Gauge problems

[84camino]

Hi. I am having problems with my gauges. I had a cluster with an 85 mph speedometer and everything worked. Recently I bought a cluster with a 120 mph speedometer but the speedometer doesnt work now. The knob on the back makes the speedo move but when it's hooked up it doesnt move. Also my Tach doesnt work. When I start the car the needle spins around to the bottom of the dial and stays there. Any suggestions would be helpful. Thanks.

[stormspotter82]

unfortunatly i cant help you with figureing out your guage problem. i do however have a suggestion. if you get an 85 mph cluster with a tach, you can get a 140 mph decal that goes right over top of the 85 speedometer from Lauren Engineering www.laureneng.com for around $30. hope this helps.

[theelcaminofactory]

There should be no problem with the speedometer providing it was working when removed from the car it was originally in...recheck your connections. As for the tach, is your Elky a V8 or V6 and did the tach you purchased come out of a car with a V8 or V6 this may be your problem. Was the tach filter included? If you get the speedo working however, it will probably not register correctly without changing the gears in the trans to the correct gears for a 120mph speedo. Let me guess...bought it off Ebay didn't you?

[ElkyPete]

Originally Posted by theelcaminofactory

If you get the speedo working however, it will probably not register correctly without changing the gears in the trans to the correct gears for a 120mph speedo.

Your speedometer drive is mechanical, if you can spin the back of the new speedo and it regesters then when it is hooked up to the cable it will work. If it is not then it is not hooked up correctly or the cable end is not making contact with the inside of the drive.

You are not going to have to change the drive or driven gears in the transmission to make it work. Either it works or not. GM did vary some Speedometers turn ratios but that was done at the speedo not in the transmission and yours is not one that they did that with and neiter is the replacement. Most speedo drives (Mechanical) work from a fixed ratio and all are pretty much the same. That is why people like Autometer don't make a Speedometer for a Chevy and one for a Ford "Specifically" just Speedometers.

The tach could be out of a 6 and it could have a bad connection also. The thing on that is, are those from the same type vehicles and same years? They're electrical and could be different. One could use some type of filter and one doesn't or the connections to the harness are different. Factory stuff is not as simple as aftermarket stuff. Chances are that 120 cluster is out of a much later model year.

[87ElCamino]

Originally Posted by theelcaminofactory

If you get the speedo working however, it will probably not register correctly without changing the gears in the trans to the correct gears for a 120mph speedo.

It's not necessary to change anything. The 85 MPH and 120 MPH speedos are interchangeable without any modifications to the speedo gears or elsewhere. The 120 MPH speedo will work correctly. I installed a 120 MPH MCSS speedo in my 87 El Camino and it works just fine. All of the GM G-body speedos were designed so that 1000 RPM of the speedo cable equals 60 MPH.

[84camino]

It's a V8. And no I didnt get the tach from ebay. I got it from a junkyard.
Thanks for the tips.