Last night I called every auto parts supplier within 50 miles. No one here carries Red Line products. So I ordered 3 quarts of MT-90 from Amazon. Previous to starting this thread, I had no idea that certain gear lube will damage the synchros. Thanks to all for the lesson. So now I'm really chomping on the bit here. I have every single thing ready to go, except for the gear oil, and waiting for the new dust cover coming from Zcarsouce. And even if everything goes together and works as it should, I can't even take it for a test drive. Still lots of salt and snow on the roads here in Iowa. All I'll be able to do is back it out of the garage and go back in. Probably should have started this project in March. It's gonna be at least another month, maybe two, before I can hit the road. 

The sulfur question is more complicated than just GL-4 versus GL-5.  There are GL-5 rated lubes out there that work fine with "yellow-metal" synchros.  The GL spec. is a performance specification, and doesn't tell anything about how the formulator made the lube hit the spec. number.  It's a pretty interesting area if you're in to that kind of thing.

 

But, overall, it's most effective to just go with what has worked for other people.  Redline has a great reputation.  

True GL4 oil. Not GL5.

 

+1

 

Years ago with an internet search I found a very good explanation of the differences of the lubricant specs and why GL5 is not an "upgrade" to GL4 but a completely different spec.  (You'll notice Nissan specifies GL4 for the manual transmission and GL5 for the differential)

 

I've used both Pennzoil Syncromesh and MTL-90 in my late "close ratio" 5-speed, but I settled on a standard GL4 product from Sta-Lube (SAE 85W90 Multi-Purpose Hypoid Gear Oil).

"The sulfur question is more complicated than just GL-4 versus GL-5.  There are GL-5 rated lubes out there that work fine with "yellow-metal" synchros.  The GL spec. is a performance specification, and doesn't tell anything about how the formulator made the lube hit the spec. number.  It's a pretty interesting area if you're in to that kind of thing."

 

Has anyone tried Royal Purple Max Gear 75W-90? Says it's non-corrosive for soft yellow metals and synchronizers.  Also it's GL4 or 5 formulated for LSD's.  It's the only thing i could find locally and I'm getting ready to swap back to a 4-speed until I can get the wide ratio 5-speed rebuilt.  Should I save it for my son's celica or put it in the Z?  I did order some Redline but that is probably a week away from delivery 

Has anyone tried Royal Purple Max Gear 75W-90? Says it's non-corrosive for soft yellow metals and synchronizers.  Also it's GL4 or 5 formulated for LSD's.  

 

Edit! - no offense to anyone who lives by the "avoid GL-5" rule.  I'm just offering a little more background to the issue.

 

 

If they address the issue, odds are good that it will work fine.  Royal Purple is a well-established company.

 

Probably, way back in the past, somebody produced a GL-5 rated high pressure lube that caused synchros to get trashed.  From then on, the only identifier that people could tie to the problem was "GL-5".  Forevermore, "GL-5 is bad for synchros".  This is how out-dated products live on.  Wouldn't be surprised (actually I think that I've seen ad copy that does this) if manufacturers of old products helped spread the rumor.  

 

I'm using GL-5 rated Swepco 201 right now in my 1980 5 speed.  It's been in there for about 20,000 miles at least.  Not a single sign of a problem.

 

It's just one of those comfort-level things, and as shown by the Royal Purple product, looking at what the product was designed for.  The spec. is just one of many factors. One product can meet several specs.  Staying comfortable can be limiting.

 

http://www.royalpurpleindustrial.com/assets/MAX-GEAR-PDS.pdf

 

http://royalpurpleindustrial.com/assets/Max-Gear-product-sheet.pdf

 

http://www.swepcolube.com/products/swepco-201-multi-purpose-gear-lube

 

Here's an old PDF file from Swepco that tells a few things about the confusion.  Doesn't seem to be around on the internet anymore.

SWEPCO GL4 and 5 TG_199508.pdf

Edited March 3, 201510 yr by Zed Head

I was looking through a Jeep forum and found a thread on where to buy GL-4 and a poster mentioned that he contacted valvoline about it. he said:

"I called Valvoline regarding this. They indicated that the problem with some GL-5 is activated sulfates. They indicated that they do not use activated sulfates and their GL-5 is safe for yellow metal... "

**---->> confirmed from another forum source:

"Apparently activated sulfate (used in some GL5 lubes) can eat brass synchros. Valvoline indicated: "The Valvoline High Performance Gear Oil 80-w90 can be used for both GL4 and GL5. The real concern is the type of sulfate used in the gear oil. You can not use an active sulfate for GL-4 applications. Valvoline uses an inactive sulfate that will not harm any yellow metal such as bronze. This allows our products to be used in manual transmissions that have bronze synchronizers."

What is your input on this? Is there a way to confirm the truth to this?

I didn't know GL4 from GL5 till this forum......I use Valvoline 75-90 limited slip. It says it can be used in transmissions calling for GL4 or GL5. Anyone know if I can use this in Datsun transmissions? Sounds like its OK, but I have no idea. Any thoughts?

Edited March 4, 201510 yr by Diseazd

Has anyone used the Valvoline GL-5 -- what have the results been for you so far? THANKS!

> Date: Wed, 17 Mar 2010 14:56:55 -0400

> From: ValvTechLine@ashland.com

> To: 1969buickGS

> Subject: Re: GL-4 and GL-5 manual transmission lubricants

The Valvoline Gear Oils can be used for both GL4 and GL5. The real concern is the type of sulfate used in the gear oil. You can not use an active sulfate for GL-4 applications. Valvoline uses an inactive sulfate that will not harm any yellow metal such as bronze. This allows our products to be used in manual transmissions that have bronze synchronizers and differentials without causing any type of corrosion to yellow metals.

----------------------------

Another post from Valvoline on the subject.......looks like Valvoline Limited Slip High Performance 75-90 gear oil is fine for yellow metals. It's approved for GL4 or GL5 apps.

The thing about "limited-slip" lube is that it is designed specifically for limited slip clutches.  Which may have different needs than synchro rings.  They both slip then grab, but that may not be good enough.

 

The only reason I tried the Swepco, which is really an out-of-left-field option, is because jmortensen recommended it, and had lots of experience with it from working in a shop that used it on hundreds or thousands of cars.  It was a proven lubricant.  Even so, it's still an odd usage, blended with ATF fluid, which is not GL-4 or -5 rated.

 

Anyway, personally, if I was starting from scratch, I wouldn't use anything that didn't say "okay for yellow metal synchros" on the label.  That's what everyone should look for, not GL-5.  In my opinion.  The GL-5 issue is very well known so if a manufacturer doesn't bring it up, they probably haven't tested.  Why they would take a chance on causing damage though, doesn't make sense.  They should either have a warning or a comforting message.

I use the classic line from Kroon, it's a Dutch brand.

Specifications say:

 

Classic Gear EP 90 minerale ( mineral )  SAE 90 transmissieolie

 

Productspecificaties

API GL-4
Mil-L-2105
MB 235.1