Yesterday ended early...broken sector shaft.

skylarkguy · Sep 19, 2013

So yesterday I'm cooking along. Newly sharpened blades on the brush hog making quick work of a neglected section of my yard. I got a little sideways in a ditch with the 2 right wheels in the ditch and the left wheels out. The steering was hard to the left. I tried to back out of the ditch to take a new cut and bam...instantly had no steering. The sector shaft of the steering box snapped right at the base of the pitman arm.

I managed to get it pulled out and turned around with a come along, chain etc. Then pointed it to the garage and walked back in low idle. Outside of the spookiness of walking next to your tractor and pushing on the front wheels to steer it, it went just fine.

Does anyone have any experience repairing a sector shaft? Anyone have a steering box they would be willing to part with or the internals to put mine back together? How about model interchangeability. Will an MT160 steering box fit my MT372 (found one relatively locally).

Hoping to mow the entire place. (12 acres) before the rains really start....blurgh!

Kernopelli · Sep 23, 2013

Mitsubishi used the same steering parts on a LOT of models. I would be surprised if the MT160 box wasn't compatible. Sector shafts are available online for many models... cheapest price I saw was $149 w/ free SH on Ebay. If you get your box apart and the shaft is 5 tooth, 15/16">1" Tapered, 36 splines, it appears to cross over to almost all the old Mitsubishi models.

skylarkguy · Sep 24, 2013

Well I called the guys in Dixon Illinois and they quoted me a price for a rebuilt box at over 400 bucks...contingent on a rebuild-able core. I took it to a machine shop in town and he said he could put it together for 95/hr. Minimum 2 hours. I found another guy locally and he looked at it as well. He quoted me a price of $100 to put it together...Here is what he did...( I mostly watched).

First we put dye on it to evaluate how well it was contacting the pitman arm. Turns out not too well. The arm was a bit wallowed out and the taper didn't contact very much. We decided that the shaft had been broken in the past and welded before. The weld penetration wasn't very much compared to the thickness of the shaft. Combined with the movement of the pitman arm it was only a matter of time.

Put it in the 3 jaw on the lathe

Set the angle of the lathe cutting head based on the previous taper of the shaft.

Ground a 45 degree angle on the shaft. Leaving a about 1/8 inch flat at the very point.

Did the same thing on the broken piece.

Flamed off the grease with a torch.

Put the 2 pieces together at the flat points on the lathe.

Checked for straightness.

Tacked the two together with Millermatic 251 mig welder. 70000 pound wire.

Rechecked for straightness. (no picture) The shaft was ultimately with 5 thousands of straight...
Continued to build up material...

Then slowly turned it back down on the lathe.

We then heat treated it. First is was heated up to cherry red and slowly brought back down to ambient temp in a container of sand.

I went home and did some other things while it cooled. It was then heated back up with torch and quenched in oil. At which point I picked it back up and did the last treatment. 1 hour in the oven at 425 degrees then left it in the oven while it cooled down overnight. Here is what it looked like at the end.

we had to do some cleanup of the pitman arm spline and a little on the shaft as well. I also assembled it with some permatex bearing mount for worn parts (item number 20297) for good measure.

I reassembled it and got it back on the tractor yesterday and put about 5 hours on the machine. The steering has never felt better.

Just FYI. Matt the guy who did this works out of his home and does machine fabrication and repair for a good rate. PM me for his number if you need help on metal working project.

LD1 · Sep 24, 2013

Thats a whole lot cheaper than I would do something like that for.

What did he have?? 4-5 hours in it??

skylarkguy · Sep 24, 2013

I rolled in at 9:15, rolled out at 11:30...so that is 2.25 hrs...a bit of time to do the heat and quench so say 2.5 hrs total. we chatted about it for about 45 minutes the night before so there is some time there. If anything I probably slowed him down by being around taking pictures etc.
I showed up and he had written a checklist for the entire process to keep things on track. I was pretty impressed. He is a rare breed indeed.