The Stovebolt Site Forums The Shop Area Driveline SM420 & Mobil ‘1’ Synthetic Gear Lubricant?

Hey Ken, this one’s for you, hope you can put your two cents worth in.
For years now I’ve been using Mystik (Citgo) JT-7 80W-140 Multi-Purpose Gear Lubricant which I get from the Farm & Fleet stores around here. Since I just finished up rebuilding the SM420 in my ‘50 this week I thought I’d go with a synthetic oil, after all 50,000 racers can‘t be wrong. So I just topped off the trans with a quart and a half of Mobil ‘1’ 75W-140 LS Synthetic Gear Lubricant. It says Light Truck & SUV Formula on the jug. Since the old gal has been put out to pasture and isn’t going to do any heavy hauling any more, unless one considers my “big old wife” as heavy hauling, I figure she falls into the light truck category. The Mobil ‘1’ seems quite a bit thinner than the Mystik but both of the gear lubricants meet API GL-5 quality so does anyone see any problem with using the Mobil ‘1’ synthetic, other than it costs four times as much????

Denny Graham
Sandwich, IL

I'm not sure about the lubricant question, but I hope your wife doesn't read this post, or you'll have bigger problems! (grin)

Aw, she's always pickin' on me any way. You know, chasing me out of the kitchen with a rolling pin or fry pan.
But after 40 years she taint found anyone else that can fix all the stuff that she breaks around the house so I guess she's gonna keep me around for the duration.

Didn't really expect to hear from anyone over here, hardly anybody looks in this forum. But they won't let me post in the General Truck Talk forum anymore so I'm stuck in places like this.
DG

Denny, first of all synthetic and petroleum based lubricants don't mix. All of the service bulletins that came out about 20 years ago recommended making the switch at rebuild time. OEM has been using synthetic for about 20 years. Second, the 75W140 is a hypoid lubricant and not meant for transmissions. I don't like to recommend brands because I have sold lubricants all my life. But I don't like Citgo because the company is wholly owned by the Venezuela dictator Hugo Chavez. If you want to use synthetic in a transmission like I have been the last 20+ years, this is the stuff Mobil makes for manual transmissions.

http://www.mobil.com/USA-English/Lu...vac_Synthetic_Transmission_Fluid_50.aspx

Thanks for tuning in Ken I was hoping you would set me straight.
Maybe you missunderstood me, I'm not mixing the two oils. I've been using the Mystik 80W-140, which is not a synthetic, in everything for 25 or 30 years and I'm still using it in the differential on my '50, 3600.
I just finished rebuilding the SM420 and thought I'd start out fresh with a synthetic in it instead of the Mystik 80W-140 like I had been using.

The labeling on the Mobil '1' is a little misleading then, because it says it offers: Outstanding protction of Hybrid differentials, Gear shifting ease and reduction of chatter.
So I just assumed they were including manual transmission in their recomendation.

Also from Mobil's product data sheet is this:
•Mobil 1 Synthetic Gear Lubricant LS 75W-140 is recommended for use in modern high performance vehicles like sport utility vehicles, vans and light duty trucks requiring API GL-5 performance that require excellent durability.

•Mobil 1 Synthetic Gear Lubricant LS 75W-140 is intended for initial fill, topping-off or refilling differentials, final drives, transfer cases and other gear applications where lubricants meeting API Service GL-5 and multi-purpose or mild EP gear lubricants are recommended

I guess I'll have to drain the thirty five bucks worth of Mobil '1' out and try to find some of the Delvac 50. I've never seen it in any of the local stores, maybe I need to ask for it. Looks like this manual transmission fill up is gonna cost me close to $75.

Thanks for the tip.

Denny Graham
Sandwich, IL

Spent a couple of hours last night and again this morning reading what I could find or understand about gear oils. To say the water is muddy would be an understatement.

I just can't find a solid reason for not using the same multi-purpose "gear oil" in a standard differential or standard manual transmission. Other than using a 80W-140 or 75W-140 synthetic in the transmission may cause it to shift a little stiffer when its cold because it's a heavier viscosity. As far as the lubricating properties in a transmission it sounds to me like it would be over kill if anything.

All of the Chevrolet Shop manuals even a way back 50 or 60 years ago OK the use of 90 weight multi-purpose gear lubricants in both the differential and transmission.

I mean I've run the plain old 80W-140 I’ve gotten from the Farm Supply stores in both the differentials and transmissions for most of my adult life and never seen a problem with it.

Anyone out there have a logical answer to this??

Denny Graham
Sandwich, IL

Denny,

Here is some more reading for you, scroll to the bottom.
http://www.novak-adapt.com/knowledge/sm420.htm

Denny, I don't think any of the oils will kill a transmission. However, rears need the EP additives for the hypoid gears. I used straight mineral 90w in transmissions for many years, because that was all there was and I changed it annually. When synthetic came out, I switched it and I never change it. I have never had a transmission failure with synthetic 50 and I have run some of them a million miles without changing oil. This is a lot farther then the recommended intervals, but the transmissions are out of warranty is out anyway. My opinion is that if you are going to put out the money for synthetic, why not put the lubricant in that was designed for transmissions. I have not changed fluids in a transmission in or rear in 20 years. The only failures I have had was the power divider on rear ends and that was due to the driver leaving the power divider locked on hard ground. I have been thinking of mounting something like a backup alarm inside the cab to remind them the power divider is locked.

Thanks a bunch buddy for coming back on this. Ya got me cornvinced so I left this morning on a quest for some manual transmission gear oil by Mobil, specifically Mobil Delvac Synthetic Transmission Fluid 50.
Left the house at 0700 and literally stopped at every parts house in a 40 mile radius north, south and east of me, NOTA!!!!
Not any gear oil for a manual transmission at any of them. Seems that manual transmissions have gone the way of the dinosaur.
I looked it up at Grainger’s website last night and by now it was 1130 so my last resort was the Grainger 35 miles east of me. Yep they had it……but it was in their warehouse way north of there. However, they had a delivery coming at 1400 so I paid the $59.33 for the gallon (no quarts available) and went looking for some where to kill three hours. Got back over to the store at 1430 and strapped the gallon jug to the back of the Triumph and headed home. Construction and road closures at every turn, had to drive back east 20 miles to get around the closed railroad crossing and finally got home at 1625. Looooong day it was. So what did I get done on my Stovebolt today, you just heard it, nuttin” much!!!!!!

But, now I do have the “correct” gear lubricant for my SM420 and tomorrow we drain and refill and then,,,,,I’ll be ready for the road and won’t have to worry bout that trans for a million miles, right Ken???

Tks again,
Denny Graham
Sandwich, IL

Hey Denny,
If you have a speed shop around, they may have some.

Dennis

Denny, I did a little research about 50w trans. fluid. It seems as though the Heavy truck industry has been using 50w for quite sum time in powershift transmissions. It seems as though just about all oil manufacturers make it. Maybe try a Kenworth dealer next time:-)

Tks, but there seems to be some cornfusion here, Grainger stocks it and I got a gallon a couple of weeks ago when I installed my SM420. Sooooo all is right with the world.

DG

Just rattling your cage. I didn't even know Grainger sold oil. I guess you learn something everyday.