Gears in 4x4

[Toby218]

I know I'm going to get the stupid question of the day award with this, but......
In a 4x4 do you have to run the same gears in the rear as the front? Can you put 3:90 in the rear and have 4:10 in the front? I have a shot at some 3:90s and a locker diff for a good price.

 

[smokey]

Yes they must be a matched set.
Otherwise is creates a bind and breaks the drive train.
Same goes go tires all need to be the same size on all four points to run in 4 wheel mode.

 

[Toby218]

Thats what I thought. As long as I don't shift the transfer to 4x4 I'm ok. But if I do one end tries to go faster than the other and I break stuff.

 

[john112deere]

Yeah- if you never use 4x4 it's OK...though I'd try to avoid that situation if at all possible.

Friend of mine did run a truck like that for a little while- he blew up his rear end and decided it was a good time to change to lower gears...but for some reason couldn't get the front regeared at the same time. Ran around in 2wd until he collected the parts he needed. Far as I know he didn't hurt anything, and I'm pretty sure he'd have said so if he found any damage.

 

[m78]

Take the front drive shaft out. Or if you wanna be crazy,take the rear ds out.

 

[DNFXDLI]

There can be slight variances in gear ratios...3.50/3.54, 3.70/3.73, 4.09/4.11 etc but the ones you mentioned are too far apart.
The gears in my big truck are 4.88/4.92

 

[Toby218]

This brings back memories of my Grandpa's wise words. If you can't do it right just don't do it at all. I think I'll wait and change front and back at the same time. What gears should I use to get the best fuel mileage and still keep my off road abilities?

 

[SuperCab]

As high as you can get... Probably 3.55:1 is the highest you can get.

You'll lose a lot of off the line grunt but overall your power shouldn't be too affected...

 

[Workin' Rig]

Sometimes guys will run a higher gear ratio in the front and a lower one in the back on mud only trucks....

But on a truck that sees any kind of duty other then that i wouldnt reccommend it.

 

[LEB Ben]

The guys covered it...but IIRC, you have a 73 250??? I'm having a helluva time coming up with 3.90's for D60, everything I'm seeing is 3.73 then a jump to 4.10ish.

Sometimes guys will run a higher gear ratio in the front and a lower one in the back on mud only trucks....

I was gonna say the same thing, but even then, you're still talking a max of a 10% difference.

 

[m78]

A lot of 4x4's come factory with a faster set of gears in the front to keep the vehicle from "hopping" when bogged in dirt. For instance, 4.10 /4.11.

 

[DNFXDLI]

I'm not sure it's because of that...those kind of variences aren't noticeable...my understanding was it was dependent upon manufacturer.

 

[Workin' Rig]

The only reason i can see for it is because why the mud boggers do it, the front end is the heaviest part of the vehicle and it needs to "float" more then the *** does, with a faster ratio in the front the front tires can spin faster and keep the nose above the mud while the back digs....if the front digs to much then you end up with a plowing effect and you go no where.

 

[DNFXDLI]

The only reason i can see for it is because why the mud boggers do it, the front end is the heaviest part of the vehicle and it needs to "float" more then the *** does, with a faster ratio in the front the front tires can spin faster and keep the nose above the mud while the back digs....if the front digs to much then you end up with a plowing effect and you go no where.

That is valid...but not when there is less than a couple of points in value.

 

[Workin' Rig]

That is valid...but not when there is less than a couple of points in value.

No i understand that....They usually run like 4.10 rear with 3.73 front or a lil less even.

A difference between 3.54's and 3.55's (or whatever) is probley due to whoever makeing the front axle not offering EXACTLY the same ratio as the back one.

 

[Mil1ion]

The axle gears are different so as to cause the Front axle to run a little faster keeping the truck with a axle load on it to prevent bad things from happening

You will NEVER see a 3.73 rear mated with something other than a 3.73

Yet with a 4.11 or 4.10 can be mated with a 4.10 and 4.09 respectively

 

[DNFXDLI]

No i understand that....They usually run like 4.10 rear with 3.73 front or a lil less even.

A difference between 3.54's and 3.55's (or whatever) is probley due to whoever makeing the front axle not offering EXACTLY the same ratio as the back one.

Exactly

The axle gears are different so as to cause the Front axle to run a little faster keeping the truck with a axle load on it to prevent bad things from happening

You will NEVER see a 3.73 rear mated with something other than a 3.73

Yet with a 4.11 or 4.10 can be mated with a 4.10 and 4.09 respectively

Not so...different speeds are what cause driveline bind.
In a perfect world the ratios would be the same.
You most certainly will see a different gear mated with a 3.73...you will see a 3.70 like in a 9''.

 

[dave]

my 73 highboy had 4.09 frt. 410 rears