Diff gears question

chief · 16-01-2007, 10:58 PM

When changing diff gears your speedo will be out, so how does one get around this problem. I thought the edit would be able to do it, but have heard it cant.

If I goto 3.7 gears how much will my speedo be out? This will stuff up the auto shift points as well, wouldn't it?

So to the people that have changed diff gears. How did you fix this delima? (sp?)

EvilChief · 17-01-2007, 01:14 AM

i used to have 3.7s in teh rear, inc ombination with the 17/255 is was running the speeda was only 5% out which wasnt too bad.

but it was the ideal ratio choice between taking off and quater mile shifting were perfect

**Stav** · 17-01-2007, 09:32 AM

The edit will fix the shiftpoints.I changed speedo cog in the gearbox to correct the problem somewhat.Ultmately a good electronic speedo corrector should do the job.There are people who can do it for a fee

xr8ute · 17-01-2007, 10:59 AM

Speedo corrector between the vehicle speed sensor, and the Dash. Then either the edit (to change value for diff ratio), OR another speedo corrector between the dash and the ECU to reverse the correction you made for the speedo/dash...

howesy · 17-01-2007, 02:52 PM

If you get a speedo corrector and intercept the wire as it comes away from the box then the value has changed before it goes anywhere. First you need to get a gps and work out how many K's you are out and percentage it. Mine worked out to be around 11% out after changing the diff and correcting the factory. Mine was way out now at 100kph i am doing 99 which is where i want it. I went from 3.45 to 3.08 but the principle is the same you are just going the other way. And if your not really patient and double and triple check the orientation of each piece on the board then dont build your own kit. There is one from states that does the job, bit more expensive but you can have dual settings so when you change diffs you flick a switch back to original or other setting.
http://www.superlift.com/accessories/truspeed.asp
Just one available

ClassicAU · 17-01-2007, 09:25 PM

i have a 3.73 LSD and 235/45/17 tyres and my speedo is out by 6km/s at 100km/h. This was corrected from an insane 22km/h difference by a number 19 speedo gear in the transmition. I dont know if a bigger gear exists to get it closer.

Casper · 17-01-2007, 09:32 PM

Quote:

Originally Posted by ClassicAU

i have a 3.73 LSD and 235/45/17 tyres and my speedo is out by 6km/s at 100km/h. This was corrected from an insane 22km/h difference by a number 19 speedo gear in the transmition. I dont know if a bigger gear exists to get it closer.

is that the black gear?

ClassicAU · 17-01-2007, 09:48 PM

[QUOTE=Casper]is that the black gear?[/QUOTE

I honestly cannot remember what colour it is. All I know is its a number 19 as it was the largest one my mechanic had at the time. But thinking about it, for some reason red sounds more familiar, but I am still not quite sure. Sorry about that Casper.

Sleeperau · 17-01-2007, 10:48 PM

Quote:

Originally Posted by chief

When changing diff gears your speedo will be out, so how does one get around this problem. I thought the edit would be able to do it, but have heard it cant.

If I goto 3.7 gears how much will my speedo be out? This will stuff up the auto shift points as well, wouldn't it?

So to the people that have changed diff gears. How did you fix this delima? (sp?)

There is a speedo calibration guide on www.fordmods.com.au. This takes into account tyre size, diff etc. Mine was exactly 10km out at 100kmph. I used the black speedo cog. Shift points are affected. A unichip can't help but as previously mentioned an edit or Chiptorque chip will fix the problem.

Free347 · 17-01-2007, 10:51 PM

Black is for a 3.45 as far as I can recall.