Synchros

[mdbrandy]

OK, I admit it. I have never taken a transmission apart, and I don't know how synchronizers in a manual transmission work. :stupid: As a degreed engineer, I feel really silly about that, and want to rectify the situation . It's one of the only parts of our cars that I don't at least have a basic understanding of. I love books, and if anyone has a suggestion for a good book about transmissions in general (manual and auto), I'd love to have the title, author, etc. Otherwise, anyone want to post an explanation? I have several spare trans sitting around, and I'm planning on taking one apart soon, so I'd like to know they actually operate before I dig in :paranoid: .

Thanks.

[panchovisa]

I've never taken apart a tranny either. With that in mind, my understanding is that syncros are meant to "crash" and capture opposing gears to somewhat match the rotation of each gear and also to align "peak" of one gear with "valley" of the other.

Syncros are designed to accept the "crash" which the actual gears are not.

I have driven several cars with bad syncros and they can be shifted without grinding gears, but you must give gears time to slow down first and you must shift the lever slowly to mesh gears. Not fun, but can be done.

[Murph]

For anyone that doesn't quite understand exactly how a manual transmission works and what exactly the synchros do, go and have a read of this:

http://auto.howstuffworks.com/transmission.htm

Doesn't really show you the specifics of how exactly the synchros work however. This is something I'd also like to know.

[Mr Camouflage]

I know how synchros and gear and all that work, but the gearbox is one of the things i leave to the experts. Theres alot of specialist tools required isnt there?

[mdbrandy]

For anyone that doesn't quite understand exactly how a manual transmission works and what exactly the synchros do, go and have a read of this:

http://auto.howstuffworks.com/transmission.htm

Doesn't really show you the specifics of how exactly the synchros work however. This is something I'd also like to know.

Nice site! I didn't know about it. The explanation there is very basic, but had more info than I knew. I didn't even know that you aren't really moving the gears! Very interesting. I knew that the synchros had "cones", and so I figured there was friction involved somewhere. This site's explanation at least gives me a good, general picture. If anyone knows of decent books, I'd still like to get reference to one or more. Since the synchros are friction-based, how long a life do they usually have? I assume there isn't really "friction-material" in them (like clutch or brakes) since they are bathed in oil - is it metal-to-metal with oil between?

[mdbrandy]

I know how synchros and gear and all that work, but the gearbox is one of the things i leave to the experts. Theres alot of specialist tools required isnt there?

If I was trying to mess with the transmission on my daily driver Z, I would be a lot more cautious. As it is, I have two four-speeds laying about, and I was told that the type A that I'd like to use in my 240 restoration was stuffed (it came as an extra with the car). So at least taking the gear set out of the case would allow me to look it over, even if I didn't actually disassemble it. If, of course, I can learn what needs to be looked over! :laugh:

[kmack]

If anyone knows of decent books, I'd still like to get reference to one or more. Since the synchros are friction-based, how long a life do they usually have? I assume there isn't really "friction-material" in them (like clutch or brakes) since they are bathed in oil - is it metal-to-metal with oil between?

I can't direct you to any book in particular other than maybe any one of the available service manuals. The Haynes book has some pretty good detail as does the FSM.

The easiest way I found to work on trannys, is to sit down with a service book (with pretty good pictures) and actually just tear one apart. Manual transmissions are the easiest to work on because they only go back together one way! It's like a puzzle. If it's in the wrong place, it won't fit.

I could try to explain the inner workings a bit, but I lack the specific terminology and I'd just get you confused. I'd probably even confuse my self! But I'll give it a shot.

You're right with your statement above that the gears don't actually move. The moving parts are with the synchro "packs" themselves. Each "pack" has 2 synchros, one on each side for each corresponding gear. There is a ring on the outside of the "pack" that rides inside the shifter forks. These are the moving parts. (When I say moving, I mean transverse - front to back - movement as opposed to rotating movement.)

Each synchronizer is made out of brass (or a brass alloy) and does in fact use friction to slow each corresponding gear so that ring can lock in place, thus selecting that gear for use. It is a metal-to-metal contact with an oil layer in between. Most of the time, the synchro will last a long time. I've seen some outlast bearings. But if you run the tranny low on fluid, it severely shortens synchro life.

Hope I didn't confuse you any. Like I said, just jump into it and you'll figure it out as you take it apart. But give yourself a lot of room to lay out pieces, a 4'x8' spot will work good. Make sure you can leave this area undisturbed for awhile, too. As you pull a piece off, lay it down in its approximate location relative to other pieces. Makes putting things back together a lot easier.

Plan on getting dirty and very greasy (oily).

[mdbrandy]

You're right with your statement above that the gears don't actually move. The moving parts are with the synchro "packs" themselves. Each "pack" has 2 synchros, one on each side for each corresponding gear. There is a ring on the outside of the "pack" that rides inside the shifter forks. These are the moving parts. (When I say moving, I mean transverse - front to back - movement as opposed to rotating movement.)

Each synchronizer is made out of brass (or a brass alloy) and does in fact use friction to slow each corresponding gear so that ring can lock in place, thus selecting that gear for use. It is a metal-to-metal contact with an oil layer in between. Most of the time, the synchro will last a long time. I've seen some outlast bearings. But if you run the tranny low on fluid, it severely shortens synchro life.

Plan on getting dirty and very greasy (oily).

I think from that web site and these couple of posts, I have a decent basic idea of what's going on. Much better than before I posted! Seems like a fairly simple system - just complicated linkages to choose the right fork and move the right synchro to the right gear. Seems to me that there has to be a lot of friction to slow the input gear as quickly as needed for fast shifts. Is it really viscous drag of the oil layer between the steel gear cone and the brass synchro cone that slows the gear to match the output shaft speed so that the ring can lock? I can see how steel directly on brass (or brass alloy) without oil would eat up the brass very quickly!

And the inside of the tranny can't be too much more of a mess than the last few hours I've spent scraping the grease, grime, and dirt off the front suspension parts of my 280Z that I'm rebuilding right now! All of the ball joint and tie rod boots were pretty much disolved, and sticky, dirty grease was everywhere! That's what soap's for, right :laugh: ? I just don't clean up in my wife's sink! :stupid:

[Murph]

And the inside of the tranny can't be too much more of a mess than the last few hours I've spent scraping the grease, grime, and dirt off the front suspension parts of my 280Z that I'm rebuilding right now! All of the ball joint and tie rod boots were pretty much disolved, and sticky, dirty grease was everywhere! That's what soap's for, right :laugh: ? I just don't clean up in my wife's sink! :stupid:

I did exactly that job in my sunny not long ago.....not fun!