Speedo Overreading By A Long Way

[notamondayfan 44]

hey guys,

 

just taken the new car out for a spin and it seems that the speedo is overreading by loads.

 

i dont understand why it would do this, ive just done an mi16 conversion, but kept the origional gear box that came with the car. i believe it is a 1.9 gti gear box, but as i bought the car as a none starter i have never actually seen the speedo work before today.

 

ive read some posts that says the speedo can overread when using a mi16 box. this may (although probably not) be the case, if so how do i identify a mi box to a gti box? if it is the gti box, does anyone know what may be the problem?

 

thanks, dean

[James_R 3]

You want to remove the speedo worm drive in the box which then just needs switching with the correct one.

 

Remove the drivers side shaft and unbolt the bit sticking out the side of the diff housing (that the speedo cable sits in to) and check which colour you have.

 

James

[notamondayfan 44]

what colour should it be?

 

thanks james , dean

[notamondayfan 44]

i removed the part (although i didnt need to remove the drive shaft), and its red with 17 teeth. i also have a spare gti gearbox and took the on out of that and its exactly the same.

 

i took it for another spin, this time with the sat nav plugged in to see how far out i was.

 

when doing 30mph the speedo said 35mph

 

when doing 40mph the speedo said 45-50mph

 

when doing 70mph the speedo said 85mph

 

 

any ideas? thanks, dean

[notamondayfan 44]

anyone have any ideas?

[TEKNOPUG 3]

This is not an answer, more a guess.

 

I had a box fitted with custom gears - TD final drive - so extended all gears by 10%

 

Speedo read exactly the same speed at the same revs as before (80mph @ 4k in 5th when should have been 88mph) hmmm......

 

A few months later I swapped dashes over. Obviosly had to remove and then refit speedo cable from clocks. Upon first drive, speedo instantly showed correct speed/revs (88mph @ 4k in 5th)

 

Can't explain how or why - just an anecdote really.....

[notamondayfan 44]

as far as i can see, the speedo runs off the driveshaft, so which ever box im running shouldnt make any difference, yea?

 

so its probably best to try some different clocks?

 

thanks, dean

[TEKNOPUG 3]

sorry - forgot to add, I changed clocks at the same time too

[Foltan 0]

At least it's overreading the right way! You'll never get done for speeding and your mates with think your car's ridiculously quick

[notamondayfan 44]

haha yea i was suprised myself when i hit 100 and thought. bloody hell this is quick! sadly it wasnt to be!!

 

anyway tekno, so you swapped your dials the same time you swapped you box, and that gave false readings yea? then later you swapped the dials and now its all ok?

 

did you notice anything different between the clocks?

 

is there a way of telling if im using the correct clocks?

 

thanks, dean

[AdamP 0]

Erm, what size tyres are you running? Are they significantly under-sized?

[notamondayfan 44]

i "think" they are 185 55 15. i know they defiantly aren't low profile.

[Grim.Badger 15]

I had this when I got my latest 205; I changed the 17 tooth pinion for a 20 tooth pinion and now it works fine.

 

Part number 2649 13

[notamondayfan 44]

ok thanks ill give that a try. will let you all know how i get on!

 

cheers, dean

[notamondayfan 44]

thanks grim badger, think thats worked

[kate205gti 4]

what colour was it out of interest?

[Grim.Badger 15]

My 20 tooth pinion was white, however so was the knackered 17 tooth one I removed. The new 17 tooth one I bought was red.

[kate205gti 4]

ahh just count the teeth then i guess!

[notamondayfan 44]

i think the one i got was light blue :S

[Henry Yorke 269 3 Cars]

I was under reading by 15mph @ 70mph on mine until I swapped the clocks for some others and now it reads spot on!

 

I think there must be differences between some clock sets