Speedometer Readout Problems

[SteveF]

I have an 84 C4 and around town I've noticed my speedometer display is off about 5mph slower than actual speed . At highway speeds its about 10-12mph.
Is this just due to age & they need rebuilt or do I have other problems?

Any ideas?

Thanks in advance.

 

[JonM]

I am wondering if someone in the past changed the rear end gears and didn't change the gear in the transmision for the speedo

 

[SteveF]

JonM
Thanks for the reply.
As far as I can find out the car is stock. Was able to contact the last owner who wasn't aware of any gear changes.

 

[Moonunit 451]

Tires and wheels too? Going to 17's or a different tire size will have an effetct.
http://w1.601.telia.com/~u60113743/corvette_wheels/

 

[SteveF]

Car has stock wheels & 255/50ZR16 tires mounted.

Thanks for the nice site on tires.

 

[JonM]

The next thing is taking the speedo out and cleaning the contacts....anything after that and you would need to send it out for repair.

Here are a few of my bookmarks about the dash

http://www.corvettedashclusterservice.com/Ucandoprocess1.html

http://www.batee.com/corvette/

http://www.corvettemagazine.com/1999/dec99/dash/dashp1.asp

Couple of the above sites are down right now...they should be back up later on.

 

[SteveF]

JonM

Thanks for the sites. I'll look into cleaning the contacts & if that doesn't work I guess I'll have another "winter project" for the car when the snow flies here in Pennsylvania

 

[SteveF]

I was given another idea before removing the dash. It was suggested I first use a GPS or tech1 to check the speed to see if how far it is off. Never thought of trying a GPS. I'll have to give it a try before disassembly.