What you’re doing: “Gear ratio adjustment” on a Toyota Hilux normally means changing or correctly setting the final-drive (ring-and-pinion) geometry and backlash in the rear (or front) differential so the gears mesh correctly and give the desired ratio. This is not a simple “turn a screw” job — it’s precision mechanical set-up. Below I’ll explain the theory, every major component you’ll touch, the tools, a clear step-by-step overview of the procedure, what can go wrong, and how to check the work. Read everything before you start and get the factory service manual for the exact specs for your model/year.

Why this is done (theory, in beginner terms)
- Purpose of final drive: The engine/transmission output spins the driveshaft. The pinion gear (small) on the driveshaft meshes with the ring gear (large) fixed to the differential carrier. That pair converts rotation 90° and multiplies torque (depends on their teeth count — the gear ratio). A lower ratio (numerically higher, e.g., 4.11:1) gives more torque at wheels, higher ratio (lower numerically, e.g., 3.73:1) gives higher top speed.
- Why adjust: If you change tire size, swap a transmission, fit a different ring-and-pinion set, or replace worn bearings/gears, the ring & pinion must be installed and adjusted precisely. Wrong setup causes noisy gears, poor power delivery, premature bearing/gear failure, and incorrect speedometer readings.
- Analogy: Think of the pinion and ring as two interlocking bicycle chainrings. If they’re not aligned (depth/backlash incorrect), the chain will skip and wear. Correct alignment keeps the “teeth” engaging smoothly.

Key components and what they do
- Pinion gear: Small gear driven by the driveshaft. Converts longitudinal rotation to drive the ring gear.
- Pinion bearings (inner and outer): Support the pinion, keep it in the correct axial and radial position. Their preload is critical.
- Pinion seal: Keeps gear oil from leaking out where the driveshaft enters the housing.
- Pinion nut / crush sleeve or shims: Holds pinion preload. Older designs use a crush sleeve (single-use) that the pinion nut crushes to set preload. Some use shims for fine adjustment.
- Ring gear: Large gear bolted to the differential carrier. Works with the pinion to transfer torque to the carrier.
- Carrier (differential carrier/case): Houses the spider gears and supports the side gears. The ring gear is bolted to it.
- Carrier bearings: Support the carrier in the housing. Backlash is set by moving the carrier left/right using shims or an adjuster.
- Carrier bearing caps: Bolts that clamp the carrier bearings in the housing. Torque sequence/values are important.
- Backlash-adjusting shims or screw-type adjusters: Change the carrier’s lateral position to set how far the ring gear is away from the pinion (backlash).
- Spider gears/side gears and axle shafts: The differential internals that let the wheels rotate at different speeds while sharing torque.
- Axle seals and axle shafts: Seal and transmit drive to the wheels.
- Differential housing and cover: The housing contains and supports everything; the cover seals the gearbox and holds oil.
- Gear oil and gear marking compound: Lubricant for normal operation, marking compound for checking tooth contact pattern.

Important tools and what they’re for
- Factory service manual or ring-and-pinion spec sheet (must-have for torque and spec numbers).
- Proper-size sockets, breaker bars, torque wrench (for caps and pinion nut).
- Hydraulic jack and good jackstands (safety).
- Dial indicator with magnetic base (measures backlash).
- Gear marking compound (to check tooth contact pattern).
- Pinion depth tool or dial-caliper method (sets pinion depth).
- Micrometer / calipers (measures shim thickness and dimensions).
- Bearing puller / press (remove/install bearings).
- Dead-blow hammer, brass drift, seal driver set.
- Bearing race driver or press.
- Pinion nut socket and breaker bar (heavy torque).
- Crush sleeve tool (if installing crush sleeve).
- Shop press (for pressing bearings/races).
- Clean rags, solvent, gear oil pump.
- Torque angle gauge if required.
- Threadlocker and sealant as specified by manual.

High-level procedure (step-by-step overview — detailed but safe)
Note: This is a precise mechanical task. Use the factory manual for exact specs (torque, backlash range, pinion depth) and required part numbers (ring & pinion are a matched set). Many steps require special tools and clean, controlled conditions. If you are not confident pressing bearings and setting preload, get a shop to do it.

1) Preparation and safety
- Work on level ground. Chock front wheels. Jack vehicle and support on jackstands under the axle housing and frame. Never rely on a jack alone.
- Remove wheels and parking brakes as necessary. Drain differential oil and remove the cover (or remove whole axle shaft assemblies where required).
- Clean the housing and inspect for obvious damage/corrosion.

