Speedo is way out ???

[LS5]

Ok guys I am drawing a blank here.....

1970 chevelle 454 4spd car Has Factory 12 bolt rear end and correct M21 and correct Factory size tires as seen in picture so correct Bias Ply tires... Speedo says I am going 50 miles per hour when in actual fact I am going 65mph..??? Speedo does not jump or bounce and registers normally when I pull away so there is no delay in increase speed registering. The speedo makes no unusual noises nor does the cable while driveing I have had them shot in the past to know what they sound like when cooked.......So I am stumped... The only thing I can draw here is the Speedo is shot possibly.??? The speedo in our cars run like a sprung magnetic gear I think I recall..... any input here guys would help.????

Darren.

[monte70car]

Darren was the rear gear changed? Or maybe the speedily gears in the tail shaft?

[dbreese]

That is odd. I'm guessing that your 4 speed still uses the drive/driven gear in the tail shaft section of the transmission like in an auto. Just a wild guess but maybe the driven gear or drive gear may be worn just enough and not making a good gear mesh and giving you a false reading at the speedometer head but not so bad that it makes the speedo jump and act all wacky. I know on a th350 the driven gear is easy to remove for inspection. not to sure on a 4 speed. Hey you could always put a taller tire in the back to slow the reading down.

 

Hope you figure it out.

 

David

[bigtankjones]

Mine finally took a dump this spring. Mine was jumping around but would only read 30mph. So it looks like a new speedometer is in order for my Monte.