after finding out how much it costs for new gearbox parts, i am seriously considering adding a pump, filter, and cooler to my trans...

No amount of oil cooling will fix poor shifting technique or a maladjusted tranz.

How about SuperTech 80w-90 GL-5 from......Wal-Mart.

Already have some to put in my Bug

(Don't beat me!)

Swepco 201 is great. Like Andy I've been using it for years.

Rich Bontempi (High Performance House) told me about it an put the first refill in my transmission. FUI Rich is also a well know racer and car builder.

Probably the best test of transmission fluid would be the guys running longer events. There are a bunch of people running longer track sessions and their experience would be invaluable.

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?

Make sure the car is at least close to level when you do this... Don't ask how I know.

--DD

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

Being a ten year old thread you might as well start it up again! I use chicken grease in mine it clucks less from first to second

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.

I believe Dr. Evil said plain old nothing fancy 80/90w GL5 is what you want with these transmissions. 13 years ago.

As always I use amsoil products,they specify GL5. Now the reasons synthethic is so much better than conventional oil go to their website click on Performance Test Archive scroll down to 75W-90 synthethic vs petroleum gear oil testing and decide for yourself.

Last I read synthetic is too slippery for our synchro's and not to use it. Just standard 90w gear oil.

Here is a good question....will adding Lucas Oil Stabilizer alter the GL4 properties that I am searching for? Will it make the tranny oil too slippery or what exactly will it do ?
Thank you,
gg

Kendall MS-NP Hypoid gear oil 80-90W.

@‘second wind’

No snake oil required. Oil OEMs spend a lot of time and testing to ensure it meets GL standards - no need to modify what they have done.

You want GL-5 for the hypoid differential in our transaxles (per Dr Evil and per standard engineering practice for hypoid differential). The synchros in a 901 transaxle are steel - not brass so don’t worry about the nuances about brass synchros needing GL-4.

I have to agree. After trying a few brands including Valvoline, I found Kendall to provide the best shifting.