3.45 Diff Centre Swap & Speedo

[chich]

Hi Guys,

I have been thinking of changing my EF Fairmonts diff centre to the 3.45:1 LSD unit used in the EF/EL XR range however reading through some posts has left me a little confused. Changing to 3.45s will increase my speedo error (its already a little inaccurate as a result of my 17s) however the auto will shift properly. Changing the speedo gear to the corresponding 3:45 gear will apparently stuff the shift points and you run the risk of revving the thing into redline on upshifts. Whats the go ??

Cheers,
Anthony

[NC_Steve]

At full throttle the ECU uses only the speedo signal to change gears, hence why changing the VSS gear also changes the shift points at full throttle. You can fix this by correcting the speedometer signal only.

[OED666]

Your speedo wont be out much at all with 17" wheels... It would only be out if you kept the same profile tyre as you had on your 15's.

I went from 14's to 17's and there was like 2mm Overall Diameter difference... Made no difference to speedo read out.

Ages ago, i found out my OD with 14" and 17" wheels from the bridgestone catalogue. thats how i found out there was only 2mm difference...

I know people who have put the correct speedo teeth on the speedo transducer in the gearbox, and its makes the speedo read correctly. You shouldnt have any problems at all...

If you get the diff gears, and corresponding speedo transducer cogs you will be fine...

[chich]

Okay, so what you guys are saying is that with the corresponding 3.45:1 speedo gear it will indicate the correct speed and shift as its supposed to - correct?

[OED666]

Yea, i think you will be fine with the correct speedo gear...

[EF_Frmnt]

The ECU shifts according to throttle position and RPM... changing the transducer gear (speedo gear) will not affect the shift points at all. Go into your local friendly for dealer an you should get one for under 10 bucks its just a little piece of plastic.. ask for one out of an XR.