The necessity for a transmission in an automobile is a result of the characteristics for the internal-combustion motor. Motors usually run over a selection of 600 to about 7000 rpm (though this changes, and is typically less for diesel engines), whilst automobile's tires rotate between 0 rpm and around 1800 rpm.
In addition, the system provides their finest torque and energy outputs unevenly throughout the rev number resulting in a torque band and an electric band. Usually the best torque is needed as soon as the car is going from rest or traveling slowly, while greatest energy becomes necessary at high speed. Therefore, something is needed that transforms the engine's output so that it can supply large torque at reduced rates, but in addition operate at highway rates because of the engine still operating within its limitations. Transmissions do this transformation.
a drawing contrasting the ability and torque groups of a "torquey" engine versus a "peaky" one
The dynamics of an automobile differ with speed: at low rates, acceleration is bound because of the inertia of vehicular gross mass; while at cruising or maximum speeds breeze opposition could be the dominant barrier.
Most transmissions and gears used in automotive and truck applications are found in a cast-iron instance, though more often aluminum can be used for lower weight especially in cars. You will find usually three shafts: a mainshaft, a countershaft, and an idler shaft.
The mainshaft stretches outside of the case in both guidelines: the input shaft towards system, in addition to production shaft towards the rear axle (on backside wheel drive vehicles. Front-wheel drives generally speaking possess engine and transmission mounted transversely, the differential being part of the transmission installation.) The shaft was suspended by the main bearings, and it is separate towards feedback end. During the aim of the separate, a pilot bearing keeps the shafts together. The gears and clutches ride on mainshaft, the gears being able to switch relative to the mainshaft except when engaged by the clutches.
Handbook transmissions often showcase a driver-operated clutch and a movable equipment stick. Many automobile guide transmissions let the motorist to pick any forward gear ratio ("gear") at any time, however some, like those commonly attached to motorbikes and some kinds of rushing vehicles, only allow the motorist to choose the next-higher or next-lower equipment. This sort of transmission is sometimes labeled as a sequential handbook transmission.
In a manual transmission, the flywheel are connected to the engine's crankshaft and spins along side it. The clutch disk is within between the stress dish therefore the flywheel, and is presented contrary to the flywheel under some pressure from stress dish. Whenever motor are operating together with clutch was involved (i.e., clutch pedal up), the flywheel spins the clutch plate and therefore the transmission. As the clutch pedal try depressed, the throw out bearing are activated, which in turn causes the pressure plate to end applying pressure towards clutch disk. This will make the clutch plate avoid getting power from the system, so your gear may be shifted without harming the transmission. If the clutch pedal try released, the throw out bearing is deactivated, together with clutch disk is once again held up against the flywheel, allowing it to start getting energy from system.
Handbook transmissions are described as equipment ratios that are selectable by locking chosen gear sets to the result shaft inside transmission. Alternatively, most automated transmissions function epicyclic (planetary) gearing influenced by brake groups and/or clutch bundle to select gear ratio. Automated transmissions that allow the driver to manually choose the present equipment are known as manumatics. A manual-style transmission managed by computer is actually labeled as an automated transmission instead of an automatic, even though no difference between your two terminology need-be made.
Modern automobile manual transmissions typically incorporate 4-6 forward equipment ratios and another reverse equipment, although customer vehicle manual transmissions are built with merely two and as numerous as seven gears. Transmissions for hefty vehicles and other hefty products often have 8 to 25 gears so that the transmission could offer both an array of gears and close gear ratios to help keep the motor operating into the power musical organization. Operating aforementioned transmissions usually use the exact same pattern of shifter action with one or several switches to engage the following series of equipment selection.
Unsynchronized transmission
Principal article: Non-synchronous transmission
Cherrier two-speed gear, circa 1900
The initial kind of a manual transmission is believed having been invented by Joe Clulow and mile Levassor in belated nineteenth century. This sort of transmission offered numerous gear ratios and, more often than not, reverse. The gears are typically engaged by sliding them to their shafts (thus the term shifting gears), which required mindful time and throttle manipulation whenever moving, therefore the gears could be rotating at about the same speeds when involved; usually, tooth would will not mesh. These transmissions are known as sliding mesh transmissions or sometimes crash boxes, due to the difficulty in altering gears therefore the noisy grinding sound that often followed. Newer guide transmissions on vehicles have all gears mesh always and generally are described as constant-mesh transmissions, with "synchro-mesh" being an additional refinement of continual mesh concept.
