Recommended transmission fluid

[Hemibear426]

What fluid is recommended these days for a standard/manual 3-speed floor shifted transmission? I know the service manual says 50WT engine oil but I am wondering if something might be better? I don't think I want to go synthetic.Our transmission is marked D-11 (1939?). Thanks for any input or guidance.

Mike

[Sam Buchanan]

You will get various opinions about this (try asking what kind of motor oil to use.....) but the closest thing we have now to what was used back in the day is GL-1 lubricant. The more modern GL-4 and GL-5 have components that can lead to deterioration of the brass synchronizers in our old trannys. I started out with a GL-4 in the '48 P15 but had issues with the 1st-to-2nd shift being crunchy until the transmission got hot. I changed to Red Line MTL which eliminated the crunchiness and is also formulated to play nice with the brass synchronizers. It is a little pricey but should last a very long time in our cars.

[BobT-47P15]

One local auto supply (O'Reilly) has a container of gear lube marked "80w 90" weight. 

On my 47 Plymouth the book says 90 weight for the differential and 80 weight for the transmission.

 

Man at the auto supply said this oil should be OK for both.    Otherwise you have to shop around for the single weight stuff.   

Sounds logical to me.  Think I will use the 80/90 in the trans.

[RobertKB]

I’ve been told GL-1 is the best to use rather than GL-4 or GL-5. It is supposed to be easier in the brass parts and synchros work better with it. Only problem is I have been unable to find any. 
 

I presently run an 80/90W GL-5 right now in my ‘51 Dodge business Coupe’s totally rebuilt tranny. Grinds a bit if I shift too quickly from 2 to 3. Fine if I shift quite slowly. Better when warmed up. I’ll live with it until I can find some GL-1 gear oil. 

Edited May 18, 2020 by RobertKB

[Sam Buchanan]

1 hour ago, RobertKB said:

I’ve been told GL-1 is the best to use rather than GL-4 or GL-5. It is supposed to be easier in the brass parts and synchros work better with it. Only problem is I have been unable to find any. 
 

I presently run an 80/90W GL-5 right now in my ‘51 Dodge business Coupe’s totally rebuilt tranny. Grinds a bit if I shift too quickly from 2 to 3. Fine if I shift quite slowly. Better when warmed up. I’ll live with it until I can find some GL-1 gear oil. 

The RedLine MTL should fix your problem and protect the syncros. 

[Sam Buchanan]

2 hours ago, BobT-47P15 said:

One local auto supply (O'Reilly) has a container of gear lube marked "80w 90" weight. 

On my 47 Plymouth the book says 90 weight for the differential and 80 weight for the transmission.

 

Man at the auto supply said this oil should be OK for both.    Otherwise you have to shop around for the single weight stuff.   

Sounds logical to me.  Think I will use the 80/90 in the trans.

The auto parts store oil is almost certainly GL4 or GL5. Both can be too slippery for smooth shifting a cold transmission. 

Edited May 18, 2020 by Sam Buchanan

[keithb7]

Putting my ‘38 tranny back together today. I’ll try the Redline MTL. 

[Plymouthy Adams]

GL1 is readily available at NAPA..if not in stock is in their inventory and available on an overnight....maybe same day if you get there early....it is gallon container but relax, that gallon is better priced than many quarts of other similar lubes....I bought a gallon not long back for under 17.00

[Plymouthy Adams]

as an added and in case  you get an inexperienced counter attendant...(notice I did not say parts agent).....Napa stock this in their inventory under part number  65-201

 

 

[Hemibear426]

Thanks so much! Went to Redlines website and found 6 different ones to choose from.Any recommendations on which Redline MTL to use? 75W80?

[Plymouthy Adams]

follow the book recommendation......the API is what ensures that they are equal to those specs...

[Sam Buchanan]

4 hours ago, Hemibear426 said:

Thanks so much! Went to Redlines website and found 6 different ones to choose from.Any recommendations on which Redline MTL to use? 75W80?

There is only one MTL, it is 75W80.

[Loren]

I've told this story before. I used to work as a SAAB technician back in the pre-GM days. While the VW guys changed engines every 40,000 miles we were changing transmissions. The cost to the customer was about the same but for me the SAAB gearbox was a lot less grubby work.

