The speedo on my 91 formula t5 is acting up only in 5th gear under load, and only when it is cold. When I apply load, the speedo needle will drop to 0. When I take my foot off the gass, it goes back up. It doesn't do it in any of the other gears, and after I have driven the car for a while and it has warmed up, the problem diminishes and eventually disappears. The problem is far less apparent when the weather is warm. Also, when I try to use the cruse control under the conditions that my speedo fails, the cruse control also fails to engage. I suspect that I have a speed sensor that is going bad. However, my Haynes repair manual has nothing on replacing the speed sensor in the 5 speed manual. How hard is it to do the job, and does the transmission oil need to be drained to complete the work?
Thanks in advance, any help would be greatly appreciated.

 

It's really not the speed sensor itself....

It's the main shaft of the transmission having just enough slack in the extension housing bushing, that when it's in 5th (which pushes the main shaft toward the opposite "side" from other gears), the speedo gears can unmesh.

Find a trans shop that can change out the bushing without disassembling the transmission. That takes a special puller, that has real thin jaws with real small teeth pointed outwards; and a bushing driver that's hollow, like a pipe. Call the trans shops in your area and ask them if they have that tool set. Last time I needed that done, I paid I think it was $25, and it took the guy like 10 minutes.

 

Would driving the car with this kind of slack in the main shaft cause any other damage to the transmission, other than the speedo not working.
Thanks

 

I doubt it...