93 Griffith 4.3LHD no transducer sensor in diff?

[HVGRIFF430]

My speedo fals out after about 3-4mls driving. Then suddenly it lives again while driving, then it fals out again. Everytime when cold it works about 3-4mls sometimes a little longer. Now i am checking the sensors. I was reading the forum and they talk about a sensor in the gearbox and on on the diff.
Mine has none on the diff. Is this possibel? My car has the rover box.

Thank you

[HVGRIFF430]

Forgot to mention, it has the stewart warner gauges.

[HVGRIFF430]

Yes it has. What is strange on the racing green site ,that the one transducer is fit from chassisnr 1925 onwards from may 1992 until the T5 gearbox came,the other earlier. My car is chassisnr 1153 and from January 1993 ......so will it be 8 pulse or 4pulse ??

[HVGRIFF430]

I think it is also not so easy to get it out with the gearbox in the car?