901 synchronisers

[chris_seven]

Does any one know the purpose of the 'actuating' tab on the 901 first gear syncho brake band energiser.



This isn't a feature io any of the other brake band energisers and I an keen to understand why.

[304065]

Chris,

The 2-4 synchros are required to work in both directions, both upshift and downshift. From first however, there is no downshift, only upshift, so the extended energizer grabs the brake band and expands it more readily than the 2-4 design. One of the brake bands is shorter as a result. Dr. Evil reports no ill effects from doing away with the special 1st gear energizer and using a 2-4 and the associated brake band in all gears, but you should check with him directly to verify.

He is a denizen of the 914 world but occasionally posts here, I have reached out to him to flag this thread.

http://www.early911sregistry.org/for...highlight=evil

[Dr Evil]

Exactly correct! Oddly enough, 5th gear (or 4th if it is your top gear) only gets up-shifted into and has bands for both directions. Putting the 2-4(5) stuff on the 1st gear is perfectly fine.

[chris_seven]

Thanks guys, having now read the Volume 1 Workshop Manual Text it does explain and this will teach me to read more carefully but it is good to get a detailed explanation.

We have been looking to try to speed up the shift and have considered replacing the synchronisers with Dog Rings. I think this would be a reasonable idea for racing - although it would be an issue with FIA cars - but probably wouldn't be a positive change for cars that are used on the street.

The alternative would be to use a Borg Warner style synchroniser and see if this offers an improvement.

I have just bought a set of bronze synchronisers from a gearbox that has a great gearshift and we will draw up the matching parts to try to convert the 901 to this style of synchroniser and see what results we can obtain.

It is easier to try to use commercially available synchronisers and the parts we are trying to use are also available in Moly Coated Steel for motorsport applications.