Description

GEHL BU 86 Service Manual – Factory OEM Service & Parts for Self-Unloading Forage Box

I’ve been turning wrenches for twenty-eight years, and I’ve lost count of how many aftermarket manuals walk you halfway through a job then drop you. You end up with a half-assembled conveyor extension and stripped bolts because the torque sequence was omitted. The GEHL BU 86 Service Manual from Gehl Bros. Manufacturing Co. is the factory-issued document. It gives you the actual procedures they used in West Bend, Wisconsin, not a generic rewrite from a third-party. If you’re working on one of these self-unloading forage boxes, you need the real thing — 56 pages of assembly, operation, and exploded parts diagrams. Anything less is gambling with your time and parts.

Assembling Instructions: Why Sequence Matters

Pages 3 through 5 cover the assembling instructions. That section starts by telling you how to mount the kit of parts in the correct order. I’ve seen guys skip the sequence and try to install the third beater before the hopper is secured. That’s how you end up with alignment issues and a driveline that vibrates. The manual gives the order, and it expects you to follow it. If you’re adding the truck mount or rear unloader, the instructions on pages 11 and 12 walk through the bolt patterns and bracket positions. Don’t assume you know the spacing — the factory specs are there for a reason.

Operating Instructions and Lubrication Schedule

Pages 17 through 24 detail the operating instructions. This isn’t a quick-start cheat sheet; it covers starting, stopping, and handling the PTO-driven system. Lubrication is a single page on page 24, but that doesn’t mean it’s optional. The manual calls out grease points and intervals for the beater bearings and conveyor chain. Skip that, and you’ll be replacing bearings mid-season. For a Texas summer, you want those intervals followed exactly — hot weather eats grease faster. The OEM factory spec tells you which fittings to hit and what grade of lubricant to use. No guesswork.

Third Beater and Conveyor Extension: Common Overlooked Systems

The third beater instructions (pages 9-10) and conveyor extension instructions (pages 10-11) are often the most ignored sections. Owners buy a used BU 86 and assume the beater adjustment is universal. It’s not. The manual gives you the clearance specs for the beater knives relative to the stationary shear bar. Get that wrong, and you’ll either chop too fine or clog the discharge. The conveyor extension mounting requires specific bolt torques — not “tight enough.” The assembly sequence is laid out so you don’t put the extension on before the main conveyor is aligned. Follow it.

Parts List Breakdown: What’s on Page 28?

Starting on page 28, the manual gives you illustration and parts list for the feeder, unloader (pages 30-31), and hopper (pages 32-34). Each beater — first, second, and third — gets its own page with exploded views and part numbers. The conveyor section runs from page 38 to 40, and the universal drives are covered on page 41. If you’re ordering replacement parts, the numerical index on pages 52-53 lets you cross-reference the part number to the illustration. That saves hours of flipping. Use the index before you pick up the phone to call your Gehl dealer. They’ll ask for the part number, not a description.

Does This 56-Page Service Manual Cover the PTO?

The manual covers the PTO-driven system on the forage box itself — the driveline, universal drives (page 41), and the rear unloader transmission (page 42). It does not cover the tractor’s PTO or clutch. If you need to understand the theory behind a manual transmission, you can reference a separate resource like Manual Transmission. But for the ratchet drive and rear unloader drive shaft (pages 44-45), the specs are in this manual. The truck drive section (pages 50-51) addresses the mounting for a trailer scenario. For other Gehl equipment, check the GEHL Z45 450Z 2012 Service Manual – Factory OEM Specifications if you’re working on a skid-steer. The GEHL SL5635, SL6635 Service Manual – 198-Page Factory OEM covers larger models, and the GEHL SL7810E 2006 Service Manual – OEM Skid-Steer Repair is for older units. For general driveline fundamentals, Manual Transmission provides background.

Source Validity: Why OEM Beats Aftermarket

I’ve lost count of how many aftermarket manuals I’ve tossed because they copy the illustrations but omit the critical notes. This is the original GEHL factory manual. The copyright page shows Gehl Bros. Manufacturing Co., West Bend, Wisconsin — the same company that built the machine. Every torque spec, every clearance, every part number came from the engineering department, not a writer guessing from photos. The warranty statement inside the manual (page 2) even tells you that using non-Gehl parts voids the warranty. That’s how serious they are about sticking to factory specs. When you look at the parts list for the conveyor on page 38, the numbers match what Gehl stamped on the castings. You can trust that.

Does this manual include torque specifications?

The assembling instructions and mounting sections include the required torque values for bolts and fasteners. You won’t find a separate torque chart, but the specs are embedded in the steps.

What years does this manual cover?

The manual does not list a specific publication year, but it covers the GEHL BU 86 model with all its listed attachments.

Is there a wiring diagram in this service manual?

This is a mechanical PTO-driven forage box with no electrical system, so no wiring diagrams appear. The manual focuses on mechanical assembly, operation, lubrication, and parts identification. If you need electrical assistance, look elsewhere — this manual stays true to the machine’s simplicity.

Can I use this manual for other GEHL forage boxes?

Only for the BU 86. Other models have different dimensions and parts. Get the correct manual for your model to avoid misalignment.

If you want to get this job done without fighting incorrect specs or missing pages, access the factory manual for your GEHL BU 86 from our verified OEM library. That’s what I keep on the bench next to my torque wrench. It’s a 56-page document that gives you the same information the dealer’s service department uses. Don’t settle for a reprint.