Non-synchro GL-5 gear oil for a Muncie

[Patrick B.]

Generally, I assume that the API oil service designations are all one needs to know about what lubricants to use. Yesterday, I bought Valvoline High Performance 75W-90 Gear Oil and my local NAPA store to fill my fresh 67 M-21. However, the label on the back says "recommended for hypoid differentials (conventional and limited slip) where API GL-4 or API GL-5 is specified and non-synchronized manual transmissions where API GL-5 fluid is specified" without a mention of synchronized transmissions.

Is there a special GL-5 designation for non-synchronized transmissions? Is GL-4 and GL-5 for differentials different from the GL-4 designations discussed here as appropriate for Corvette 4-speeds? Is there any reason why I should not use this stuff?

I was hoping to fill the trans today, and I hope one of our oil experts can enlighten me.

[Edward J.]

Re: Non-synchro GL-5 gear oil for a Muncie

Pat there was a recent restorer with some good reading on he gear oil for the transmisson, it may have been a couple of issues ago and it really will give you some good in site on which way to go.

[Donald H.]

Re: Non-synchro GL-5 gear oil for a Muncie

Pat,

I just filled my freshly rebuild 66 M21 with Valvoline 80W-90 High Performance gear oil. The back of it states "Recommended for all hypoid differentials (conventional and limited slip) and manual transmissions where an API GL-4 or GL-5 fluid is specified."

Seems like the only difference is that your bottle of 75W-90 says non-synchronized manual transmissions.

Don

[Donald H.]

Re: Non-synchro GL-5 gear oil for a Muncie

The restorer article is in Volume 41 Number 4, Spring 2015 is specific to Muncie and some different oils.

The authors first recommendation is 80w-90 with just the GL-4 rating. He specifically names Sta-Lube from NAPA. His second choice was the Valvoline HP.

Don

[Duke W.]

Re: Non-synchro GL-5 gear oil for a Muncie

If you look at your owner's manual or CSM the likely recommended manual transmission lubricant is Mil-L-2105. This mil spec was canceled over ten years ago and replaced with the commercial specification - 80W-90 GL-5.

Duke

[Patrick B.]

Re: Non-synchro GL-5 gear oil for a Muncie

I Returned the Valvoline high performance gear oil for non-synchro and got Valvoline full synthetic 75 w- 90 that says for all manual transmissions where GL-5 is specified. I guess Duke's comment means that GL-5 is the right spec for a Muncie. I hope the full synthetic is not a problem. It seems a bit thin sloshing around in the bottle.

[Larry M.]

Re: Non-synchro GL-5 gear oil for a Muncie

Pat:

Most of us use the conventional dino oil, and not the synthetic in these old transmissions. That is also my recommendation to you.

A lot of folks like the Sta-Lube from NAPA. I personally use GM # 89021671 80W-90 GL4+. Worked for over 20 years.

Larry

[Patrick B.]

Re: Non-synchro GL-5 gear oil for a Muncie

I just got home and read the Restorer article. The original Valvoline HP 75w-90 was the second choice recommendatiion despite its labeling about non-synchro trans. The Synthetic was not recommended because of leak tendencies. My exchange was unwise as well as double the price. I bought both of these at NAPA but did not see Sta-lube there. Do GM car dealers commonly sell 89021671?

[Bill L.]

Re: Non-synchro GL-5 gear oil for a Muncie

I just got home and read the Restorer article. The original Valvoline HP 75w-90 was the second choice recommendatiion despite its labeling about non-synchro trans. The Synthetic was not recommended because of leak tendencies. My exchange was unwise as well as double the price. I bought both of these at NAPA but did not see Sta-lube there. Do GM car dealers commonly sell 89021671?

Typically NAPA keeps the Sta -Lube in an area where you might not expect to find it. I know all the NAPA stores around here carry the Sta Lube. Around here is Maryland and Virginia.

Also check with NAPA on line. Maybe another NAPA will have Sta Lube in stock.