The SAAB aircraft engineers struggled with transmissions (SAAB never built helicopters so they never really figured out transmissions). Every time they did a redesign they doubled the size of synchros, gears, bearings, shafts and it still wasn't enough. One place they did good research on was lubrication and the first thing they learned was that viscosity had a lot to do with the temperature the gearbox ran at. It's no secret higher temps lead to bearing failures. The spec originally was for 90wt gear lube but if you ran 75wt which is water thin, you could lower the temperature dramatically on the order of 20-30%. The change over to 75wt was troublesome as the factory had to stock it and ship it because it wasn't always available locally. More research lead to a much better solution which was the approval of using motor oil in the transmissions. Motor oil (of any type) did not attack the brass synchro rings or the special moly coating on some of them and it didn't attack the seals and gaskets.

For off road racing we found that Redline had a lube that could stand high temperatures better than anything else and not generate them because of viscosity drag. The SAAB transaxle had a limited slip differential, an on center ring and pinion (non-hypoid) and a sprag clutch freewheeling unit (which we always used to relieve the back lash forces against the ring & pinion). We never had any transmission problems while using the Redline product.

What would I use in a Plymouth transmission? Redline products are about as good as it gets and I am sure MTL is even better than what we used to use.

I am certain a Plymouth transmission is way under stressed for power the engine produces and the weight of the car. From my experience you could use just about anything in it and you wouldn't hurt it. You have to remember they were designed at a time when lube oils were not very good at all so the engineers were very conservative.

[T120]

Loren, I found your comment about using motor oil in standard transmissions interesting. Several years ago I was at a shop that specializes in rebuilding transmissions, I asked what they use in standard transmissions.The answer was SAE 50 motor oil...While it is not what I use, nor am I recommending using motor oil, I found this viscosity comparison chart ...

 

[T120]

This is a page I scanned from my 1937 Chrysler owners handbook with recommended transmission fluids...

On the right hand page there is reference to using Aircraft oil or Engine oil for use with the overdrive transmission.

 

Edited May 19, 2020 by T120
added text

[Loren]

Thanks for that page!

In my project car I am putting an overdrive transmission. One of the things that caught my eye was the "Drained, Flushed and re-filled" statement. What "flushed" is usually written up as is filling with Kerosene then draining (perhaps with a trip around the block). The Overdrive has a Sprag Clutch as part of its mechanism. My experience with the SAAB freewheeling was that they (the SAAB Sprag Clutch not necessarily the B-W Overdrive sprag) would pack up with crud and slip if not used regularly. A drain and re-fill with ATF (the cheapest B-W/Ford approved type F) would clean the inside of the gearbox like it was a brand new clock! Which made overhauling one much easier. So for my money any time I rebuild a transmission it gets the ATF treatment first. Kerosene doesn't sound like it would do the job as well as ATF and besides Automatic Transmissions have Sprag Clutches. Mercedes manual transmissions used to specify ATF and the rather fragile SAAB transmissions responded very well to it. I would not be afraid to use it in an older transmission especially if it leaks a little (show me one that doesn't) and you don't want to spend $15 a quart to fill it. When you finally get around to changing gaskets and seals you will be delighted at how clean it is inside.

6,000 miles is way too early and wasteful to change transmission oil now days. Modern oil does not oxidize like the old stuff did. Most transmissions on late model cars don't even have drain plugs so they are lubed for life.

 

[keithb7]

Well I might be more stumped now about this manual tranny oil controversy than before I recently started doing research.

 

I located a GL-1 oil here locally that I can get. However I must buy a lifetime supply. It only comes in a 5 gallon pail. I agree that GL-4 and GL-5 is too slippery for synchros. I have been studying how they work and I can see how those new oils may be detrimental to speed matching adjacent gears.

 

The MTL Redline stuff is pretty pricy around here. About $10 USD per pint. I may go that route. My manual tranny need 2 ½ pints.