2) Remove components to access ring & pinion
- Remove axle shafts or half-shafts per the model procedure (C-clips on some Hilux models; hubs or flange bolts on others).
- Remove the carrier bearing caps and support the carrier as you remove it. Mark bearing cap orientation and placement — they go back exactly where they came from and in the same orientation.
- Remove the old ring gear from the carrier (if you’re replacing rings). Mark orientation of carrier and ring gear if reinstalling same parts (but usually ring & pinion replaced as a matched set).

3) Inspect parts and replace as necessary
- Ring & pinion should be replaced together as a matched set. Replace worn/damaged bearings, races, pinion seal, shims/crush sleeve as needed.
- Clean the housing thoroughly — no dirt, no old compound.

4) Install pinion and set pinion depth and preload
- Install new inner pinion bearing and race. Lubricate per manual.
- For pinion depth: some installations use shims or a specific pinion-depth tool. The depth is the lateral distance from a reference on the housing to the pinion center and determines where the pinion teeth meet the ring teeth.
- Fit the pinion and new outer bearing and install the pinion nut. If the axle uses a crush sleeve, tighten the nut carefully to the prescribed torque to crush the sleeve and achieve correct bearing preload. For shim-type, use the correct shim thickness and torque the nut to spec.
- Check pinion bearing preload (radial play) per manual (using a torque wrench on the pinion nut to feel rotational torque, or measuring endplay). Set to specification. Too loose = noisy and worn bearings; too tight = binding and heat/failure.

5) Install ring gear on carrier (if using new set) and mount carrier
- Bolt ring gear to carrier and torque bolts to spec in proper sequence.
- Install carrier with new or checked bearings. Do not fully torque bearing caps yet — follow manual.

6) Set backlash
- Backlash is the small amount of movement (lash) between ring and pinion teeth. It’s measured with a dial indicator at the ring gear teeth while you try to rock the ring back and forth.
- To change backlash, add or remove shims behind the carrier bearings (or use screw-type adjusters). More shim one side moves the carrier closer/further to the pinion.
- Aim for the factory backlash spec range. Typical backlash values vary by vehicle and ring gear size — use the manual. Typical method: hold dial indicator tip on one tooth, rotate ring to the other side of the tooth and read the bite (movement).
- Adjust shims in small increments and re-check until within spec.

7) Check gear tooth contact pattern
- Apply gear marking compound to several teeth on ring gear. Rotate the ring several revolutions by turning the pinion (not by rotating wheels under load) and check the contact pattern left by the compound.
- Ideal pattern: centered on the tooth face (not too close to heel or toe, and not too close to the face or flank). The pattern location tells you whether pinion depth is correct (pattern fore/aft) and whether backlash is correct (pattern lateral position).
- If pattern shows contact too close to the face or toe, pinion depth is wrong — adjust pinion shims/crush sleeve and repeat. If pattern is offset circumferentially, adjust backlash via carrier shims. Repeat checking until pattern is ideal.

8) Final bearing preload and torques
- Once pattern and backlash are correct, torque the carrier bearing caps to spec. Ensure bearing preload is correct (turning torque or measured preload per manual).
- Install the pinion nut to final torque; install and tighten any lock tab, nut-retainer, or procedure required.
- Install pinion seal and axle seals, using new seals.

9) Reassemble, fill, and test
- Install differential cover with new gasket/sealant, torque bolts to spec.
- Reinstall axles/wheels; refill with specified gear oil to correct level.
- Test drive and listen for noise. After a short break-in distance, re-check carrier cap torques and gear oil level. Some manuals recommend re-torquing after initial miles.

What can go wrong (and how to avoid it)
- Wrong tooth contact pattern: causes noise and rapid gear wear. Avoid by iterative checking with gear-marking compound and adjusting pinion depth/backlash.
- Wrong pinion preload: too loose → bearing wear and noise; too tight → bearings overheat and fail. Set preload precisely (measuring rotational torque or endplay) using the specified method.
- Wrong backlash: too tight → binding and heat; too loose → gear knock and broken teeth. Use dial indicator and correct shimming.
- Re-using parts incorrectly: Ring and pinion are a matched set — mixing halves can produce wrong contact pattern and failure. Always replace as a set when worn.
- Using wrong shims or incorrect shim order or mis-marking bearing caps: mark everything when you disassemble. Bearing caps and shims belong in specific positions.
- Over-torquing or under-torquing carrier caps or pinion nut: follow torque specs exactly.
- Contamination: dirt or grit in bearings/gears → rapid wear. Work clean.
- Seals not installed correctly: leaks lead to oil loss and failure.
- Not using correct axle oil: wrong viscosity or additive can damage limited-slip components.

