They Bought a 12k Hour Dozer at Auction & It’s a $50K Nightmare

This 12k-hour John Deere 850J was bought at auction… and it turned into a $50,000 nightmare.
Finals destroyed, missing parts, bad previous shop work — and that was only the beginning.
The customer’s John Deere 850J showed up with the right final “locking up.” We dug in and found the left side had been butchered by a previous shop—missing parts, ruined threads, the works. We fully rebuilt both finals (new bearings/gears), cleaned/retapped hardware, sealed everything up, and used a Milwaukee porta-power to release the brake and line up splines without a fight.

Then… after we hung the ripper, the left track intermittently crept backwards and nearly turned the dozer into my toolbox. Final drives were clean, transmission filter was clean—problem pointed to control. We jacked the cab and replaced the original PCP (pressure control pilot) on the left pump (the right had been replaced previously). Also tidied some scary 24V cable routing. One self-own: we lost a funnel cone into the tank while pulling vacuum, so we dropped the sight glass and went fishing… then refilled with fresh oil on our dime.

Result: multiple test runs, smooth tracking, no noise beyond “12k-hour dozer sounds.” We left calibration alone since it was tracking true. Customer gets two fresh finals, rebuilt brakes, fresh High-Guard-spec oil, and a new PCP. Fingers crossed it stays out of the shop… but you know how that goes. 😅

0:00 “Professional fork truck driver”… fired 😂
0:16 What’s wrong with this 850J? Customer complaint & previous shop mess
1:02 Rebuilt finals: bearings, gears, hardware, sealing (Loctite 515, O-rings)
1:46 Releasing the brake w/ porta-power (target ~300–350 PSI) to align splines
3:36 Lining up the motor & splines; dowels and forklift ballet
5:14 Sprocket alignment tricks; turning with brake released
7:03 Button-up: sealant, O-rings, anti-rust/“rust-jacking” prevention
11:12 Fill procedures (JD High-Guard spec), inside vs outside quantities
12:47 First fire-up & spin test — sounds right
15:25 Ripper install… then sudden track lock/creep scare
27:35 Diagnostics: finals/trans filter clean → suspect control, not gear train
29:04 Plan: order PCP valve, raise cab, chase intermittent control issue
30:00 Under the cab: pumps layout, what PCP/EDCV do, wiring concerns
34:44 Swap the PCP (left pump), cable tidy, hardware refresh
36:44 Oops: funnel cone into tank → sight glass off → fishing mission
38:20 Refill with fresh oil; controlled tests with cab up
41:00 Tracks straight; no calibration since it’s true
44:58 Heat, hardware, and reassembly marathon
46:45 Extended test run — passes; minor ripper bolt replaced
49:05 Root cause recap & cost reality on old iron
50:22 Wrap-up, merch, and subscribe

#JohnDeere850J #Bulldozer #ConstructionEquipment