Shift interlock repair — Massey Ferguson MF20 baler (beginner mechanic). Direct, step-by-step, with component descriptions, theory, common failures, tools, safety, and tests. No questions.

Theory (why this is needed)
- Purpose: The shift interlock prevents the baler’s drive/gearbox or clutch from being shifted or engaged when unsafe (e.g., under load, or when components are out of position). It keeps the machine from trying to change gear or engage the plunger/knotter when teeth, dog clutches, or linkages would be forced, preventing damage and safety hazards.
- How it works (simple analogy): Think of it like a door latch that only allows the door to open when a key is turned. The interlock is the key/ latch combination: a lever/pawl holds a detent or lock plate until conditions (control lever position, PTO off, plunger parked) release it so the selector can move freely.
- Failure consequence: If the interlock sticks or breaks, you can’t shift, the gearbox may shear teeth, or the machine may unexpectedly engage causing jams, broken linkages, or injury.

Components and detailed descriptions (what to find and what each does)
- Shift lever / control lever: The operator’s handle. Connects by rod/linkage to the interlock assembly.
- Control rod / push-pull linkage: Steel rod or tube that transfers lever motion to the interlock or selector. Has clevis ends and cotter pins.
- Clevis, clevis pin, cotter pin: Fasteners that attach rods to levers; allow pivot. Cotter pins keep pins from working out.
- Interlock lever (pawl lever): Pivoting arm that either allows or blocks the selector. It bears against the detent plate or selector dog.
- Pawl (locking dog): The actual catch that engages teeth/notches on the detent plate or selector drum. Stops movement until released.
- Detent plate / notched plate / selector plate: Plate with notches that define allowed positions. Pawl rests in a notch to hold a gear position.
- Spring(s): Tension spring(s) pull the pawl into engagement or return levers to safe positions.
- Pivot pin / bushings / sleeves: Pivot points for the lever and pawl. Bushings wear and cause slop.
- Interlock actuator (if fitted): Could be mechanical or hydraulic depending on model and options. On mechanical MF20s it’s usually just levers/springs.
- Lock pin / safety pin: Some systems use a removable pin that physically locks mechanism for maintenance.
- Housing / bracket / cover: Mounting for the assembly and protection from debris.
- Linkage adjustment screws or stop bolts: Allow position fine-tuning.
- Fasteners: Bolts, nuts, washers, circlips holding parts in place.

Tools and parts to have
- Tools: set of metric/imperial spanners and sockets (common up to 19 mm), screwdrivers, pliers, needle-nose, hammer, punch, drift, bench vise, small pry bar, torque wrench (if available), grease gun, wire brush.
- Safety: gloves, goggles, chocks, supports (jack stands or blocks), lockout device for PTO/tractor.
- Consumables/parts: replacement spring(s), new clevis pins/cotter pins, pivot bushings/sleeves, replacement pawl or detent plate (if worn), grease, anti-seize, penetrating oil (PB Blaster), threadlocker (medium), rags.
- Optional: replacement selector plate or a OEM parts diagram/kit (good to have part numbers).

Safety first — do this before you start
1. Park baler on level ground, block wheels, put tractor in park/neutral, remove key.
2. Lower baler to ground and secure so it cannot move or drop. Support any raised components with stands/blocks before working under or around them.
3. Disengage and lock out PTO. Remove belt or disconnect power where applicable.
4. Wear eye protection and gloves. Keep hands away from pinch points while testing.
5. If working under covers, prop them securely.

Step-by-step repair procedure (practical, beginner-friendly)
1. Visual inspection
- Remove covers to expose the interlock/selector area (usually near the gearbox and shift lever).
- Clean off dirt, old grease, and rust with a wire brush and rag. Use penetrating oil where parts look seized.
- Identify the shift lever, interlock lever/pawl, detent plate and springs. Photograph connections for reassembly.

2. Check fasteners and pins
- Verify clevis pins/cotter pins are present and intact. Replace any missing or badly corroded cotter pins.
- Wiggle the linkage to feel for excessive play at pivots. Slop means worn pin/bushing.

3. Test operation by hand (no load)
- With PTO locked out and baler secured, move the operator lever and watch the pawl/detent behavior.
- The pawl should lift/clear the detent smoothly when lever is moved; it should spring back into notch cleanly.
- Note any sticking, grinding, missing notches, or inability to hold position.

4. Remove worn components
- If pawl, pivot pin or bushings are seized/worn, remove retaining circlip or bolt, drive out pivot pin, and extract pawl.
- Replace bushings/sleeves if worn. If bushings are pressed in, knock them out with punch and install new ones.
- Replace any broken or stretched springs. Springs must provide sufficient force to return pawl.