Symptoms that tell you the differential needs work
- Growling or howling at steady speed → likely worn or improperly set ring & pinion/backlash.
- Clunking on acceleration or deceleration → excess backlash or worn spider gears/axles.
- Vibration or binding → possible bearing preload or assembly problems.
- Oil on the outside of housing or wheels → leaking pinion or axle seals.

Checks after repair
- Measure backlash with the dial indicator to confirm it’s in spec.
- Verify correct tooth contact with gear-marking compound.
- Check rotational torque/feel of the carrier per the manual (some measure inch-pounds).
- Road test gently, then re-check mounting bolts, torques, and oil level after warm-up and after initial miles.

Practical tips for a beginner mechanic
- Get the factory service manual for your exact Hilux year and diff type — specs and sequences differ.
- Do the job in a clean, well-lit area with a bench and tools. Pressing bearings and measuring need space.
- If you don’t have a press, pinion depth tool, or the ability to press and set bearings precisely, consider having a reputable machine shop or differential specialist do the press-fitting and setup, or at least check your work.
- Take many photos and mark parts during disassembly so reassembly goes back the same way.
- Replace bearings, seals, and the crush sleeve (if applicable) rather than trying to re-use them.

Wrap-up
Adjusting ring-and-pinion geometry and gear ratio is precise work: the goal is correct pinion depth, correct pinion bearing preload, and correct backlash so the tooth contact pattern is centered and even. Do it methodically: measure, adjust, measure again. If you follow the manual, use proper tools, keep things clean, and take it slow, you can do it — but if anything feels uncertain (press-fit bearings, interpreting patterns), a specialist will save you time and money in the long run.
rteeqp73

### Tools Needed:
1. **Socket Set** (including ratchet and extension)
2. **Wrench Set**
3. **Pliers**
4. **Hose Clamp Pliers** (optional but recommended)
5. **Screwdriver Set** (flat and Phillips)
6. **Fluid Catch Pan**
7. **Rags or Shop Towels**
8. **Replacement Hoses** (specific to your model)
9. **Hose Clamps** (if not reusing old ones)
10. **Safety Glasses**
11. **Gloves**

### Safety Precautions:
1. Ensure the vehicle is parked on a level surface, and the engine is cool.
2. Wear safety glasses and gloves to protect against coolant and debris.
3. Disconnect the negative battery terminal to prevent electrical issues.

### Step-by-Step Replacement of Hoses:

#### Step 1: Identify the Hoses
- Determine which hoses need replacement (e.g., radiator hoses, heater hoses, etc.).

#### Step 2: Prepare the Work Area
- Place a fluid catch pan under the vehicle to catch any coolant or fluid that might spill.

#### Step 3: Remove the Old Hoses
1. **Loosen Hose Clamps:**
- Use pliers or a screwdriver to loosen the clamps holding the hoses in place. If using hose clamp pliers, position them properly to grip the clamp and squeeze to release.

2. **Remove Hoses:**
- Gently twist and pull the hoses off. If they are stuck, you may need to wiggle them back and forth.

3. **Drain Fluids:**
- Allow any remaining coolant to drain into the catch pan.

#### Step 4: Install New Hoses
1. **Position New Hoses:**
- Compare the old hoses with the new ones to ensure a proper fit. Position the new hoses onto their respective fittings.

2. **Secure with Hose Clamps:**
- Slide the hose clamps back into position, ensuring they are tightly secured around the hoses. Use pliers to make sure they are sufficiently tight to prevent leaks.

#### Step 5: Refill Coolant
- If applicable, refill the cooling system with the appropriate coolant type, following the manufacturer’s specifications.

#### Step 6: Test for Leaks
1. **Reconnect Battery:**
- Reconnect the negative battery terminal.

2. **Start Engine:**
- Let the engine run for a few minutes, checking for leaks around the new hoses.

3. **Check Fluid Levels:**
- After the engine has warmed up and cooled down, check the coolant level and top off if necessary.

### Common Pitfalls to Avoid:
- **Using Incorrect Hose Size:** Always verify that the replacement hoses match the specifications of your vehicle.
- **Overtightening Clamps:** This can damage the hose and lead to leaks.
- **Forgetting to Refill Coolant:** Ensure the system is filled before running the engine after replacement.
- **Not Checking for Additional Damage:** Inspect surrounding components for wear or damage while the hoses are removed.

