94 Corolla Speedometer/Tranny Jump

I have a 94 Corolla that has been randomly giving me fits. The speedometer will jump, causing the transmission to jump with it. It will do this for a short while, and then either fix itself and register the correct speed letting the transmission run smoothly, or the speedometer will go to 0 and the transmission seems to slip into neutral untill the speedometer corrects itself. This causes a check engine light since my rpms shoot up. Also, I have found that while the speedometer is at 0 the o/d light will flash.
I noticed that if I tap on the glass or the base of the steeringwheel right under the speedometer while it is jumping, than the speedometer will fall to 0 and the transmission will act properly.
I don't know what the problem is...The person I bought it from said that she had to replace the speed sensor and bought the newsed part from a junkyard, so I was wondering if that part might be bad?:screwy:

Mom's 94 corolla having similar problem: speedometer suddenly drops to 0 then comes back up in seconds, sometimes seems to jump out of gear and back in, sometimes seems engine revs. Her mechanic has replaced speed sensor and prob persists--- did you ever find a solution to your problem?? would love to help put this worry to an end!!

I too have a '94 Corolla with a Speedometer problem... I don't have an automatic, so my RPMs don't shoot up as I'm manually controlling the transmission. My problem is more geared toward getting speeding tickets which I'd prolly get even with a working speedometer.

Anyway, I too did as you guys did and replaced the speed sensor as it was the easiest and cheapest fix, but it wasn't the right fix. The only other part of the speedometer left is the gauge. And, in deed, none of my gauges work... speedometer is only at 0 or jumps to 60 once I start going ~45 or ~50mph, fuel is miscalibrated by more than half a tank, thermometer always lies on cold.

I have read of at least 2 other people that fixed this same problem by replacing the instrument cluster. I'm just not so keen on paying $150 or whatever to replace it with another faulty cluster...

So, you guys lemme know how it goes. Especially lemme know if there are aftermarket clusters you can get (doubtful, tho.. not too many aftermarket parts for Corollas)
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Did any of you solve the problem? I have a friend that has the same problem on a 1998 Corolla. Thought about speed sensor replacement but the above comments indicate that's not the real fix.