5. Repair or replace detent plate/selector
- Inspect notches for rounding/flattening. Slight burrs can be dressed with a file; major wear needs plate replacement.
- If the detent plate is bent or has missing teeth, replace it. Do not try to rely on a bent/weak plate.

6. Clean, lubricate, and reassemble
- Clean mating surfaces and apply light grease to pivots/bushings (do not use heavy grease where metal-to-metal engagement requires friction — some pawls need light oil; check component function).
- Reinstall pawl, pivot pin, spring, and secure with correct circlips/bolts/cotter pins.
- Ensure all clevis pins are tight enough to remove slop but free to pivot.

7. Adjust linkage
- Adjust control rod length/clevis so the lever reaches full travel and the pawl aligns with detent notches.
- Use stops/adjust screws to set neutral and engaged positions. Aim for minimal free-play but not binding.

8. Test under controlled conditions
- With covers off but area clear, re-engage PTO with a helper at low engine speed OR, if possible, slowly operate the control manually (without load) to verify smooth shifting.
- Listen for grinding or clunks. If something binds, stop immediately and re-check alignment.
- Final test with normal operation: small loads only initially; confirm the interlock holds position and releases correctly.

Adjustment specifics and what "right" feels like
- Pawl engagement: pawl should seat firmly in notch with positive stop — not bouncing out under slight movement.
- Return spring: strong enough to fully engage pawl when lever released.
- Linkage free-play: minimal but enough to prevent binding; about a few millimeters of play at the lever is typical for hand-actuated devices.
- If lever is too loose or won’t hold, reduce rod length incrementally to remove excessive free-play; if too tight, lengthen.

Common failure modes, diagnostics, and fixes
- Symptom: Can’t shift or pawl won’t release
Cause: Seized pivot from rust/grime, stuck spring, or bent lever.
Fix: Clean, free pivot with penetrating oil, replace spring/pivot/bushing as needed.

- Symptom: Shift lever moves but gearbox doesn’t change/position not held
Cause: Worn pawl or rounded detent notch; broken clevis pin; excessive linkage play.
Fix: Replace pawl/detent or pins; replace bushings; adjust linkage.

- Symptom: Interlock releases unexpectedly or pops out of position
Cause: Weak/incorrect spring, worn detent, missing retaining pin.
Fix: Replace spring; replace detent plate; confirm retaining hardware installed.

- Symptom: Grinding when shifting
Cause: Shifting under load because interlock didn’t fully engage; damaged dog teeth.
Fix: Inspect gearbox dogs/teeth; replace damaged parts, correct interlock function before reuse.

- Symptom: Continuous slop in lever
Cause: Worn bushings/pivots or stretched linkage.
Fix: Replace bushings/pins, tighten/replace linkage.

Tips, gotchas, and best practices
- Replace small fasteners: cotter pins, circlips and worn clevis pins are cheap and critical.
- Do not rely on heavy grease to fix slack. Worn metal needs replacement, not packing with grease.
- Compare parts to OEM diagrams when ordering. Take photos and measure lengths if uncertain.
- If detent teeth are damaged/stripped, do not attempt to operate the baler: replace plate or assembly first.
- Avoid overtightening pivot bolts — binds create false symptoms.
- If unsure about gearbox internal damage after a grinding event, stop and inspect internal dogs/gears; continuing risks catastrophic damage.

Final checks before returning to service
- All guards and covers reinstalled.
- All pins secured with new cotter or retaining clips.
- Linkage moves smoothly through full range.
- Perform slow, monitored test runs at low load, then normal load after confirming reliability.
- Keep a maintenance log: note replaced parts and adjustments.

Parts to replace commonly
- Pivot bushings/sleeves, pawl, return spring(s), clevis pins and cotter pins, detent plate (if worn), linkage rod if bent.

Closing (concise)
- The interlock is a mechanical safety catch: clean, replace worn pins/bushings/springs, align linkage, and test. Replace any worn detent/pawl rather than trying to jury-rig; that’s the usual cause of repeat failure. Always lock out PTO and support the baler before working.

That’s the full, practical repair and diagnostic walk-through suitable for a beginner mechanic.
rteeqp73

massey ferguson 20 baler balenpers Af gelopen zaterdag de mf 20 pers eens geprobeerd.

Haymaking Using Vintage Tractors / Baler ( 2018 ) Hi. Here I'm haymaking using vintage tractors / baler ( 2018 ). I'm using a Zetor 5545 (1968) and a Massey Ferguson 20-8 baler ...

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