Those With Dying Synchros Should Read

[ClutchBurndout-:(]

If i am incorrect in any of the below, please correct me.

I was speaking to a mechanic not long ago regarding my gearbox and its rare crunching habits it has, i was asking him about additives to help with the crunching, i suggested the commonly used Nulon teflon additive that you stick in your box to help lube up everything so it slips in easier thus reducing the crunching, but, this isnt the case with dying syncro's, syncro's are what cause the crunching, because the syncro's are worn down/expanded so much that it cant slow down the gear set for the next gear to engage safely (without crunching).

Now lets look at what the Nulon teflon additive does exactly, its a lube that helps with friction and lowers it, thus being great for gearboxes and its life, a very good additive to use with a gearbox in good nick, NOT with worn syncro's, look at a syncro, and how they work, they use friction to slow down the gear set correct? and what will Nulon teflon do to the syncro? lube it up and reduce friction correct? thus making it harder for the syncro to slow down the gear set, which can ultimately make the crunching worse (not usually by a lot, but still...)

What to do instead

ive been a big fan of motul oil for gearboxes over the years, and more specifically, "gear 300" (im pretty sure thats what its called) it aint cheap, if your filling your whole gearbox it will cost around $120. From my understanding this is good old fashion good quality shit, with no additives etc, ive always used it, it has stopped 5th gear crunches in my old car, and it has helped alot with 3rd, 4th and 5th gear crunches along with making the gearbox a lot smoother in my current car. Previously in the current car i have (R33gtst) was redline shockproof, which so many here believe is a god send, and what is redline shockproof's special ingredient? thats right, teflon, the same stuff as the Nulon additive, and perhaps it is for newer gearboxes, but i had it in my box and it wasnt doing it very good (well, just not as good as motul)

So, if your having issues with crunching (not reverse crunches, as this is most likely a clutch issue) and the shockproof oil hasnt helped, then fork out the extra money for some motul oil if you dont want to pay for a reco just yet.

Like i said at the start, i may be wrong with some of the above terminology or mechanics etc, but in a nut shell its what i have done with my gearboxes, and what a decent mechanic has told me.

[MrStabby]

FWIW Teflon's manufacturer (3M) states that it offers no benefit in these applications. Agree with what you've said about requiring a less slippery oil with worn synchros, however i have heard that shockproof also makes LSDs lock a bit harder...

[89CAL]

my understanding was that the Nulon G70 additive fills the impurities (damaged) in the syncros to kind of bring them to a restored state. Of course its not a substitue for a rebuild.

But as far as I know its not to add extra lubrication properties but to minimise the effects of worn syncros

[Kinks]

FWIW Teflon's manufacturer (3M) states that it offers no benefit in these applications.

teflon does great when it's painted onto a pan and baked at 300C to bond and form a smooth surface. suspended in oil is a different situation and i don't believe the hype.

I have always used gear 300 in my gearbox and it has stood up well. the only time it ever crunched was going into 5th at high speed so now i just stay in 4th

[KiwiRS4T]

Clutch your logic seems fine. I might try the Motul some time - I have the Redline stuff ATM.

Kinks! No need to stay in 4th. Just double declutch (without blipping the throttle of course) and slip it in to 5th. With practice there will be no "crunch".

[joeyjoejoejuniorshabadoo]

FWIW i just changed to motul and it started crunching that very day.... redline is next on the list

[KiwiRS4T]

FWIW i just changed to motul and it started crunching that very day.... redline is next on the list

What did you change from (before the Motul) and let us know how the change to Redline goes!

[ClutchBurndout-:(]

FWIW i just changed to motul and it started crunching that very day.... redline is next on the list

gear 300?

[T04GTR]

what you are missing, is that with the redlne, because of its very high sheer loading, you can put the ultra light, (yellow) in it, wich is thinner than you motul gear300 and most of the other comonly used oils, but still has the mechanical protection of a thicker oil.

so the synchros can work better because of the lower viscosity. same a the old atf trick. just with more gear protection. we have fixed many zed boxes with the yellow.

yes its meant for a dogbox but does work. however if the detent springs and stuck to the magnet theres no oil that will fix it.