Re: Syncros. Check the cone surface on your old ones. Should show little wear, still with sharp....
 

annular oil grooves. And measure the axial clearance to the driven gear. Must be some clearance for the cone clutch to work. The ones that I machined an arbitrary .020" off the face were built a little too large for the gear cone, problem solved. If this is your problem don't bother buying new, just face them.

Congrats! Few are willing to tackle such an overhaul let alone redesigning the flaky areas. BTDT on PS racks also, ZF's high pressure rod seal is a crappy design, but they sell more rebuilt racks with that sh*t.

Interesting finds, pictures inside
 

I finished taking the shafts out of the transmission case and i started taking off gears 3 and 4 from the mainshaft.
Well, what i found was far from what i expected: i thought the synchros were toast - sinking all the way into the hub.... but what i found is a pair of synchros that are in decent shape and a synchro hud/sliding gear that is messed up as hell. The dog teeth on the sliding gear are almost flat... no wonder it was grinding.
The thing was that 3rd was not grinding a lot, only skipping a few teeth and engagement was not too hard. 4th would not grind but sometimes it would kinda get stuck and not go all the way in, but only while driving. The 4th was sticking (almost engaging but not comletely -> more grinding) because the 3rd skipping a few teeth on every engagement caused a burr but the burr was small and would only catch sometimes when there was some torque between the sliding gear and the gear it slides on (forgot name).
So, i think my 4th synchro is good and i will probably replace 2nd and 3rd as the molybdenum coating is almost gone, especially on 3rd.
About the sliding gear, i don't know what to do. Should i file it down and reshape the dog teeth? I am going to find out how much a new one is because that's probably the way i want to go.
Luckily, the dog teeth on the 3rd and 4th gear look fine (quite interesting) and that makes me believe that the sliding gear is not hardened enough.
Look at the pics, if you look at the bottom side you can actually see that the teeth are almost flat.
This is the side facing 4th gear
<img src="http://pictureposter.audiworld.com/98365/dscf0051.jpg" alt="Side facing 4th gear">
This is the side facing 3rd gear
<img src="http://pictureposter.audiworld.com/98365/dscf0052.jpg" alt="Side facing 3rd gear">
This is the 3rd gear synchro - it's getting replaced
<img src="http://pictureposter.audiworld.com/98365/dscf0047.jpg" alt="3rd gear synchro">

Any input on this would be highly appreciated!
PS: now i can definately tell that one of the previous two owners of this car did not know how to drive a manual. :(

The clearance issue is a good point because there has to be space for the oil to escape.....
 

as the synchro meets the cone.

That is interesting stuff. I did suspect that the reluctant shift into 2nd might be cause by....
 

some resistance or wear on the shaft but I did not expect that on 4th from what you said.<ul><li><a href="http://cgi.ebay.co.uk/AUDI-S4-6-SPEED-GEAR-BOX-L-K-L-K_W0QQitemZ170069392595QQihZ007QQcategoryZ10372QQr dZ1QQcmdZViewItem">Maybe this would be worth investigating. You would need your final drive I think.</a></li></ul>

First, it's worth rebuilding, only a few parts needed and about the link...
 

the item is in uk and says pickup only.
Also, buying used is always a gamble, the used one could be worse than mine. I just need two synchros and a collar, no biggie...

I know - better the devil you know.....and you now have experience of...
 

the manual box re-build.

Are you going to need new gaskets or is it all silicon seals?

Re: I know - better the devil you know.....and you now have experience of...
 

I will go with new gaskets because it's only two of them... i don't really like the sillicone

Edd, Your reason is not a valid point. Oil escapes both ends of the cone. Face clearance is needed..
 

such that the cone surfaces can come into actual contact. But before they do, the increasing fluid shear friction forces within the thinning oil film will grag the gear to the syncro velocity. The syncro and gear make metal to metal contact at zero relative velocity.
Thus, short of abuse, a well designed syncro should last forever.

Well, i have a car with 225k on it and the manual trans still works like new...

Called the dealer, $200 for sliding gear... it's getting replaced...
 

Also, i am going to replace the 2nd and 3rd synchros. The 4th one looks great and will stay.
I'm figuring, it's gonna cost me about $400 so far but i think even $500 for a "like-new" transmission is a great deal since used ones go for 800-1000 at least.