Gear Ratios

[BroncoJeff]

Does anyone know what the stock gear ratios for an 88 bronco w/h 351w would be?

 

[FORDPLAY]

what tranny?

 

[Justshootme84]

3.55 rear/3.54 front is most common, 3.08 and 4.10 are possible. Need to chekc the axle code, or the ID tag on the differential cover to tell, JSM84

 

[FORDPLAY]

i was going to say i had 4.10s stock but i swaped my bronco from a 6 poper to a 351 W...4 speed

 

[Broncobill78]

JSM is right. 90% or more of the factory Broncos came w/3.55's. 3.08's & 4.10's are optional (usually the 4.10's come w/the trac-loc rearends). Ck the axle tag (if it's still there) or the door sticker to see what you have.

 

[BroncoJoe19]

3.55 rear/3.54 front is most common, 3.08 and 4.10 are possible. Need to chekc the axle code, or the ID tag on the differential cover to tell, JSM84

You guys amaze me with the little bits of information tucked away in your brain cells!

I am surprised that the ratios are just a little bit different from front to rear... 3.55 rear/3.54 front. IF I guess it is because of a slight change in the transfer case, would I be right?

 

[Broncobill78]

Ya know I've always wondered about that myself. When I built my 78/79's I ran into this as well. I could get 4.11's for the rear (9" & D60) but all I ever found for the fronts (D44 & D60) were 4.10's. Now I know that *some* 9" center sections need to be ground for clearance to run the 4.56's but clearance shouldn'd be an issue for these smaller gears. I'm sure it's not random and I've always assumed that the difference in ratios is to keep the front axle pulling against the rear to prevent the rear from "overrunning" the front axle or pushing the truck. There's plenty enough combined slack (if you're running CV's on both driveshafts you have *6* U-joints in the two of them, 2 more in the front axle, two sets of slip yokes PLUS all the backlash in the Xfer case, add it all up and you've got plenty of slop for slippage engineered right into the drivetrain) in the drivetrain to allow for a 0.01 difference in gear ratios. That's the only logical reason I've ever come up with for it, When I competed there were guys in the unlimited class running 4.88's out back and 5.13's up front to help pull the truck thru the mud and to help it run straight (those guys would literally *float* over the mud they ran so hard). Now 0.25 is *way* too much difference to even consider running on a street truck but if you keep it on the dirt/mud and/or unlock the front axle then it's a workable compromise in a ******** toy but there's just no reason to ever do something that extreme in a daily driver or a rig that's primarily street driven.