I have been having issues with my speedometer in my 91 5 speed formula. Ever since I got the car almost 2 years ago, I have been having issues with the speedo only in 5th gear, when the weather is cold and under load. The speedometer needle will drop down to zero, and when I let off the gas it comes back up. Now it just started doing the same thing in 1st gear also. Under hard acceleration in first the needle drops down to 0 MPH, and when I let of the gas comes back up. There are no strange vibrations noises or issues with the transmission that I have noticed in any speed. It shifts fine and stays in gear. How do I go about figuring out what's rong with my speedometer? Can it be done without taking the transmission off, or without throwing parts at it in hopes of fixing. Any help on how to troubleshoot this problem would be greatly appreciated. Thanks in advance.

 

It sounds to me like it might be the speed sensor on the back of the gauge cluster, the ties the tach to the speedo. But you said it is only in fifth gear and just starting to show up in first, which could also indicate a problem with the adapter on the side of the tranny where the speedo cable goes in.

 

A 91 wouldn't have a cable.

JamesC

 

i am pretty sure it would other wise how would the speedometer work, plus i have looked up speedo cables for plenty of 90 modle cars

 

Camaro speedos were mechanical from 82-89, electric from 90-92.

JamesC

 

So here is some update on the situation. I ended up crawling around under my car today to find out if there was anything obvious that could be causing my speedometer issues.
The first thing I found was that when I unplugged the speed sensor connector, it was wet with oil inside. I doubt that this is normal, but have never had to deal with a speed sensor before. Is there any way for oil to get in there?
I also looked and felt around the back of the extension housing, where the shaft that the drive shaft attaches to comes out. There seems to be a little bit of trans fluid coming out. Not enough to make a mess, but just a small seep. Does this mean that my extension housing bushing could be the culprit after all. I tied moving the shaft up and down by hand, and did not notice any play. However, I am sure that I did not move it with the same load that the engine puts on that shaft. Any suggestions would be greatly appreciated.
Thanks for all replies.

 

Both have seals, which can leak. I doubt that your problem lies there.

JamesC

 

Why do you think that this is not the problem? What else can the problem be? Any help in figuring this out would be greatly appreciated. The trans shifts and performs just fine, other than this annoying speedometer issue.

 

Leaks seals won't have anything to do with the operation of the speedo. I have no experience with electronic speedos, but from what I've read, the VSS is a common problem.

JamesC

 

JamesC,
Thanks for the reply. Do you know if I have to drain the trans fluid in order to replace the VSS?
Thanks

 

Once you remove the VSS, there'll be a bit of a leak (try to jack the rear higher than the front if you can), but nothing serious.

JamesC