### Conclusion:
Replacing hoses on a Toyota Hilux is a straightforward process if you follow the steps carefully. Ensure you have the right tools, take safety precautions, and double-check your work to avoid common mistakes.
rteeqp73

Short version first: the “blow‑by tube” on a Hilux is the hose that routes crankcase vapors (blow‑by) from the valve cover/oil separator back into the intake (or to the turbo inlet) so they can be burned instead of vented to atmosphere. Repair usually means: inspect/replace the hose, clean/replace the oil separator/PCV valve and grommets, and restore seals so crankcase pressure and oil carry‑over are normal. Below is a beginner‑friendly, step‑by‑step guide with component descriptions, why it’s needed, how it works, and common failure modes.

Why this repair may be needed (the theory)
- Combustion gases leak past piston rings into the crankcase (this is “blow‑by”). Those gases contain unburned fuel, combustion gases and oil mist. If allowed to vent to atmosphere, you get oily smoke, contamination and emissions problems.
- The PCV/crankcase ventilation system collects those gases and routes them back into the intake to be burned. If hoses/clamp/grommets/PCV components fail, crankcase pressure can build, oil is pushed out (seals/gaskets leak or oil gets into intake), and performance/emissions suffer.
- Think of the system like a lung/air filter: the engine breathes out through the crankcase and this system filters and redirects those gases back into the “mouth” (intake). If the “airway” is blocked, pressure builds and oil leaks like water forced from a squeezed sponge.

Main components and what each does (with simple analogies)
- Valve cover (top of engine): houses the valve train and contains the crankcase vent ports; acts like the engine’s head “lid.”
- Grommets/seals (rubber seals where hoses plug into the valve cover): keep the seal between the hose and valve cover. Analogy: the rubber gasket on a bottle cap—if it fails, the bottle leaks.
- Oil separator / PCV valve / breather assembly: separates oil droplets from the blow‑by gas and often contains a one‑way valve. Analogy: a tea strainer that lets vapour pass but catches the oil droplets.
- Blow‑by tube / hose (rubber/plastic hose from valve cover to intake/turbo): carries the cleaned gas back to the intake. Analogy: the snorkel tube for the engine’s “breathing.”
- Clamps (spring clamps or worm‑drive clamps): hold the hose onto fittings so it won’t pop off.
- Intake manifold/turbo inlet where the hose connects: the destination for the breather gas.
- Valve cover bolts and gasket (if you need to remove the cover): keep oil contained; replacing cover seals is often required if they leak.
- Crankcase (inside the engine): where the blow‑by accumulates.

Tools and parts you’ll typically need
- Basic hand tools: ratchet, metric sockets (8–14mm common), screwdrivers, pliers
- Hose clamp pliers or screwdriver for worm clamps
- New blow‑by hose (OEM or quality aftermarket), new grommets, new clamps
- New valve cover gasket and gaskets if you remove cover
- Replacement oil separator / PCV valve if worn/clogged
- Rags, parts cleaner (degreaser), toothbrush or small brush, compressed air (optional)
- Drain pan for catching oil, gloves, safety glasses
- Torque wrench (recommended when reinstalling valve cover bolts; consult factory manual for torque values)

Step‑by‑step repair (beginner friendly)
Preparation and safety
1. Work on a cool engine. Hot parts and oil will burn you. Park on level ground, set the parking brake.
2. Disconnect the negative battery terminal if you’ll be removing sensors or the valve cover—safer and avoids accidental starts.

Locate the blow‑by tube
3. Remove any engine covers or components blocking access (many Hilux models have a plastic engine cover that pulls off). The blow‑by hose runs from the valve cover (top of the engine) to the intake manifold or turbo inlet. Trace the hose visually.

Inspect before removing
4. Look for oil deposits around the hose ends, wet valve cover, oil pooling under the truck, or oil in the intake. Check hose for cracks, hardening, soft spots, kinks or collapsed sections. Check clamps and grommets for age and brittleness.

Remove the hose
5. Loosen the clamp(s) at both ends (or squeeze spring clamps) and gently twist and pull the hose free. If it’s stuck, break the seal carefully with pliers or a flat screwdriver and lift—don’t slice the hose. Catch any oil that drips.
6. Inspect the hose interior: look for heavy oil sludge, cyan/black gummy deposits or metal shavings (metal indicates internal engine wear).