Bill

[Gary R.]

Re: Non-synchro GL-5 gear oil for a Muncie

I use the Sta-Lube in the ST-10's and Muncies I build. NAPA has it in the back room or they get it from their stockhouse.

[Patrick B.]

Re: Non-synchro GL-5 gear oil for a Muncie

Thanks guys. Here is Md and Va for me too.

[Larry M.]

Re: Non-synchro GL-5 gear oil for a Muncie

I just got home and read the Restorer article. The original Valvoline HP 75w-90 was the second choice recommendatiion despite its labeling about non-synchro trans. The Synthetic was not recommended because of leak tendencies. My exchange was unwise as well as double the price. I bought both of these at NAPA but did not see Sta-lube there. Do GM car dealers commonly sell 89021671?

It was recently discontinued, but is available on-line from various GM dealers with old stock. I bought enough on-line from a GM dealer in the mid-west to last me and my 1967 car until its next/new owner...........probably another 10-15 years.

Larry

[Joe L.]

Re: Non-synchro GL-5 gear oil for a Muncie

Many years ago I decided I was going to go "unconventional" for the lubricant for my 1969's Muncie. I filled it with Red Line 75-90 synthetic gear oil. The result: noticeably smoother shifting, cooler operation, and no leaks.

[Duke W.]

Re: Non-synchro GL-5 gear oil for a Muncie

The spec for most modern transmissions and transaxles that do not have a hypoid gear sets is GL-4. GL-5 has an EP additive that is a MUST for hypoid gear axles due to the high tooth loading of this type of gear set.

Many owners of vintage cars appear to be using GL-4 in the transmission, but I have never seen any long term durability tests. They bought into the GL-5 "yellow metal corrosion" myth. 80W-90 GL-5 or its antecedents going back to the old Mil-L-2105 spec have been in these vintage transmissions since at least the 1940s, and I have never actually seen nor ever heard of observed brass corrosion. Wear, yes, corrosion, no.

There's an old adage: If it works, don't fix it, and I think it applies to manual transmission oil. 75W-90 is a "synthetic", which has a wider viscosity range than 80W-90. It will allow smoother shifting especially during warmup in cold weather, but most of us don't drive our vintage Corvette's in cold weather, which is why I recommend conventional 80W-90 GL-5. As with engine oil, brand is not important. You just need to verify that the API "donut" says 80W-90 GL-5, and it's less than half the price of 75W-90 GL-5. And since you need to use the same spec oil in the axle you don't have to have two different types of gear oil around or risk getting them mixed up. 80W-90 GL-5 should be available at any auto parts store.

GM never recommended manual transmission oil changes. The BW T-10 in my SWC has a drain plug, but I don't think later Muncies have one, so you have to siphon the oil out of the fill plug. I think it's a good idea to change the transmission oil every 30 to 60K miles... same with the axle since Positraction clutch wear particles can contaminate the oil.

Most four-speeds take 2.5 pints, so you'll need to buy two quarts, and you'll have plenty left over to top offs of either the trans or axle, if needed.

Duke

[Mark E.]

Re: Non-synchro GL-5 gear oil for a Muncie

This thread prompted me to look at my supply of GM 80W-90 Rear Axle Lubricant I got over 15 years ago.

I just noticed it's a mix of two part numbers, 1052271 and 12345977:
-- The 2271 bottle reads CAS # 64742-65-0 on the back
-- The 5977 label says GL-5 on the front and CAS # 64742-65-0, CAS 72623-83-7 on the back.

Also, the 5977 is noticeably darker in color (see photos. Sorry- no obvious way to rotate them once uploaded; they are right side up on my PC).

When purchased from the dealer back in the day, each were sold as the proper fill for my 1970 M20 (and its differential when the supplement is added). The different PNs were probably purchased in different years.

I wonder why neither label lists GL-4?


GM Gear Oil 5977 2271.jpgGM Gear Oil 5977.jpgGM Gear Oil 2271.jpg