Summary first: transmission fluid (gear oil) leaks on an MF35 usually come from failing seals or gaskets or from loose/drained plugs. Fixing them means: find the exact leak source, remove the component that gives access to the seal or gasket, replace the seal/gasket correctly, clean and reassemble, refill with the correct gear oil, and test. Below I give the working theory, a clear description of every relevant component, what commonly goes wrong, and step‑by‑step repair procedures and practical tips for a beginner mechanic.

Why this repair is needed (theory, simple)
- The gearbox/transmission contains gear oil to lubricate gears and bearings and (on tractors with combined systems) to supply hydraulic/remote lift systems. If oil leaks out, lubrication drops, bearings and gears overheat and wear quickly, clutch operation can be affected, and hydraulic lift performance can suffer. Left too long, leaks lead to major gear and bearing damage and a much more expensive rebuild.
- Seals and gaskets are the barriers that keep oil inside while letting shafts and bolts pass through. They are like the rubber around a door hinge: flexible to allow movement but tight enough to keep water out. Over time seals harden, shrink, or get cut; gaskets compress or get gouged; bolts/threads can loosen → oil finds a way out.

How the system works — components and what each does (detailed)
Think of the transmission as a sealed “box” that changes torque and speed (gears) and moves that power out through shafts (PTO, rear axles). Components:

- Gearbox housing / case: cast metal box that holds gears, shafts, bearings and oil. It has ports for filler/dipstick, drain plug, and bolted covers. Surface faces between parts use gaskets or sealant.
- Gears: input gear, layshaft (cluster) gears, main/drive gear(s). They mesh to change speed/torque.
- Input shaft: the shaft coming from the clutch/engine into the gearbox. Has a rotating seal where it enters the box.
- Output shaft(s): shafts that carry power out — PTO shaft, rear drive shafts/axles. Each shaft that passes through the housing has a seal.
- Bearings: support the shafts inside the case. If bearings wear, shafts can wobble and cut seals.
- Oil seals (shaft seals): rubber or lip seals pressed into housings around shafts to prevent oil passage. Often called radial shaft seals. They have a metal case and flexible lip(s).
- Gaskets: flat compressible material between cover to case joints (e.g., top cover, side cover, tail housing). They fill small irregularities and keep oil in.
- Filler/dipstick and breather: filler/dipstick tube to add/check oil; breather allows pressure equalization. If breather is blocked, pressure can build and force oil out seals.
- Drain plug: bolt at bottom to drain oil; has crush washer or O-ring on some models to seal.
- Clutch housing / bell housing: separates engine clutch and gearbox; the gearbox input seal can be here or inside clutch housing.
- PTO housing, rear housing, hydraulic pump interface (on tractors with live hydraulics): these areas have seals/gaskets where shafts and pumps connect.

Common leak locations on MF35 (typical)
- Input shaft seal where gearbox meets clutch/bell housing.
- Output shaft/PTO seal at rear of gearbox.
- Top cover gasket (shift cover) or selector housing gasket.
- Drain/filler plug crush washers.
- Rear tail housing / linkage gaskets (around the three-point lift housing).
- Breather/vent blocked forcing oil out.
- Seals around hydraulic pump or its fittings (if fitted).

Diagnosis — find the leak (do this first)
1. Safety: park level, engine off, handbrake on, wheels chocked. Disconnect battery ground if you’ll be under the tractor or removing heavy parts.
2. Clean: degrease the gearbox and surrounding areas (brake cleaner or parts cleaner) and wipe dry. This removes old oil so you can see fresh leaks.
3. Inspect: start engine briefly or run on low idle with stationary tractor (if safe), watch where fresh oil starts to appear. Use a piece of cardboard under suspected areas to catch drips.
4. Use UV dye (optional): add a small amount of fluorescent dye to the gearbox oil, run briefly, inspect with UV lamp to pinpoint leak.
5. Check fasteners: sometimes a loose cover bolt or drain plug is the cause. Check tightness (not over-tightening). Also inspect breather: blocked breather will push oil out seals.
6. Note whether oil is coming from a shaft seal, flange gasket, or a plug — this determines repair steps.

