Helping a buddy out with his 1989 mustang gt convertible.
We did a transmission r&r, and redid it (craigslist trans wouldn't upshift past 1st gear!), and just got it on the road last week.
It's been sitting since.
Just drove it 5mi back from the shop, and a funny thing happened about 3mi in on the freeway.
Doing around 60-70mph and suddenly the speedometer needle jumps to 140mph+ and just stays there, oscillating.
As I get off the exit ramp, whenever I hit the brakes it actually jumps to a higher speed (even further past 140mph) and the amplitude of the oscillation gets worse. As I come close to a stop and pick up speed again going up the hill past the exit ramp, it recovers and acts normally; 10mph, 20mph, behaving as it should.
Now my own car is a 1990 grand marquis. Lots of the same parts, really. I know 1990 has an electric speedo. My sister drives a 1989 grand marquis, and it has an all-mechanical speedo.
As I understand it, there's simply a coiled spring, like a flex shaft for a drill. Her speedo wobbles/oscillates at low speeds, and this is almost certainly, I've been informed, because the coil is sticking inside its housing. If i pulled it apart and cleaned it and re-lubricated, it might work correctly.
However, on this 1989 mustang,even if the cable is all mechanical, what would explain wobbling AND jumping to 140mph+, full speed and beyond? sticking wouldn't explain going faster [than the car is actually going]...
thanks!
-Bernard
We did a transmission r&r, and redid it (craigslist trans wouldn't upshift past 1st gear!), and just got it on the road last week.
It's been sitting since.
Just drove it 5mi back from the shop, and a funny thing happened about 3mi in on the freeway.
Doing around 60-70mph and suddenly the speedometer needle jumps to 140mph+ and just stays there, oscillating.
As I get off the exit ramp, whenever I hit the brakes it actually jumps to a higher speed (even further past 140mph) and the amplitude of the oscillation gets worse. As I come close to a stop and pick up speed again going up the hill past the exit ramp, it recovers and acts normally; 10mph, 20mph, behaving as it should.
Now my own car is a 1990 grand marquis. Lots of the same parts, really. I know 1990 has an electric speedo. My sister drives a 1989 grand marquis, and it has an all-mechanical speedo.
As I understand it, there's simply a coiled spring, like a flex shaft for a drill. Her speedo wobbles/oscillates at low speeds, and this is almost certainly, I've been informed, because the coil is sticking inside its housing. If i pulled it apart and cleaned it and re-lubricated, it might work correctly.
However, on this 1989 mustang,even if the cable is all mechanical, what would explain wobbling AND jumping to 140mph+, full speed and beyond? sticking wouldn't explain going faster [than the car is actually going]...
thanks!
-Bernard
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