1. Synchro Gearbox Replacement Parts
2. B16 Synchros
3. Syncro Gearboxes Slickshift
4. Synchro Gearbox Repair
5. Synchro Gearbox Problems
6. Synchro Gearbox

Synchronized manual transmissions are widely used globally in both commercial vehicles and passenger cars, although they are less common in North America. These transmissions contain a complex array of components and materials that deliver longer service and better performance when the correct, dedicated lubricant is used.

From the launch, the MGB was fitted with a 3-synchro 4spd gearbox. Overdrive was an optional extra. Later, a 4 synchro box was fitted and again, o/d was an option. On the later 1977 onwards UK cars, o/d became standard fit. An automatic option was available for a while. Synchromesh Gearbox is similar to the Constant Mesh Gearbox in which dog clutches in the Constant Mesh Gearbox are replaced by Synchromesh devices for smoother engagement of gears. The gears on the main shaft are free to rotate w.r.t the main shaft whereas the gears on the layshaft are fixed I.e. There is no relative motion between them.

Manual transmissions come in two main types: synchronized and unsynchronized. Unsynchronized transmissions require manual synchronizing, which depends on the skill of the driver at each shift event to synchronize gear speeds, particularly on the downshift. Unsynchronized transmissions are usually only found in motorsport applications or heavy-duty commercial vehicles. North American heavy trucks are typically equipped with unsynchronized manual transmissions, whereas European truck manufacturers tend to favor synchronized manual transmissions.

A synchronizer does exactly as the name suggests. It equalizes its speed with that of the next gear to be engaged, allowing a smooth, crunch-free selection. Modern synchronized manual transmissions are of the “constant mesh” variety. This means that idling (free spinning) gears on a main shaft are in constant mesh with a corresponding set of gears, machined as one single component and forming a second “lay shaft.”

The most common synchronizer design is the “cone clutch” or “blocker ring” type. Typically, gears are arranged on the main shaft in pairs; for example, first and second gears are adjacent, as are third and fourth. In between each pair is a synchronizer unit fixed to the shaft. The two key components in the synchronizer unit are the sleeve and the “blocker,” or “synchronizer,” ring. Gears are selected by the sleeve, which can be moved in either direction by the gearshift mechanism. When the driver selects first gear, the sleeve will move to the first gear and lock onto its gear engagement teeth (also known as “dogs”). The gear is then effectively locked to the main shaft and drive is taken up. When the driver de-clutches and selects second gear, the sleeve moves the other way, de-selecting first gear and selecting second in the same way.

Before the sleeve can lock on to each gear, however, the speed of both sleeve and gear must be synchronized. This is accomplished by a blocker (synchronizer) ring, one of which sits between the synchronizer and each gear. The inner face of the ring is conical and this locates over a cone on the face of the hardened steel gear with a gripping action, as the shift event is taking place. As the surfaces of this “cone clutch” grip, the rotational speed of the gear becomes synchronized with that of the synchronizer sleeve and gear selection can be completed.

These blocker rings were traditionally made of brass; the internal conical surface was faced with fine grooves in order to provide better grip on the surface of the gear cone. In an older transmission, synchronization begins to fail (leading to crunching gears) when the internal surface of these blocker rings becomes significantly worn and their ability to grip the gear is reduced.

Earlier or more basic synchronized manual transmissions are equipped with one blocker, or “synchro,” ring per gear. However, the latest generation transmissions now feature double or triple cone synchronizers on the lower gears to facilitate smoother shifting and shorten the synchronization phase. Materials technology has improved, too. Brass is being replaced by molybdenum-based materials in commercial vehicles, sinter compositions, phenolics in Japan, and carbon materials. Each is chosen for its wear and friction performance.

Commercial vehicle and passenger car synchronizers follow similar principles, but the choice of materials reflects the much higher torque commercial vehicle transmissions must transmit. A typical heavy duty synchronization ring can be made from steel coated with molybdenum or carbon, with torque capacities as high as 18,000 Nm (13,276 lb ft).

Although the process of synchronization might seem simple, in engineering terms it is defined by nine different stages. These are:

1. Disengagement
2. Neutral
3. Neutral détente
4. Pre-synchronization
5. Synchronizing
6. Synchronization
7. Blocking release
8. Engagement tooth contact
9. Full engagement

Lubricating synchronizers is a complex proposition. Clearly, there is a need to prevent wear, but the synchronizer blocker rings still need to generate sufficient friction to perform the synchronization. That same lubricant also has to protect bearings and seals and resist degradation in the face of increasingly extended drain periods. It must also survive higher temperatures caused by reduced airflow due to improved vehicle aerodynamics and the increased energy density typical of modern, high performance powertrains.

Considering the long and hard life of synchronizers and their mechanical complexity, it becomes easier to understand the importance of using the correct fluid. Maintenance mistakes that shorten the life of a manual transmission include filling with engine oil or even automatic transmission fluid (ATF).

Dedicated manual transmission fluids (MTF) offer far better protection against wear and pitting. They combine high temperature resistance with high levels of gear and bearing protection, and they are individually designed to adapt to the behaviors of various synchronizor materials. Additive and viscosity modifier technology can be tailored during the design process to meet individual OEM specifications, so as to provide a fluid that functions as an integral component of the transmission.

