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

I am sure this has been asked before but I was wondering what everyone is running for gear lube in the trans and differential of their 41-48 Chevy cars. I understand their is concern about some of the gear lubes attacking the soft yellow metals and causing problems. If possible I would like to avoid that. I also don't understand the difference between the GL4 and GL5 types. It seems like everyone stocks the GL5 and the GL4 is harder to find. I was planning on running 85W-90 unless there is a reason to run something heavier like 85W-140. How about synthetic versus traditional? Any input would be great!

You are right, the subject has been discussed before. The general concensus is to use the 85/140 or a bit thicker if you can get it.I havent got my truck driveable as yet but have just put gearbox and rear axle back together with new bearings so I have been watching these posts.
Tony

RM,

I prefer 85-90 while Gene prefers 85-140. He seems to think that the heavier oil is better while I think the lighter is better.

In all applications I think the lighter oil that can do the job is better than the heaviest oil that can do the job. My reasoning is that one of the benefits of the lighter oil is that it is better at flowing and carrying off the heat of friction wherever and whatever its source. There is a relatively large quantity of oil in the transmission, crankcase and differential to allow for cooling once the hot oil created at the source of friction has been carried off.

Oil needs to be somewhat hot in order to do its best job. That is why there is a thermostat in the engine (hotter water for the heater and defroster are merely byproducts of the increased heat). A thermostat is not needed with 85-140 because it is thin enough to start with and will do a good job.

When using it to 85-140 there will be a need to create a source of cooling for the transmission and differential. That is why you see the rear pan on some applications with the heat transfer ridges on them like as in air cooled engines. See note.


The above is my opinion and reasoning. Gene's seems to be that 140 wasn't around when the service manual was made. If so, that is what the manufacturer would have advised. Seems a reach to me. Let him explain.

Gene, will advise you that todays oils are far superior to those made in the 30s and 40s. He is right. Either weight oil (85-90 or 85-140) will serve without any problems. it's mainly a personal preference. (I hope I have this right, Gene)

Charlie

Note: Owing to Gene's recommendation I have put 85W-140 into the differential of my 41 project car. It keeps me up at night worrying about it and causes nightmares, so I may yet pull the plug on it and put in 65-90. It's an itch I can't scratch. Dang!

The 85/140 is best for summer use in te transmission and is usually GL4. The 85-140 is not so thick when cold but keeps it viscoosity better when hot. This helps tp prevent clutch chatter and gear rattle when backing up and oil is hot.
There is no reason it can not be used in the differential also. I used it for years in both my modern and old cars with no problems.
It is like 10W-30 multi-viscosity oil, cover more temp. ranges.

Sta Lube makes 2 weights of gear oil that state right on the bottle that it will not harm brass parts. Part # SL24229 is 85W-90 wt and #SL24228 is a straight 140 wt. I get it at Napa.

I wouldn't recommend straight #140 for a 1937 or later transmission or differential.

"I prefer 85-90 while Gene prefers 85-140. He seems to think that the heavier oil is better while I think the lighter is better.

In all applications I think the lighter oil that can do the job is better than the heaviest oil that can do the job. My reasoning is that one of the benefits of the lighter oil is that it is better at flowing and carrying off the heat of friction wherever and whatever its source."

Charlie,

One of the interesting things about forums like this, whether it's about cars or trucks, restorations or street rods is the abundance of opinions. On many of these subjects the manufacturers of the products in question have technical departments where engineers are actually delighted to answer questions from interested amateurs. They are extremely helpful.

Here's an example. I have a Chevy Vega steering box in my 1932 Ford roadster street rod. When looking for lube for that steering box I found that it has a GM part number but is is no longer available from any GM dealers. A call to Shell Oil tech services hooked me up with a lubrication engineer. I gave him the GM specification number on the grease and he matched it to a currently available Shell product. He wasn't done yet. He asked me for my shipping information and sent me a quart of it as a "sample".

I had a similar experience when I started pulling a travel trailer with my '71 Dodge van that I still have. The extra load of trailer towing had the effect of drastically reducing U-joint life. A call to Quaker State tech support hooked me up with a lubrication engineer and he recommended synthetic grease. He also was not done and sent me a case of cartridges as a "sample". That was nearly 30 years ago and the problem was totally solved.

On these forums that approach seems out of the mainstream. Much more common is asking for "opinions". I notice the same thing on Stovebolt.com and the Chevy Talk Performance Related forum.

Ray W

In 1936 and prior Chevrolet said 160 in the summer and 90 in the winter.

"In 1936 and prior Chevrolet said 160 in the summer and 90 in the winter.
Gene,

The challenge is finding 160. My '36 PU trans likes 600 but even that is a little thin once it is hot, yielding a poor shift into 3rd gear. Also, 600 is a steam cylinder oil, not a gear oil which is a little worrisome.

