If you drive a early Alfa Romeo with the non moly coated sychro rings in your transmission then you will probably want to read this article very slowly and take in all there is to read.
I am not the expert here, but taking a collective wisdom of a lot of people to weave this into a story that we all can learn from. This might be the definitive article on the transmission oils and lubricants to use in the rear axle.
In early pre-1966 transmissions the synchro rings were not moly coated. They require a very specific gear box oil to make them work properly. That oil is Shell Dentax. There used to be a “Yellow” sticker that was on the gear box letting the service person know what oil was compatible.
It used to be whale oil based until the movement to stop whaling became the big issue. Shell reformulated the oil at that point in time. The oil not only lubricates the bearings, but it also is the barrier to the surface of the synchro and the slider. The mass of the gear has to slow down enough so that the gear slides into and locks the gear with the shaft. Over time the front/leading edge of the synchro ring wears down and cannot properly slow the gear, hence you start grinding the gear. What is happening is an interference with the locking mechanism. There are little teeth on the front of the gear and slider that have to mesh. These have tapered sides. When the gear is new the teeth mesh easy. The synchro slows the gear down and every thing slides together. Again, as the synchro wears, the teeth nash together eventually wearing them round and the gear won’t engage.
Post 1966 Alfa Romeo changed the synchro rings over to moly coated. It is a coating on the outside of the synchro ring that aids in slowing down the speed of the gear and adding longevity to the synchro. The transmission oil also changed to accommodate for the newer synchro rings. The sticker was changed to a “Red” label again letting the service tech what was usable in the transmission.
Here is where it gets “tricky” as they say. The Dentax can be used in both gear boxes…early and late. However the later oil CANNOT be used in the early gear box! What happens is the early synchro gets a slick coating on the surface and it doesn’t work. You wind up grinding gears.
There are two ways to fix this should this happen. You can strip the gear box down and install new synchro’s. Given the fact that the early synchro’s are exceptionally hard to find, that becomes a bigger problem. If you do not have that many miles on the oil and the problem is light, you can do the following:
- Do NOT drive the car with this recipe in the gear box. You will destroy the bearings.
- Drain the old oil out completely.
- Add 1/2 diesel oil and 1/2 Kerosene to the gear box.
- Start the car and let it idle in neutral. This allows the main shaft to spin freely in the solution. This will allow the diesel to remove the slick coating and the kerosene will act as a flush. Allow 15-30 minutes for this to work.
- Drain completey. refill and repeat.
- Drain transmission completely, refill with new Dentax gear oil.
- Test drive to see how the synchro’s are working. There will be some synchro issues until the coating wears off. It will improve with time.
The other option is to tear down, replace the synchro’s with the later moly coated synchro’s, sliders and anything else while you are in the gear box. Then you can use any gear oil compatible for the Alfa Romeo gear box.
Redline makes a great manual gear box oil called MTL (Manual Transmission lubricant?) I like to find a muilti-viscosity oil that is like 75-90 in weight. Like when it is cold and gets stronger in weight as it warms ujp. I don’t know if you can get a wider range of oil than this. The Alfetta really liked the wide range oil because of the lighter oil when cold made the shifts easier.
Have any comments or suggestions on the oils used in the Alfa transmissions, drop me an email and I will add it to this article. Thank you for stopping by. Remember there is nothing finer than hearing an Alfa Romeo engine at red line.