Hot Rods SPEEDO GEAR HELP

I recently changed from a automatic to a 77 Camaro 5 speed manual trans. The rear gear is a 3.00. The original speedo gear was 20 tooth, and was about 25 to 30 mph off. I changed to a 24 tooth and speedo goes to 20 mph and that's it at about 40-50 mph. Is it speedo gear or sending unit. Any thoughts

 

Not sure this is the answer or any help , you may look into the drive gear on the output shaft , seems as I remember they have a defined range of teeth to mesh with on the speedometer gear . You maybe out of the range and gears are not meshing correctly . As I said not sure that is any help or not . Really seems strange to only go to 20 now , did it go higher with 20 tooth gear ?

 

this formula may help sort it out

Driven Gear Teeth = Drive gear teeth x axle ratio x tire revs/mile

 

I don't believe that a 77 had a 5 spd.. someone has obviously changed it over.


Sent from my iPhone using H.A.M.B.

 

What speed was it 25 to 30 mph off at? And which way was it off? was it reading faster or slower than you were driving?

but more importantly, how is the odometer doing? what does it show you've driven, when you actually drive 1.0 mile?

 

The 24 tooth was used in 60's Pontiac's and is to large for your application, it will damage the drive gear.
You are to far off for a driven gear change. You will need to change drive and driven gears as a set or I can build a ratio adapter to correct the error.
Give me a measured mile figure and we can get it dialed in.

Sent from my SAMSUNG-SM-G890A using The H.A.M.B. mobile app

 

The gentleman above knows what he saying and does a great job!

 

He does know all about speedometers!

But I'm also curious about this 1977 Camaro 5 speed transmission it's a new one on me.

 

I think at one point I pulled a 305 and 5 speed from a 1977 Camaro RS. Now if it was original or not is another story. Also read something that said no manual transmissions available in Cal. for 1977 Camaro, but it looked like from what I saw they were available elsewhere.

 

why running a tall set of rear gears?

 

In '77 the only Chevy with a 5 speed trans would have been a Vega or Monza.

 

My bad!meant to type 87 Camaro

 

Let us know what the odometer is doing...how many miles it shows you travel when you actually drive one measured mile (like using the mile markers on a highway, or using a phone GPS speedometer app)

It looks like the 87 camaro was available with rear gear ratios from 2.73 to 3.73, so there should be a speedometer gear available that works for your setup