4.10 gears in my astro

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vorteXtreme759

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I recently had 4.10 r&p installed in my 99 chevy astro van, The reason for the change is I have 1200 pounds of tools and occasionally tow a trailer.. I previously had the 3.23 gears and the engine would turn 1700rpm with a 4l60e on the highway at 70mph!

But the van had a hard time maintain speed. And anything under 70mph would lug the engine and it would kick in and out of overdrive. . Now with the 4.10s the gas mileage has improved around 3-4 mpg city & 2 mpg Highway. .So I couldn't be happier.

Now for my question what gear oil should I run in this rear end? It is equipped with the g80 locking diff right now I have it filed with lucas 85w140, I would like to use a conventional oil I just wanted to hear some opinions.
 
Isn't 85w140 thicker than necessary?

First off, glad your gears are working out, that's interesting the gas mileage went up.

Second off, Lucas gear oils are not great. I've seen them fail tests that cheap gearooils passed. If you're stuck on 85w140 try Supertech but you could probably go with something more readily available.

I would use an 80w90 GL5 as oem recommendation and synthetic if possible.
 
keeping in mind that the amsoil test was in 2007 and everything has possibly been reformulated..

lucas is below average.

I'd be happier with supertech or valvoline conv. than lucas.
 
Originally Posted By: Rand
keeping in mind that the amsoil test was in 2007 and everything has possibly been reformulated..

lucas is below average.

I'd be happier with supertech or valvoline conv. than lucas.



Yes the work is dated, but it goes to show you what they are offering.

Redline gear oils are worth the price if you ask me.
 
If you were in NY, I would think the 85w140 was too thick. I think in Florida you should be a-ok.

Your engine and transmission are definitely thanking you for the upgrade!
 
My 'stro has 3.42 gears, I agree how it seems to bog at times. I know 3.73's were available from the factory, but I have never seen one. I heard it was a rare option. I personally wish it had a small V8 versus the 4.3 Vortec.....
 
Redline gear oil is the only gear oil I'll buy,at whatever the cost.

I completely believe a fuel economy increase at the gear swap. The engine now puts more torque to the wheel at less pedal pressures so it would attain and maintain speed with less throttle inputs.
 
Stick with 80w-90 or 75w-90 synthetic. No friction modifiers with a G80 Gov-Bomb.

Even though Red Line 75W-90 contains friction modifiers, I still use it without additional additives in my '03 Safari with no ill effects. So far.....
 
Thanks for all the replys. I previously ran amsoil severe gear 75w90. The diff was very quiet but the g80 gov lock did chatter and bang on lock and unlock... Now with the lucas 85w140 I can't even feel it lock or unlock. I verified it is working. And the guy who installed the gears said only run conventional 85w140 when towing in Florida. So I would like to stick with a good Quality conventional. Any input on this would be greatly appreciated!
 
He claimed the quality synthetic already has too much friction modifier in it for a gov lock. . Which in my experience seems to be true.
 
Originally Posted By: Clevy
Redline gear oil is the only gear oil I'll buy,at whatever the cost.

I completely believe a fuel economy increase at the gear swap. The engine now puts more torque to the wheel at less pedal pressures so it would attain and maintain speed with less throttle inputs.


A 4.10 gear means the engine rpm is higher and the transmissions tailshaft speed is higher.

You are developing more torque for the axles, but how do you get better mpg when the engine has to rev higher?

As others have recommended, both Amsoil SVG or Redline in 75W110 should be more than adequate.
 
Last edited:
Are you accounting for the new gearings with your odometer readings? You need to multiply your odometer readings by the 3.23 / 4.10 to compare gas mileage or change the odometer gears in the transmission...
 
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Thanks molakule i am hesitant to use the synthetic due to the previous issues. And the installers recommendation. But if I'm correct I believe gm spec'd the same fluid for their lsd's as the gov loc g80 but they probably did recommend extra additive if necessary for the lsd unit's. But im sure this isn't the first time this had been brought up. So I will try the redline 75w10.
 
Originally Posted By: MolaKule


A 4.10 gear means the engine rpm is higher and the transmissions tailshaft speed is higher.

You are developing more torque for the axles, but how do you get better mpg when the engine has to rev higher?


Less load on the engine means less heat and less fuel= more efficient.
 
Originally Posted By: MolaKule
Originally Posted By: Clevy
Redline gear oil is the only gear oil I'll buy,at whatever the cost.

I completely believe a fuel economy increase at the gear swap. The engine now puts more torque to the wheel at less pedal pressures so it would attain and maintain speed with less throttle inputs.


A 4.10 gear means the engine rpm is higher and the transmissions tailshaft speed is higher.

You are developing more torque for the axles, but how do you get better mpg when the engine has to rev higher?

As others have recommended, both Amsoil SVG or Redline in 75W110 should be more than adequate.


It's not a linear function - check out BSFC charts for various engines.

An engine with no load will get better mileage with lower RPMs, but once you load up the engine, it needs to be closer to it's power band in order to get better fuel mileage.

A lot of times, vehicles will have tall gearing to get better fuel economy on the EPA test cycle (Crown Vic, we're looking at you).

Jeep 4.0 engines don't mind lugging, but they get their best fuel economy when cruising on the highway between 1800 and 2300 RPM.

From the factory, the 5 speed manual 4.0s came with 3.07 gears. Numerous people have swapped in 3.55 or 3.73 gears, left the Jeep stock, and got much better highway fuel economy. The engine itself doesn't mind the lugging, but BSFC charts put it most efficient around 2000RPM give or take a few hundred.
 
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