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speedometer jumps around,


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jayschevy
User

Mar 3, 2010, 4:51 PM

Post #1 of 8 (4368 views)
speedometer jumps around, Sign In

i own a 1986 chevy monte carlo with a 305 eng. a 2004r tranny. and lots of miles on it.my speedometer started jumping around 3 days ago.started at around 55mph.now it starts at 35.sometimes it will stop and work correctly.
just had the trans rblt 2 mos. ago,btw i put a new pinion seal in 2 wks ago and pushed the driveshaft spline further into the tranny so my fluid wouldnt leak out.did i do something wrong?
if the cable was broke wouldnt it stop working altogether.i am at a loss as to what could be wrong.any help will be greatly appreciated.

jay


steve01832
Veteran
steve01832 profile image

Mar 3, 2010, 4:58 PM

Post #2 of 8 (4363 views)
Re: speedometer jumps around, Sign In

This could be a problem with the Vehicle Speed Sensor circuit. You should test drive the vehicle with a scan tool hooked up to see what the PCM shows for mph. Then compare it to your speedo. If the PCM shows erratic speeds, check the vehicle speed sensor circuit. If the PCM shows normal as your speedo is bouncing around, the problem could be the instrument panel cluster or wiring.

Steve


jayschevy
User

Mar 3, 2010, 5:57 PM

Post #3 of 8 (4361 views)
Re: speedometer jumps around, Sign In

thanks for the reply,what kind of scan tool? i dont have any tools like that.as an aside,i just went to the bank,and the speedo didnt jump,i was wary about it.then i stopped at a light and looked at the speedo,and it wasnt on zero.sitting at about 5mph.i backed up later on and it almost went to zero,but after that it sat at 5mph


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Mar 4, 2010, 4:57 AM

Post #4 of 8 (4355 views)
Re: speedometer jumps around, Sign In

Steve - Jay,

Quote">>1986 chevy monte carlo<<"

1986! Don't all of those use a plain cable? If so the inside comes out from dash end to be lubed. Was common for the era if a cable,

T



jayschevy
User

Mar 4, 2010, 4:14 PM

Post #5 of 8 (4348 views)
Re: speedometer jumps around, Sign In

you are correct tom,there is a cable.i will check it tomorrow,there is also a vehicle speed sensor right beside where it plugs in.i am hoping its just the cable,so i wont have to take the ins. panel out twice.
will post back with news after im done.


steve01832
Veteran
steve01832 profile image

Mar 4, 2010, 5:01 PM

Post #6 of 8 (4342 views)
Re: speedometer jumps around, Sign In

OOPS!!. Sorry, I misread the year. Yes, a cable indeed. One of the problems GM had was the teflon speedo gear in the back of the cluster. When it started to wear out, it would cause the speedometer to bounce. Also, a worn out cable can do the same thing.

Steve


jayschevy
User

Mar 5, 2010, 5:33 PM

Post #7 of 8 (4326 views)
Re: speedometer jumps around, Sign In

well i checked the speedo cable today.pulling the dash out sucks.it wasn't broke,i shot some wd-40 down the cable sheath.while there i noticed there is an extension about 20 in. long connected to the tranny.the end will pull out some,i didnt force the issue.put it back together and went for a drive.it jumped around.then it would stop and work correctly.

so now i think that might be the problem,or the plastic speedo gears in the tranny.will get a new cable setup tomorrow and put the ext. on.hopefully that will fix it.


jayschevy
User

Mar 6, 2010, 9:27 PM

Post #8 of 8 (4311 views)
Re: speedometer jumps around, Sign In

it was the extension cable,the very end of the tip was broken off.i replaced it w\a new cable that was about 2in. shorter,yet it fits fine.the pointer moves very smoothly now.took a 20 mile trip to test it seems great so far.so guys thanks for the help.






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