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The 1-2 grind

384 Views 3 Replies 3 Participants Last post by  ADEQ8
Someone had asked earlier how the temperature of the transmission could effect the 1-2 shift. I could not find the original post but here is what I came up with. Pretty much a gathering of all the explanations we have been throwing around here for some time.

In plain English,,,,,,,,,
The synchros which are automatic speed matching devices for your transmission, used during shifting gears to match speeds of the transmission and your engine so you don't have to, don't work well when the fluid is cold. When the fluid is hot then the synchros can work like they should. Wait till it warms up...

One step above plain English,
Manual transmissions in modern cars use synchronizers to eliminate the need for double-clutching. A synchro's purpose is to allow the collar and the gear to make frictional contact before the dog teeth make contact so that the collar and the gear can synchronize their speeds before the teeth need to engage. The dog teeth trying to engage the collar is what you hear grinding, not actually the gears.

Most gear oils are very viscous at lower temperatures. This higher viscosity requires increased shift effort to move the synchronizer gears with the shift fork and to squeeze the oil from between the synchronizer cone and the mating surface attached to the gear.

Without contact of these two surfaces, the gear speeds will not be synchronized and locking of the synchromesh gears will not occur. Excessive viscosity results in a longer time required to synchronize before locking occurs.

What to do..............
When the fluid is cold you need to shift slower, apply steady pressure against the shifter and allow time for the synchros to squeeze the fluid out then the synchros can make contact and synchronize speed between the dog teeth and the collar and the shifter will fall into gear.

Using a fluid that flows better cold will help to eliminate this or will reduce it. Two fluids that people have been using is GM Synchromesh or Red Line's D4 ATF.

We are not the only people with this problem. I found lots of other modern cars that are experiencing the same problem. From Kias to Miatas. We are not alone. Too bad Ford could not have come out and explained this to us last year.

Some people have been getting their transmission replaced and they are fine for now. I would look at getting an improved ATF in it as soon as possible though.

Need more info on how the trans works? I borrowed from here (borrowed is nicer than stole)
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MidLifeCrisis #388, I think I may be the one who was wondering why the grind goes away after the trans warms up... I know the other evening I was musing on how much money these different fluids cost and how there was absolutely no difference in the 1-2 shift regardless of fluid. I've gone through the original Mobil 1, then Red Line D4 (with and without Prolong), and now GM Synchromesh. If I knew then what I know now I would've left well enough alone! Oh well, live and learn. The problem with that is I'm running out of life and I still have so much learning to do! Thanks for the clarity. Cheers, Tony
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