Speedometer not working/erratic; transmission not shifting/errratic shift

Tiny
MARBERT
  • MEMBER
  • 2000 GMC C2500
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 230,000 MILES
Out of the blue, while slowing from 70 mph, the speedo begins bouncing up and down; the transmission then seemed to be "slipping" as I continued to slow down. Further testing: speedo is erratic; trans will engage all gears normally while not moving. Begin moving and shifting of trans is erratic.
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Tuesday, October 20th, 2015 AT 7:21 AM

4 Replies

Tiny
HMAC300
  • EXPERT
Have an auto parts scan for codes to see if your speed sensor has gone bad. They scan for codes for free. If not it may be a tcm problem as well at least for the shifting part on your trans. However with your mileage it may be an internal trans problem or a wiring issue as well. But from your question i' would lean towards an internal trans problem like a clutch pak/seal or something similar to that.
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Tuesday, October 20th, 2015 AT 9:27 AM
Tiny
MARBERT
  • MEMBER
I replaced the speed sensor that is on the tail shaft of the transfer case: no change in the symptoms.
What is the "tcm"? Is that a part that I can replace myself?
If the problem is internal, "clutch pak/seal ", does that affect the speedo? If so, is that solution a new transmission?
Where can I find a troubleshooting guide to my problem?

M G Moore
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Tuesday, October 20th, 2015 AT 9:57 AM
Tiny
HMAC300
  • EXPERT
Tcm is transmission control module which a trans guy has to replace and use a scanner to code in your vin as they are vin specific. But with your mileage I really think that the clutchpak/or seal is bad meaning that the clutch is not applying and not putting power out the output shaft so it wont go anywhere. If you can still check fluid as a lot cannot and the fluid is dark brown or black then that is pretty much an indicator that trans has burnt up.
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Tuesday, October 20th, 2015 AT 12:01 PM
Tiny
HMAC300
  • EXPERT
Trouble shooting guides are normally found in manuals.
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Tuesday, October 20th, 2015 AT 12:02 PM

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