Using GL4 gear lube when factory calls for GL5

[Mike_Br]

I changed the rear axle lube in my 82 Chevy pickup a while back using some 80W-90 GL4 lube I had on the shelf. Just now read where GM specified 80W-90 GL5. Is it anything I should worry about? The truck is a light duty 1/2 ton model, averages around 50 miles per week, and never hauls more than a few hundred pounds.

 

[simple_gifts]

http://www.widman.biz/uploads/Transaxle_oil.pdf

Little tidbit typed up by a forum member.

You should use a gl5 lube.

 

[Shannow]

If they SPEC a GL5, there's every good reason for them to do so.

Change it.

 

[Mike_Br]

I understand the GL4/GL5 difference when it comes to brass synchronizer rings, which is why I had the GL4 laying around for use in an old Muncie trans. However, the article doesn't really address differentials, from what I could see.

 

[simple_gifts]

hypoid gears = differential.

Quote:


A traditional GL-4 gear oil of any given viscosity has about
½ of the level of sulfur/phosphorous additive that would be in the GL-5 product.....

This means that the GL-4 product provides a little less extreme
pressure protection, so in the differential of a high powered car, it would not be the ideal product in the differential.

 

[widman]

It won't cost you much to put the right stuff in. Many differentials have high angles that could be damages with less protection. The transaxles designed for GL-4 stay away from those angles or oversize the contact area.

 

[MolaKule]

They spec GL-5 for the diffy because it contains EP (Extreme Pressure) additives, because the gearing and bearings in diffy's operate under higher loads.

GL-4 lubes only provide AW additives.


Replace what you have in there now with a 75W90, or better yet a 75W110, and your diffy will thank you.

 

[Mike_Br]

Kind of a PITA with no drain plug. What was GM thinking? I'll either leave it alone or use a vacuum pump to suck out as much as I can through the fill hole, and top off with GL5.

On the other hand, the lube that was in there looked like mud, so just about anything would be an improvement.

 

[Ducman]

Originally Posted By: Mike_Br
Kind of a PITA with no drain plug. What was GM thinking? I'll either leave it alone or use a vacuum pump to suck out as much as I can through the fill hole, and top off with GL5.

On the other hand, the lube that was in there looked like mud, so just about anything would be an improvement.

Sounds like all too much bother really.
Should just leave it in there until it turns to mud like the old stuff then change it when you get around to it.

The other side of it is the damage is possibly already done.
You could leave it be until the diff gets too noisy for you and put another one in.

 

[meborder]

 

[Mike_Br]

After 205K miles, damage may have been already done. However, in the two years I've owned the truck, I haven't heard any whining or clunks from the rear end. The old lube contained no metal particles that I could feel, and ring/pinion backlash is around .012". I changed the axle seals, but the wheel bearings looked and felt OK. Ring gear and spider gear teeth looked fine.

After starting this thread and reading your comments, I've done a little research. Turns out my truck's differential (8.5" 10-bolt) was first used by GM in 1970, However, GL-5 wasn't introduced until the mid-1970s. I doubt GM redesigned the diff for use with GL-5, but instead simply specified the latest and greatest lube. It's kind of like specifying SG motor oil when it became available instead of SF.

All that said, I do agree that GL-5 would be better.

Thanks for your comments.

 

[zeng]

Originally Posted By: Mike_Br
and ring/pinion backlash is around .012".bearings looked and felt OK. Ring gear and spider gear teeth looked fine.

Turns out my truck's differential (8.5" 10-bolt) was first used by GM in 1970, However, GL-5 wasn't introduced until the mid-1970s. I doubt GM redesigned the diff for use with GL-5, but instead simply specified the latest and greatest lube.



It appears to me a backlash of .012" for a 8.5" ring gear diferrential is out of specs.

Did you not adjust to tighter backlash ?

 

[asand1]

I don't think GL-4 is for hypoid gears. The GL-4 rating may not have existed in 1970, but hypoid gear oil did have large amounts of sulfur in 1970 and GL-4 does not.

 

[MolaKule]

Hypoid gearing has been with us for some time.

What determines if a differential fluid needs to have a GL-4 or GL-5 rating and formulation is dependent on a factor called the "offset."

Modern hypoid gearing uses a highly offset configuration requiring a gear lube with a GL-5 protection rating.

 

[zeng]

Timelines of introduction of:

a )Hypoid gear (axles) by Gleason Works in 1925 ;

b )API GL-4 and MIL-L-2105 specs in 1943/1948;

Subsequently updated to :

c )API GL-5 and MIL-L-2105A in 1957.

Note: Some GL-4's in 1948 contains limited slip additives.