Hi Guys,

I have a Mazdaspeed rear diff (4.8 ratio) and it puts the speedo out by about 20km at 100km/h (my speedo reads 120km/h at real speed of 100).

Ive searched around for ages and cant find any way to have this corrected. Surely there are a number of people that have change out their diff and had the same problem.

Is there any way to adjust the factory speedo?

 

I'll be installing a 4.44 ratio (out of an RX-8) so I'll be looking for something as well.

 

I'm just guessing...But I expect its the speed sensor in the transmission you change? As opposed to the cluster.

 

I know that some cars can have the speedo configured. Anyone know if it is possible to do with the FD Speedo? I found in my search that there is someone in the states that can do this if you send them your cluster but being that Im in NZ its not really worth me shipping my cluster all the way over there.

 

On my FD (1993), the speedo has a electrical sender unit which is gear-driven by another gear which is on the output shaft of the trans.

One way to fix it is to take apart your transmission and repace the gear with another one which matches your new diff. This is a decent amount of work and I am not even sure if you can buy one like this.

Another option is to get an electronic box that lets you screw with the signal coming from the sender. I think the way it works (at a basic level) is that the stock sender sends pulses as the trans shaft turns. The faster you go, the faster the pulses come. It is possible to build an electronic box that will compress or expand (depending on what you need) to make your speedo and odometer read right again.

Something like this : http://www.yellr.com/

 

dakota digital also makes signal converter boxes like the one needed. try to search for them on google

 

4.8 final drive, yikes! That's some serious cruising rpm on the highway.

I'm running 4.3s but when I had my 275/40 17 rear Fikses (25.7 inch rolling diameter vs stock 24.9), it effectively gave me the stock 4.10 back. I briefly ran some other wheels with stock rolling diameter and I saw the effect on the speedo (and the odometer), but I really liked the increase in acceleration

 

The sending unit is adjustible for gear engagement by undoing the bolt and turning the sending unit .The gear is plastic on the sending unit ,cut in the opposite direction then a sec gen gear , .I have made a new gear to fit the sending unit out of some nylon bar stock .You should be able to make a gear one tooth bigger or one tooth smaller at least,maybe more . The shaft has a flat or something for a drive key I drilled a center hole then filed a place for a small flat sheet metal key tab ,the best I remember . This was several years ago .

 

Called my local Jaycar and they actully have a kit for under $100NZD that Im going to use

http://www.jaycar.co.nz/productView....Max=&SUBCATID=

Makes life WAY easier.

 

There's always GPS speedos.