What’s wrong with my VW T3 gearbox? A brief introduction to
common problems and causes
What’s wrong with my VW T3 gearbox? Is a question I am often asked in most cases the problems and causes of many T3 gearboxes can only be found out by completely stripping and inspecting the gearbox. It is very difficult to be sure what is going on with it apart from terminal cases. Even a functioning gearbox may be hiding some potentially terminal faults. Most T3 gearboxes are around the 30 year old mark and may have been subject to a general lack of maintenance, no oil changes, various driving styles, wear, worn shifting, corrosion. Some may have been rebuilt incorrectly leading to more damage, one example being the pinion lock ring was not synched on one box I purchased it ran fine until it came loose just before I arrived at my house, and it then sounded like someone had filled a washing machine with nuts and bolts, which was the sound of my crown and pinion eating each other!!!
What I shall do below is to try and outline some of the most common faults found in gearboxes. By no means is it an extensive list and I shall try and make this as simple and short as possible so as not to bore you.
Most common gearbox problems
Not enough or dirty oil
All gearboxes need oil to lubricate and cool their components, however gearbox oil is neglected, seals may also leak, cases become corroded over the life of the box and leak leading to less oil and an increase in temperatures, compounded with dirty oil that may be full of tiny metal particles leads to a very reduced lifespan for components, bearings can overheat, wear and fail, resulting in blackening of components and shafts, misaligned running, excessive wear and friction welding. Dirty oil has an accumulation of tiny particles which when carried in the oil become a grinding paste leading to more wear and more particles perpetuating the cycle. With more wear, larger particles can become damaged and dislodge which is course cause debris damage to major components.
An oil change is the cheapest and quickest thing you can do to extend and improve your gearboxes life.
Gear linkage worn or improperly set up
Surprisingly the most common gearbox problems do not stem from the gearbox but that of your gear linkage. As the T3 gear linkage is so long approximately 3metres a tiny amount of play at one end is multiplied by the time it reaches the other. Couple this with multiple 30 year old components and bushes along the way and you have a recipe for disaster. Repairing your gear linkage is probably one of the cheaper jobs you can do for approximately 200 euros you can buy the whole kit to replace every component and once you have your linkage set up correctly it will transform the drivability of your van making it feel like a modern car.
Worn linkages also will affect your gearbox leading to more stress and wear on both the shifting components and on syncro rings hubs and even the gears themselves all of which are much more expensive.
Often age related wear can lead to lead to poor shifting and noisy running most components are after 30 years of service just worn out leading to play.
Given that gearboxes work to very fine tolerances, wear can lead displacement of shafts and sloppiness in gear alignment and interface. This is most evident in the major bearings which is why it is imperative to replace these in every build.
Play in the pinion bearing can lead to variance in the pinion height and backlash which are the two most critical measurements in your gearbox. This can be seen in the wear patterns on the crown wheel and pinion head. If optimal mating of the crown wheel and pinion is not achieved this will cause undue stress on the teeth and can lead to metal fatigue and the catastrophic failure of these components. Pinion bearing wear can often be heard as a whining when driving or accelerating.
Due to the forces transmitted through the gears along the pinion shaft and mainshaft there is a tendency for the mainshaft bearing to move forward in the case VW in there wisdom installed a stop in the case to stop this happening however over time both the case and the stop often exhibit signs of wear allowing slight movement of the shafts thus resulting in extra strain upon the running and shifting abilities of the gearbox. This can also result in wear and in some cases friction welding of components especially in 5 speed and syncro boxes where there is less space for components to move and tolerances are more critical. This can be remedied by the installation of a new bearing and a plate to physically stop the mainshaft bearing moving.
Wear in the selector lever bore in the main case leads to slop in the selector lever and will lead to less accurate shifting within the box and through all the shifting components. This is often caused by a combination of wear in the gear linkage and general wear. It is remedied by re-boring and re-sleeving the case.
Syncro rings enable smooth shifting by slowing down the freewheeling gear and allow for smooth shifting. They are made of brass and are a wear component. As they are softer than the gears and the synchronising rings they wear more quickly. Most syncro rings can be often worn out and need to be replaced sometimes then can also be broken, this will lead to poor shifting and often grinding when changing gears.
Synchronising hubs and rings
Earlier synchronising hubs had square cut outs with sharp corners which often are cracked and can in time disintegrate leading to poor shifting and lack of or poor transmission of power. Points on the selector rings can become blunted lessening their ability to grip and causing poor shifting and potentially jumping out of gear.
Reverse and or 1st gear (5 speed) or G gear Synchronising hubs
Rivets can become loose on these and the points can be blunted leading again to poor shifting and power transmission.
Free wheeling gears have a cone and a ring of dog teeth. The cone is used as a surface for the syncro ring to slow the gear like a cone clutch so the selector ring to engage with the gear if the faces and points of the dog teeth are worn or blunted this can lead to poor selection and potentially jumping out of gear.
Due to salty roads, and dirt and the life of the box often times cases are can be quite corroded, especially around the bottom of the box and in particular around the reverse shift housing, % speed boxes are also very prone to corrosion on the main case which can often result in a multitude of tiny pinholes which can allow oil to escape resulting in overheating of the box and the components.
Output flanges can rust or collect dirt which gets picked up on the seal and literally scores the sealing surface leading to oil loss and in turn the box running hot.
The purpose of this piece is to outline some of the most common T3 gearbox problems, it is by no means an extensive list but a brief overview as to what can go wrong. please free to add any other bits I have missed.
Thanks and hope this is of help,