Changing from 115 mph to 150 mph speedometer ?

[droptop94]

I now have a 115 mph speedometer and I got a 150 mph speedometer.
Both are out of a 94 Z28. Do I have to change any thing else to make the speed-read right?
Has anyone else done this?
Thanks.

[GreyGoose006]

id like to know... BUMP

[Earlsfat]

Assuming the connections are the same.... if you haven't changed anything in the drivetrain (IE: tire height, rear gears, trans gears, etc) it should read fine.

[droptop94]

Originally Posted by Earlsfat

Assuming the connections are the same.... if you haven't changed anything in the drivetrain (IE: tire height, rear gears, trans gears, etc) it should read fine.

I have not changed anything on my car, but was not sure if the cars that came with the 150 speedometer were geared the same as the one's with 115.
I think the only differnce is that the 150 mph had higher speed rated tires and the topend limiter in the computer was set higher.
Any how hope to put it in sunday and take it for a spin.
Will let yall know how it works.
Thanks.

[droptop94]

Well desided I could not wait till sunday.
Just got back from a test ride.
I used a portable gps to check it with and it worked fine.

[Earlsfat]

Yeah.. the internals on them are the same... what you would need to change would be the driven gear in the transmission that controls what the speedo reads. You would only do that if you changed the drivetrain components from original spec's. A big one is if you change from stock rear ratio or if you change tire sizes on the rear... for example.

[stone_mound_camaro]

wait..doesnt he have to change something? i mean if he just puts the 150 speedo with out changing anything else, wont he get incorrect readings(speed reads higher than it should) because the numbers are closer together on a 150 speedo? and the needle still moves the same distance right? the car doesnt know that the printed numbers have changed...so it would still think the 115 speedo is there, right? i mean..im just sayin...

[Earlsfat]

NO... think about it... the only thing that affects a speedo is the components of a drivetrain... that is why when you change something you get a new driven gear (little plastice gear that drives the speedo cable) not a new speedo. AND when you buy a new speedo you can get whatever gradiations you want... 100MPH, 120 MPH, 160 MPH... they are all the same thing - that is the mechanical ones... the electronic ones are different, just push a button and is re-calbrates itself. Nice, but expensive.

In other words... if the part that goes into the speedo is spinning at 4 rotations per second and that equals 90 MPH - it doesn't matter what kind of speedo you have - 4 rotations per second will read 90 mph on any mechanical speedo...

[droptop94]

The only thing I changed was the Cluster in the dash. Speedometer, tac, gas, temp. All one unit. Pluged right up. I tested it with a portable GPS and it read right.
Thanks for all the input.