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Transmission & Rear End Fluids


likeold
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Okay now that we have gone round and round with every ones opinion on what engine motor oil to use (I reverted to non-detergent) I need to move on to what fluid to use in the tranny and rear end, I hope it's not as contentious and straight forward. I figure while I'm under there changing the engine oil and painting the timing marks on the flywheel, I mine as well change out these oils too, thanks.

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From another thread -- https://forums.aaca.org/topic/370347-what-engine-oil-do-you-use/#comment-2289266

 

I recently switched my transmission oil again in the search for the best shifting possible in my 41 Century. I have tried several both synthetic and non and per a suggestion in this forum I investigated the Redline 75/140 NS synthetic specifically formulated for vintage/antique manual syncro transmissions and says so on the back label which is the first time I have ever seen an oil product specify this feature. After using it through the summer season when my hot trans can get balky I would say its far and away the best trans oil I have ever used. From the first shift it was apparent and my worn 2nd gear syncro got a new lease on life. Also unaffected by hot weather. I refilled my Moto Guzzi motorcycle trans with it and its never felt this good from new. 

 

Having switched to Redline MTL in my '64 GP's T-10, I am not surprised.  I'm switching my '38 to Redline when it's time to change...  ;)

Edited by EmTee (see edit history)
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Let me be the first :   In my 38-46s I have used the modern standard 85W140  gear oil.    Any multi weight gear oil is good.     I have used that in my 38 and my  35.     If you have the over drive installed, ( I installed in both my cars )   you need to use the  'GL-1' gear lub. in that unit only.       The sun gears can not used the more slippery oils of today so  i went to Tractor Supply and bought their brand - Traveler brand.   90 wt. all mineral    P/N. 591550.    It designed for Ford Tractor transmissions.    This is better than our old pre-war lubrications.    So I go to my Walmart and get GL-5 rated 85-140 gear oil for both the tranny and rear end lubrication needs.  And thats my story and I'm sticking to it....

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So I just want to make sure I understand. I do not have over drive so can I use any standard (not GL-1)  85W140 gear oil in the transmission and rear end? The oil I have on the shelf is GL-5 I'm not sure what the GL numbers stand for.

Edited by likeold (see edit history)
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Use the GL-5 rated gear oil.  Its the latest lube.   My guess is that  'GL' means 'gear lube'.   Gear lube has special additives to keep the lube in place on gear surfaces under forces the want to push it away from gear surfaces,   'anti-foaming' additives.   So any GL-4 or GL-5  85w140 will keep you in great shape.      If you are unsure about the old lube,  empty the old lube and replace with  new lube to the proper levels and run for +30 days.  Then drain and refill again to the proper levels and forget it for 30 to 50,000 miles.   Our new lubes can last much longer but our problem is we don't put enough miles to cause issues.   Old pre-war lubricants were only fair in keeping our cars in good shape.    When was the last time you changed your transmission lube ? rear end lube ?   World of difference in quality and performance over the last 75 100 years.   JMHO 

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If you want to really drive your  '38'  on modern roads and keep from being a speed bump,  our '38' rear ratios are a 4.44 : 1.   That is good enough for approx. 50 to maybe 55 mph if you push it.    All depending on engine condition - operating temps etc.   That also puts your operating rpm's at 3000 rpm and above.    Our engines do not like to operate over 3000 rpm for any extended time.   Look at your power / rpm charts and you will see that your cruise  rpm's put you around 50 mph.    If you had the '60' series 3.90 rear gears you could drive 55 mph  most of the time.    So GM designed their cars for roads in the 30's and 40's.    50 and 55 mph was a good point.    Other mfg's decided that running their engines slower at cruise would make them last longer.   So, today I would get run over trying to cruise 65 mph on almost all roads.   I chose to use Borg Warners over drive ( x.70) would let me drive my Great old Buicks and be able to keep up with slower traffic.   with my over drive,  I can drive 65 mph all day and my engine runs 2350 rpm's.    My engine loves that operating range and I'm happy.   I can even go 70+ when necessary and still not get close to the maximum (my limit) of 3000 rpm.   So,  I recommend installing over drive and I also get better mileage.   (+16 mpg on my trip to Tenn. from Tampa).  I you want any questions answered - ask.

