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Transmission oil after rebuild


SteveR
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In reading a few posts on rebuilt engines, I have a question:

I rebuilt my 39 transmission late last year. I used assembly lube for the needle bearings. Do I now have to change the oil now that it is up and running?

The new parts I had to change were the bearings, main shaft, 2 brass synchro rings, and 3 stop pins

Edited by SteveR
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I would also suspect that it should be okay, assuming you did not pack it full of assembly lube 😄

I disagree about the GL1, though. Sounds a bit like using beef tallow oil, for extra authenticity 😉

Edited by Ivan_B
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Thanks for the replys

I only used enough assembly lube to hold the needle bearings in place. The oil that I used is Miller Oil 90 GL1. So far I have had no problems. I just don't want any in the future.

The joy of removing the tranny and figuring out what I had was bad enough but putting it all back together on the drive wasn't much fun and the clutch release lever was, well had it not been for my wife inside the car with another set of eyes it would still be sitting there.

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31 minutes ago, Ivan_B said:

Sounds like your transmission was in good condition

1st and reverse gears were worn as usual but nothing broken and my funds were not there to replace them. So far it has not posed a problem.

At some point, this tranny had been gone through. It also was from a junkyard with a big '39 DOD__' painted on the side in yellow. My car is a 37. Inside the stop plates were broken and the stop rings were all worn out. In trying to find the parts for this I found that the stop rings and stop plates were from a 1940/41 transmission.

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Modern hypoid trans lubes have additives that don't play nice with brass,  bronze, and other "white metals".  How long these parts of your transmission can stand up to the play ground bullies is any one's guess.  If you only put a couple K miles on a year, they may last your life time.  And since the sensitive parts are related to your synchro, it may never cause an issue except grindy down shifts.  And unless you are doing a lot of mountain roads...who knows?

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49 minutes ago, greg g said:

Modern hypoid trans lubes have additives that don't play nice with brass,  bronze, and other "white metals". 

So a GL1 oil is not recommended?

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30 minutes ago, SteveR said:

So a GL1 oil is not recommended?

That is exactly what is recommended by the factory.

 

GL4 MTL might be acceptable. 

 

GL5 is frowned upon due to concerns about it's effect on the brass synchros.

 

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I think Red Line MTL has been mentioned around here before as a great xmsn oil. Fairly pricey. So maybe not ideal for the folks with a leaky transmission. 😉

 

Some good info here:

https://www.redlineoil.com/mtl-75w80-gl-4-gear-oil

 

They talk about GL-1, synchos, (clutch gears) GL-5 etc. Seems like the golden nectar for old Mopar trannies. 

Edited by keithb7
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2 hours ago, Sniper said:

GL5 is frowned upon due to concerns about it's effect on the brass synchros.

Hrm, sure hope the concerns are not actual known facts.

I plan to change oil tomorrow on my trans/rear diff ....

85/140 gear lubricant .... A multipurpose extreme pressure gear lubricant to be used where API-GL5 is recommended.

For manual shift transmissions, conventional differentials, rear axles & steering gear boxes found on passenger cars, trucks, farm tractors ... Recommended for limited slip/posi traction rear axles.

Protects against rust, foam, high temperature and corrosion of copper or bronze bushings.

 

This is super tech oil from walmart. Pretty pleased with the engine oil since I switched to it ..... I drive a average of 4000-5000 miles per year on my daily driver.

I just change it every 6 months by age & not by miles. ..... Usually a quart low on oil by 2500 miles, still right on the full line ...... I'm getting behind on my oil change date.

 

I'm going to give the supertech gear oil a try in my truck.

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21 hours ago, Ivan_B said:

I would also suspect that it should be okay, assuming you did not pack it full of assembly lube 😄

I disagree about the GL1, though. Sounds a bit like using beef tallow oil, for extra authenticity 😉

GL 1 is required to protect the brass components.

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Just changed the gear oil in my 41 Plymouth a few weeks ago. For a manual of that vintage, GL-1 is what is called for and all it needs. Shifts great, especially compared to the very old oil that was replaced. Used this:

NAPA GL-1 90W Gear Oil, 1 gal
Part # NHF 65201
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So I guess what I am hearing to my original question is, Yes it is ok to leave your GL1 oil with the small amount of assembly lube in it without changing the oil as you would do in a rebuilt engine.

