does anyone know if there is or what the mathmatical equation to figure out what gears i might have?

i wonder because i think i might have aftermarket gears but i don't know. the PO of my truck said he ran 33s on it but i got the truck with the stock 28s. i have 31s and the other day i checked my speedometer calibration and its spot on. now i figure the PO was smart enough to change the gears for 33s but well lets just say he was . i can only hope he matched front and rear gears as well since iv been using 4wd no problems so far so they prob match but you never know.

anyway lend me your insight.

 

you have to count the teeth on the pinion head and ring gear and then I want to say you divide the two to get the ratio

 

ok. i was kinda hoping maybe an equation without taking my diffs apart. is there anything using the tire size and the speedo being dead on or anything. of course the speedo could have been recalibrated. i don't know im just hoping theres an easy way

 

Not that I know of but I really doubt there is an easy eqation like that.

I bet someone else will post up

 

thanks.

anyone got any ideas?

 

Lift up one rear tire, mark the tire and d-shaft.

Spin the tire 20 times, count the number of rotations of the d-shaft, divide that number by 10 and you have your gear ratio.

for 33' tires and a 5sp you want 4.88 gearing.

dont ever count on your speedo to be really correct... I have seen speedos that became more accurate as the gearing and tire size were mismatched (stock gears and bigger tires).

Mine reads a few km fast... Doesnt bother me

 

there ya go You know I totaly forgot about doing that. but definetly an easy way for ya

 

It really is super easy

I setup my video camera to tape the d-shaft rotating, that made things much easier

 

thanks. thats what im looking for.

could i do it for the front too to see if they match?

 

you can do the front like that too. i believe 31's were the stock size tire for your truck.

 

ok cool

31s were stock on my truck? i could be wrong since its so old but the spare seemed to be the original and compared to my buddys truck whose spare was original they were the same tire and they were 28s, roughly. but you never know how things will change over 21 years

 

I don't think the 31" tire option was offered until the early '90s, so you likely had 28" stock tires, and probably 4.10 gears for a 5 speed trans:
- http://www.4crawler.com/4x4/4R_TechI...oDetermination

 

just checked discounttires.com and put in the info for your year truck and i'm deffinitly wrong they say stock size is 225/75/15 which is 28" if i remember correctly. like one of the comments said before speedo's are hardly ever spot on. I had a jeep cherokee with stock gears and 32's stock size is 235/75/15 and with the larger tires the speedo was spot on when checking it with a gps.

 

thanks now i know what stock should be. so we will find out what i have when i do the test. if they are aftermarket im thinking they may be 4:56 or something like that.

yeah i did check my speedo calibration with my gps. it seems to be pretty close i tested it in a couple different trucks. my ranger with 29" tires over 26" stock was def a change my f-150 with actually 1" smaller than stock tires was a change so im gonna assume its pretty close but i really shouldn't say "spot on" but u know what i mean.