VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 What gear lube is best for the trans and diff

This lube you have, combined with one of the recommended lubes from that list might make a really good combined trans fluid. Certainly minimal risk in trying a combo like this I would think.

Wonder if there are heavier GL4 products in Europe or Australia that could work for these transmissions??

https://media.napaonline.com/is/image/GenuinePartsCompany/NWMDC?$Product=GenuinePartsCompany/23304

Copy and paste to bring up information.
Napa part number # SL24229

There are lots of good quality GL4 lubes around in the 85w90 weight range which could work fine, especially in a cooler climate but many of us are hoping to find something heavier like a 75w140 that is preferably a GL4 and NOT a GL5.

Looking for something like this available in North America or at least a distributor that will ship it.
https://www.castrol.com/en_sg/singa...smission-fluids/manual-gl-4-85w-140.html

or this https://www.rymax-lubricants.com/products/gevitro-gl-4-sae-85w-140/

If you want some oil to put in a synchromesh transmission, it would probably pay to buy some oil made for that purpose. It isn't uncommon these days.

In the 1930s, hypoid gear lube was just barely good enough to do it's job protecting hypoid gears. It probably made sense to just stick the same stuff in the transmission.

GL4 and GL5 are ratings relate to the suitability of a gear oil as a hypoid gear lubricant. That rating system is mostly useless where a synchromesh transmission is concerned. There are no hypoid gears in our transmissions.

Hypoid gear oil is necessary to protect hypoid gears, because they not only have extreme pressures at the contact area, but also have a wiping motion that scrapes off the oil.

Synchronizers are a brake. They need metal to metal contact in order to work. Using any super slippery hypoid oil, like GL4 or GL5 insures that the oil is doing everything it possibly can to make sure the synchros cannot do their job.

Even motor oil would be a better choice.

Okay....we've got a great thread going here! How about Royal Purple Max Gear 85W-140? They say its for GL5 and GL4 "It is non-corrosive to soft yellow metals (brass, bronze, copper, etc.) and synchronizer safe"

http://royalpurpledirect.com/product/max-gear-85w-140/

We've gone full circle lol. Gene has been recommending an oil like this all along and has used these himself.

We got steered away as anything that is GL5 compliant is intended to be a gear lube as Bloo alludes to and not fully meant for syncros in a transmission. As per Wideman's article the oils are buffered to prevent corrosion to yellow metals but MAY still cause syncro wear.

That's why we were hoping to find a GL4 85w140 or similar. Unless you can brew your own or find old stock, a GL5 might be the only simple option unless you find an 85w90 synthetic that is on the thick end of the spec.

At the end of the day these cars will see low, easy use, with clean fluid. The Royal Purple is way better than originally available and all of these GL5's are going to vary their chemistry so some may be better on syncros than others as they each have their own blend. Ideally a 85w140 GL4 meant for transmissions would be perfect but not easy to find in North America.

I say it's worth using, even if it's just while we all continue to hunt for the "perfect" fluid out there...

It's to simple ! Just buy a quart of your choice 80/90 GL4 and a quart of straight 140 GL4 and
mix at a 1 to 1 ratio and ( Wham ) the perfect mix.
Only in is it soooooo easy.

P.K. pretty much nailed the best option for the transmission by brewing your own. Ideally stick with the same brand and if you go with synthetic it will improve shifting when cold. This combo works out to roughly a 110w115. If you find it thick, replace it at some point and simply change the ratio of each to give you more of the lighter weight.

I think you folks have made this Tx oil thing way too complicated. I agree with Gene.Use 90w. I bought my '40 in 1963 with 60,000 miles on it and have put about 360,000 miles more on. I rebuilt the transmission at about 400.000 miles and the rear end is still going. I've never used anything but 90w as it came from Western Auto now Advance Auto. Didn't know such a thing as GL existed until this string. When these old cars were built, lubricants were not nearly as good as they are now and accordingly the old cars are very tolerant. I cannot imagine my farmer dad ever thinking about such a thing as GL when he put Tx grease in his '36 Chevy during WWII. We put the same grease in our Farmall tractors.