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The difference is a engine has several small oil passages going through crank , rod, cam bearings. Of course the block has provisions for these small passages.

The engine could easily get a issue with one of these small passages blocked.

Also a rebuilt engine will have small metal filings that will contaminate the oil & get run through the bearings.

 

A rebuilt transmission will not have small passages so assembly lube is not going to clog ..... not sure if assembly lube is used on transmissions.

Any new machined surfaces or gears will create small microscopic metal filings & contaminate the oil & bearings.

Just not as critical on a gear box vrs a engine.

 

The stink is over do we use modern oils or old school oil?

I'm a firm believer any modern oil far surpasses the old oil ..... that up to you to decide.

Either way, engine or gear box just rebuilt, I would run it then change the oil. A gear box I would wait for 200-300 miles to let the gears find their happy place. then change it. 

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OK, here is the issue with GL-1 vs other oils. The newer oils were designed to work with syncros made of harder materials so they could handle the higher torque and compressive forces within newer design transmissions. The problem is that the additives, over time, become a corrosive to the brass, bronze and other soft metals used in our transmissions. It is not the mechanical qualities of the newer oils that is the issue, it is the chemical makeup that is not conducive to our transmissions.

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(SAE 75W-90, SAE 80W-90, SAE 85W-140 etc.). The first number of the designation specify the oil viscosity at cold temperature, the second number specifies the oil viscosity at high temperature.

 

So if your transmission calls for 80-90 .... 85-140 .... not quite 80 in cold temps, a little thicker .... the 140 is just how high the oil will perform under high heat.

It will out performs 80-90

 

 

EP oils may be either mineral or synthetic base. They contain EP additives, rust and oxidation inhibitors, anti-foaming agents and demulsifiers. The viscosity of EP oils according to the ISO grading system is between 68 to 1500.

 

Use the chart below, The higher the GL, the more protection you will get.

 

Designation of gear oils by performance

American Petroleum Institute (API) established a performance grading system for gear oils (mostly automotive gear oils). According to the system gear oils are designated by the letters GL (Gear Lubricant) followed by a number 1,2,3,4 or 5:

  • GL-1

GL-1 gear oil has rust and oxidation protection effect but it does not contain extra pressure (EP) additives. the oil is used in low load applications only.

  • GL-2

GL-2 gear oil contain more additives than GL-1, but without EP effect. It is used in medium loaded worm gears.

  • GL-3

GL-3 gear oil possesses light EP effect. It is used in non-hypoid gears.

  • GL-4

GL-4 gear oil possesses moderate EP effect. It is most widely used oil.

  • GL-5

GL-5 gear oil possesses high EP effect. It is used in hypoid and other highly loaded gears.

 

 

This is how I make up my mind, I want to use the best oil I can for a reasonable price.

I'm using 85-140 GL-5 from walmart for $25 per gallon & smiling about it.

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On 5/28/2023 at 8:47 PM, SteveR said:

So I guess what I am hearing to my original question is, Yes it is ok to leave your GL1 oil with the small amount of assembly lube in it without changing the oil as you would do in a rebuilt engine.

 

I am sorry, I did not mean to start another oil debate with my earlier reply 😅 You are perfectly fine with GL1 since, as it was correctly mentioned by others, this appears to be what is actually recommended by the factory. I just probably would not choose a lower grade oil on purpose, if a better quality oil is available, that's it.

 

As it was also correctly pointed-out above, some higher grade oils might not work well with the brass synchros and other alloy components, since these are primarily designed for hypoid rear axle gears, etc. So, when choosing the correct gear oil, make sure that the jug says it is fully compatible with brass synchros! I've also heard good information about, and myself used RedLine and AMSOIL products before. These are expensive, though.

 

Also used the 85-140 GL-5 from Walmart. Once the weather got cold, the car would stall as soon as I let go of the clutch in gear... Very thick stuff 😉

Edited by Ivan_B
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