Transmission oil....synthetic bad????

[Anonymous]

I just rebuilt by 3spd this past week and was told to get some synthetic transmission oil for it....right...so i called to partsource, but was to expensive...so phoned a guy i knew at a wholesalers i knew.....asked him what he had.....he said not to put synthetic oil in that tranny because it reacts and corrodes with the brass parts


Now my question is this true...what do you guys suggest....so on and so forth

thanks
btw the car is a 65 mustang, 200 3spd

 

[Luckyman]

Synthetic Good!

I have not read or heard anything about synthetic oil being hard on any metals. I put Mobil 1 synthetic gear oil (equivelent to 75-90 conventional) in my NP435 4 speed and couldnt be happier. The trans is much quieter and smoother shifting. I could not believe the difference.

You might want to break the trans in on conventional oil before using the synthetic. I know that is what is recommended for new engines.

 

[MandarinaRacing]

Some Toploader rebuilders say that synthetic MAY cause poor shifting conditions because those transmissions requiere some amount of "friction" in order to work properly. You could try it and see how it goes.

Alex

 

[wsa111]

I have used 75w-90 either redline or mobil 1 in all the differentials I run or build. The auto manufacturers even now use it in their performance diffs & or in all towing packages.
i have used synthetic in manual transmissions for many years with very positive results, better shifting in very cold weather & just smoother shifting, plus less internal friction & transmission wear, maybe the toploader is different?? William

 

[Lazy JW]

Actually it is the older type regular gear lubes which have a high sulfer content that reacts with brass. Never heard of the synthetics being a problem though.
Joe

 

[Anonymous]

Well after I got my new Toploader I put standard oil in the start, after about 150 miles of break in I changed it out to synthetic and it worked just fine and dandy. 8)

 

[rickwrench]

It depends on the transmission. My NWC T5 likes synthetic just fine. My Corvair's saginaw 4 speed was balky to shift with syth but easy with old 90wt.
Rick(wrench)

 

[quaddriver]

It is true that the modifiers in GL5 spec oil can harm 'white metal' parts in gearboxes...but.....most of todays gear oils (synthetic included) are rated both GL5 and GL4 (which is required for white metal)

I ran across this in the early 90's when speccing oil for my boats lower unit...I was running Amsoil 75-90 GL4 but have noticed that Mobil1 Mobillube (which is named by name for my VP CobraSX) is GL4/5

Synthetic Good.