Hi art,

I know you've had your car just over a year now so I was wondering, were you having a issue with the transmission OR did you change the lube as just part of maintenance so you knew what you had.

Now as to your original question


Question, Did you know what came out and did you notice any improvement in shifting after you put in the Lucas?

I don't think changing from one synthetic 85W140 to another synthetic 85W140 will fix the leak. You will probably end up changing the seal. But, be sure to let us all know.

Good luck!!!!

So I'm sure most of you can agree with the following....if it ain’t broke, don’t fix it!

This 48 beauty had no issue with shifting when I got it last year. I then got the bright idea to change the fluid in the trans and diff.
I noticed within a week that I started having oil leaks at the rear of the trans at the torque tube joint.

The shifting has gotten rough ever since putting in the Lucas 85W140!

I ended up replacing the Clutch because....well...you get the gist....I thought, why not! It's gotta make it better in the long run.

Clutch did make a big difference. 1st gear is the grinder though! I gotta be kind and mindful when shifting into 1st, it's better dropping into neutral for a bit, then into 1st and I can skip the grinding.

At this point, I've purchased the Sta Lube 85W90 and will return the 140W stuff. It should come in Tuesday and I'll take the 48 to workplace and change the oil. I got it on the net for around 7 bucks! Not bad! Worst case scenario....I turn into a chemist and start mixing 140 into the 85W90 until I get the right brew

First is unsynchronized, and will grind. That is the nature of the beast. At a stoplight, touch second or third to stop first from turning, and then put it in first gear.

Heavy oil makes the gear slow down, or stop turning quicker. It is noticeable at stoplights if you are not touching another gear before going into first.

If you are trying to shift into first from second while underway, you have to match RPM, and the gear is unsynchronized. That means either double clutching or floating 1st gear, because it's speed has to come up in order to match.

Balkiness with the synchronized gears (that wasn't present before) is probably the oil. When I drained and replaced the trans oil in my 36 Pontiac, I put in some Master Pro SAE 140 GL4 because several people had reported good results with it on the AACA boards. The transmission got a little balky, especially cold. It wasn't horrible after it warmed up, but definitely a downgrade from whatever ancient oil I drained out. I have Redline 75W140NS (note the NS) oil in it now, and it shifts like it used to.

Redline 75W140NS is a GL5 rated oil intended for transaxles that contain both hypoid gears and brass synchronizers. It does seem kind of thin. Time will tell if it all runs past the torque tube seal into the rearend. It is still too early to know. It does shift nice.

I know I'm replying to an older thread but was wondering how the Redline 75W140NS worked out for you "bloo"?

It still shifts good. I like it. I have a habit of tapping second when going into first quickly at a stoplight in traffic, so I prevent grinding first gear that way.

I was a little concerned since it's thinner that it would drain back into the axle, but so far that has not been a problem. I checked the oil in the axle before I put it away this winter, and it was not overfull. I also checked the trans and it was not low. Maybe it leaked a little but not very much. You should keep an eye on that no matter what oil you use.

I was getting a bit of clutch chatter before I put it away for the winter. I suppose oil could have got out on the clutch, but I think it is more likely just some slop in the motor mounts. They're adjustable on my car.

Glad to hear your trans shifts good with that gear oil. I do the same thing as you before shifting into 1st gear to stop the grinding.

I'm about to change the fluid again on my trans and rear end. I used the Sta Lube 85w90 last time around and was wondering if I should try the fluid you used. I'm curious about the RedLine MT-90 75w90. I might try this one first to compare to the Sta Lube.

I also need to adjust the shift selector lever. Ever since I put those darn Fenton Headers on, it messed up my vacuum shift and overall shift quality.