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Just my opinion, but I definitely would not use GL-5. The higher sulphur content can eat away at brass parts, plus the extra "slipperiness" (engineering term!) can make your synchros slip more, leading to biting if you upshift or downshift too quickly. If your synchros are worn at all this will make it worse. My 40 uses GL-4 and it works fine. My 38 bites a bit with GL-4 especially when hot so I am going to change to GL-1 next Spring. I also use GL-4 in the rear of both cars.

 

My 38 66S has the 3.90 but I put a 3.6 into my 40. Cruises nice.

 

Cheers, Dave

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Yup,  the 3.60 rear is very nice.   Hard to find but simplifies for good cruising.    With synchro's hard to find,  I treat my gear shifting according.    I can run my 3rd gear down to around 25 and not shift.  By using my over drive, I'm good over a wide range of speed just using my OD  in / out with out shifting.    Just my opinion and the way I operate my '38'.    My '35' has a 4.88 rear so that was a 45 mph car.    I had to put OD on it just to be able to drive in my city / county traffic.    ahhaa what crosses we bear - - -

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BTW,   I put the GL-1  in both my OD and tranny.   And GL-4 is also good.  Actually GL-1  is better than any lube from those years.   That simplifies stocking oil...  I keep a quart in my trunk for trips JIC....    I think I mentioned the GL-1   I got from Tractor Supply.     I was only sold in 2 gal containers.    Just saved a quart  container from my regular cars and used that. 

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Your right about the cruising speed, seems my car likes it at 40-45 mph had up to 55 once I'm fine with 40 mph, never go on the highway. Okay sounds like I should consider GL-4. Probably will do a change now put a few miles on before winter and do another change when I pull her out in the spring.

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The "GL" rating system is worse than useless for choosing lube for a transmission. It has nothing to do with a transmission. Back in the 30s when Hypoid gears came along in automotive rear axles, the typical gear oil of the time was not good enough. Why? Because the sliding motion of the hypoid gears was constantly wiping the lube off of the teeth. Before that, with spiral bevel or bevel gears, the oil was under a lot of pressure, but was not getting wiped off as every tooth passed. "EP" gear oil was the solution for the new hypoid gears, generally in SAE 90 rather than the SAE 160 mineral oil or "600W" steam cylinder oil that was used earlier, in both transmissions and rear axles.

 

Since the new "EP" gear oil was just barely good enough to do the job in the hypoid rear axle, automakers continued using the same oil in transmissions as rear axles. They even did it with synchromesh transmissions, which were fairly new at the time.

 

As the EP oil got better, it got less and less good for synchromesh transmissions. A synchronizer is a brake, and it has to scrape the oil off to work. EP gear oil is designed not to scrape off.

 

GL-1 means "mineral oil", in other words "oil", with probably not a lot of additives. GL-4 means the oil is slippery enough for medium duty hypoid gear service. GL-5 means the oil is slippery enough for extreme duty hypoid service.

 

The old saw about "GL4 for transmissions, GL-5 for rear axles" has not been true for decades, and only worked by accident when it was sort of true. I believed it until 1995, when I discovered that it didn't work anymore.

 

In a hypoid rear axle use the highest quality hypoid gear oil you can get your hands on. If there is any brass or bronze in the rear axle, then you need one that will not attack "white metals". There will be a rating for that in the datasheet. Read it.

 

In a synchromesh transmission, use an oil made specifically for synchromesh transmissions. It will shift better, and you won't have to worry much about whether it eats the brass, because synchros are assumed to almost always be made of brass. There are many synchromesh oils to choose from these days.

 

Edited by Bloo (see edit history)
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Following a recommendation made some time ago in this forum I gave this a try...

Redline makes a synthetic oil blended especially for vintage syncromesh transmissions and it says as much right on the container. I know of no other similar products. I have tried all of the lubricants mentioned here and more including synthetics and special additives so I didnt expect much from Redline.

Sold as Redline 75/140 NS Synthetic.

My balky 2nd gear syncro feels rebuilt and even in summer heat when shifting used to degrade it stays smooth. I have tried countless lubricants over the years hoping something would improve shifting. It works so well I filled my old Moto Guzzi trans and its never shifted better. Hands down the best trans oil I have ever used and with truly observable improvements. Its that good

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And…there’s always an and. 

 

Some lube suppliers will say they ‘meet’ API requirements but unless they show the API trademark of certification, you are taking the suppliers word for it. If the trademark is shown then you have the assurance that the product meets the rigorous API testing and is continually monitored to meet it.  
 

API also monitors who uses their trademark and using it falsely will get a big lawsuit. 
 

 

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