running different gear ratios front/back

[yodaman1151]

so first off i want you to know that I know it is bad to run different gear ratios front and rear that it stresses the parts such as u-joints and the t-case. my question is... can i run 3.54 front and 3.45 rear? can anyone tell me exactly what kind of damage i can expect? i'm really asking this for the general knowledge to be informed instead of just knowing "yeah thats a bad idea"

 

[John Smith]

it would be fine .....

so first off i want you to know that I know it is bad to run different gear ratios front and rear that it stresses the parts such as u-joints and the t-case. my question is... can i run 3.54 front and 3.45 rear? can anyone tell me exactly what kind of damage i can expect? i'm really asking this for the general knowledge to be informed instead of just knowing "yeah thats a bad idea"

In 2wd.....

but in 4 wd....the rear axle will try to pass the front....I'm not sure how that would handle ...

i have heard of running a SLIGHTLY higher ratio in the front..( a tooth or so) in early jeeps?....so the front wheels would actually pull the back thru..but not the other way around.....maybe that was just a rumor...

best to runs front and rear fears in "sets"....it would seem to be like a chain failing in it's weakest link if ran much ....whatever the weakest link may be...one end fighting the other...and handling somewhat awful....trying to swap ends?....

 

[yodaman1151]

In 2wd.....

but in 4 wd....the rear axle will try to pass the front....I'm not sure how that would handle ...

i have heard of running a SLIGHTLY higher ratio in the front..( a tooth or so) in early jeeps?....so the front wheels would actually pull the back thru..but not the other way around.....maybe that was just a rumor...

best to runs front and rear fears in "sets"....it would seem to be like a chain failing in it's weakest link if ran much ....whatever the weakest link may be...one end fighting the other...and handling somewhat awful....trying to swap ends?....

no i'm doing a d30 swap and i have to gear it and i'm looking at what my options are as far as money available and i want to go lower like 3.73 or 4.10 cuz i wanna do a 8.8 swap later and i know i can find those ratios but i wanna wheel it in the mean time and i believe i have 3.45's in my truck.... i understand 2wd won't matter at all but i am talking about 4wd just to clarify

 

[-Nathan-]

if its in a lot of snow, or a lot of mud, then youd be okay. The minute you hook up, its going to buck you about, and probably smash that pinner 7.5 to bits, or the dana 30. Either way, if you get traction, youre going to break something. I think acceptible values are around 0.06 difference, anything more than that and youre askign for trouble.

 

[crusin93]

3.54x10=354
3.45x10=345

For every 10 revolutions of the pinion gears, the rear pinion will be 9 revolutions behind the front. This equals about 2.8 ring gear revolutions w/3.54 ratio. Therefore, for every thousand revolutions the spread becomes 90 pinion revolutions and 25.4 ring revolutions and so on. The important thing to understand is 1 ring gear revolution equals 1 tire rotation. I would expect that if the truck was forced to move with these gears, something in the transfer case, differentials or driveshafts would quickly fail. The difference between front and rear ratios is too great.

 

[yodaman1151]

3.54x10=354
3.45x10=345

For every 10 revolutions of the pinion gears, the rear pinion will be 9 revolutions behind the front. This equals about 2.8 ring gear revolutions w/3.54 ratio. Therefore, for every thousand revolutions the spread becomes 90 pinion revolutions and 25.4 ring revolutions and so on. The important thing to understand is 1 ring gear revolution equals 1 tire rotation. I would expect that if the truck was forced to move with these gears, something in the transfer case, differentials or driveshafts would quickly fail. The difference between front and rear ratios is too great.

technically it would be
3.54x10= 35.4
3.45x10= 34.5

just kidding... just being a smart a$$. but thats exactly what i was looking for. something a little more in depth of an explanation. so if you ran 4.10's and 4.11's you'd be alright but i would be too far a distance the rear related to the front to be able to make up for it. i would have to have either both front or both rear tires without traction to make it work and at that point i might as well be wheeling a honda cuz i ain't going anywhere right?

 

[-Nathan-]

you got it. In fact some vehicles came from the factory with ratios varying 0.01, but thats small enough it wouldnt matter. In your case, the spread is just too much.

 

[crusin93]

Yeah, sorry if the math was not spot on but you get the idea. Think about that guy with the huge knoby mud boggers and 1'' deep tread. The back and front tires are not exactly worn equally, maybe way different. Yet the truck still moves in 4wd. Small differences might not effect a thing.

 

[yodaman1151]

Yeah, sorry if the math was not spot on but you get the idea. Think about that guy with the huge knoby mud boggers and 1'' deep tread. The back and front tires are not exactly worn equally, maybe way different. Yet the truck still moves in 4wd. Small differences might not effect a thing.

I've got interco's I know exactly what you mean ha ha. That's wierd they would be mis matched from factory. Well I eventually wanna go 35-36 tires so I think 4.10's should be sufficient... No?

 

[C_Root]

Check the tire size / gearing ration chart in the tech section. IIRC 31/32 is right for 4.10's and 4.55's for 35's and 36's i would ass-u-me
Croot

 

[crusin93]

I dont know man. I've got 31's w/4.10's and I'm already lookin' for 4.56's.

 

[yodaman1151]

I don't know what it is but I got 33's and 3.45's (at least the tag up front says so no rear tag) and my supercab pulls WAY harder than my bII did with 31's. From the sounds of it I shouldn't be moving with 33's and my gears

 

[Toms01PSD]

I've got interco's I know exactly what you mean ha ha. That's wierd they would be mis matched from factory. Well I eventually wanna go 35-36 tires so I think 4.10's should be sufficient... No?

Save yourself the trouble and go 4.88 or 5.13.

 

[yodaman1151]

That's a good idea and I'd love to but this is a budget rig and I want to use j-yard gears. I know I'll catch crap for that but call me stupid

 

[TheTopher]

I think the best description of what happens would be when the trak lok guys are pulling something heavy and all of a sudden the truck "unloads" and shakes from the wheels not being able to spin a little different when you shift lanes and whatnot. Except your truck will be doing that every single moment it's on pavement.


Your driveshaflts, u joints, differentials and axles are all going to act like a giant spring. The more difference you get between them the more they'll fight each other and store energy. Eventually just like if you keep winding a spring something will snap. If you're lucky it will be the tires.


Of course, if you can keep away from engaging 4wd except in low traction environments you won't have any problems since that will guarantee the tires will slip. Keep up on your tire rotations to compensate for the uneven tread wear and you'll be fine.



+1 on the jeeps being geared a tad different. When my mom bought her 98 Cherokee the dealer was telling her to make sure she never used 4wd on pavement because of that.