There are gear oils for industrial use. I've tried viscosity 460 and it seems like SAE 140. The next more viscous is 680 but that's available only in 5 gallon minimum quantities for about $100. That's kind of pricey for an experiment requiring only a little over one quart.

Ray W

I found that all 600 gear oil is not of the same viscosity. The first I bought years back (for mt '34) was so heavy when the car was in neutral, (oil cold but in summer) the engine would slow down greatly til warmed-up.
The next brand I bought was more in reason. Over the years I just use straight 140 which is fairly easy to find.
600 = 160.

GL5 eats copper/brass/bronze... period.
I use GL4 in the trans because the trans has bronze parts in it.
Only GL4 I can find is 85-90 Sta-Lube at NAPA.
The diff parts are all steel or cast iron so GL5 is ok.

"GL5 eats copper/brass/bronze... period"

Boardwalk,

What is the source of that statement?

I have asked various lubrication engineers about that and gotten the same answer from all of them. What they say is that occurs at temperatures above what exist in an automotive manual transmission. They further explain that the highest temperatures occur at gear tooth interfaces, not at bushing-shaft interfaces.

On purely layman's level, when I've disassembled transmissions that have been filled with GL5 there are no noticeable effects on brass synchronizer surfaces or bronze bushings.

It would be interesting to see any test data on this subject.

Ray W

Boardwalk,

There are countless articles on the subject of yellow metals and GL-5 oil. It would take a lifetime to read them all but here's just one:

http://www.macysgarage.com/myweb6/gear_lube.htm

Ray W

Sorry to bring this back up but what brand GL4 do you guys recommend? I cannot seem to find 85W140 in the GL4. I don't think the Lucas stuff is GL4.

Anyone hear of Dynolite 90W gear oil? It's GL4 and seems like it might work for my trans. After I did the gearbox oil change with Lucas, I noticed I started having oil leaks at the rear of the trans.

As stated above GL4 85W140 is extinct, at least in the USA. Also as stated above Sta-Lube GL4 85W90 is still available at NAPA auto parts. My store has it on the shelf. Google "Sta-Lube gear oil".

Use a 75w140 instead and it's available from many of the big name companies and Amazon. Even Delco has some. It covers a wider range and will be a bit nicer when the transmission is cold.

Edit: Just noticed many of these 75w140 are GL5. I recall some past discussions on this forum where the GL5 was fine to use but doublecheck and do your homework for your application. I believe some early GL5 was hard on yellow metals like brass/bronze but seem to think this may be a non-issue now but doublecheck. Some GL5 I have used actually made note on the bottle it was safe for yellow metals.

Maybe Chipper will add some thoughts on the concerns regarding yellow metals.

I have used GL5 in the transmissions for years with no problems. Differentials have no brass parts.
Most GL5 have buffers to prevent harm to brass.

Let me stir the pot. A good read.
https://www.widman.biz/uploads/Transaxle_oil.pdf

Written by a expert and a member.

That's a great read. I always like Widman's explanations.

Good point on the potential syncro wear with the GL5. Likely not an issue for an infrequently and lightly driven car that will likely outlast most owners themselves, but will certainly bug me now that I'm aware.

In my modern cars I use Red Line Synthetic MT-90 75W-90 GL-4 Manual Transmission fluid which is on his recommended list but maybe a bit light for these older transmissions.
He also recommended a SAE 50 diesel oil. Makes me think about making a blend in these old transmissions. They are not picky so maybe half Redline MT-90 / half SAE 50 diesel oil to thicken the mixture or half Redline MT-90 / half GL5 to reduce the effect on the syncros. I wonder if Chipper could recommend a blend?

Of course just having modern, clean fluid at the correct level and being driven lightly, most of us might be just fine with almost any current fluid...

When Chevrolet made special "economy" engines they specified noth but #30 oil for the transmission. The first one was in 1935.

In previous posts on this topic Gene has recommended thicker gear oils to compensate for a worn synchronizer gear. The theory being the thicker oils slow the gear down faster allowing for smoother shifting (less grind) when shifting from 1st to 2nd gear. I have addressed my old tired transmission with a grind problem by shifting into neutral and counting to 5 then shifting into 2nd. Works for me in my town where 95% of the speed limits are 35 MPH and the rest 45.

Good luck, Mike

I USED GL5 IN MY 1939 AND AT 100,000 MILES IT WAS ABOUT THE ONLY MAJOR ASSEMBLY THAT NEVER WAS APART AND SHIFTED LIKE A DREAM HOT OR COLD

Great info! I ended up buying some Sta Lube 140W from Napa. Gonna give this a try for a while.

Straight 140 is too heavy for a 1948. #90 was specified but an 85-140 can be used.

Aalso for the hypoid differential gears it requires a GL4 or 5.

No disrespect to anyone but please remember GL5 has been around only since 1995 or so. So the gear oil used before 1995 would not be a GL5. At least that is my understanding.