In both types, a particular equipment combination is only able to be engaged if the two section to activate (either gears or clutches) are at exactly the same speed. To move to a higher equipment, the transmission are invest basic and also the motor permitted to decelerate before transmission areas for the following equipment are in a proper speeds to activate. The vehicle furthermore slows while in basic and therefore slows more transmission areas, and so the time in natural is dependent on the class, wind, also these types of factors. To move to a diminished equipment, the transmission is place in neutral plus the throttle is employed to increase the engine and therefore the relevant transmission parts, to complement speeds for engaging next lower equipment. Both for upshifts and downshifts, the clutch is revealed (engaged) while in basic. Some drivers utilize the clutch limited to starting from an end, and changes were finished without clutch. More motorists will depress (disengage) the clutch, shift to basic, after that engage the clutch momentarily to make transmission areas to fit the engine speed, then depress the clutch again to move to another equipment, an activity called dual clutching. Dual clutching is a lot easier to have smooth, as rates which are close although not very matched should speed up or delay only transmission components, whereas using the clutch involved towards motor, mismatched speeds are combat the rotational inertia and energy of this engine.
Despite the fact that vehicle and lighter truck transmissions are now actually almost universally synchronized, transmissions for hefty trucks and equipment, motorcycles, as well as devoted racing are often not. Non-synchronized transmission design are used for several reasons. The friction product, such brass, in synchronizers is much more prone to don and breakage than gears, that are forged metal, and ease of use of the procedure gets better dependability and reduces price. Besides, the entire process of moving a synchromesh transmission is slow than compared to moving a non-synchromesh transmission. For race of production-based transmissions, occasionally half one's teeth on dog clutches were eliminated to speed the shifting techniques, at the expense of greater wear.
High quality trucks often use unsynchronized transmissions, though army vehicles normally have synchronized transmissions, enabling untrained workers to use them in emergencies. In america, traffic safety principles refer to non-synchronous transmissions in classes of bigger commercial motor vehicles. In European countries, heavy-duty vehicles incorporate synchronized gearboxes as standard.
Similarly, most modern motorcycles use unsynchronized transmissions: their particular lower gear inertias and higher strengths mean that pushing the gears to alter rate is certainly not damaging, plus the pedal run selector on modern-day motorcycles, without natural position between gears (except, commonly, 1st and 2nd), isn't conducive to using the lengthy shift period of a synchronized gearbox. On bicycles with a 1-N-2(-3-4...) transmission, it's important either to quit, delay, or synchronize gear rates by blipping the throttle whenever shifting from 2nd into 1st.
Synchronized transmission
Top and side view of the manual transmission, in this instance a Ford Toploader, utilized in automobiles with exterior flooring shifters.
Modern manual-transmission cars were fitted with a synchronized equipment field. Transmission gears are often in mesh and rotating, but gears on one shaft can freely turn or perhaps locked to your shaft. The fastener for an equipment contains a collar (or dog collar) regarding shaft which will be able to slip laterally to make certain that teeth (or dogs) on its internal area bridge two circular bands with teeth to their outer circumference: one attached to the equipment, anyone to the shaft hub. If the bands is bridged because of the collar, that equipment is rotationally closed towards shaft and find the result speed of the transmission. The gearshift lever manipulates the collars utilizing a set of linkages, so organized so one collar might be allowed to lock only one equipment at anyone time; whenever "moving gears", the locking collar from 1 gear try disengaged before compared to another try engaged. One collar frequently serves for two gears; sliding in a single movement chooses one transmission speeds, when you look at the other direction selects another.
In a synchromesh gearbox, to precisely match the speed associated with gear to that particular associated with shaft once the equipment is engaged the collar at first applies a force to a cone-shaped brass clutch connected to the equipment, which brings the speeds to match before the collar locking into put. The collar are avoided from bridging the securing bands as soon as the rates are mismatched by synchro rings (also referred to as blocker bands or baulk rings, the latter becoming spelled balk into the U.S.). The synchro ring rotates somewhat as a result of the frictional torque from the cone clutch. Within place, your dog clutch is avoided from engaging. The brass clutch band gradually causes parts to twist at the exact same speeds. If they do twist similar speeds, there is no more torque through the cone clutch as well as the puppy clutch try permitted to fall under engagement. In today's gearbox, the action of all of the of the elements is so smooth and quick its barely noticed.
