Aight so my new 91 RS project (5.0, 700r4) has a few issues. Mainly the speedometer doesnt work at all (wont show any speed) and the tach shows a constant 2000-3000 rpm over what it's actually runnin at. Easiest way to fix? I tore the dash apart and far as I can tell there are no damaged circuits... how can i tell if the speedo sensor on the transmission is good without just replacing it? It's an electronic speedo. Thanks y'all!

 

Oh if it matters, my guess is it's somewhere in the gauge because the cruise control works and I don't think it would without the VSS working...?

 

the 700r4 uses a mechanical electronic speed sensor, theres a gear on the end of the sensor that meshes with a gear in the tail of the trans and sends an electrical signal to the gauge.

it looks a lot like this

 

I know the basic idea of it... it has a sensor pig tail and receiver though instead of the nice simple ones unlike -_- can I use a volt meter to test it some how?

 

i was thinking maybe the gear was stripped but just noticed your cruise works so its defiantly not the VSS.

 

Your tachometer being way off is practically considered "normal" for a 90-92. The tach in my 91 read double. Read this: 90-92 Tachometer fix.... - Third Generation F-Body Message Boards

 

So does that pretty much just point straight to the gauge? What about the tach?

 

Thanks 69! I'll read more in depth this week and see if I can't fiddle with it

 

Yeah, there's a lot of "stuff" there to read and soak in. I tried replacing the whole cluster with another used one, but got the same results. I did a bit of research at the time, but didn't feel it was worth all the messing around to dig that deep into it. The possible causes seem to be with either the ignition module, or the electronics on the tach. That write up I posted seems to fix the problem by replacing a resistor on the tach board. But I'm not sure if the original resistor is the problem, or if replacing the resistor with a different one is compensating for a bad signal. The tach being off was more of a nuisance to me than anything. I just did the division to keep my math skills sharp!

 

Well with it being automatic it isn't really super needed but if I wanna flip it n sell it I would like it to work haha