GL 5 Hypoid Gear Oil in Transmission

[sclor]

I have a transmission question that I was hoping you could advise on. A few years ago, I installed a 3 speed with overdrive transmission in my truck. I used Lucas Hypoid 85W/140W GL5 gear oil in my tranny when I installed it. Lately, I have been reading how such oils may damage "yellow metals" in the tranny due to high sulphur content. The tranny that I installed didn't have a drain plug, so I am a bit hesitant to go through changing the fluid unless I have created a real problem for my synchros. No problems with shifting or performance with the gear oil, but I am a bit concerned that I could be harming it through this choice. Have you seen this discussion and do you have any advice?

Thanks for your help.
Regards,
Steve
New Orleans

[raycow]

Originally Posted by sclor

I have been reading how such oils may damage "yellow metals" in the tranny due to high sulphur content. The tranny that I installed didn't have a drain plug, so I am a bit hesitant to go through changing the fluid unless I have created a real problem for my synchros. No problems with shifting or performance with the gear oil, but I am a bit concerned that I could be harming it through this choice. Have you seen this discussion and do you have any advice?

Yes, that story is true. GL5 lubricants contain sulphur-based extreme pressure additives which are harmful to some copper alloys. As you correctly concluded, that would include the brass synchro rings. They won't get eaten today or tomorrow, but it will happen eventually.

I have never seen a GM 3 speed + OD transmission that didn't have a drain plug, but if you have a SM318, I strongly suggest that you do whatever is necessary to get that GL5 out of there as soon as possible. The synchro rings in a SM318 are an integral part of the 2-3 shift sleeve (GM calls it a clutch) and that part is no longer available from GM. If you have a SM326 (Saginaw), that has the normal type of synchro rings and those are still available.

Ray

[sclor]

Ray:
Thanks. Your advice was the one I was looking for. It is an SM 326 with the seven bolt side cover. I read an article about drilling and tapping for a drain plug, but didn't pursue it. Now I wish I had. What fluid are you running in your overdrive trannies?
Regards,
Steve
New Orleans

[BarryGMC]

has anyone ever drained that stinky old oil out of their trans or rear end? GM put it in from the factory. Its MP 80-90 rated oil. Its the sulfur that you smell. The sulfur problem is a myth. The sulfur creates an acid if exposed to heat and moisture over time and is not changed. the acid eats the brass faster than the steel. But will harm the steel eventually. your anti freeze creates an acid over time also and will tear up a radiator if not changed out regularly. your motor oil will do the same over time also. that is why there is a time given on intervals for change, plus the mileage. the creation is expedited by the unburned hydrocarbons. So do ever what you want but when you crack open that bottle of gear lube and smell that smell its the sulfur. And the old MP 80-90 that gm specified actually has a higher content than the GL5.

[BarryGMC]

Barry GMC is out of here. Way to much mis info for me to digest. I have bought 2 drivetrains because the folks thought you could not get clutches. The t5 and 200r4 stuff is unbelievable. these are medium duty engines they need medium duty drivetrains. Impress your friends with the tough old jimmy's not a bunch of poser trucks. leave that to the chevy's. And now this! Remember me when you try to wash the stink out of your hands after you tackle your next trans job. Barry.

[FetchMeAPepsi]

Not to but...


Both Jay Leno (known for his love of old vehicles) and Redline recommend 75W90NS oil in these older transmissions. Its worth noting that GL4 and GL5 are performance ratings, not formulation ratings. What's in one may not be in another.

Most major manufacturers stopped using formulas with active sulfur EP additives to avoid pitting yellow metals (they do include inactive sulpher EP additives that do not affect brass etc). In general the API GL-5 Multigear EP SAE 80w-90 oil by Exxon-Mobil, Chevron, BP-Amoco, Castrol, Valvoline and Pennzoil would be safe for yellow metals. Also, well-known companies such as Redline, who make specialized racing lubricants, would have recommendations that don't eat yellow metals.

Stay away from other brands that are no-name or house brand. They typically contain active Sulfur, Chlorine and other undesirable additives.

Thats what I found in my research. I'm putting the Redline in Cecilia when I get her back up and running.

[Clyde]

When I was in the motorcycle business I use to sell a GL 1 transmission oil manufactured by Spectro out of CT. From what I had learned a GL1 will work in any transmission, it is a non hypoid oil.

[raycow]

Originally Posted by sclor

Ray:
Thanks. Your advice was the one I was looking for. It is an SM 326 with the seven bolt side cover. I read an article about drilling and tapping for a drain plug, but didn't pursue it. Now I wish I had. What fluid are you running in your overdrive trannies?
Regards,
Steve
New Orleans

Steve, I didn't realize you had sent me a PM until today. I thought I was supposed to get a pop-up notice when a PM came in, but I didn't get one this time. I have a new email address now, which I will PM to you. Thanks to the esteemed Mr. Snowden, I lost my nerdshack email. If you haven't heard the story behind that, just google "lavabit".

Anyway, I put GL1 in all of my manual transmissions when I can get it. When I couldn't find any I used straight 30 weight engine oil.

I bought a new SM326 with OD in 1966 and it came filled with ATF. The parts counter guy I bought it from (at a legitimate Chevy dealer) said it came from the St. Louis assembly plant and I thought it best not to ask any questions. Btw, that one DID have a drain plug.

Ray

[FetchMeAPepsi]

Another update on gear oil. I just heard back from Red Line on this and they include a special copper deactivator that works on any leftover active sulphers in your transmission as well as preventing synchro pitting etc.