I have an 85 Firebird with an 85mph speedo, i have the 305 but i found a 140mph speedo dash and i was wondering if it would fit inot mine? or what it would take to put it in? Thanks

 

should just be able to swap them out no problem at all

 

bEWARE!! I think your speedo is a mechanical type that is driven by a cable. All the 140 speedos were electronic in firebirds that I am aware of...
82-84 Mechanical All speedos (cable driven)
85 ?????
86-92 with gages were electronic
86+ with idiot lights were mechanical (cable driven)
John

 

You can do it with a VSS from a later model plus speedo buffer. There's a tech article on it.

 

definately need some help then...is my speedo mechanical?? Its an 85 Firebird, LG4 motor max on tach...6k max speedo 85mph.
Also is there a way i could check? Like disconnect my gauges fuse???That way nothing on the gauge panel would work?? Thanks guys

 

the easy way to check is to look in your engine compartment and look for the cable...

or you could crawl underneeth and look at the trans, if there is a wire harness going to the back of your trans then its electronic, if there is a kind of stiff cable coming out there then you have a mechanical...

John

 

so if i have a cable driven speedometer can i convert it to electrical?? i really want to use this dash it looks much better than mine

 

I know the speedo's use pulses like the tachometers to operate and calculate speed... you might be able to retrofit everything in there, but I am not really sure how.

Where I would start would be to do some research and look at the wiring harness' coming into the Cluster itself. remove the plugs from the dash and look at the wires to make sure there all in the same places with the same colors. If you have some missing that might just be for the speedo.

If there both the same, with the exception of the speedo wires, then I would venture to guess that you might be able to get the sending unit from the transmission, run the wires, plug the wires into the dash wiring harness where your IP plugs in. You might even be able to re-wire the plugs that go into your IP to make it work...

might take some research at the service manuals from the library too. You will ahve to look at wiring diagrams of both your car and the donor car...

Of course, if you have a big ole will to modify your car to a lter style, you could possibly transform your car into the other car by replacing everything from the dash to the engine wire harness etc...

My 87 LG4 Formula used the electronic speedo, and it would actually register speed without a battery, When I bought the car I had a friend with a Suburbon tow me and I remember saying, "well, the speedo works" The car had sat for 3 years before I bought it.

so I know that the info probably does not answer your question, but you can probably do it if you want to take the time and figure out how to do it... Since I have never done the converison, I really do not know what it entails, but it might be a potentially HUGE job. or it could be very simple.

I hope that helps

John