Been awhile commenting on this situation: speedometer pulsing/stuttering/bouncing.
From the above Posts, the tach is working properly, not bouncing, in my '93 73.idi.
The speedometer still pulsing/stuttering/bouncing, I'll explain here:
1. speedometer needle holds where it should until over 45 mph, then it will pulse/boince some. It increases the activity the higher mph's I go. Example: at 70 mph, it will hold for a second or three, then it bounces back down to 60 mph. Keeps on doing this.
2. have seen comments this might be due to air infiltration/leak in the fule line(s), somewhere?
3. a few days ago, on my way back from Wyoming to Montana, had checked the tranny fluid and when closed the hood, it didn't close/latch all the way down/closed. As I was back out on the Interstate and up to around 70+ mph, noticed the speedometer needle was bouncing/jumping from 70 mph clear down to 30 mph, all places inbetween and the back-n-forth - very quickly up n' down the needle went. I noticed the hood wasn't closed all the way/tightly. I immediately pulled to the side of the road and closed the hood tightly.
4. when back out on the Interstate and up to 70 mph again, the speedometer needle did its usual 70 mph down to 60 mph and bauncing bacnk-n-forth again.
5. when the truck gets up over 40-45 mph, there is x amount of air flow through the engine compartment/underneath the truck. When get up to 70 mph the air flow is increased much higher. When the hood was not closed all the way, that greatly increased the air flow through the engine compartment, causing the speedometer needle to REALLY go spastic.
6. the various levels of air flow contributes to the air infiltration/flow across fuel lines. Meaning(?), with an open/infiltration condition in a fuel line, the various increases in speedometer needl bouncing is caused?
What think you out there?
thanks and hope this helps others...