Welcome to ZK MasterTech.
Follow Master John Deere Ag Technician Zeth Key as he takes you behind the scenes of diagnosing, repairing, and rebuilding some of the most advanced farm equipment in the world. From massive 9RX tractors to S-Series combines, this channel shows the real work required to keep modern agriculture moving.
Zeth is a 2007 Automotive Graduate of WyoTech in Laramie, Wyoming and a 2023 WyoTech Hall of Fame Inductee. He currently works for Sloan Implement in Atwood, Illinois, bringing over 16 years of experience servicing and repairing John Deere equipment across central Illinois.
ZK MasterTech gives viewers an inside look at the technical side of agriculture — real diagnostics, field service calls, major repairs, and the problem-solving it takes to keep farmers running.
If you enjoy seeing big iron torn down, diagnosed, and put back to work, you’re in the right place.
Subscribe and follow along as we keep that green iron moving! 🔧💚
ZK MasterTech
Greta’s story is finally all in one place…
This John Deere 9100 started as a RUNAWAY… screaming up to 3,000 RPM — then turned into a no-start, a start-and-die, and one of the most drawn-out diagnostic fights I’ve dealt with.
This one tested everything.
The FULL Greta story drops tomorrow at 3:00 PM — start to finish, no jumping between videos.
If you’ve ever chased an issue that made zero sense… this one’s for you.
Be there 👊
Also, Spring 26' Service calls series will be coming soon! Who's pumped for that?
3 days ago | [YT] | 387
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ZK MasterTech
The FULL Lt. Dan story drops today at 3 PM.
This is the entire 9RX 640 saga — from catastrophic rear axle failure to complete rebuild — all packed into one 45-minute episode.
Zero lube pressure. Destroyed pinion gears. Full teardown. Precision rebuild. First fire-up.
And here’s the cool part — I kept this video under 60 minutes so it will be available in 22 languages. Right now they’re all processing.
Set a reminder — you don’t want to miss this one.
1 week ago | [YT] | 358
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ZK MasterTech
What was your favorite moment in the finale of LT. DAN the 9RX?
2 weeks ago | [YT] | 105
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ZK MasterTech
LT. DAN IS BACK. 💪
The 9RX 640 is finally back together — and with the wide stance tracks installed, this thing looks meaner and tougher than ever.
This wasn’t just a repair… this was a full comeback. And you already know we don’t do anything halfway around here.
Video drops TODAY at 3pm.
2 weeks ago | [YT] | 272
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ZK MasterTech
This one got BIG… real big 😅
Full 9RX differential rebuild!
We’re diving into:
🔧 Full differential assembly
⚙️ Setting preload & backlash
🔥 Assembling the Input housing
💪 And yeah… flipping some HEAVY iron around
This is one of the most in-depth repairs I’ve ever put on the channel.
If you’ve ever wanted to see what it really takes to set one of these up correctly — this is the one.
⏰ Dropping later today
👇 Who’s watching as soon as it goes live?
3 weeks ago | [YT] | 596
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ZK MasterTech
Don’t miss the update on LT. Dan the 9RX with no legs! And I have time for a couple service calls! Check it out now!
Coolant in the Intake?! John Deere 9530T EGR Failure + 8R 370 Diagnosis
https://youtu.be/OHeRLglJyIY
4 weeks ago | [YT] | 248
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ZK MasterTech
The rear differential is FINALLY out of the 9RX 640.
What we found on the pinion gear is something none of us expected.
Full video is live now:
https://youtu.be/WQsdG1iU6SY
1 month ago | [YT] | 595
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ZK MasterTech
The next chapter of the 9RX 640 teardown is finally here.
After discovering the failed pump stack that caused the rear axle to lose lubrication pressure, we had to tear half the tractor apart just to get to the rear differential.
Fuel tank, track belts, track frames, final drives, PTO, hitch frame… everything had to come off.
Today at 3 PM you’ll finally see the moment the rear differential comes out — and the damage to the pinion gear is something I’ve never seen before.
This one is wild.
See you at 3 PM. 👀
And as always — keep that green iron moving! 💚🔧
1 month ago | [YT] | 811
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ZK MasterTech
Today’s video is not a routine repair.
This machine came in with zero lube pressure — and what we found inside explains everything.
We’re talking:
• Major drivetrain damage
• Metal where metal should NEVER be
• Cab coming off
• Pump stack removal
• Digging deeper after the first failure revealed even more
This one snowballed fast… and the teardown only gets worse the farther we go.
If you like real diagnostics, real damage, and real decisions that cost real money — this is the episode.
Drops at 3PM.
1 month ago | [YT] | 765
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ZK MasterTech
Just got back from the National Farm Machinery Show 2026 in Louisville and it was awesome meeting so many of you at the Sloan Express booth. Thank you to everyone who stopped by the Meet & Greet — truly appreciate the support.
Once back in the shop, I tackled a catastrophic discharge beater bearing failure on a John Deere S790 combine that melted wiring and took out both bearings.
Then the big project finally arrived.
The 9RX 640 is now in the shop with no rear track drive, zero axle lube pressure, and completely destroyed pinion gears. I walk through the full diagnosis and explain what caused the failure and what it will take to repair it.
This is just the beginning of this major repair series.
Watch the full video here → https://youtu.be/wKKLABIGUmM
1 month ago | [YT] | 397
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