Tools, supplies, and parts you’ll need
- Basic hand tools: socket set, spanners, screwdrivers, pliers.
- Seal puller / pry bar; small slide hammer (helpful for stubborn seals).
- Bearing puller or gear puller (if removing shafts).
- Torque wrench (important — follow manual torque specs).
- Gasket scraper and wire brush.
- New seals (correct size/type for MF35 — buy by application: input seal, output/PTO seal, etc.). Use correct material (Nitrile/HNBR recommended for gear oil).
- New gaskets or gasket material and sealant (per manual: some joints require anaerobic/sealant, others gasket only).
- New crush washer for drain plug if needed.
- Clean rags, degreaser, solvent.
- Replacement bearings if bearings show wear.
- Gear oil of correct grade (consult manual; typical older tractors use SAE 80W-90 hypoid gear oil — confirm).
- Jack and axle stands or appropriate supports; wooden blocks.
- Gloves, eye protection.
- Catch pan for old oil, and container to dispose of used oil legally.

Step-by-step repair procedures (typical leak points)

A. Simple fixes first (easy; try these before full teardown)
- Tighten drain/fill plug and replace crush washer. Procedure: drain a small amount if needed, remove plug, fit new washer, torque to spec (or snug if spec unknown but don’t overtighten).
- Clear/replace breather: remove and clean or replace breather cap. A blocked breather can force oil out seals.
- Replace top cover or shift housing gasket: drain oil enough to drop cover, remove bolts, lift cover, replace gasket and reseal per manual.
- Replace visible external O-rings or hose fittings (on hydraulic lines or pumps).

B. Replacing a shaft seal (input or output/PTO) — general method
Note: exact steps vary depending on whether the seal sits inside a removable cover, the tail housing, or the clutch/bell housing. Below is a general approach.

1. Safety & access:
- Park, chock wheels, disconnect battery.
- Raise rear if necessary and support on stands. Remove three-point linkage or PTO components that block access (mark positions for reassembly).
- Remove wheels if needed for access.

2. Drain gearbox oil:
- Place drain pan, remove drain plug, drain fully. Keep old oil for inspection if needed.
- Reinstall drain plug with new washer and hand‑tighten for now.

3. Remove components blocking seal:
- For input seal: you usually must remove clutch assembly and possibly bell housing or separate clutch housing from gearbox. Mark/clutch plate alignment if disassembling clutch.
- For output/PTO seal: remove PTO shaft, rear flange or tail housing bolts to access the seal.
- For rear axle seal: may need to remove axle or end housing.

4. Remove the old seal:
- Pry out seal carefully with a seal puller. Avoid scratching the bore or shaft. If seal lip is very tight, cut it and pull out in pieces.
- Inspect the shaft surface where the seal rides. Look for grooves, pitting, or scoring. A lightly grooved shaft may be polished with fine emery cloth; deep grooves require replacement or sleeve.

5. Inspect bearings and bores:
- If shaft wobble or rough bearings were present, replace bearings now. A failing bearing will ruin a new seal quickly.
- Clean the bore and check for corrosion or burrs. Lightly oil the new seal lip with gear oil.

6. Install new seal:
- Use the correct orientation (lip towards oil). The seal lip typically faces the oil side.
- Use a seal driver or socket of correct diameter and tap evenly until the seal sits flush. Don’t install cocked — ensure full seating.
- If the seal has an outer metal case, it may require a press or careful tapping. Don’t hit the lip or damage the rubber.

7. Reassemble:
- Refit any housings/shafts/clutch. Replace gaskets where parts mate; use sealant only where manual specifies.
- Torque bolts to spec (if you don’t have manual, torque evenly and don’t overtighten — overtightening can distort parts and cause leaks).

8. Refill with correct oil, check level:
- Refill to recommended level. On MF35, gear oil grade is commonly 80W-90 hypoid, but confirm with the manual for your specific MF35 model.
- Replace filler/dipstick and run engine briefly, put transmission through gears (if safe), and recheck for leaks.

