So it has finally been nice here on Long Island and I took the old girl out for a cruise. I've only had her since December, so my time with it has been limited. Anyway, I'm on the parkway and I think I'm doing 70mph, at least that's what the speedo says. People are passing me like its no tomorrow. It gets to the point where I start thinking, "Am I really going slower than the speedo says?" I pass one of the radar signs that tells you how fast you're going and it said 48, I look at the speedo and its on the 50, so its close. I pass another radar sign on the way home and the speedo says 65, the radar sign said 59.

So it appears my speedo says I'm going faster than I really am. The car has not had a gear or tire size change, it's all stock. I do have a speedo that only goes to 85mph which I found odd being that the trim is a Trans Am and not base Firebird. My trip odometer is also broken, it won't reset. I know it's a mechanical speedo and I was wondering if I could swap it out with another mechanical speedo from another F-Body with a speedo that reads higher than 85 and at the same time get a working trip odometer.

Anyone have any tips regarding the swap or any idea why the speedo is inaccurate?

 

"Anyone have any tips regarding the swap or any idea why the speedo is inaccurate? "

Different rear, trans, or tires than the car was set up for. I believe there's a sticky for which speedo gears to get for XX tires + XX rear end ratio.

 

The rear and trans has not been touched, its all as it came from the factory according to the PO. The tires are brand new in the stock size. Could it be that the gear is just worn or maybe it was changed and the wrong one is in there?

 

Are you sure it's a mechanical speedo??

 

That's what I read in previous forum posts.

 

I could be wrong but I dont think TAs in 85 had a 85 mph speedo,I't might have been switched.

 

I thought that too but I've seen a few other 85's with the same speedo.