speedometer box


Veteran Member
Gold Member
Mar 1, 2020
My 4.10 geared 70 z28 with the original M21 had no adapter on the transmission. I’m in the restoration process so no idea if the speedo will read right. Were these required on this trans/rear end ratio and if so which would I need to buy?


Veteran Member
Lifetime Gold Member
Feb 12, 2011
atlanta, ga
typically (best results) have simply bolted everything together, run it....see how far off speedo is...check how much speedo gear can be had or is needed and adjust accordingly. Those ratio adapters USED to be adjustable (little gear sets) but now I think you gotta order specifically what you need.