all right, here's a question i've been puzzling for some time now. I have a 74 big block with 3.08 gears, but for some reason my speedometer says i'm going 60 when i'm actually going 70, definitely not a good thing when it comes to getting speeding tickets. I am completely lost as to how the speedometer could be off by that much. I do have 255 60's on the car, but that would by no means cause even close to that much of a difference. Any help would be great. thanks guys

even with my speedometer issue i have yet to get a speeding ticket, "knock on wood"

You might have the wrong driven gear where the speedometer connects to the tranny. These have different number of teeth and someone could have replaced the wrong one. This could cause the speedometer to read wrong.

Glenn

3.08 sounds like a pretty tall factory rear axle ratio for the car, so if the rear has been swapped out sometime over the years, that could certainly account for a mismatch between the true speed of the car and the indicated speed. It's not at all uncommon for people to make a rear end change and neglect to install the appropriate gear where the speedometer cable goes in the transmission.

Check with a Chevy dealer or one of the specialty houses and tell them what rear axle ratio you have so you can get the proper speedometer cable gear. I would think this should solve your problem.

The only other possibility I can think of, though remote, is if you have cruise control and the transducer has gone bad. It can make for a wrong speedometer reading, but this is ususally more erratic than a steady wrong reading.

i thought of the chance of the rear end being swapped, but a lower set of gears, such as 3.53's or something like that would actually make the car be going slower than it says, that's why i can't figure it out. Thanks for the suggestions guys.

Howdy
I would check the nylon gear that goes in the tranny to make sure it has the correct number of teeth!

yes but if your car was a 3.36 originally and now its a 3.08 it would behave as you describe...

60 @3.36 might equal 70@3.08

i dont know about what was offered your year..

but in 69, the default rear end with an l-36 BB was a 3.36

econony =3.08
perf = 3.55
spec perf = 3.70

its also possible that being from st louis they installed the wrong gear at the factory... sounds far fetched but considering the notoriously poor QC as St.louis.. it is possible..