Gear ratio/viscous coupler question

[The Beast I Drive]

Hey ya'll, I couldn't decide which would be the best forum for this question, but since its an off-road mod, I should ask here.

 

Will .01 difference in gear ratio front to back be enough to burn up an early Legacy 5-speed viscous coupler if I drive it on the street alot? I ask because I have definite plans to put a straight axle under the rear of the Beast and run a 4.11 RX/EJ hybrid tranny, but the rear axle ratio is 4.10, not 4.11. I figure, if nothing else, it would be ok for off-road only, and trailer it to the trails, but would it really hurt it to drive it on the street? If nothing else, I could always fab a driveline disconnect to go where the carrier bearing is, but if I dont have to that would be nice...

 

Axle in question is from a 90's Isuzu Rodeo Thanks

 

-Bill

[monstaru]

word on the street is that 10% is an ok difference.

so, 1% is definitely ok......

 

 

there are several posts about it at NW-WHEELERS...........thats where i get almost all of my hardcore info:grin:, and pirate4x4 of course.

but there are a couple of guys running more than 1%..........and say that it is fine....

cheers, brian

[The Beast I Drive]

Thanks Brain, sounds like this project is a go then

 

-Bill

[Qman]

Actually, a lot of old GM stuff ran 4.11-4.10. It is more than fine.

[Uberoo]

My dodge has 3:55's in front and 3:54's in the back or vice versa and it works fine.Although I can't have it in 4wd on anything like pavement though... something about transfer case wind-up around corners or something...

[Numbchux]

hold up, all your references (AFAIK) are part-time 4WD vehicles. little differences like that are fine off-road with a locked center. But that's not really applicable to a EJ VLSD AWD drivetrain.

 

 

 

let's say you're running 30" tires. at 70mph, that's 784 rotations.

 

4.10 R&P = 3,214.4rpm

4.111 = 3,223

 

8.6 rpm difference at speed

 

 

typically speaking, subarus can tolerate a max of 2/32s difference in tread depth. so that's 4/32s in overall tire diameter.

 

stock WRX tire size of 24.87" = 945.42 rpm @ 70 * 4.111 = 3,886.6

that minus 4/32s is 24.75" = 950.19 = 3,906.2

 

19.6 rpm difference at speed.

 

 

 

so...yea. you should be fine.

[idosubaru]

Nice hit Chux, that's what I suggested but it either got deleted or lost in cyberworld. Should be helpful too if anyone has similar questions of different ratios.