I have a 71 cutlass 455 4bl, th400 tranny 342 rear end.

Can anyone help me with my problem?

Currently when I drive down the road, I am about 6-7 miles under what the speedometer is reading.
How do I adjust that?

Thanks for your help.

 

You will need to change the speedometer gear in the tranny. Remove the speedometer cable from the tranny and the gear is at the end of it....You will need to change that gear......Go to www.transmissioncenter.net and learn a great deal about that plus see the gears etc.

 

If the tires and wheels are not the original sizes it's possible you have tires and wheels
that have a different diameter than the originals. Inflation pressure can also be a factor.
The smaller the diameter , the faster and farther you go according to the speedometer.

Dave

 

Thank you for the information.