C. Replacing a top/side cover gasket (shift cover)
1. Drain oil to below cover level.
2. Remove bolts and lift cover. Note any shims or detents; keep parts in order.
3. Clean mating surfaces, remove old gasket material. Don’t gouge surfaces.
4. Fit new gasket or use approved gasket maker as the manual allows. Replace any dowels or seals.
5. Reassemble, torque bolts evenly, refill with oil.

What can go wrong (and how to avoid it)
- Misdiagnosis: replacing the wrong seal wastes time. Always clean and observe to be sure of leak source.
- Damaged shaft surface: a scored shaft will cut a new seal. Inspect shaft and repair/replace if needed. Don’t ignore bearings.
- Installing seal backwards: lip must face oil. If installed backwards, it will leak immediately.
- Imperfect seating: seal installed cocked will leak. Use correct driver and seat flush.
- Over-tightening bolts or damaging threads: use a torque wrench and follow specs. If thread damage occurs, use helicoil/repair kit properly.
- Not replacing bearings when needed: new seal on bad bearing is temporary fix. Check bearings for play and roughness.
- Using wrong seal material or size: match the seal type and dimensions exactly.
- Not replacing gasket or using wrong sealant: surfaces that require a new gasket must get one or leak returns.
- Not addressing breather: if blocked, pressure will force oil out new seals.
- Cross-contamination or wrong oil: use recommended oil — some tractors need specific types for wet clutches or hydraulic compatibility.

Practical tips and beginner mistakes
- Work clean. Dirt contaminates seals and gear oil.
- Keep parts organized: take pictures/mark parts if you remove multiple pieces so you reassemble correctly.
- Use new crush washers and fresh gaskets.
- Don’t pry on mating faces with excessive force — casting can crack.
- If bearing replacement is needed and you are unsure, consider a local shop for pressing bearings. Pressing shafts/bearings needs care.
- If you can feel axial play in shafts, investigate bearings and internal gearbox wear.
- If the gearbox has been run very low on oil, check internal parts for overheating or discoloration (blue/black gear edges), and metal filings — may indicate internal damage.

Testing after repair
- Refill oil to correct level, run engine to normal temp, cycle gears, and watch for leaks while running and after shutdown.
- Recheck oil level after a short test run and again after a day’s work — small leaks may appear when oil warms and expands.
- Road/field test under normal load and recheck for leaks and oil level.

Environmental & safety
- Dispose of used oil properly at a recycling center.
- Wear gloves and eye protection; support tractor securely — heavy components can crush.
- Use correct lifting equipment; don’t crawl under a tractor supported only by a jack.

When to get professional help
- If shafts or bearings need pressing out/in and you don’t have the tools.
- If internal gear damage, severe wear, or multiple leaking points exist — a gearbox shop may be better.
- If you are unsure about clutch re-indexing or alignment after removing the clutch.

Quick checklist for a typical seal replacement job
1. Clean area & identify leak.
2. Gather correct replacement seal(s), gaskets, oil, tools.
3. Support tractor safely, drain oil.
4. Remove obstructing components to access seal.
5. Remove old seal, inspect shaft & bearings.
6. Install new seal correctly, clean surfaces, fit new gasket.
7. Reassemble, torque bolts, refill oil.
8. Test run and inspect for leaks, recheck oil level.

Final note
Do the job methodically. The most common causes of repeat leakage are misinstalled seals, damaged shaft surfaces, and neglected bearings. Replace the seal only after confirming the sealing surface and bearings are in good condition. If you follow the diagnostic steps and the installation care above, you’ll have a good chance of a durable repair.

No yapping — done.
rteeqp73

Safety first: wear eye protection, gloves, block the flywheel, disconnect battery, and relieve any stored energy. Work with a valve spring compressor or securely support the valve when removing retainers — compressed springs can cause injury.

