Early vs late differential - vehicle speed sensor

[Cyrix2k]

I swapped a 1985 2.79 LSD into my 1991 318i. While it bolts up fine, the plug for the vehicle speed sensor is different. Can I resolve this by swapping in a '91 speed sensor or there more to it? It kind of sucks not having a speedometer.

[reelizmpro]

Changing the sensor should solve your problem.

[Bmr]

Does it hit the back in the diff?

[Cyrix2k]

I swapped the sensors and the speedometer works. I think it's off by a wide margin though - I swear it reads 55 mph at 2000 rpm and 80 mph at 2500 rpm. The calculated speeds based on gear / wheel size should be 49.6 mph at 2000 rpm and 62 mph at 2500 rpm. Any ideas on that one? I'll have to check this with GPS.

[Holland]

Changing the sensor should solve your problem.

This. Had to do the same thing when putting a late diff in my 85.

[AndrewBird]

Using the factory tire size (195/65-14) and the gear ratios found here for the Getrag 240, you should be taching 1720 RPM at 55 and 2502 RPM at 80.

Here is the calculator I made and use. Click the download link at the top to download the file and open in Excel.

https://docs.google.com/file/d/0B4aqWiGB57OSYjQ5TzZVb1gxUzg/edit?usp=sharing

[Cyrix2k]

Using the factory tire size (195/65-14) and the gear ratios found here for the Getrag 240, you should be taching 1720 RPM at 55 and 2502 RPM at 80.

Here is the calculator I made and use. Click the download link at the top to download the file and open in Excel.

https://docs.google.com/file/d/0B4aq...it?usp=sharing

Thanks, I'm an idiot. I thought 5th was 1:1 on the 240... my speedometer is reading correctly and I recalled the rpms incorrectly in the post above.