LUVTruck.com

I just swapped out my old 4.10 set for a 3.73 set this week, and thought I'd pass along some notes:

• 3.73's have an 11-tooth pinion and a 41-tooth ring gear; 4.10's have 10 & 41.
• It's a direct, factory parts swap; no additional parts are needed (unless you find something worn or broken).
• You'll notice right away that the engine is turning less RPM on the highway; I don't have a tach, but you can definitely tell the engine is calmer, and the mechanic who swapped it estimates an 800 RPM drop. I run 215/75- R14's on the rear, 26" dia.
• You may have to downshift on real low-speed hills, or give it a little more gas on high-speed hills, but I've only noticed it once or twice on my 38 mile commute.
• I've noticed I'm using less gas for sure, but haven't measured it yet; need a good road trip.

Also was slinging oil from the 4-speed tailshaft, so a new output shaft seal was installed. The part used was a Timken #1987S.

This is looking like the best thing I've done to this truck since the Weber carb.

How close is your speedo now?
To correct you will need to know how many teeth on the cable driven gear (usually 20 for 4.10 gears) and how close the speedo was before the diffy swap. Then you can calculate the proper number of teeth needed an a new gear from JLEMOND, or a salvage yard maybe.

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'78 Chevy LUV,1.9,4sp,headers,31's,SAS Dana 30,Dana 20,SOA rear w/Aussie Locker, rough body, bought new 12/4/78.
'87 Trooper,2.3,5sp,headers,31's,ball joint flip & spacer,Aussie Locker rear,Superwinch hubs,brush guard w/5.5K winch,more to come.

The speedo used to read about 5-7 mph higher than actual speed, and now reads right on- I followed my wife with her cruise control set at 50 & 60 mph. I bought this truck used back in 1991, so I don't know the history of it; it may have had the wrong diff in it all along.

With your advice, I did contact JLEMOND, and he has the speedo gears, but I'm not sure I'm going to need them.

Thanks for all your input!

If you're wondering....

http://richmondgear.com/streetcalculators.html

with 4.1 gears and a 26" high tire it turns 3444 rpms.
with 3.73s it turns 3133

Not quite an 800 rpm drop, but definitely a healthy one. Right where it should be. Mine had the 4.56 gears when it was stock. 70mph sounded like a disaster was imminent.

that drop is just about the same as adding the 5sp so 2X that RPM drop if a person did both mods, "rear diff and 5sp".

with the 3.73s you can run a bigger tire, and help rpms some more. or go to a 5sp there 14.5% unless you find one from a isuzu car thats a 20.0% O\D
but if you go to a 3.42 then stock or smaller tires are needed to hold the rpms in the 2,700/2,900 range.

a 3.42 with a 5sp will burn more gas than a 3.42 with a 4sp.
just to low of rpms for the little 4 bangers.


just think of how a diesel is with the 4.11s and the auto trans, no O\D plus add 150/250 rpm cuse the converter will not lock up
takes the epa rating down about 7/10 mpg

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86trooperT/D 2.2
84 L\B 4x4Diesel LS 2.2
84 S\B 4X4 gas rust bucket 1.9
86 L\B 4X4 gas 5 speed 2.3
the twins, 81 pup and 81 LUV both are diesel 2.2



The Energizer Bunny is trying to keep up, and is starting to gasp for air!!