LUVTruck.com

Hi Folks,

I am planning to swap out my 4.56 rear axle for something taller. Would like to hear your opinions on 4.10, 3.73, and 3.42 axles in a bone stock '72 LUV from the perspective of torque and driveability. My concern is turning too many revs on the freeway, I'd really like to be able to drive this farther than Bob's Big Boy. Like to San Diego for example. A boost in fuel economy would be welcome too. Locally, I can get the 4.10 and 3.73 rears from dismantlers; I haven't found a 3.42 locally. Of course I don't want to go too tall so that it doesn't drive around town well. Whaddayathink?

A lot will depend on your tire size. Shorter tires is like putting in lower gears. Shorter than stock tires goto the 3:73's, taller than stock go to the 4:10's. A 26" tall tire with 4:10 would be about 3200 at 65 mph. Some where I have a dream wheel that calculated this. You can do it with a calculator.
I'd buy both if you can get them, as they are getting harder to get. Unless there real expensive.

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The light at the end of the tunnel, may just be a train coming!

so you have the old 1 to 1 4 speed trans, or is it a 3 speed auto trans if its a auto stay with the 4.11s 1st gear will be very steep with 3.73 gears.
each step 4.11 3.73 3.42 is going to be around 250/400~ rpms.
also comparing say P225/75/15 to LT31/10.50/15 are about 300~ rpms as well.

my 0.01C

get bolth rear ends, run 3.73 gears with 225/75 or smaller rubber that will make over all MPG and drivability the best in my opinon.

if you find a 3.42 run small tires

if its to tall go to the 4.11s.

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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!!

I have 195/17R14 tires on it with the 4 speed manual. Sounds like I will be OK with the 3.73 rear. Thanks guys, any more comments are welcome.

Say, does anybody know what you have to do to get a LUV driveshaft to bolt to an Isuzu pinion yoke? I will be getting an Isuzu rear end if I get the 3.73. A 4.10 rear from a LUV should bolt right up.

Yeah here I am replying to my own posts again, but it's better than starting a new thread right?

Bought me a 3.73 third member from an 83 Isuzu Pup. The driveshaft yoke is the same as that of a LUV...which is good. (They had an authentic LUV 4.10 third member where I was so I compared). One thing that is different is that on the Isuzu 3rd member, 2 of the bolts have to go through a hole that's a good 3 inches long (meaning the original stud won't work). I think this is because the 3.73 pinion is larger and they had to add meat to the case. Anybody seen this before? I think I'll be able to get around this by removing two studs from the rear axle (I've verified they thread in and are removable) and using long bolts. They are of course metric, M8-1.25 if anybody cares.

Swap is done, test drove and it's like I got a new truck! Went on the freeway no problem, even passed a couple big rigs. Now using motor torque in the right spot instead of going past it and high revving. Only thing I would worry about is if I had a full load and I was at a stoplight pointing uphill.

You guys were right, with the stock tires 3.73 is pleasant. Wouldn't want to go any higher than that, however.

I'm guessing that the very competent Japanese engineers (I mean that seriously, those guys are the sH*t and I'm not making fun of them) figured out that under full loading, with 75 HP, they would have to give it 4.56 gears to be able to go up the steepest mountain. They were probably right. But I don't think a lot of us drive the LUVs that way and for example have/use a bigger truck for heavy hauling.

Your mileage may vary but I know that mine is going to get better after the swap. Thanks for the advice, it was good. Oh and if you like to drive fast and burn tires and whatnot this swap is probably not for you. I am just used to driving slow cars I guess.

yes it depends on where and how you drive.

thats why theres any thing from a 3.42 to a 4.55
3 speed auto or 4/5 speed manual
though the pup 3.42 and the 5 speed was never sold as one LOL

in about a year you will be driveing a little faster, and youll be wanting lower RPMs, thus putting in a 5 speed

_________________
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!!

i have a 3.31 in a automatic and a 3.15
in my 4 speed with these gears in the 4 speed
1st ....3.79-1
2nd ....2.17-1
3rd...1.42-1
4th...1.00-1

i have 185/70/12 tires so what would the beast combo be for ties and speed... i never under stood this stuff


sorry didnt want to hijack just borrow

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My old but now gone Luv...

Just for your information, I had a 81 Diesel powered Luv with a 5 speed and it had 3:42 gears. Fifth gear was only good for downhills, way to high for the little 60 HP diesel! I finally swaped out the diesel for a SBC 305 with a 700R4 and it is a ideal combination! Lots of low end, yet cruise at 65 around 2800 RPMs, this is with stock 195-78 14" tires.
Sounds like you have the right setup now, you can always experiment with taller tires, not wider ones, just taller ones.

I think you should play with the calculator linked in the info section. I'll re-print the link here

http://www.idavette.net/tech/ratioc.htm

You can put in your tire height, gear ratio, and speed and then calculate RPM. Or any other three, and calculate the 4th. If you are in high gear (e.g., 3rd on the auto or 4th on the manual), the ratio you enter is your rear end ratio. If you are in any other gear, multiply the number for that gear by your rear axle ratio; 3rd gear on your manual with 3.15 axle means 3.15*1.42=4.473 final drive. You can see that if you are in 3rd on your truck it was like 4th with my old rear end gear.

Theoretically for the fastest speed you want the highest (numerically lowest) rear axle ratio possible. That of course assumes infinite torque and horsepower, which is never possible. It is my theory that when you are cruising on the freeway, say at 70 mph, you want your engine turning the RPM that gives the peak torque. For our G180 motors I'd guess that to be somewhere near 3400 RPM. Somebody on here probably knows the real answer to that, e.g. they've put their truck on a dyno.

I like using this calculator best. You get the rpms though the power band. Especially at 60,70 & 80 mph, for freeway driving.

http://www.kabamus.com/garage/gears.html