Regearing and why you need to do it (1 Viewer)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

My new 40 axles have 4.88s I like the 4.10's. I don't drive the 40 on the road much so the 4.88 will work well.
 
Just some information gearing wise. Had my 40 out the other day after doing some transfer case work on it and noted that at 60MPH (GPS verified, my speedometer is a Dakota Digital that is easily calibrated) the engine is turning 3000 RPM. The truck has 4.88 gears in the axles and it's running 35" tires. I've never really gone over 65 MPH with the old girl as I try to avoid running the 2F much higher than 3200 RPM.
Over the last few years I've thought about swapping the 4.88's out for a pair of 3.70 third members. It would sure make it easier on the engine running down the highway. S.

370s and 33s are not bad.
370s and 35s wouldnt be terrible with an h41 or h55, but with an h42 its going to be hateful.
 
Was gonna start looking for an e-locker third member from an 80 series truck. Thinking if I find one at a reasonable price I'll get a set of 4.88 gears for it and slip it into the rear axle. Then it dawned on me I'd have to get a different locker-side rear axle because the e-locker thirds require a longer splined area than a standard axle.
Now I'm thinking about just buying a new selectable locker and replacing the Detroit with it. Would be a relatively easy change. Having had the 40 out today and going 62 MPH with it on the way home I've decided the gears are just fine the way it is and I just want to lose the Detroit in the rear.
 
Recently I was asking somone what gear ratio they had. They were looking at swapping in a different 3rd member. The pricier was they didn't know what they had. When you can count the teeth of the gears it's easy to figure out.

For example: 41 teeth on the ring gear divided by 10 on the pinion gear is 4.10:1 ratio.

It's' harder when you can't see the gears like when they are installed in a axle.

Spools,arb and electric lockers are easy. Engage the locker. Jack up the axle and make some marks on the drive shaft and tire. Spin the tire 10 revolutions and count the number of times the driveshaft goes around. Divide the drive shaft revolutions by 10 and round off to nearest possible ratio.

Open rears are a little harder. Jack up one tire spin it 20 times, count the driveshaft revolutions and divide by 10.

I think I'm remembering correctly. If this dosent work or I'm wrong please tell me. It' been a long time since I did this.
 
Yeah, I'm trying to figure out what to buy. My transfer case is shot in my 91 80. Mechanic has not got in any further, but metal came out of the oil in the transfer case, but no transmission fluid! So I think my trans is okay. I'm scouring info on Marlin. I've heard low low is what I need. I have 33's now but will be going to 35's.
For a daily driver, a 3FE equipped 80 with 4.88 gears and 33s is pretty good. I ran this way for years on my 91. 33s on the street and 36 Swampers on the trail.
If you want to run 35s on the street, I would go with 5.29 as that will keep you in the torque band and help offset the additional weight.
I run 35s and 4.88 on my LX450 and it can almost get out of its own way, but it has more available ponies.
 
For a daily driver, a 3FE equipped 80 with 4.88 gears and 33s is pretty good. I ran this way for years on my 91. 33s on the street and 36 Swampers on the trail.
If you want to run 35s on the street, I would go with 5.29 as that will keep you in the torque band and help offset the additional weight.
I run 35s and 4.88 on my LX450 and it can almost get out of its own way, but it has more available ponies.
Mmm, 36" Swampers.

hqdefault-1.jpg
 
So for anyone interested in learning how to set up gears or trying to find someone that knows yotas check out zuk at www.gearinstalls.com
 

Users who are viewing this thread

Back
Top Bottom