85 IROC- Z manual cable speedo. I just changed to 145 from the 85. i hate the 85. problem is if i do 30 mph it feels like i'm go faster than that. i haven't driven a camaro in a while. don't if it just seems fast in that vehicle. on the freeway im doing 55mph so it says, and keeping up with everyone else. i know there not doing 55 in a 60 zone. do i need to change the gearing at the transmission and if so what is it actually called so i know what to get

 

Unless you've replaced the gears in the rearend or changed to larger diameter tires the speedometer should read correctly.

 

The speedometer head could need to be recalibrated.

 

how do i recalibrate?

 

It would have to be done by a speedometer shop.

 

You can calibrate it the poor mans way. Take the gauge trim and clear lens cover off and also the speedo needle. Have a friend with a speedo you can trust, drive ahead of you on the highway. Get on your cell phone and when he's at a steady 60 mph put you needle back on. There, sort of calibrated speedo. It's better to do it on the highway since that's where you can get into the most trouble.

 

On my 91, I switched out the 145 mph gauge cluster from a 1990 350 irocz. The way I did it was lift the rear end and put it on jack stands... and put the needle in and then stepped on the gas and would see if the needle would go up properly.

 

Seems doesn't count. Time your car between mile markers before you get too carried away.

JamesC

 

That will work if you've got a constant error, like if the speed is 10 mph off at all speeds (including stopped), which is almost never the problem unless you've removed the needle. Usually it's a linear error where the error increases proportionally with speed (1 mph off at 10 mph, 2 mph off at 20 mph, 10 mph off at 100 mph, etc.), and usually it reads low.

The speedometer head has a pair of magnets inside it that are spun by the cable. These magnets are inside a metal cup attached to the needle. As the magnets spin, they "drag" the cup behind them against the tension of the return spring, which moves the needle. The magnets seem to like to get weaker over time in these cars for some reason. I've got a 240 km/h head with this problem that I have to send in one of these days to have done. A speedometer shop can repair or replace the magnets and recalibrate the spring tension so the speedometer is correct at all speeds.

 

I agree totally with you Apeiron that my way is not the proper way but if Tripingeorge lives in an area like I do, there is no such thing as a speedometer shop. The closest speedo shop to me is probably in Ontario so us east coast guys learn to improvise.

 

You can improvise, but moving the needle only makes it read correctly at one speed, and you risk damaging it when you pull it off. The nearest speedometer shop to me as far as I know is in Calgary. I could have it shipped there and back in a couple of days if I get around to it.

Unfortunately having the speedo head rebuilt and calibrated isn't cheap. If it wasn't for the relative scarcity of the 240 km/h head, I'd just keep replace mine until I found one that worked.

 

i never even knew the was a such thing as a speedometer shop. is there ny other alternatives. i just wanted the better looking 145 speedo, not the crappy 85.

 

Have you tried driving a measured distance to see how far off it is?

 

What about the speedometer gears in the tranny tail housing ??? check those out yet? they are usually set for the speedo as well

 

that's what i was origanally thinking. But what is the name for that piece and where would i get it?

 

Not a problem unless the rear end is swapped out of another with a different gear ratio.

 

the 145 speedo came out of a newer camaro i guess. don't know about that gearing.

 

Forget about the speedometer gears in the transmission. If your old speedometer read correctly, they're not the problem.