I have two Civic HBs both with same issue.
The '94 DX has had this issue going on for 2.5 yrs.. I'll be driving down the road in the early morning and the speedo. is working fine.
Then I hit a bump, accelerate too abruptly, or hit the brakes too hard and the speedo stops working.
There is a little engine movement compared to my other HB with urethane filled mounts.
I keep driving and the speedo will not work until I hit another bump or brake hard.
I notice that the colder it gets the less frequent. I thought maybe a wire is pinch or bent and as the wire warms up the contact breaks.
I looked at all the wires to the VSS under the hood to the shock tower and they all look good.
I cleaned the contacts to the VSS and the harness with contact cleaner and no improvement.
The VSS is mounted tight.
I was driving and hit the dash and the speedo started working again. When the speedo stop working I hit the dash again and nothing.
I have not cleaned the contacts on the speedo. to harness in the dash yet so I may try that.
I have switch out VSS with no differences.
With '92 S/C HB the speedo will work some times and other time not, similar to the '94.
I would like to get it work perfect all the time b/c I want to use the Crome launch control. ;D
Any ideas guys?