Thoughts on Synthetic Transmission oil

[oneoldtruckguy]

I am getting ready to install a new clutch and rebuilt 3 speed top loader in my 1950 F1 Pickup. What would be your thoughts on using LUCAS Synthetic SAE 75W-140 Gear Oil in it? transmission was completely gone thru by a good tranny shop with all new gaskets and seals. Anyone else using a synthetic in the tranny? And what are You using? Thanks Fordbarn.

[trulyvintage]

I would not use it.

There is some legitimate concern that full synthetic fluid is " too slippery "
and can lead to premature failure.

Maybe sometimes " newer " is not always " better " .



Jim

[34PKUP]

Originally Posted by trulyvintage

I would not use it.

There is some legitimate concern that full synthetic fluid is " too slippery "
and can lead to premature failure.

Maybe sometimes " newer " is not always " better " .



Jim

Wow! Please direct us to the published source of the information so that we may all benefit.

[51 MERC-CT]

Don't have a manual tranny to use it in but if I did I most likely would.
I have been using synthetic in my steering box for some time without any issues.
Run it past your re builder and see if he has any thoughts.
So far as premature failures is concerned, there probably has been more with conventional oil than there ever has been with synthetic.

[Scotty's 52 F3]

I have some personal experience in a non Ford transmission. My trans spec was for GL4 fluid. Everything now is GL5 which is supposed to be perfectly fine to use.

However, my trans shifting was "notchy" or "clunky" feeling when I used the newer oil. I had new synchros and fresh bearings but, it seemed like the synchros were not doing their job. The gears hadn't really slowed down enough to smoothly engage.

I was told to find some GL4 oil as the GL5 is "slicker". I didn't believe it but, I tried it and it worked. Shifts way better with GL4.

I have since used both conventional (Sta-Lube) and synthetic (Redline) GL4 oil and both shift fine. It is the GL5 that affects the shifting. Yet it is technically OK to use.

This may be where the new oil is slicker comments come from. I have also read about sulfur content of oils affecting brass synchros. The label on the oil should specify if safe for brass.

[SofaKing]

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Like others here, I have found that shifting is affected by the lube and some experimentation is helpful. I have also observed that the synthetic seemed to leak from one transmission at a greater rate than conventional lube. I don't have a shred of "science" to support it and I am not interested in debating it, just saying because you asked. Notwithstanding that, I use synthetic exclusively in my modern car engines. I see you are in Montana so you may find that viscosity spread useful in the winter; my experience with 70W weight is the trans shifted roughly compared to 90W. What have you to lose by trying, its cheap and easy to change if you don't like it?

[rotorwrench]

Ester base synthetic oil is a bit on the pricy side for me. I use the old mineral based stuff just like Grandad did. The only thing you have to be concerned about these days is what type of Extra Pressure additives are in the oil you choose. Sulfuric additives can be harsh for yellow metals like the brass blocker rings and the phosphor bronze bushings on the main shaft and the reverse idler gear. Low or mild EP gear lubes like GL1 or GL3 are harder to source these days but they are out there. Some use GL4 since it is has a mild EP that is less harmful than GL5 hypoid lubes. I used Aeroshell 100 SAE 50 motor oil in my 51 Merc overdrive so I won't have problems with the one way clutch.

[NealinCA]

Chevron's DELO gear lubes use Borate EP technology, so no worries about sulfur based EP additives and yellow metals. The 80w-90 works well in old Ford 3-speeds.

[expavr]

"I have also observed that the synthetic seemed to leak from one transmission at a greater rate than conventional lube."

After I rebuilt the 49 Merc O/D trans I'm using in the truck I tried a synthetic lube and had a similar experience with the synthetic lube leaking past the the reverse idler shaft and countershaft at an excessive rate. I ended up dumping the synthetic and am now using a mix of 90 wt GL 1 (75%) and Lucas HD oil stabilizer (25%) which slowed the leak to a weep and finally stabilized it all together. I noticed no difference in ease of shifting between the synthetic and the conventional lube. QUOTE][/QUOTE]

[A bones]

My experience is the same as post #5... Scotty's 52 F3-... Including GL4.

For the word of the 'gospel' shoot a line to Mac VP (Van Pelt)

Just an afterthought synthetic gear lube, I believe, is most useful in long range, heavy haul.
We are fine with with standard. I learned of GL4 here, but have not enough miles to know of any problem. Just sayin'

[gwmartin55]

Experience should allow you to benefit from our trials. I run a Van Pelt tranny and since he is the best in my opinion, I tried everything including synthetics. Call for him recommendation.
We drive thousands of miles a year on the Great Race and other similar events, and I regularly have mine to Mac out of an abundance of caution. Since changing to his recommended oil I can tell a difference. Old school is better in this case.

[john in illinois]

What is the recommendation?

John

[Talkwrench]

I think if synthetic was any good we'd know about it by now. You shouldn't be using a GL5 in it only GL4 or less ( GL1) a mild EP type. use an appropriate weight warm climate 140. Remember there are no seals for the counter shafts, also the gaskets are very thin, so a thin oil will leak easier .

[rotorwrench]

The aviation community (especially helicopters) have been using ester based oils & lubricants for over 50 years and they are very good lubricants for their intended purpose. The turbine oils have gone through several changes over the years to prevent coking up in the extreme temperature areas of the engines. The synthetic gear lubes were developed a lot later since they were an attempt to make the standard oils used for engines into a better gear lubricant.

The seals we use to keep these oils from leaking out have gone through the most evolution of all. They still don't have seals that work as well as folks would like them to. Bottom line is that the synthetic oil is expensive to use and hard to contain so if you use it, don't be surprised if the old tech seals don't hold it in very well.

[AnthonyG]

Synthetic lubricating fluids are great for correct applications. By design they are more slippery , a good thing as they reduce wear significantly. Having said that the older gears and syncros were designed with the viscosity and friction characteristics of the time. It is likely that while you will reduce wear the shift characteristics designed in from the era of design will change the feel during shifting. Feel is a fairly undefined concept. If the mechanics are working without any grinding, and the shifter is not hanging up you will get used the the new feel. The wear will be reduced ( simply the physics of less friction and better lube coat / adherence ). Again having said all that, if your putting a few thousand miles per year why bother. The mechanicals will last more years than you will be driving the vehicle with the normal requirement lubrication. If on the other hand your driving 20K mile / yr. or more you will notice ( wear characteristics reduced by multiple factor using synthetic lubrication, again science / physics and you will require less frequent mechanical attention) and benefit from the decreased wear.

[supereal]

Synthetic oils have a couple of drawbacks in old transmissions. They tend to leak past the primitive seals, and usually don't have enough viscosity to slow down the cluster gear between shifts, making shifting tricky. That is why we suggest 140 weight in old gear boxes. Synthetic oils are becoming the standard today, and will undoubtedly make the others obsolete. Conventional oils are miles ahead of the type used in our old cars originally, and are certainly less cost if you run an old engine that requires 500 mile drains.

[Drbrown]

For my tranny I changed from 140w to Sta-Lube GL-4 80w-90 and it shifts noticably smoother. Use GL-4 140w in my OD and rear end.