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Just had the car serviced (the 150k biggy) and my mechanic says there's ATF in the gearbox! He reckons the previous owner has probably done this to make life easier on the synchros. Me - I like things the way they should be, and the synchros seem fine to me. Dunno if this is doing any harm, or good for that matter.
Suggestions or comments?

Auto Trans Fluid

I can't remember if my little Suzuki takes ATF in the manual box-which is normal.

Toyota did this to my last Hiace van...

They reckoned it was due to it being a commercial vehicle it needed a thinner fluid and gear oill would be too harsh for it.

I still think it shortened the lifespan of the synchros as i needed a new gearbox after 90000Km (it wasn't my driving honest )

ATF is common is plenty of manual boxes...hasnt done any harm in any box ive seen it used in. it will clean out any gunk in their also.

ATF works in some boxes that like to take a thin oil, like say Honda gearboxes (where the recommended oil is often 10/30W engine oil).

IMHO I don't think the MX5 gearbox is one of those gearboxes which like a thin fluid

My experience after many years of gearbox work is to use exactly the oil that is recomended by the manufacturer. Of course some gearboxes are less fussy than others.
ATF or Hydraulic oil is not suitable for gear lubrication

ATF or Hydraulic oil is not suitable for gear lubrication

Then why did my ST185 Celica owners manual specify Dextron as the reccomended gear oil? In short, i use whatever the manufacturer tells me to... after all, thats the oil they designed the gearbox to take!

Oil viscosity is actually very important in gear boxes as there are little fingers and pipes that use capillary action to pass oil onto several of the critical parts. Changing the oil visocity can affect how the oil flows in these devices and hence can change the amount of oil certain aprts are recieving. This is true in both instances as using too thick an oil will mean some componants are oil starved, whilst using too thin an oil may put undue stress on some of the tight clearances between the componants due to an oversupply of oil.

I'm pretty sure my sister's old Laser used ATF in it's gearbox.

Thanks guys, guess I'll put the right lube in and see what happens. The shift is pretty stiff, but I've a new (phosphor bronze) shift bush to put in anyways. And if worse comes to worst, I can always put ATF back in!

My commodore uses it too...Oh it's auto though