Transmission Fluid, ???? Options

[mxhondarider832]

I have a '74 914 and the transmission is a little leaky and need to change the fluid, the book says to use straight 90w oil but I am having a really tough time finding it so I was wondering if there was a newer substitute that I could use. This is my first 914 and I am struggling a little bit and could use some help thanks

[0396]

Like its been said...it's like religion. I've used M1 trans oil, Swepco and the local FLAPS
I've even used a cocktail of M1 with Swepco..I know Swepco cost more but like some have mentioned, if you track your car, why not simply put the one product that saved the 934/935's gear boxes during Porsches finest hr.
.02$

[d962r]

Like its been said...it's like religion. I've used M1 trans oil, Swepco and the local FLAPS
I've even used a cocktail of M1 with Swepco..I know Swepco cost more but like some have mentioned, if you track your car, why not simply put the one product that saved the 934/935's gear boxes during Porsches finest hr.
.02$

So has anyone tried any of the Lucas Oil additives?

[monkeyboy]

Like its been said...it's like religion. I've used M1 trans oil, Swepco and the local FLAPS
I've even used a cocktail of M1 with Swepco..I know Swepco cost more but like some have mentioned, if you track your car, why not simply put the one product that saved the 934/935's gear boxes during Porsches finest hr.
.02$

So has anyone tried any of the Lucas Oil additives?

I don't use the additives, but I have used their transmission oil with good results.

[second wind]

Like its been said...it's like religion. I've used M1 trans oil, Swepco and the local FLAPS
I've even used a cocktail of M1 with Swepco..I know Swepco cost more but like some have mentioned, if you track your car, why not simply put the one product that saved the 934/935's gear boxes during Porsches finest hr.
.02$

So has anyone tried any of the Lucas Oil additives?

I don't use the additives, but I have used their transmission oil with good results.

Ok....is it just me or is this thread REALLY CONFUSING??? I believe a 914 is supposed to use conventional GL4 tranny oil....how did it get to this confused controversy that allows GL5? I am getting a headache over all of this double talk.....someone please tell the truth....thank you,
gg

[zoomCat]

Ok....is it just me or is this thread REALLY CONFUSING??? I believe a 914 is supposed to use conventional GL4 tranny oil....how did it get to this confused controversy that allows GL5? I am getting a headache over all of this double talk.....someone please tell the truth....thank you,
gg

The owners manual in my car specifies 90 weight MIL 2105 A gear lube. That translates roughly to GL4 in modern parlance, I suspect it may have been the highest grade gear oil commonly available in the late 60s but I haven’t been able to find much discussion of the historical development of the standards. Note that the factory also specified 12,000 mile change intervals.

The difference between GL4 and GL5 is the amount of EP (extreme pressure) protection, usually provided by phosphorous/sulfur compounds that bind to wear surfaces and sacrifice themselves to protect the underlying parts. The anti wear compound is actually harder than the brass commonly used in synchronizers, and binds to that surface with enough tenacity that it will compromise the synchro; GL5 has enough EP additives that is it counter indicated for brass synchros. GL5 is typically rated only for unsynchronized transmissions, but Porsche used steel synchros so this shouldn’t be an issue for the 901 used in 914s. The geometry of the differential should benefit from the increased EP protection.

Shifting quality is largely a function of viscosity and any friction modifiers, whether deviations from the original specs improve anything are a different discussion.

Personally I’m going to use 80w90 GL5, nothing exotic, and change at 12k (or earlier if I have the whim). Others will have varying opinions, I’m sure, and may have more specifics.