracks and lay in some quality welds. Check the area frequetly especially after washing the vehicle. ( you do wash it don't you? )
Not too worried about that frame, I picked up a totaled out 93. You know how insurance companies work, 16 year old truck gets a good hit and they total it. So I'm swaping my body and suspension over, along with gussets on all panhard and upper/lower links mounts.
I never thought I was the first or only person to crack an 80 frame, I just wanted those who where unaware or this to go look at there frame and check. Better safe than sorry, right...
Thought I'd add some pics of my damage. I knew I had small stress cracks around the steering box holes and it was on my list of things to fix but it never got done. Yesterday while driving into my garage i heard a metal clacking sound while doing tight turning. After some investigation I found it was the frame seperating aling a 6" gash and then smacking back together again!
Oh well, hopefully I'll have it fixed by the end of the day, it's a good thing I'm slow at work right now. Here's some pics of the extent of the damage.
There is even a crack across the top, if you look hard you can just see the line. Good thing I caught this when I did.
Considering how much stress the gear box and that whole area in general see with wheeling, I am not surprised.
The common areas of stress:
1. Front control arms to axle housing
2. Steering gear box to frame rail
3. Panhard to axle housing and frame rail
4. Rear panhard
5. rear lower control arms to frame and axle housing.
Get the grinder out, get the welder out, and get to work as Jon says.
EDIT: Since I have my gear box off....here are pics of my rust belt rig.....
It's funny this thread popped up today. I just got back from a little wheeling. I noticed a rattling sound after crawling through a washout, I went on a wiggling expedition under the truck and found my passenger side radius arm completely separated from the axle! It cracked on the radius arm side of the weld all the way around, I didn't lose any gear oil like I've heard some have.
I had inspected for cracks a few months back when I fixed my frame around the steering box and found nothing, guess I missed it. The other radius arm held the axle straight so there was no other damage. I was able to use all my ratchet straps to hold it together and limp home. I'll post some pics when I fix it, I'll probably re weld the other one as well.
Slight surface rust, but shiny metal in the middle. My thoughts are it just fatigued over the years and finally had enough. I think the fact that I wheel with the sway bar in adds to the stress, I might have to look into making some disconnects. My driverside has some stress cracks as well that I'll have to grind out and re weld before it gets any worse.
