Lessons learned....

[3rdgendslmech]

I'm sure we've all been in a position at some point in our career where the boss or company owner wants their equipment up and running ASAP.
So a couple years ago the company I work for purchased a spare transmission for our 4 D8N tractors that we use to push up deicing salt.
It takes me and another mechanic 6-8 hours to do a swap out, vs a week + waiting on parts while the machine is down.

About a month ago a transmission in 1 D8 goes out ( 1st gear clutch pack worn out and would push ), I swapped it out, changed filters, screens and sent it on its way. Been running every day since with no problems.

Rebuilt the transmission that I pulled out and about the time I was going to set it into a storage box, a different D8 loses its forward clutch pack. Pulled the screen out and found rubber that had gotten hot and stuck to the screen filter in the bottom of the transmission. Different mechanic took this job as I was busy working on trucks that week. He did the same thing I did, swapped the transmission, flushed the system and power train oil lines, rebuilt the trans. control valve, changed filters etc etc..... A whole 12 hours later what happens??? No forward in any speed. Right away all fingers get pointed at me because lets face it I rebuilt the transmission. So I go take a look real quick in between working on trucks and find the screen once again packed full of melted rubber. So now I take on the task of figuring out "did I miss something somewhere" or is it "operator error" or maybe the other mechanic missed something.

Well this particular D8 is a 5TJ serial # and the other 3 are 9TC serial numbers so the main difference in the transmission is that the priority valve is mounted on top of the frame above the transmission instead of being bolted to the control valve of the transmission itself. Started with checking pressures before I pulled the 2nd burnt up transmission out, brake release pressures good on both sides. Pump pressure good. Speed and direction (other than FWD due to blown clutch piston seals) good. Trans lube pressure good. What isnt good......priority valve pressure....FML :Banghead At an idle i had 380 PSI, cat recommends 420 give or take 20. After about 15-20 minutes of doing other tests, a phone call and what not priority valve pressure is only reading 100 lbs.

Come to find out that a 3 dollar o ring on a check valve had blown and started dumping oil caused the death of 2 transmissions. Now I know some companies have procedures when doing rebuilds as far as setting and checking pressures after repairs. But when the owner says he wants it up and running by morning, you kind of skip a few steps. Turns out this one cost him about 2K in parts plus my time.

 

[Nige]

I think we've all been there. The question I always have is why does it end up costing SO much money to put the problem right..?

 

[dirty4fun]

Not enough time to do it right, but plenty of time to fix it latter. To bad it happens that way, on some jobs.

 

[lantraxco]

It's called a learning curve... some are steeper and more painful than others.... mine usually look like a wall, lol.

 

[Shimmy1]

I think we've all been there. The question I always have is why does it end up costing SO much money to put the problem right..?

If they didn't cost as much as they do, we wouldn't learn from them. We would call them an "oops" instead of a lesson.

 

[inthedirt]

Well.... i guess i have one too. Customer says his dipper (stick, to the non-Case folks) lever is locked up. When i get there not only the lever physically unmoveable, but the dipper will free-swing. Found out the piston bolt came loose, trashed out the inside of the cylinder and sent a huge handful of metal chunks into the control valve. The metal really didn't go farther than the work port of the valve, but it scarred up the spool and bore. We swung in a new cylinder and control valve. Before hooking up the lines for the dipper circuit, i used brake clean and a rubber-tipped blowgun to blow out both lines both directions several times. I figured this would flush out any debris left. I put it all together, changed oil and filter and back to work. Customer calls a day later, says it ran 2 hours and did the same thing. Sure enough there was another wad of metal in the dipper work port. Took the new cylinder apart and it was very apparent that debris had been smashed against the end of the piston, and then worked between the piston and tube and trashed out the cylinder again. I wish i could point the finger somewhere else, but there obviously was metal debris left in the hoses. I guess i learned the lesson that just because air will go though cleanly doesn’t mean there isn't still chunks that oil will dislodge.