ratio change???

[renegade600sdi]

Hi! i have a 2008 f-350 4x4 SRW with 3.73 ratio, i would like to have 4.10 instead. is there a way of doing this??? should i deal with my ford dealer of is there a good aftermarket company that produce a good auto lock axle or differential??

Thank and sorry for my bad english.

M.B.

[Little General]

I was thinking the same thing except I was going to maybe 4.56 and 37" tires on my stock 20" rims. I seen in the 4 wheel parts catalog they have a special for about $600 per axle. Check their website .

[Stymie]

just find a shop that will do a gear install. you will need a set of gears for each axle, and a master install kit. expect about 900 in parts, and another 500-700 in labor, of course that is america dollars.

[dt75flh]

I have done this on my f-350 srw.....you can get away with aftermarket gears in the front axle....but if you tow I would buy the FORD gearset for the rear axle as I had to switch out the cheaper aftermarket rears due to some gear whine.....and yes they were set up correctly, and the company that sold the gears admitted the rear will whine,..... so the shop that put in my gears only charged me for the upgraded gearset cost and they r&r the gears and oil for free...

also with a 325-60-20 toyo on my factory 20" rim..the 4.10 gears corrected my speedo to within 2mph at 80 mph....gps verified...if I was goin to run 37" tires I would look into the 4.30 gearset.....

this change raised my rpms 200....with 4.30 it would raise them 300 rpms


and just my .02....i would stay away from 4wheel parts....they have good prices but some shops have not so great techs and they shortcut things a little too much.....I personally and a few friends that have had lifts put on will not go back there

[JW350]

Originally Posted by dt75flh

...also with a 325-60-20 toyo on my factory 20" rim..the 4.10 gears corrected my speedo to within 2mph at 80 mph...

Previously, gear changes had no affect on the speedo. Did this change for the '08 models?

[ZeroOne]

Originally Posted by JW350

Previously, gear changes had no affect on the speedo. Did this change for the '08 models?

No change, same as previous models. Speed is taken from a tone ring on the differential carrier that rotates at the same rate as the tires. A different pinion to ring gear count (ratio) will not affect it.

I have 4.56 on 38's, no change from 3.73, as far as the speedometer goes.

[dt75flh]

correct on the tone ring.....however going from a 34 " ish tire to a 35.5 " tire with the stock gears....the computer reads (x) number of revolutions per mile for a given tire size that is pre programed in for the factory tire sizes.....when you put larger than stock tires on,

the revolutions per mile decrease...

so for example if the stock tire turns 675 revolutions per mile the larger tire turns less times to run the same mile like say 650.

basically it means when i was running the larger tire b-4 the gear change my speedo was reading 70 mph when in reality i was going around 77 mph..about 10% faster than the speedo was reading....gps verified....
the 4.10 ratio made up for that 10% and my speedo and odometer are correct...

this also applies to people who lift their rigs and put plus 2 or 3 size tires on without correcting the speedo...the real mileage on the truck is higher than whats reading on the odometer due to the same principle

[dt75flh]

Originally Posted by JW350

Previously, gear changes had no affect on the speedo. Did this change for the '08 models?

this would be correct if you keep the stock size tire on the truck