When driving down the hiway my speedometer will suddenly jump up 10 to 15 mph and a few seconds later drop back to normal.

Is this a sign that it is about to need replacement? I would have thought if the drive gear was worn or cable frayed, it would reduce the speed reading, not increase it.

I am putting the interior back together and now would be the time to replace it if this is a symptom of impending failure.

I am curious to hear what you guys have to say about this :confused:


[Modified by molchaser, 12:23 AM 9/5/2003]

 

i am also curious about this as i have noticed mine starting to act the same way...
BTW...my cable is about 3000 miles old...

 

Guys, dont forget these cars are very old now, the speedos and many tachs are mechanical, and like anything mechanical that old, the lube is dried out...

you can NOT finish lube the think while it's all together....you have to pop the needle, remove the 'compass card', and then take the entire assy apart...best done under bright light on a clean kitchen table.....

when you get down to seeing two largish screws holding a final aluminum U shaped support onto the casting, remove them, and you fill find a pin point bearing inside the aluminum cup where the spinning magnet is located, you have to remove dried out oils and use just a dap of very LIGHT oil...I just used WD40, and then reassemble...you can clean out and re lube the bronze input bearing while it's assembled, no reason to pull all that crap apart....it's pressed/rivited in place anyway.....
this and the speedo cable itself, and the SHROUD the cable rides in....are your maintanance points.....

I just spary carb cleaner on everything for cleaning...great solvent...and then you may try swabbing out the shroud with a fish tape...and paper wadding,...maybe a gun patch....

I preferr lock graphite for cables...oil for the unit itself....

GENE

 

I have this exact same problem only sometimes it jumps as much as 100 mph! It took my wife (a total mechanical inebriate) to diagnos the problem. As it turns out it never happens when she drives. She said it has something to do with the correlation between the nerves in the right leg and the free flow of testosterone. :lolg: :lolg: :lolg:

Sorry, just couldn't pass this one up.
Dave

 

Mine did the same thing. First i replaced the cable which helped some but the speedo needed to be rebuilt. Cost about $100.00 if you remove and replace yourself, which is not a fun job. :cool:

 

My speedo was real jumpy below 50 mph. There was almost a constant 3-5 mph change, and sometimes 15 mph jumps on acceleration. In addition, I always heard this wooshing sound coming from it. I just disconnected the cable from the tranny and the back of the speedo, pulled apart the cable, inspected it (all was good), cleaned it off with some degreaser, lubed it up with some graphite grease, and now it's pretty much stable at all speeds and quiet.

Matt

 

Another thing to check is this: do you have cruise control?

If so, the cruise control transducer commonly causes this very problem. Usually the grease inside the transducer goes out then the gears go and you get a jumpy speedo.

Clean and lube the cables first, and if you still have the problem I would bet it's your transducer.

Good luck.