Odometer/ change speedo cog

[theburna57]

I changed my grandsons cog last week from an ebay site. It says it is a 25 teeth cog. The speedo says the car is travelling at 60 but the speed alert says 80. I have seen that some cogs have 20 teeth. Would the wrong cog make this happen. The guy I purchsed the cog from is pretty defensive that he has done nothing wrong, all I am after is the right information.
Any help is appreciated.

 

[rambunctious]

I changed my grandsons cog last week from an ebay site. It says it is a 25 teeth cog. The speedo says the car is travelling at 60 but the speed alert says 80. I have seen that some cogs have 20 teeth. Would the wrong cog make this happen. The guy I purchsed the cog from is pretty defensive that he has done nothing wrong, all I am after is the right information.
Any help is appreciated.

Assume you are referring to the driven gear on the cable/sender unit.
If the cog you fitted has the same number of teeth as the one you removed, there should be no change to the speedo
This may help http://centauriaudio.com.au/tchc4878/speedocalc.html
FWIW I have a driven gear in the shed of no use to me along with a number of drive gears and driven gears from the HQ HZ vehicles
I will have a look later and see how many teeth it has

 

[theburna57]

Sorry not its the cog up in the cluster. I assumed that is was fine and didn't realise the need to count the teeth.

 

[_R_J_K_]

Would the wrong cog make this happen.

AFAIK the cog only controls the manual counter on the odo dial, nothing to do with speed which is calculated using pulses from the speed sensor otherwise the speedo would not work at all when the cog breaks. I'm guessing the odo cog is driven by the speedo unit in the cluster somehow, so there might be an issue with the cog fouling on something and stopping the needle moving freely. Couple of other things that could cause the wrong speedo, changing the diff ratio, wrong size wheels/tyres (but probably not to the effect of 20km), wrong speed sensor with a gearbox swap.

Before approaching the ebay guy I'd at least try to find your old cog and pull the one out that you received to compare them. Even if he is in the wrong you have to pull it out anyway to replace it.

Thing I'd do first though is get a GPS speed app on a phone (should be a few free ones) or a GPS nav unit and compare the car as it is now to that.

 

[vs-lover]

Yes I agree that this gear cog you are replacing is only for the odometer and not the speedo itself. The other gear that is available is for Series 3 utes as things changed during production with VT being produced alongside the S3 utes.

The following is the only guy I'd be dealing with as he knows his stuff pretty well.

Below is the later VS issued 20 tooth gear set to suit the very late utes that had non VDO fitted clusters.

 

[The_Captain_1971]

I'd be buying a couple of clusters to keep as spare. They are "cheap" now if you search hard and well worth keeping just in case the one in the car goes. Take a look at VL clusters now - as rare as rocking horse poo

Cheers and Beers