Ordered procedure with theory (MF35 pushrod OHV engine — rocker-cover/top-end access):

1) Preparation and diagnosis (theory)
- Symptom/why: Weak or broken valve springs cause valve float, reduced compression, misfire, rough running, loss of power, backfiring and burned valves. Confirm symptoms and inspect for noisy valve gear or visible broken spring.
- Get the MF35 workshop manual for valve clearance and torque specs, and new springs/retainers/keepers of correct spec.

2) Access the valve gear
- Remove rocker cover and any obstructions (air cleaner linkages, fuel lines) to expose the rocker assembly and pushrods.
- Theory: You must remove components that prevent access to the top of the valves and springs.

3) Set engine to a safe position
- Rotate the engine to TDC on the compression stroke of the cylinder you’ll work on first, or place the piston at mid-stroke to prevent valves dropping into the cylinder if you remove springs and keepers.
- Theory: At TDC on compression, both valves are closed and the cam lobe for that cylinder is on its base circle, making spring removal safer and easier.

4) Remove rocker assembly or individual rocker (as needed)
- Loosen and remove the rocker shaft/clamps or individual rocker arms to free the pushrod and expose the spring retainer.
- Theory: On MF35-type pushrod engines the rockers and pushrods obstruct direct access to the valve spring retainers; removing them gives straight-line access for a compressor and prevents damage to rockers/pushrods.

5) Remove pushrod and mark orientation
- Pull out each pushrod and keep them in order; mark them so they return to their original locations.
- Theory: Pushrods are paired to lifters and wear patterns match; swapping can introduce noise and uneven wear.

6) Inspect components before disturbing springs
- Check valve stems, retainers, collets (keepers), spring condition, and tappet faces. Note carbon build-up, pitting, cracks, broken coils, or sagged springs.
- Theory: Springs with reduced free length, broken coils, or rusted retainers are mechanical faults that reduce spring seat pressure or allow slippage.

7) Use a valve spring compressor
- Fit an appropriate compressor (top-side compressor for remove/fit through the rocker area). Compress the spring until the keepers clear the retainer groove. Remove the keepers, then the retainer and spring.
- Theory: Compressor relieves spring load so keepers can be removed without the valve dropping suddenly. Proper tool ensures safe controlled removal.

8) Inspect valve and guide condition
- With spring off, slowly depress the valve and check for guide wear (rocking) and valve-seat condition. Look for bent valve stems, scored stems, or poor seating.
- Theory: Weak springs can allow valves to float and bounce, leading to seat damage and burned edges; replacing springs may not fix badly damaged seats/valves — these must be repaired.

9) Measure old spring(s)
- Measure free length and compare to new part spec; if you have a spring tester, measure seat and open pressures at specified lift. Replace springs that are out of spec or inconsistent between cylinders.
- Theory: Replacement is based on loss of spring tension (sag) or asymmetric springs causing uneven valve control.

10) Fit new spring, retainer and keepers
- Place the seat (if separate), the spring, and retainer. Compress with the valve spring compressor, drop the keepers into the retainer groove, and carefully release the compressor to seat the keepers.
- Theory: New spring restores correct closing force and dynamic control across the cam profile; correctly seated keepers retain the spring under dynamic loads.

11) Reassemble pushrod and rockers
- Refit pushrods in original order and reinstall the rocker shaft or individual rockers, lightly tightening to hold but allowing adjustment.
- Theory: Correct reassembly preserves original wear patterns; re-torquing to spec avoids rocker movement or shaft distortion.

12) Set valve clearances
- Rotate the engine to the appropriate cam position (usually base circle for the valve being adjusted) and set tappet/rocker clearances to the factory cold spec.
- Theory: Correct clearance ensures valves open/close at the intended cam timing and provides a thermal expansion allowance; too tight gives burned valves, too loose gives noise and lost lift.

13) Torque and final assembly
- Torque rocker shaft bolts, valve cover, and any removed components to spec. Reconnect fuel/air/electrical lines removed earlier.
- Theory: Proper torque keeps the valve train geometry stable under load; leaks or loose parts cause misalignment and wear.