Inspect and replace oil separator / PCV valve and grommets
7. Many Toyota engines have a removable oil separator or PCV valve housed in the valve cover or attached inline. Remove it per its mounting screws/clips. Check or replace the one‑way valve (fits inside the separator) — it should allow flow from valve cover to intake but not the other way.
8. Inspect grommets where the hose plugs into the valve cover. If brittle, cracked, or flattened, replace them—these are common leak points.

Clean passages and parts
9. Use a rag and parts cleaner to remove oil and sludge from the valve cover port, oil separator, and hose ends. Use a small brush to clean stubborn deposits. Compressed air can blow out loose deposits (wear eye protection and block ports so debris doesn’t go inside).
10. If the oil separator is clogged with thick sludge, replace it. Cleaning sometimes works, but replacement is usually safer.

Replace hose and reassemble
11. Fit new grommets/clamps as needed. Install the new blow‑by hose, push it fully onto the fittings, and secure clamps snugly. Don’t overtighten worm clamps—the hose or plastic fitting can be damaged. Spring clamps should be seated evenly.
12. If you removed the valve cover: inspect and replace the valve cover gasket, clean mating surfaces, re‑install the cover and torque bolts in the proper sequence to the specified torque (consult the factory service manual for your model/year). If you don’t have the manual, tighten evenly and moderately—do not over‑torque.

Testing and post‑repair checks
13. Reconnect the battery if disconnected. Start the engine and let it idle. Watch for oil leaks around hose connections and valve cover. Feel the replaced hose for movement and sniff for strong fuel/combustion smells indicating a leak.
14. Check engine vacuum/idle stability. If the engine idles rough or the check engine light returns, you may have introduced a vacuum leak by a loose/disconnected hose or damaged grommet—recheck all connections.
15. Road test and watch engine oil level over the next few days; continued oil consumption or smoke indicates deeper problems (worn rings, turbo seals, clogged EGR).

What can go wrong (failure modes and how to spot them)
- Cracked or collapsed hose: causes vacuum leak or blocked flow; symptoms: rough idle, check engine light, oily smoke.
- Failed grommet or loose clamp: oil leaks at valve cover; visible oil seepage and smell.
- Clogged oil separator/PCV valve: high crankcase pressure, oil pushed out of seals, oil in intake; symptoms: excessive oil consumption, blowback at oil filler cap, poor turbo performance if turbo inlet gets oil.
- One‑way valve failure: allows boosted pressure back into crankcase (on turbo engines) causing pressurization and leaks, or fails to vent under vacuum.
- Turbo seal wear: lets oil into intake—looks similar to PCV issues; inspect turbo for oil leaks and exhaust for blue smoke under boost.
- Excessive mechanical blow‑by (worn piston rings/cylinder walls): causes lots of blow‑by that even a good PCV can’t handle. Symptoms: very oily intake, white/blue smoke, high oil consumption. This is an engine overhaul job.
- Broken plastic fittings or valve cover damage when removing/putting back parts: replace damaged parts and use correct torque when reassembling.

Troubleshooting quick checklist
- After replacement, still oily intake? Check turbo seals and air filter housing for oil. Remove and inspect PCV/oil separator again for clogging.
- Rough idle after reconnect? Find vacuum leak at the hose ends or a disconnected sensor.
- Oil pooling under vehicle after stop? Follow leak to source—valve cover gasket or hose connection.

Maintenance tips to avoid repeat problems
- Replace the rubber hose and grommets every few years or at first sign of hardening or cracking.
- Replace PCV/oil separator as preventive maintenance if engine has high miles or oil looks sludgy.
- Use good quality engine oil and change it at recommended intervals—sludge builds up faster with poor oil/long intervals.
- Check for turbo oil leaks on turbocharged Hilux regularly.

Final notes and cautions
- Don’t start working on a hot engine. Wear gloves and eye protection.
- If you’re unsure about re‑torquing the valve cover or dealing with turbo oil seals, consult a factory manual or a professional. Torque specs vary by engine model and are important to prevent leaks or broken parts.
- If symptoms persist after fixing the blow‑by tube and PCV parts (very smoky exhaust, very high oil consumption), the underlying cause could be worn piston rings or a failing turbo—those require deeper engine work.

That’s the practical, beginner‑level walk‑through: identify the hose and related parts, remove and inspect, replace worn hose/grommets/PCV, clean passages, reassemble carefully, and test.
rteeqp73