D8 trackframe broken..

Wow, that looks nasty.....it isn't just about "gluing" it back together......the challenge will be aligning the track frame so there is a chance of keeping the rails straight and parallel.

Yep, common problem on old tractors with high hours and that have been worked hard on rock. The older channel-type track frames are more prone to this problem than the later boxed style (the boxed-style was supposed to be the solution to track frame cracking) .. but the boxed ones crack, too. I've fixed numerous broken D6 and D7 boxed-style frames in this exact area.

Just jack up the frame .. align the broken sections with a string line .. vee out the crack .. practise your very best 7018 vertical weld .. 😄 .. and then grind the weld, and fishplate the area with a 12"-15" long, 1/2" thick plate, that has tapered ends.
Run the welds on the fishplate down the taper, but then run them out parallel, so they don't join. This eliminates stress areas and any further cracking.

The alignment problem isn't something to get too concerned about .. you can get alignment reasonably accurate using a string line .. then adjust idler shims/sprocket hub adjustment to align the track components.

You can get real perfectionist about alignment, when rejoining these two broken sections .. then you find that the front two extensions of the frame, each side of the idler, are twisted, anyway .. and creating more misalignment than you'd get with a misaligned join in this area.

If ya wanna do it factory-style, you'd pull the whole frame, strip it .. then lay it out on a jig, and measure every dimension, in every plane, to make it perfect. That might be O.K. for a company D11, but you're operating an old wreck, compared to most company operations.
Fixing old dozers isn't a perfect science, you gotta do what you can, generally under some adverse conditions, and within a very tight budget.

To me the bigger problem is what's going on with the inner track frame brace.....which is now carrying (bending) with the load. Good chance you will need to cut the diagonal brace loose from the frame, repair the track frame rail then weld back the brace when you've got it reasonably aligned.

Would have been nice to fix that at the first sign of cracking. I agree with Oz I'd be jacking and trying to weld that best I could. Then go about adjusting the tracks. What ever is bent is going to be near impossible to straighten. And with such a beat machine you could make more problems. Weld it up and see what happens what do you have to loose. Good luck

I don't see any problem with the track frame inner diagonal brace. The inner brace is there to keep the track frames aligned in a horizontal plane and parallel. There may be a slight twisting action being applied to the inner brace, but nothing that it can't withstand.

The wear in the inner brace bearing will usually compensate for any slight twisting. If a lot of old tractor owners got the measuring tape out, and accurately measured track frame misalignment (in the vertical plane, the horizontal plane, and for parallel), they'd likely be totally appalled at what they find .. at what they never suspected .. but which is still performing O.K.

Track frames are notorious for regular misalignment. Not 6 mths after I took delivery of my new D6C's, Cat issued a re-design/upgrade order, involving reinforcing patches for the D6C inner braces .. which consisted of plating the entire length of the braces with a huge "Y"-shaped fishplate, to strengthen them.

I am always inpressed with Old Magnet, OzDozer, and SJ there is not much that you guys have not done or seen. thanks for adding to the BB whenever possible.

Horizontal and parallel alignment is what I'm referring to. The shims on the final hub and front idler will only allow side movement.....doesn't do a thing if you have a "dog tracking" undercarriage. See what you can get jacking the frame, but if you can't get the dog tracking or twist out of the assembly I'd still cut the inner arm loose (maybe closer to the inner bearing journal) and re weld.
Depends on how bad it is. Seen lots of "cobbled up" undercarriage.....it all does work for a while.

Hi Guys
Thanks for all the responses. Lots of things I didn't think to do. One thing I'm still unclear about is if this section of the track frame is hollow or is it a c-channel. It appears to be attached to a big cast piece going around the front of the sprocket. I've got my wife pressure washing the machine today so I'll have a better look tonight after work. I walked it about a mile uphill to my shop with my brother watching the crack. It opened and closed going over any bump. When I parked it I got the crack to close up and the track frame is straight by measuring the clearance from the idler end to the frame. Same on both sides and same on the other 14a I have. So I'll string it and weld it.
I'll take pictures of the progress.
LeRoy

In checking the parts book it appears the broken section is boxed with a short fish plate blocking the ends. The break is at the weakest point...between the rebound spring buttress and the bearing block.