What is a double synchro? A double synchro is a synchronizer assembly that uses 2 blocker rings to speed up or slow down ‘synchronize’ the gear you are shifting into. In other words, it’s like popping a big set of brakes on the gears.
Below is a picture of synchro blocker rings. These are OEM factory single synchro units. The one on the left has what is called an organic lining which was used only on early first gen trannies. The unit on the right is an all bronze unit which is an upgrade to our standard tranny builds. The all bronze unit lasts longer, and work better than the old lining style unit. If your tranny comes in with the old lining blockers, we will upgrade them to the all bronze units as part of our standard rebuild.
The organic units are known to burn up and literally fall apart. They are also very sensitive to the type of oil used and can wear very quickly. Close-up pic below of a lined blocker.
The next pic below is of the all bronze unit. This unit has small oil channels to allow the oil to escape for faster and smoother shifting. The bronze will never age, is not sensitive to the type of oil used and is the standard for our rebuilds:
Now the double synchro. The pic below is of a double synchro unit that we use. As you can see, it uses two bronze synchro blocker rings instead of just one. These units are capable of 10,000RPM shifts with a dual disk 7.25” clutch or smaller. Unit on the left is complete; unit on the right is apart to show the two bronze rings:
Advantage is they will not fall apart due to old age, they are not as sensitive to oil, and they will make the car almost twice as easy to shift at high RPM than factory units. Which gears need the double synchro the most? It all depends on the vehicles intended use. Most will upgrade in level of importance/mostly used: 2nd, 1st 3rd, 4th. We can also double synchro 5th, but it is not needed. So if only double synchronizing two is within your budget, 1st and 2nd would be the way to go.
We have the unique capability of machining your OEM factory gears to accept the double synchro assembly. This eliminates the need to buy new gears and will leave your tranny with the original matching gear set. Pics below are of a stock factory original 2nd gear that is getting machined to fit a double cone synchro. Machining the unit instead of replacing allows for big cost savings on your rebuild which makes our prices lower than anyone else. Plus, you don’t have to worry about wearing-in a new gear set.
Our machining process makes your OEM gear identical in quality and strength to a new gear purchased with the same configuration.