Thanks for replying

Thanks to all for the foregoing, a real education for me. I plan to use AMSOIL 75W-90 synthetic ML-4, a Widman recommendation and readily available. My challenge is my trans leaks. I plan to add Lucas Transmission Fix in hopes to slow the leakage and chatted with Lucas on line to learn if it is safe for yellow metals/synchro-mesh. I was told the product is safe BUT the recommended I use their Engine Oil Stop Leak product in stead as it is more compatible with gear oils, while the Transmission Fix product is better used with transmissions using ATF fluid. Would welcome any advice/comments on use of the Engine Oil Stop Leak product in our transmissions versus other approaches used to lessen leaks....short of pulling the trans for an overhaul. Thanks, Bob

I will be very surprised if the stop leak does anything to address the leakage problem you have.

My guess is that the major leak is between the outside diameter of the bell shield and the mating inside portion of the fixed retainer. That joint constantly rotates as the car travels. The cork seal wears away and dirt gets ground into the metal bell. Leakage is normal given the age of the seals and mating parts.

I cannot remember if your transmission still uses a slinger for the front seal. Even if it is a sealed bearing the stop leak is probably not going to work on that old a seal.

I suggest that you clean the transmission off as good as you can and drive the car a short distance. Then check to find the origin of the leak. The side cover gasket can be replace without removing the transmission. Did you use any type of sealing compound on the fill and drain plugs?

Rusty, I did not use sealing compound on either the fill or drain plugs. That said, do not appear to be leaking. It does appear that the most active leak is towards the front of the trans. My hope is that the leaks might be slowed, not really expecting a fix. But I would like to try a product that will hopefully improve the situation and not risk doing something that would do damage.

If the leak is towards the front I have to wonder if it is really engine oil. Check the head and block below the rear end of valve cover.

Unless the transmission case is cracked there is not much to leak up front. I did confirm that your transmission has a slinger in front of the input bearing for oil control. There is no seal on the bearing.

Let us know what you find.

Thanks, will have a fresh look around and get back with observations. Cheers, Bob

OK, definitely the trans leaking....from front, from the fill plug (sorry I was wrong about that earlier, and on opposite side of trans near shift linkage, but this latter location appears minimal. The fill plug should be easier to correct somehow, but bottom line, I'm back to also using the best, low risk additive for leak suppression in our transmissions. I know in the long run that bad boy is going to need to come out and be rebuilt.....just can't swallow that this year. So my question is whether to use the Lucas Transmission Fix or Lucas Engine Oil Stop Leak as recommended by Lucas, or some other product. I feel that I should follow the Lucas suggestion but I the advisor may not have had experience in our era vehicles. Further thoughts on best approach for an anti-leak additive to use with the AMSOIL synthetic 75W-90 ML 4 gear oil?

Use whatever is easiest for you to get.

Remember to not overfill the transmission. The slinger bearing design at the front does not like overfilled transmissions.

I remember my father talking about ruining a clutch in a '47 Chevy when he parked with the front end pointed down a steep incline. The gear lube ran up the bearing cover drain hole and out the cover onto the whole clutch assembly.

Oooo, yet another chance to sow my ignorance....so if one fills the transmission until the oil drips from the fill plug hole it is overfilled? So I have been over-filling my trans?

You want to leave the plug out until the dripping stops since your problem is related to this. Ideally it should just be a hair below the opening when the car is level. Seal the plug with teflon tape or sealer made specifically for the plugs. You can buy at Napa.

75w90 is on the thinner side and may cause at least some weeping in a worn transmission. I wouldn't monkey with leak stop products as the only thing that will likely make a difference beyond a rebuild, is a thicker viscosity. I would put a 75w140 or 85w140 in it and seal the plug and your problem will likely be greatly reduced.

The normal thing back in those days was to stick the first joint of your pinky in the hole, bend it down against the inside of the case and you should be just barely able to touch the oil. Especially true on rear axles. I'm not 100% sure if that applies to you without looking in the shop manual (there were exceptions), but it probably does. Overfilling definitely leads to leaks on cars that do not have seals. Someone in this thread will know for sure.