Goldoni differential case repair

[svcguy]

I know cast iron welding is always a good topic, but thought I would offer a brazing example. Purchased a nice little Goldoni Base 20 (John Deere 20A) with 208 hours. The owner had water in the rear differential that froze solid (locking his left rear wheel) and he tried to free it up by repeatedly dumping the clutch in low range first gear. Well, apparently it worked, dragging the ice right up inside the final drive bull gear, hitting the drive and exploding through the case and axle tower. Bad for him, good for me since it took about $4000 off the value of the machine. The bull gear, axle and diff drive unit which were damaged were $1000. A new case would be another $1000, so I decided to braze it back together. Note the axle spline twist, that little Lombardini diesel has some torque. The hole in the case is where a section of the bull gear pushed through. The drive stub is the result.

 

[svcguy]

It was also unfortunate that he never kept the broken piece (or pieces) that came off the case, so I decided to create a weldment. Since welding a steel insert into a cast iron block presents a few challenges, I decided on brazing it in. I prepared the case and welded up the new piece out of four pieces of scrap (the curve, the web, the top and an inside stub to be drilled and tapped for the missing stud).

 

[svcguy]

A good friend of mine (a mill wright) has a lot of experience brazing and welding cast iron, so I had Dale braze it in. We heated the entire fixture with a propane rose bud to about 300 degrees, then heated up the area to be fixed and brazed it. While watching Dale, I realized I tend to overheat the material I braze, so it was a worthwhile experience. After, I took a carbide and blended it into the case.

 

[svcguy]

Last step was to mill the flange surface flat and clean up. Needed to spot a few areas with a carbide to fit the axle tower in and now just need to drill and tap for the stud. Once it's finessed a bit and painted, I think it will look pretty good. Brazing a part like this in is quite strong and I don't anticipate any issues.

 

[dynasim]

I havve never heard of brazing cast iron. Can this be done for cracks, as well as this sort of thing? Does it prevent the cracking associated with trying to weld it with nickel?

That repair turned out beautiful. Thanks for sharing.

Chris

 

[yomax4]

Brazing Cast is an easy option and holds fairly well as long as there is not a lot of expansion and contraction going on. The 2 base metals expand and contract at very different temps. Low Fuming Bronze ( Brazing Rod ) is not nearly as hard as Nickel but it has good ductillity so it can take some flexing.. In applications where there is a combustion chamber or exhaust it gets a little more tricky and Powder or Stick Nickel is best. I did braze a pillow block once that is still holding. Just clean, clean, clean and use plenty of flux.

 

[BeezFun]

Guys like you are what made this country great, looks like you could do anything. I have brazed cast iron once, and it turned out so horrible looking I'll never try it again. It held, but I don't even walk by that corner of the manure spreader when I use it because I can't stand to see it.

 

[svcguy]

I have had some challenges brazing cast iron in the past, but after working with Dale I realized I had just been putting too much heat to the cast. When brazing cast, it seems best to follow a couple of steps for success.

1) Right before brazing, freshen up the surfaces with a burr or brush well (stainless).
2) Preheat the entire piece evenly with a propane torch (weed burning bud) or oven.
3) Right temp is up for debate, but 250-350 degrees seems good for preheat.
4) Heat area to be brazed, but it's important not to overheat.
5) When the cast is beginning to be a very (very) dull reddish color, try tinning the area with a prefluxed brazing rod. Tinning the surfaces slightly ahead of brazing as you go works well. Melt the rod into the V, filling and melting as you go along.
6) When finished, use the big torch again to heat areas more evenly.
7) Cool down everything as slowly as practical using welding blankets or heat. The old timers used to bury critical pieces in lime and leave it until cold, often a couple of days.

Cracks can be filled but should be ground U shaped prior to brazing. Some people like to freshen the surfaces with a file, as the carbon in cast can smear and braze will not stick to the carbon. This is why overheating is a problem, burning out the metal and contaminating the surfaces with migrating carbon.

Brazing is strong, much stronger than people think. Many planes, motorcycles and racing vehicles have brazed frames. A good example is the Caterham Lotus, which I believe still brazes the frames. Elongation and strength are quite good when the right rod is used. Very forgiving with cast iron. In this case we used 'Super Bronze', a common, general use prefluxed rod.

 

[turbo36]

Guys like you are what made this country great, looks like you could do anything. I have brazed cast iron once, and it turned out so horrible looking I'll never try it again. It held, but I don't even walk by that corner of the manure spreader when I use it because I can't stand to see it.

When did we annex Canada?:laughing:

 

[svcguy]

He actually said "Guys LIKE me made America great". That means Canadians get some recognition too, which is pretty nice. I'm just going to take the compliment and run with it! Thanks BEEZFUN.