GageBrand

I have a 1985 Iroc z28, my speedometer doesn't work and has a clicking noise coming from it so I am certain it needs a new cable, so I went and purchased a new one but as I have been doing my research I noticed that most online posts say that the 85 Iroc had a speedometer that only went up to 85mph but on mine it goes up to 110, so now I'm puzzled, is this the original speedometer? Or did someone swap it in? Its a 305 TPI. If this is a swapped speedometer will the cable still work properly on it? When I purchased it I bought it for a 1985 Iroc 305 TPI. Did the 85 Irocs only come stock with 85mph or also with a 110mph gauge?

sofakingdom

iTrader: (1)

It's been swapped.

In that year, it was federal law that a speedo could not indicate above 85 (except of course for police cars and such).

The max speed speed on the dial doesn't matter to the cable, or to anything else. ALL of them are 1000 revolutions of the cable per mile (NOT 1001, as you sometimes see; it advances on the 1001st rev) based on a gear train with a 100:1 ratio driving the tenths of a mile dial of the odometer, and 10:1 every step past that. (no combination of integers - whole numbers of teeth - will get you to 100.1 on that first gear train - DUH)

There's a good possibility that the root cause of the problem is the cruise control regulator. Check that and make sure it spins freely.

GageBrand

Sweet, thank you for the information. The 85s had cruise control?

JamesC

iTrader: (5)

Yes. More than likely you have a one-piece cable (speedo to trans), at least my 85 does. You might check the following link for possible cures:

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

Take a peek to ascertain what you have. Here's another link that discusses the types of cables: one-piece, two-piece, and two-piece with transducer.

https://www.thirdgen.org/forums/tran...cable-p-n.html

JamesC