Okay. I searched through the archives, and have a few ideas, but nobody seems to have had the same problem I'm suffering from.

A bit of background and the car's specs... '85 GSL (possibly an SE... Background is a little spotty and there's been a lot of modifications done to it). Originally an automatic, but converted to a manual transmission from an '87 by the previous owner.

My speedometer is all over the place. Most times the needle bounces between 45-65mph. It will occasionally read what appears to be the correct speed (usually starting around 55 or so). On deceleration, it bounces all over the place from 0 on up... Quickly at first, but slowing the pace until I finally come to a stop.

Would that be a bad cable? Stripped connection in the transmission? If so, should I use a speedo cable from the '87 transmission, and will it properly mount to my '85 gauges? Or should I just try to hunt down the correct second gen cable and speedo?

 

You have a kinked cable. Easy to replace. An 85 cable should mount to the 87 tranny, but someone else back me up before he goes and buys one.

 

If u cant find a cable from a 87 tranny u could jus buy a brand new speedometer and slap it on the dash board pretty easy to istalled im about to do that to my 7 due the the fact that top speed only goes up to 85mph because its a 82.

 

u also might be wary of the rear end gearing for the automatics, its 3.90 no? and 4.10 for a manual... that can cause speedo issues... my truck is a great example... its got a transmission from a 79 rx7, and with those 4.62 gears it never reads right...