 

I called my local NAPA asking for GL-1, they laughed as they said they'd do some research and call me back. I am not expecting a call back. What about the heaviest engine oil we coudl find? Would that work? SAE50 ? Might be ok. No? Seeing as the Chrysler article above calls for it in the trannies with Overdrive. My 1953 M6 tranny calls for SAE30 engine oil. My M6 has a pin-type synchromesh. However I think they too utilize cones, or speed ramps, to wind up or down the adjacent gear speeds.

[T120]

I have a number of vintage cars with stock standard transmissions,several are equipped with the overdrive option, (all are 1952 and older). I am hesitant to recommend  the best transmission oil to use .While there may be better products on the market today,I use the same gear oil as what Plymouthy mentioned....

I might add that the price per gallon Plymouthy quoted sounds about right, I bought mine several years ago and it was a little less expensive?

Edited May 19, 2020 by T120
added taxt

[keithb7]

19 minutes ago, T120 said:

I have a number of vintage cars with stock standard transmissions,several are equipped with the overdrive option, (all are 1952 and older). I am hesitant to recommend  the best transmission oil to use .While there may be better products on the market today,I use the same gear oil as what Plymouthy mentioned....

I might add that the price per gallon Plymouthy quoted sounds about right, I bought mine several years ago and it was a little less expensive?

 

If you can buy that Napa oil in Alberta, that's interesting. I cannot get it here in BC. Part number is not available here , they just told me.

 

https://www.napaonline.com/en/p/FNJ65201

[T120]

Keith, It is not available at NAPA in Canada...They have never heard of it, (blank stare at the counter), lol. I live not far from the US/Canada border,I phoned the NAPA dealer in Cut Bank,Montana...trucked from Billings,Montana, it was there the following morning for pick up. Without getting political...there is no French language on the container,only English and Spanish...Canada would be a very insignificant market,,,?

[Adam H P15 D30]

Last year I drained the NAPA GL-1 out of my 3spd and filled with Redline MTL, Big improvement in shifting....

[keithb7]

At $66 +tax CDN for 3 bottles of Red Line MTF,  upon reassembly of my 1938 3 speed tranny, I think I will go with 20W50 engine oil to fill and test drive it. If the tranny functions well, shifts nice and no leaks...I will switch over to Red Line MTF. No point in pouring in the liquid gold over here until I am convinced the tranny is the car to stay! See how frugal I am? lol.

 

The guts in my 1953 M6 tranny have several similar parts yet it calls for SAE 10 engine oil. Also in my 53 shop manual the 3 speed manual tranny was available. It calls for SAE 10 oil too. It has synchros...That's interesting to me. Why is the tranny oil in a 1938 3 speed SAE 160, yet in 1953 SAE 10? Different synchro engagement design I presume?

Edited May 21, 2020 by keithb7

[Plymouthy Adams]

while viscosity of engine oil and gear oil kinda overlap a bit....the motor oil does not have near the shear protection of the GL rated lubricants....the latest GL4 and 5 are extreme pressure lubes for differential and not used in transmission....some modern trannies use motor oil and some use automatic tranny fluid....these are cars however are not as such and the SAE for the time of manufacture is still the overall guide for application...modern synthetics can be substituted when the shear values are known and matched.....GL1 is still available for in truth....there is still a big need for the oil.  

[T120]

In the original owners manuals for the older cars I have, there is a cautionary note, do not use lubricants with EP additives in the transmission...GL1 oil as mentioned is still available at a reasonable price...?

Edited May 22, 2020 by T120
spelling

[Sam Buchanan]

4 hours ago, keithb7 said:

At $66 +tax CDN for 3 bottles of Red Line MTF,  upon reassembly of my 1938 3 speed tranny, I think I will go with 20W50 engine oil to fill and test drive it. If the tranny functions well, shifts nice and no leaks...I will switch over to Red Line MTF. No point in pouring in the liquid gold over here until I am convinced the tranny is the car to stay! See how frugal I am? lol.

 

If you put motor oil in it and it doesn't shift like you think it should.....is the problem with the tranny...or the oil????

 

Go ahead and buy the good stuff. If you need to go back into the tranny you can drain it and save it.....frugally. If the tranny works well, you won't need to change that oil in our lifetime.   

 

 

Edited May 22, 2020 by Sam Buchanan