If I change my rear differential ratio (from say 2.8 to 3.1), do I also need to recalibrate my speedometer in order to maintain accuracy?

John

Yes.

How would I go about the recalibration -- are there kits available? Do shops do this? Would I send it away to have it done? Any ideas?

John

Since the speedo is matched to rear ratio then it must be recalibrated.

[This message has been edited by M.B.DOC (edited 05-03-2000).]

We repair and calibrate speedos. The calibration setting is marked on the back of the unit. It represents either the number of revolutions per minute at 60mph or the input frequency at 60mph (depending whether mechanical or electronic). When units are sent to us that is how we calibrate.

If we have the car and the speedo then we can plot a curve off our chassis dyno which will allow us to calculate the difference in the 60mph calculation. Most areas have someone measuring and certifying speed with a dyno - in the state of Florida police can not use radar from a moving car unless the speedo is certified every six months. So there are plenty of test stations. With such record any speedo shop should be able to do the calculation.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

Thanks much.

John

John:

In our area, Palo Alto Speedometer is considered the best (paspeedo@pacbell.net), or you can call them directly; talk to Hartmut C. Mees (650.323.0243).

Hope this helps.

Brian