Synchro Gearbox Replacement Parts

The trend is toward lower viscosity MTFs that reduce churning losses and improve fuel efficiency, without compromising protection. This is achieved through the use of robust additive and sophisticated viscosity modifier technologies. In North America, the trend is toward SAE 75W-80 and 75W-90 viscosity grades. In emerging markets like China and India, the trend favors SAE 80W-90.

Using dedicated fluids has a major impact on the cost of equipment ownership, reducing service costs and fuel consumption, and delivering improved reliability. There’s also an environmental benefit, thanks to extended drain intervals. And, from the drivability point of view, shift quality is also improved. Using a dedicated MTF to protect manual transmissions does not represent a significant additional cost compared to using an inappropriate fluid, but it does have major benefits for both owners and drivers.

Ok, so you want to get your truck licence. You’re looking to make a change and you’ve seen that there are quite a few jobs going in the transport industry. Or you may have already been offered a job on the proviso you get your truck licence. You’ve done a bit of research, asked some questions, and you need a Heavy Rigid licence. Sorted – well nearly.

B16 Synchros

There is another question that you will need to answer before you commence your training as the answer you give could come back to bite you on the…tail shaft…both during and after your training.

At the HR level you have the choice of undertaking your training in a vehicle with either a fully automated, synchromesh, or non-synchromesh gearbox.

Syncro Gearboxes Slickshift

Over the last couple of years automatic transmissions have become more popular. Armstrongs introduced an HR Auto into its fleet in recognition of this trend. It’s true that once all the effort and concentration required to change gears effectively and efficiently is removed, clients generally perform better as they are able to focus more on road positioning and vehicle control knowing that the right gear at the right time will be selected for them. The technical term is “it’s easier.”

But when it comes to the choice of what type of gearbox you should undertake your training in, you need to keep these things in mind:

Synchro Gearbox Repair

• The type of fleet that your potential employer is operating. Are all the vehicles automatics or synchros? Is there a mix?
• What is the probability that you will be required to drive a synchromesh or non-synchromesh vehicle? A potential employer might have a fleet of ninety-nine automatics and one non-synchro. But if you are required to drive that non-synchro one day – and you can’t – then you’re not much use to that employer.
• Where do you want to take your driving career? If you see yourself progressing through to the larger license categories then there is a fair chance that you will run up against prime movers with non-synchro gearboxes for a little while yet.

Synchro Gearbox Problems

If you can’t find any information regarding the above, or don’t have any idea where or what you might end up driving then you need to know the following:

Synchro Gearbox

• If you mistakenly think that fifteen years of driving automatic Commodores and Falcons counts as driving experience (that is, you haven’t driven a manual car at all or in a very long time) and you have your heart set on getting your heavy vehicle non-synchro licence, then the odds of passing on your first attempt (or tenth!) are very small. Seriously though, the non-synchro is not for those who are challenged on the co-ordination front! Have a look at the HR Non-Synchro course page for a very helpful Youtube clip of what you’ll be required to do.
• Just to reiterate, think long and hard about whether you really need a non-synchro licence.
• If on Day 2 of your non-synchro course you find yourself thinking “why did I let my mate talk me into the non-synchro?” Unfortunately Armstrongs can’t just take you out of that course and put you into an automatic course or synchro course. Sure, we’ll help you out in any way we can but you’re going to have to rebook and that’s going to mean additional costs.
• Remember, getting your heavy vehicle licence is not a one-shot-only affair. If you get your heavy vehicle licence in an automatic or synchro, you can always come back anytime you want in order to get the ‘A’ or ‘B’ condition removed – this means you have the luxury of taking as long as you like to pass your non-synchro driving re-test without the stress of trying to learn to drive a big vehicle AND double-clutch WHILE everyone else on the road is seemingly trying to cut you off all the time!
• If you are tested in a heavy vehicle using a synchromesh gearbox then a ‘B’ condition will appear on your heavy vehicle licence and you will be restricted to driving heavy vehicles with an automatic or synchro mesh gearbox. You cannot drive heavy vehicles with a non-synchro gearbox.
• If you are the holder of a manual car licence, you can actually take your training and assessment using an automatic gearbox but you’ll still come out with a heavy vehicle licence which allows you to drive synchros also!
• But…if you have an automatic car licence and you are still on your P’s and you take your training and assessment in a heavy vehicle with an automatic gearbox you will be restricted to driving automatic heavy vehicles until the end of your probationary period. However, once you probationary period is over, your car licence will be converted to a manual licence and your heavy vehicle licence will be converted to a synchro.
• If you get your heavy vehicle licence in a non-synchro then congrats. It’s not an easy thing to master and you earned it. Have fun driving any gearbox you want.

If you want to see a demonstration of each of the different gearbox configurations in action, check out the heavy rigid automatic, synchromesh, and non-synchromesh course pages on our website, or the Armstrongs Youtube channel, or give one of the team a call today 03 9464 6464.