I hope I'm not adding to the ongoing debate regarding GL-4 vs GL-5 oils as it's not my intention. I just wanted to share my experience in reading online as to which one I should use and in what...which I found really confusing.

What started all this....my 58 has a 4-speed Muncie that shifts fine, except when I'm down shifting from 4th to 3rd...I can feel the gears on the stick shift. I have to gently and slowly ease it...and yes, I'm taking about my gear shift.

Bedause of this, I wondering...is it the synchos or perhaps the oil (viscosity) I have in the tranny? So have decided to replace it, and since I have the car jacked up, I might as well change out the oil in the OPEN differential.

I turned to this forum and read articles online to see what I should use in each and what I found was so confusing it made my head spin...especially when it comes to the manufactures.

Some people swear that GL-5 shouldn't be used in trannies with synchros as the additives in GL-5 (that allow greater loads and higher heat) causes excessive wear on them...then there are others who say they haven't experience this and it's a myth.

And if GL-4 and GL-5 wasn't confusing enough, you have different manufactures....Sta-lube, Driven, Lucas, Amsoil, SuperTech, Synthetic oils, MT-1, then there is the "buffered Sulphur" that apparently doesn't impact synchros...GL4+, GL4/GL5, GL5/MT-1...AUFKM?? (and no that is not an oil...that's a phrase).

And just cause an oil is "better" such as GL-5 over GL-4...is it really better?? All depends on where it's used. And then there is the tried and true, where people say to stick to the manufacture's recommendation...problem there is, what was used back in the 50/60's isn't readily available today, and there have been improvements.

And then there is the video by Paul Cangialosi (Muncie Guru) where he dismantles a muncie that is toast and discusses GL-4 and GL-5. He examines the viscosity of the different oils by drilling a hole in the bottom of a plastic bottle and measuring how long it takes to drain...which doesn't tell me much. I want to know what oil wears better, what is good for synchros, which one have additives, etc...however he does say he uses Driven 80w90 (GL4).

Out of everything I read, I found this article that I think is easy to understand and gets right to the point...it should be named "GL FOR DUMMIES".
The difference between GL-4 and GL-5 explained (rymax-lubricants.com)

After reading everything I could fine...I have decided to listen to my mother as she knows best...and go with Wesson Oil. She says it withstands high heat, stuff doesn't stick, and makes the best friend chicken!!

All kidding aside...from everything I have read, I'm either going with Sta-Lube 85w90 or the Driven (both GL4) in the Muncie and probably Supertech (GL5) in the differential. It's inexpensive and available from Walmart. NEVER use GL-4 in the differential.

 

I put Red Line MT-90 in my Muncie because after lots and lots of research, like you did, I decided it was better to not use GL-5, AND I found it in stock at a speed shop nearby.

I put Supertech GL 5 in the posi rear end.

I think you'll be fine. And you did a great job of sorting through the rigamarole!

 

Thank you! I was afraid that I was going to get bashed on here for bringing it up.

 

Take a look at the label on the GL-5 product you are considering to see if it's recommended for non-synchronized manual transmissions or not recommended for synchronized transmissions, like the Muncie. The synchronized transmissions have bronze/brass rings that the sulfur compounds attack.

 

I appreciate the info for those thinking of going with GL-5 in the tranny. However, as I said, I have no intention of going with GL-5 in my Muncie for all the reasons I presented and going with either Sta-Lube or Driven that are both GL-4.

Today I found Sta-Lube at the local NAPA, so I bought it. BTW....Sta-Lube also makes a GL-5, which I almost bought, so people need to double check when shopping around.

As many have pointed out in the debate of oils...the brand of oil is pretty much irrelevant and it's the API rating that's important...but hey, if people want to pay $100 for a bottle of wine that tastes as good as a $10 bottle...I say, "knock yourself out"!

 

After a similar exhaustive research effort here on CF, I replaced both my 66 Muncie and my 62 T-10 (unknown PO) fluids with Sta-Lube GL-4. All is well in the shifting world!
The Sta-Lube GL-4 prices varied widely at all the standard vendors, so I also went with trusty old NAPA, they offered a very competitive price and no shipping fee with local pickup. 😃

 

I looked unsuccessfully for GL-4 in town last year, I guess it's time to check NAPA and see if they have it. Sounds hopeful....thanks!

I used to be able to buy it everywhere.

 

Napa has it, Sta-lube, maybe the only one that has it.

 

Have used this in all my Muncies over the years.

And yes, you have reopened the can-o-worms debate on lubricants!

 

We're not debating it, we're just trying to find out where to buy the recommended stuff.

 

Having a hard time locate GL-4 80W gear oil in Halifax, Nova Scotia. Last year it was not an issue. But this year Car Quest, Napa, Canadian Tire all have Gl-5 and no Gl-4!

 

Ken,
Have you tried Summit Racing or Walmart??

https://www.summitracing.com/parts/v...EaAqvqEALw_wcB
https://www.walmart.com/ip/VP-Racing...saAqbGEALw_wcB

 

When the debate about GL4 vs GL5 really became heavily discussed about 20yrs ago, I just happen to be in my local O'Reilly store. I asked the parts guy that I preferred doing business with about the availability of GL4. He got on the computer and found two 5gal cans in the ware house. I bought them. So now I have a sufficient supply for my needs.

 

Thanks. I will check Summit & our local Walmart.