No Officer, I don't know how fast...

[G.]

...I was going.

My Speedometer broke this AM. The Odometer did too. The Tach worked, though.

Then, at the end of my commute, I happened to stomp on the gas (so my little 2.5l Boxer engine could make the Subby sort-of pass, with the AC on) and it started to work again.

Any ideas what would cause this? Despite the benefits of not having the odometer clicking off the miles, I don't want to get a ticket. I drive through many speed traps on my commute.

I had the thing up on ramps yesterday to fix some exhaust heat shield rattling. Could I have bumped something? There was a sensor near where I was working, but it went into the exhaust pipe itself.

doing car repairs in 100 degree, 100% humidity, 100% sun on your 100% blacktop driveway is not fun. Also, rust from exhaust systems sticks to sweaty skin really well.

[RacinM3]

Just buy a Valentine One radar detector. Works better than a speedometer.

That sensor was probably the O2 sensor - nothing to do with your speedo.

[grungex]

My speedometer broke this AM. The Odometer did too. The Tach worked, though.

Then, at the end of my commute, I happened to stomp on the gas (so my little 2.5l Boxer engine could make the Subby sort-of pass, with the AC on) and it started to work again.

Any ideas what would cause this? Despite the benefits of not having the odometer clicking off the miles, I don't want to get a ticket. I drive through many speed traps on my commute.

If you're car is newer, it probably picks up the speed signal electronically from one of the ABS sensors. These are usually a magnetic device that picks up pulses from a slotted wheel or ring on each axle. Debris or a bad connection can cause a malfunction here.

Older cars have a mechanical cable which is driven by a gear in the transmission. The cable spins within a flexible sheath and drives the speedo mechanically. Sometimes one of the squared-off ends of this cable wear and/orslip out of the mating square hole and stop spinning the speedo internals. If you can get to the back of the speedo see if there is a heavy stiff sheathe cable coming off of it. Usually they screw or snap on, inspect it and reassemble. It may be harder to find the other end, but you might be able to follow it where it comes through the firewall. Good luck.

[Andrew Longman]

...I was going.

My Speedometer broke this AM. The Odometer did too. The Tach worked, though.

Then, at the end of my commute, I happened to stomp on the gas (so my little 2.5l Boxer engine could make the Subby sort-of pass, with the AC on) and it started to work again.

Any ideas what would cause this? Despite the benefits of not having the odometer clicking off the miles, I don't want to get a ticket. I drive through many speed traps on my commute.

I had the thing up on ramps yesterday to fix some exhaust heat shield rattling. Could I have bumped something? There was a sensor near where I was working, but it went into the exhaust pipe itself.

doing car repairs in 100 degree, 100% humidity, 100% sun on your 100% blacktop driveway is not fun. Also, rust from exhaust systems sticks to sweaty skin really well.

I once drove a car with broken dash lights. Absolutely did not keep an officer from writing me a ticket.

As for you problem, grundex has it about right. Nothing much to add except if you do have ABS and the speed is coming off the sensor, and it happens again, you might try activating the ABS or look for the ABS idiot light. I don't know for certain, but if the sensor is not working for the speedo it might not work for the ABS too.

Finally, this heat does suck. Your story reminds me of the weeks I spent one July rebuilding a masonry wall along my parants blacktop driveway. :(

[Stu]

My Speedometer broke this AM. The Odometer did too. The Tach worked, though.[/blog]

as long as you know what gear you are in thats all you need to know how fast you are going.

[racer2c]

as long as you know what gear you are in thats all you need to know how fast you are going.

As long as you know at what RPM your speed is in any given gear. Which reminds me of this on going debate I have with my bro-in-law. he's a fellow Miata nut and hangs over on Miata.net talking to all the auto-crossers. They have him convinced that the Miata is best driven at 4000rpm in any gear.

So when he drives around town he's in second or third gear at 4000 rpm. he recently bought his second Miata (a cream puff, low mileage '99) and brought it over for me to take a spin in it. We head out and after about one mile he says "what are you doing?", I'm like "uh, what?" He says " you're bogging the engine!". We were on a four line 45 mph road and I was doing 50 in fifth gear @2300rpm, hardly "bogging" the engine. He "made me" downshift to 3rd so the rpm was @ 4000 at 45mph. I went on to tell him he was wrong in his philosophy but hey, it’s his car.

So what did I do? Downshifted into second, took it up to 7000, bounced off the rev limiter for a second and then flipped it into third and took it up to 80mph. I told him, "that's how you drive when you want to go fast; when I am just cruising I keep it in the highest gear that still pulls.

He didn't say anything. He drove back (about five miles) and kept it in third @4000rpm the entire way. I told him if he doesn't want to shift gears he should get an automatic which is a real insult to Miata guys who think they know how to drive.

[G.]

Oh great. It's an intermittant failure. My favorite. :shakehead

Happened to the wife last week, was all fine yesterday once it started working.

The car's an automatic. I don't drive it, I steer it.