Why is it So

[wazzadj]

hey guys
since i have done the 2.5 di to 2,5TDI conversion have a strange issue
the Speedo is 15km out of wack eg speedo says i am dong 100km but in reality tested with GPS says i am doing 85km and when my wife driving at 100km in front i am miles back
So i have the original Mk4 dash cluster in ( you know the one with the Clock in the Center ) cable driven from a upgraded A4LD Auto trans with the VSS connection

So the old A4ld MANUAL KICKDOWN on the 2.5DI using same Instrument Cluster worked fine
I have even tried the upgraded Cluster with the Tacho built in Cluster and have even tried the diffrent speedo cables NO Diffrence to Speed Readings
What is causing this mismatch on the Speedo ?
The 2.5TDI & Gearbox A4lD are all off the same Vehicle including the Speedo Just not the Speedo Cluster but i wouldnt think it would make a diffrence because they are both cable driven

please feel free to ponder this problem
all help Appreciated
Cheers
Wayne

[ricc]

rear wheel diameter and diff ratio will also affect the speedo accurracy. normally theres a drive gear where the speedo cable is attached to the gearbox that can be changed.
do a search for speedo drive gear.

on the bright side you wont get done for speeding

[wazzadj]

Thanks Ricc
funny you say that I go caught speeding up a hill in the van for the first time lol
so the diff running gear is diffrent between the mk4 1994 & mk5 1995

[ricc]

back axle diff ratio varies with model even different vehicles of same model , can be anything from 3.9 to 5.8 ... should be a small plate on one of the diff bolts with the ratio stamped on it . mines a 4,56 which seems to be common on mk5 with 14 inch wheels on the 5 stud axle.

[wazzadj]

Thanks Ricc
will check