The modern cone system originated by Porsche and launched when you look at the 1952 Porsche 356; cone synchronisers had been called Porsche-type for many years next. During the early 1950s, only the second-third move was synchromesh generally in most automobiles, calling for only a single synchro and a simple linkage; motorists' guides in automobiles suggested that when the motorist had a need to shift from 2nd to very first, it had been best to come to a whole stop then shift into first and start up once again. With continuing elegance of mechanical development, totally synchromesh transmissions with three speeds, after that four, after which five, became universal because of the 1980s. Many modern-day handbook transmission automobiles, specially activities automobiles, today offering six speeds. The 2012 Porsche 911 provides a seven-speed manual transmission, with the seventh equipment meant for cruising- top speed becoming accomplished on sixth.
Reverse equipment is normally not synchromesh, as discover only one reverse gear inside regular automotive transmission and changing gears into reverse while going just isn't required---and frequently highly unwelcome, especially at highest forward speeds. Furthermore, the typical way of supplying reverse, with an idler equipment sliding into location to bridge exactly what would otherwise become two mismatched forward gears, was fundamentally much like the process of a collision box. On the list of cars which have synchromesh in reverse will be the 1995--2000 Ford Contour and Mercury Mystique, '00--'05 Chevrolet Cavalier, Mercedes 190 2.3-16, the V6 prepared Alfa Romeo GTV/Spider (916), certain Chrysler, Jeep, and GM products which use the brand new endeavor NV3500 and NV3550 models, the European Ford Sierra and Granada/Scorpio designed with the MT75 gearbox, the Volvo 850, and pretty much all Lamborghinis, Hondas and BMWs.
712532 : Chevy V8 to the 1974-80 Land Cruiser FJ40, H42 4 ...
712532 : Chevy V8 to the 1974-80 Land Cruiser FJ40, H42 4 speed transmission, adapter bellhousing.
List of Toyota transmissions - Wikipedia
List of Toyota transmissions Toyota Motor Corporation uses many ... The U-series is an automatic transmission for front wheel drive applications. ... H42 4-speed ...
Transmission - Toyota Land Cruiser Fj4 6 Bj4 Repair
CUTAWAY VIEW 3-2 4-SPEED TRANSMISSION H41 amp H42 3-3 3-SPEED TRANSMISSION J30 3-42 4-Speed Manual Transmission H41 amp H42 amp Transfer 3-Speed Manual
Cruiser Outfitters
Landcruiser H42 4 Speed Trans. to Landcruiser 3 speed T-Case. This information covers the mating of the Toyota Landcruiser H42 4 speed transmission (came factory in ...
Toyota H42 Transmission illustrated parts drawing assiting ...
Drivetrain catalog offering discounted Toyota H42 transmission parts, complete repair kits, major components and troubleshooting help, including free trouble shooting ...
Manual Transmissions by Unit Code: H41 & H42: Manual ...
Manual Transmission Part .com The most complete source of Manual Transmission Parts available On-line! Standard Bearing Kits, Synchronizers, Small Parts Kits, Manual ...
H42 Transmission, Tcase, eBrake Rebuild in a '76 FJ40 ...
I will be documenting my H42 tranny rebuild here for the good of the masses since I cannot seem to find a complete one anywhere. Telling an H41 and...
H42 TRANSMISSION REBUILD KIT FITS TOYOTA LANDCRUISER '81 ...
toyota landcruiser h42 transmission rebuild kit bk254a fits 81-86
Toyota H41 H42 H50 H55F Transmission Repair Manual | eBay
Find best value and selection for your Toyota H41 H42 H50 H55F Transmission Repair Manual search on eBay. World's leading marketplace.
H42-H55F TRANSMISSION SWAP - Part II: Off-Road.com
H42-H55F TRANSMISSION SWAP - Part II: Trucks & 4x4 : Remove Transmission Output Shaft Cover and Nut Just take off the 6 bolts holding the cover on and
Short version first: on Toyota H41/H42/H50/H55F manual gearboxes the “pressure relief valve” people commonly mean is the breather/check-valve that lets expanding air escape and keeps contaminants out. If it blocks or is missing the gearbox will vent oil past seals, suck in water/dirt, or develop excessive internal pressure. Below is a beginner-friendly, step‑by‑step explanation of what the parts are, how it works (theory), how to inspect/replace/repair it, what can go wrong, and testing/tips. No fluff.
