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My speedometer is bouncing while driving

Tiny
GREASY MIKE
  • MEMBER
  • 1998 MERCURY SABLE
  • 160 MILES
3.0 ltr engine OHV, not DOHC. 6 cyl. My 1998 mercury sable speedometer fluctuates from zero to 50 mph as I am driving at 50 mph. As it starts to fluctuate the engine revs as if it were driving as normal but the car slows down, will not drive forward. The rpm gauge is normal.
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Thursday, January 5th, 2012 AT 5:58 PM

6 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Check your trans fluid if dark brown replace it and then check speed sensor have a trans guy look at it you my have a bad clutch seal or clutches.
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Thursday, January 5th, 2012 AT 6:22 PM
Tiny
GREASY MIKE
  • MEMBER
  • 13 POSTS
Hmac300, Thanks for your help. I recently had the transmission overhauled but they didn't replace the vehicle speed sensor. Which I believe is located under the car on the bottom of the transmission? There is also a transmission speed sensor. I'm not sure which speed sensor to replace. Could you advise? I appreciate it. I will check the wiring on each one. I live on a gravel road with lots of bumbps and holes so maybe something came loose. Thanks again, Mike
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Thursday, January 5th, 2012 AT 8:44 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
It should be your vss (vehicle speed sensor) it's item 4 on the pic i'm including. The other is item 13.
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Thursday, January 5th, 2012 AT 8:52 PM
Tiny
GREASY MIKE
  • MEMBER
  • 13 POSTS
Thanks for the help. I apologize for my confusion, but the item #4 is a wire harness attached to the PCM. I think. The actual VSS is located elsewhere as I am trying to figure out. I have read and believe I need to jack up car put on stands to gain access to VSS? Thanks again hmac300! Greasy Mike from Ferndale, Michigan
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Saturday, January 7th, 2012 AT 1:36 AM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
It may be item 13 then instead if 4 is just a harness connection. You should be able to reach that from the top.
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Saturday, January 7th, 2012 AT 2:21 AM
Tiny
GREASY MIKE
  • MEMBER
  • 13 POSTS
I found the vss and fixed the problem. The insulation on the wires where they meet they wiring harness had melted and the wires were touching. Must have created a short and confused the on board computer. Anyway the car runs fine no more speedometer problems. Thanks to all who helped me. Greasymike
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Saturday, January 7th, 2012 AT 11:34 PM

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