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A new Place to look for frame cracks

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BowtieBlazer

Diesel Powered
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SO, I was unbolting the last two bolts on my tranny x-member and bang, it hits the ground. What the hell?
post-3-1144705956_thumb.jpg

I looked up at the frame:eek1:
post-3-1144706006_thumb.jpg


Yup, its cracked. I found this discovery very strange being that this was and has been a stock truck with the 305 and OD tranny with 31" tires its whole life. And very rarely offroad at that....this is on a 1986 Blazer
Looks like I have some welding to do....
 
Great post. A lot of us out here probably wouldn't think to check there for cracks. I had that happen on a previous K5. I just made up my own repair like you are gonna do. I wonder if boxing the frame would be a good idea? Good luck in your repair.
 
Was anything else wrong that could have contributed to it?
 
Obviously not a common problem, but I wonder if that didn't/doesn't happen because the later truck crossmembers moved the bolts so close to each other compared to all previous.

You can see on the crossmember the "outboard" bolts, that's about how far the earlier crossmembers spaced them.
 
That would make sense huh? I didn't even notice how close the holes are until you mentioned it.
 
As an aside, it was a stock truck, so were those metal spacers on the bolts as well? (still no idea why GM started using them)

Any evidence that the bolts had been loose previous to you taking it apart, and had been allowed to hammer the frame constantly?
 
The metal spacers are to enable use of a longer bolt. Short bolts don't hold troque very well. The longer the bolt, the more it will strectch during torquing and hold that torque better. This is vastly more important on 'critical' bolts, like the ones holding the steering box to the frame. Those have long metal bushings on them as well.
 
I've seen a couple cracked around the trans crossmember. Also, if you want to look for more cracks, I've seen more cracks around the rear shock mounts than the trans crossmember. In the past couple of months I have seen probably 4 trucks with either a crack, or a repaired crack on the rear shock mounts on the frame.
 
koldsimer said:
Was anything else wrong that could have contributed to it?
Click to expand...
Nope, the bolts I bet had never been loosened, the previous owner drove this truck as a work truck from 86(new) to 88 then bought it from his company and I have a file folder 4" thick with routine maint from 88-04 when I bought it. The guy didnt hunt and had maybe taken it offroad a handful of times, with 120K on it....drove like a caddy...my theory is the same as:

dyeager535 said:
Obviously not a common problem, but I wonder if that didn't/doesn't happen because the later truck crossmembers moved the bolts so close to each other compared to all previous.

You can see on the crossmember the "outboard" bolts, that's about how far the earlier crossmembers spaced them.
Click to expand...

I plan on using my old crossmember anyway. I really think the close spacing and a bad tranny mount could do that.

Just a little suprise...:rolleyes:
 
Do you have the cross member that ties to the upper and lower c sections of the frame. I've seen some that just bolt up to the bottom. If yours' just ties to the the lower section, I would probably go to the junkyard and get the other type that has a branch to tie into the upper frame section as well.
 
Correct me if i'm wrong but it looks like you did the old drop teh t-case by putting the spacer between the crossmember and frame trick. Right? I've seen this in several trucks in our club, The spacers localize the stress around the bolt hole leading to the cracking that you have, you shouldn't need to totally box the frame, do a good repair. Maybe even plate that area, but when you put it back together use square tube or a solid block of steel or even a stack of 1/4 plate instead of the spacers to spread the load out over a large portion of the framerail.
 
My 86 cracked there too. After I repaired it. I used some large flat washers to spread the load.

John
 
mouse said:
I've seen a couple cracked around the trans crossmember. Also, if you want to look for more cracks, I've seen more cracks around the rear shock mounts than the trans crossmember. In the past couple of months I have seen probably 4 trucks with either a crack, or a repaired crack on the rear shock mounts on the frame.
Click to expand...
Just looked at a neighbors '86 3/4T 4x4 Burb. One owner little old lady from Florida, so no rust. LR shock mount broken right off! Client has a '90 1/2 V6 5 speed 4x4, LR shock mount rotted off, and cracked, but rest of frame not too bad...
 
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