14) Run-in and test
- Start engine, listen for abnormal valve noise, check for smoking, misfire, and oil leaks. Recheck clearances after a short run and again after the engine reaches operating temperature and has cooled.
- Theory: New springs may seat and settle; rechecking ensures clearances remain within spec and that dynamic behavior is correct.

How the repair fixes the fault (concise theory)
- Valve springs provide closing force and control valve motion against the cam and inertia. If springs are weak/sagged/broken they cannot keep the valve seated at high rpm or under load, causing valve float (valve not following cam), loss of compression, misfires, overheating of valve faces, and potential valve-to-piston contact.
- Replacing springs restores the specified seat and open pressures and spring rate. That returns correct valve closing speeds and contact with the cam/lifter, eliminating float, restoring compression and combustion timing, preventing burned seats and unintended valve motion — hence resolving the symptoms.

Quick inspection/acceptance checks after repair
- Measure valve clearances to spec, ensure consistent compression across cylinders (compression test), smooth idle and power delivery, and absence of valve clatter or unusual noises.

End notes (brief)
- Use correct MF35-specified parts and clearances. If valves/seats or guides are badly damaged, spring replacement alone won’t fully restore performance — head work or valve refacing/seat replacement will be required.
rteeqp73

Certainly! Here’s a breakdown of the theory behind fuel pump replacement on a Massey Ferguson MF35 tractor, along with the steps involved, and an explanation of how the repair addresses the fault.

### Theory of Fuel Pump Functionality

1. **Role of the Fuel Pump**: The fuel pump is critical in supplying fuel from the tank to the engine. It creates the necessary pressure to ensure a consistent flow of fuel for combustion.

2. **Common Failures**: Fuel pumps can fail due to wear, corrosion, or clogging. Symptoms include engine stalling, difficulty starting, or a lack of power due to insufficient fuel delivery.

3. **Repair Purpose**: Replacing a faulty fuel pump restores proper fuel flow and pressure, ensuring the engine receives the right amount of fuel for optimal performance.

### Fuel Pump Replacement Steps

1. **Preparation**:
- **Tools and Parts**: Gather necessary tools (wrenches, screwdrivers, etc.) and a new fuel pump compatible with MF35.
- **Safety Measures**: Disconnect the battery to prevent sparks and ensure safety.

2. **Locate the Fuel Pump**:
- The fuel pump is typically mounted on the engine block or near the fuel tank. Familiarize yourself with the fuel system layout.

3. **Drain Fuel**:
- If necessary, drain the fuel tank to prevent spillage and ensure a clean work environment.

4. **Disconnect Fuel Lines**:
- Carefully detach the fuel lines from the old pump. Use a container to catch any residual fuel. Note the orientation and connections for reassembly.

5. **Remove Old Fuel Pump**:
- Unscrew and remove the mounting bolts holding the old fuel pump in place. Take the pump out and inspect the gasket and mounting surface for debris.

6. **Install New Fuel Pump**:
- Position the new fuel pump in place, ensuring the gasket is intact and properly seated. Secure it with the mounting bolts.

7. **Reconnect Fuel Lines**:
- Reattach the fuel lines to the new pump in the same orientation as noted earlier. Ensure they are tight to prevent leaks.

8. **Reconnect Battery**:
- Reconnect the battery terminals.

9. **Test the System**:
- Turn the key to the "on" position to prime the fuel system without starting the engine. Check for leaks around the connections.
- Start the engine and observe its performance. Ensure it runs smoothly and responds well to throttle input.

### How the Repair Fixes the Fault

Replacing the fuel pump resolves issues caused by inadequate fuel delivery, such as stalling or difficulty starting. A new pump restores the necessary pressure and flow rate, allowing the engine to operate efficiently. This repair eliminates symptoms of fuel starvation, ensuring the engine has a reliable fuel supply for combustion.

By understanding these principles, you can appreciate how this repair directly impacts the functionality and reliability of the Massey Ferguson MF35 tractor.
rteeqp73