Highway speed speedometer shudder

[TwistedD85]

It's pretty simple, I think I have it figured out but it's safety related so I want to get a second or third opinion. While at highway speeds, 60-70, the car occasionally shudders/vibrates and slows down a few miles per hour, the RPMs never change but the speedo needle twitches. I'm thinking it's probably one of the rear brakes grabbing as we go down the road. The car is by no means well taken care of besides what the previous owner did, no job = no fixes, but since it's not messing with the engine itself I was thinking a grabbing brake was making the needle shake because one of the ABS sensors wasn't reading the same as the rest, sound right? :thankyou:

 

[CademiaX]

sounds more like unbalanced wheels to me.

 

[NotSoSlowSHO]

If your speed is changing, and the RPMs remain constant, then you have some sort of trans issue.

Sounds to me like the torque converter is unlocking momentarily.

 

[TwistedD85]

Eww... guess I was being optimistic... tranny flush in order or should I just pray? It's my only mode of transportation.

 

[zblackbeast]

im going to agree with notsoslowsho... My explorer would shudder like that for a few seconds on shifts. Tranny flush solved my problem real quick!

 

[jonmon6691]

Can you actually feel the car decelerate? My speedometer shakes between 4-5 mph sometimes, but I know the car itself is at a constant speed. This would indicate a problem with the speed sensing mechanism. The shaking/shuddering would be from wheel imbalance, a cheap job (usually free depending on where you bought you tires.)

 

[TwistedD85]

Tires are from the/a previous owner so no chance there. But I'd have to ask, I wasn't driving it at the time. Truth be told I'm usually one of the last people to freak when something's wrong with how my car runs, I just end up compensating for it, nothing I can do anyways. But I wanted to make sure it wasn't gonna grenade on me.