What it is and why it’s needed (theory, in plain terms)
- The gearbox is mostly a sealed box filled with oil. Heat from friction and gears makes the air/oil inside expand; cooling makes pressure fall. If air has nowhere to go pressure differences force oil out past seals (or pull dirty air/water in).
- A breather/pressure‑relief valve gives the case a controlled place to breathe: it lets excess pressure escape and lets the case equalize with outside air without letting water/dirt in.
- Analogy: it’s like the little valve on a pressure cooker lid or the vent on a soda bottle cap — it prevents the box from becoming a pump that forces fluid where it shouldn’t or from drawing contaminants inside.
Major components (typical breather / pressure relief valve assembly)
Note: exact appearance varies by model/year. Many H‑series boxes use a small screwed-in breather or a small valve on the case or on a breather hose. Components you will encounter:
- Breather cap / body: the external piece you can see and unscrew. Can be plastic or metal. Often has slotted holes or a labyrinth design.
- Check valve element / poppet (if fitted): a small rubber/plastic ball or rubber flap that allows air out but resists water and dirt coming in.
- Spring (sometimes): holds a poppet closed until a small positive pressure opens it.
- Seat / valve housing: the internal surface the ball/poppet seals against.
- O‑ring or gasket: seals the valve body to the gearbox case to keep oil from escaping around the threads.
- Breather hose (if used): flexible hose routing breather to a higher/more protected location. Hose clamp or bracket holds it.
- Dust screen/labyrinth: some breathers use a long pathway or mesh to prevent droplets and debris from entering.
- Case port / boss: the threaded hole or boss in the gearbox casting where the breather screws in.
How the system works (simple sequence)
- Normal: small expansions/contractions allow flow through the breather/check valve; the valve prevents liquid ingress and filters large particles.
- Overpressure: significant internal pressure pushes open the valve/poppet so air (and sometimes a little oil vapour) can escape.
- Underpressure: when cooling causes vacuum, outside air is drawn in through the breather (often filtered/filtered path).
Symptoms that indicate breather/pressure relief problems
- Oil seeping or spraying out of seals (input shaft, output shaft, shifter shaft) especially after driving — indicates internal pressure being forced out.
- Oil weeping from around the breather itself or wet trail under vehicle.
- Water, mud, or heavy dirt found inside breather or inside case (when opened) — indicates ingress through breather or missing breather.
- Excessive foamy oil (aeration) or rapid oil contamination.
- No visible breather (it’s missing) or breather pointing down into splash/water — bad routing.
Tools and supplies you’ll need
- Vehicle lift or good jack + rated jack stands, wheel chocks.
- Basic hand tools: ratchet, sockets, screwdrivers, pliers, adjustable wrench.
- Small pick or flat screwdriver to remove O‑rings.
- Clean rags, brake cleaner or solvent.
- Replacement breather assembly (OEM part or high‑quality aftermarket).
- Replacement O‑ring or gasket.
- Small hose (if replacing routing), clamps.
- Torque wrench (for any bolts specified by manual).
- Gloves, eye protection.
Safety first
- Never work under a vehicle supported only by a jack. Use stands on solid ground.
- Wear eye protection — gear oil and debris can fall into your eyes.
- Let the gearbox cool if recently driven — hot surfaces/oil can burn.
Step‑by‑step: inspect, remove, clean, replace breather / pressure relief valve
1) Locate the breather
- With the vehicle safe on stands, inspect the top/side of the gearbox case. The breather is usually a small protruding cap or threaded plug, often on the uppermost part of the case or on a small boss. Some have a hose that routes it to a higher point (near engine bay or inner wing).
2) Visual inspection
- Look for oil residues around the breather, signs of impact, corrosion, or a hose routed downwards into splash areas.
- If there’s a hose, follow it to its end — if the hose ends near the wheel arch or below the oil level on rough terrain it can draw water.
3) Remove the breather
- Clean around the breather so no dirt falls in.
- Unscrew the breather body (usually hand-tight or small spanner). Keep hand/face away from the port just in case there’s pressure.
- If it’s a hose, remove hose clamps and pull the hose off.
4) Inspect the internals
- Examine the breather cap for blockage, torn or hardened rubber, crushed mesh, or clogged labyrinth passages.
- If there is a check ball/poppet, check it moves freely. If stuck, replace assembly.
- Inspect the O‑ring/gasket: if flattened, cracked or missing replace it.
