Trans Synchro Ring Wear

[Seth Swoboda]

Mac, have you ever considered a how to rebuild book for the banjo rear ends? Your transmission book is excellent and I can imagine what a help banjo rear end book would be.

[rotorwrench]

Vern Tardel has a book on banjos.

[Seth Swoboda]

Originally Posted by rotorwrench

Vern Tardel has a book on banjos.

I have it. It doesn't go into as much detail as Mac's book about transmissions does.

[Bluebell]

Ther is another aspect of wear that many people do not consider when attempting to fix a problem gearbox that causes jumping out of gear.

If you go back to Macs pictures there is a ring of matching teeth below the bronze syncro cone (balk ring) These are part of the gear.
These lock into the syncro hub (the ring that the selector fork runs in)
These teeth are pentagon shaped (5 sides sort of) there are two flats that point to the top (as Mac's picture sits) There is the bottom face(it never wears) and then there are the two important faces which are the drive and over run faces.
These two are important. When they are new, straight edges laid against them are going away from each other at the top. (Think about the pentagon)
These faces wear and the angles eventually go the other way so that the straight edges would eventually meet. ( the load side wears more than the over run side)
Anyhow this is the important bit. These teeth "hook into the syncro hub (explain later) and under load, hold it in gear. When these teeth wear, the angle is reversed, and they "walk" out of mesh. So, on a long climb up hill (or during descent) your car jumps out of gear. You can hold the gear lever and help it, but it fights you to jump out.
If you look inside the syncro hub there are the big grooves across the inside, but each end of the grooves is angle cut "back" on both sides. This is the complimentary angle that holds the pentagon shaped teeth in gear.

All of the above is not really anything to do with "syncronising" to achieve a smooth gear change. It is just about keeping it in gear.
Problems here are exacerbated, by other issues (excessive end float is one)

Many people think it is the springs and detent balls on the selector shafts, that hold this type of gearbox in gear. That is not the case.

I hope this helps to enlighten someone. It might mean that someone has to spend more money, but that their gearbox rebuild is a successful one time effort.

[PeteVS]

Here's another link, this one from Richard Lacy's son Dennis, on transmission rebuilding.

http://www.jalopyjournal.com/forum/t...970252/page-18

[rotorwrench]

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As long as the teeth are good, the inner conical face isn't worn down too far and the two slot dimensions are still within spec, they will work.

Some of the repro ones have bad slot dimensions and the conical seats are not right. You have to have one in hand to compare to a good one to see what's wrong.

[Talkwrench]

If I remember a quick reference to see if you have problems with syncros you can see one with the filler plug missing.. probably see if you have a gap.