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speedometer jumping

A

acman60

Guest
My speedometer is jumping. And it dos not keep the speed iam going its about 10 miles off. thanks mark
 

Mr. Chuck

Well-known member
Joined
Jan 19, 2005
Messages
230
Location
Southern California
Corvette
1981 Two tone silver / dr grey
My 81 has cruise control, with two speed o cables, one from the tranny to the control module and the second from module through the fire wall to the gage. If you have a similar setup the problem may be in the control module that is begining to show it's age (wearing out / binding internally). First steps is to pull out the flex cable and inspect for rub marks or frarred points with strands showing. If the cable looks good, apply a lube (I like to use special grease for speed o cable) or a dry graphite grease you can get in stick form. The graphite does migrate away from pressure points like the wet grease will do and leave you with a problem again. You may even find that the tip of the drive cable has broken off, if so you will need a replacement. A new cable may come with the special lube or may be coated with lube, if not ask parts guy for some.
 

LVMYVT76

Well-known member
Joined
Apr 21, 2006
Messages
664
Location
springfield, mo
Corvette
1976 medium blue
I don't think a bad cable will show a 10 mph difference. I think the head needs to be serviced. The cables go thru a transducer, but thats a 1 to 1 ratio and shouldn't do anything to slow the head down.
 

srs244

Well-known member
Joined
Apr 1, 2005
Messages
462
Location
the deep south
Corvette
1978 pace car, 04 CE convert
I don't think a bad cable will show a 10 mph difference. I think the head needs to be serviced. The cables go thru a transducer, but thats a 1 to 1 ratio and shouldn't do anything to slow the head down.

i disagree some what. if the cable is stretched or frayed as mentioned above it will bind in the sheath and could be responsible for an erroneous reading. it could also be something as simple as one of the 4 connection points (at the trans, into and out of the cruise transducer, and into the speedometer itseld) has become loose and the tip isn't set into the receiver very well and is slipping. not that i think this is the problem, but you could have a defective speedometer gear at the transmission. it might have become brittle, one or more of the teeth might have chipped, it might have become stripped where the cable is set into it. i had a similar problem with a 71 el camino right after i had the transmission seals replace, and it was a loose fitting at the transmission cable end. took longer to get the car in the air that it did to make the repair, lol.
 
Y

yarb

Guest
i disagree some what. if the cable is stretched or frayed as mentioned above it will bind in the sheath and could be responsible for an erroneous reading. it could also be something as simple as one of the 4 connection points (at the trans, into and out of the cruise transducer, and into the speedometer itseld) has become loose and the tip isn't set into the receiver very well and is slipping. not that i think this is the problem, but you could have a defective speedometer gear at the transmission. it might have become brittle, one or more of the teeth might have chipped, it might have become stripped where the cable is set into it. i had a similar problem with a 71 el camino right after i had the transmission seals replace, and it was a loose fitting at the transmission cable end. took longer to get the car in the air that it did to make the repair, lol.
Good advice here. Had a similar problen with the tach on my 71. The connector was loose at the distributer.Found that out when I went to replace the tach drive gear and button with new parts $50.00 All I needed was some judicous tightening of the collar. Dont over look the speedo gear in the trans tail housing. Its plastic. Might be chipped
 

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