- Look inside the gearbox port with a torch: if you see heavy sludge, metal particles or water, that indicates other troubles — note these but the breather fix is still necessary.
5) Clean or replace
- Clean the breather with solvent if it’s lightly dirty and the check element is intact. If you find corroded parts, cracked plastics, hardened rubber, or it was clogged, replace it.
- Replace the O‑ring/gasket with new.
- If the breather hose is brittle, cracked or routed low, replace with fresh hose and re‑route upward into a protected area (engine bay or high on inner wing), clamp securely.
6) Refit
- Screw the breather back in by hand; tighten to snug. If torque is specified in the factory manual use that. Don’t over‑torque plastic caps.
- Ensure hose clamps are secure and route is protected from heat and moving parts.
7) Check seals and oil level
- After refit, check gearbox oil level and top if necessary using the fill/level plug.
- Inspect output/input/shifter seals for wetness — clean and mark wet spots with a rag so you can test after driving.
8) Test
- Start the vehicle, run it in neutral for a minute then rev briefly to let temperature/pressure change. Look for oil escaping anywhere.
- Drive the vehicle for a short test, then re-check for leaks.
- If oil still leaks from seals, internal pressure may have forced oil out earlier — replacing breather may stop future leaks but seal replacement might be needed.
How to test if the breather is blocked (simple checks)
- Remove breather and blow gently from the outside toward the case port: you should be able to push a small stream of air through (or at least feel it). Don’t overpressurize. If it’s completely blocked or air must be forced, replace it.
- With the breather removed and engine running briefly, you should not get a heavy stream of oil or smoking vapour — that indicates excessive internal pressure or fluid foaming.
Common failure modes and what can go wrong
- Clogged breather: dust, mud, oil sludge block flow -> internal pressure forces oil out seals, or vacuum draws contamination in. Symptom: oil leaks at seals or rapid oil contamination.
- Broken/brittle poppet or O‑ring: allows water/debris into case -> contamination, corrosion, gear wear.
- Hose routed low or missing: draws water/splash into breather -> contamination and rapid wear.
- Missing or incorrectly seated breather: same problems as above.
- Pressure from other causes: internal foaming (overfilling, aeration), failing seals, or an internal obstruction can cause pressure that defeating the breather or causing oil ejection. Replacing breather alone won’t fix internal gearbox mechanical failure.
- Oil foaming/aeration: if aerated oil circulates the gearbox, it’s less effective at lubrication and can raise internal pressure. Causes include incorrect fill, worn synchronizers, or air ingress via clutch hydraulics (if present).
- If you try to seal the breather completely to eliminate leaks (bad idea): you trap pressure and magnify leaks or seal damage.
When to replace seals or do more work
- If after restoring a working breather the gearbox still leaks heavily at seals, the seals themselves may be failed (replace them). Persistent heavy pressure indicates an internal cause — foamed oil, overfill, or mechanical failure — requiring inspection (drain oil, remove cover, internal inspection).
- If you find metal particles in oil or heavy sludge, plan for a gearbox inspection/overhaul.
Parts and replacements
- Use an OEM breather or an exact-fit aftermarket one. Important: match thread/pitch and O‑ring size, and if hose routed use automotive-grade hose routed high.
- Replace O‑rings and any brittle plastic breather caps.
Quick troubleshooting table (keeps it compact)
- Symptom: oil weeping from seals after driving -> likely blocked breather causing pressure -> remove/replace breather, re-route hose, test; if continuing, check seals.
- Symptom: water or mud in breather -> breather routed low or missing protective cap -> re-route and replace breather or hose.
- Symptom: foamy/oily smell and spongy shifting (if applies) -> aeration or contaminated oil -> drain & inspect oil, check clutch hydraulics, check internal condition.
Maintenance tips
- Inspect breather every major service (oil change) and after off‑road/wading.
- Re‑route breather higher if you regularly drive in deep water.
- Replace fragile plastic breathers proactively if brittle/cracked.
- Keep the breather clear of mud and avoid sealing it completely.
Final note
- The breather/pressure relief valve is a simple but critical part that protects seals and prevents contamination. Replacing it is usually straightforward: locate, remove, inspect, replace defective parts, and re-route if necessary. If problems persist after correcting the breather, expect seal replacement or internal gearbox work.
That’s the concise beginner mechanic guide. Follow safe lifting practices and use correct replacement parts.
rteeqp73