FireDemonSiC

I made a post before on my goofy speedo but it died down and I'm too lazy to find it. So I figured I'd make another one.

Long story short, my speedo likes to give false readings on the high side. By a little at low speeds, and by alot at high speeds.

I thought of a few things it might be, but something really has caught my attention. The guy I bought the car from removed the factory 85 (The car is an 85 Z28) speedo and put in a 145 speedo. I'm pretty sure he forgot to change something out of the car, and it still thinks It's operating an 85 speedo. Heres why:

If I'm doing around 25 MPH, it will report 35 or 40. For city driving, I do 35 - 40 in most areas, to which the speedo reports a speed of 60 or so. For highway driving, I usually do around 70 but the speedo reports anywhere from 110 - 120.

Take a look at these photos, and notice where these speeds on the 85 mph speedo correlate to on the 145. I really believe the car still thinks It's controlling an 85. Only question is, what was it this last owner forgot to do?

thesargster4

iTrader: (1)

Well, im pretty sure that the sending link on the trans would needs to be replaced to.. but i dont know the 'technical' name for that part, so .. anyone else?

FireDemonSiC

bump?

FireDemonSiC

BUMP!

Any takers? The last thing I want is to begin running my new engine with more mileage on the odometer than there really is.

mcbchild

iTrader: (1)

Sounds just like the speed sensor in the trans, was the rear gears replaced or the transmission? Speed sensors are located on the tailshaft of the trans.

FireDemonSiC

Rear gears are stock as far as I know.

I know they are NOT posi, so I don't see any reason why they would have been replaced.

The trans is the original too, although it does have a shift kit installed.

Now that I think of it, when I first got the car I DID get a Vehicle Speed Sensor error code from the ECM. But after I cleared it that time to try and fix the O2 code, it never surfaced again. Any ideas what to do here? I know that the stock 85MPH speedo WAS replaced with the 145MPH speedo.

I do believe the rear tires on the car are smaller than stock tires, but I don't think it would be throwing it off this bad.

89IROKCONVERT

its most likely the gear in the trans is wrong someone probably changed the trans at some point and didnt change out the gear find out your rear end gear ratio and the color of the drive gear on the output shaft in the trans and the gm dealership should be able to get you the right driven gear or spend the bucks and go to the speedo calibrating shop

JamesC

iTrader: (5)

https://www.thirdgen.org/forums/inte...eedo-woes.html

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If everything is stock to the car, the speedo head swap requires no modification and will read correctly.

JamesC

JamesC

iTrader: (5)

The VSS is located on the back of the cluster 82-89.

89IROKCONVERT

thats true the speedos are all callibrated the same