[swftiii]

Yes, I know my driving skills have a lot to do with my slow speedo...

In addition to my slow driving, I'm having a problem with my 993 speedo. The needle is moving more slowly than my speed changes. When acelerating it is only a little behind the changes, but when slowing down it can take a good amount of time to catch up.

For example: When accelerating through 2nd gear to about red line the speedo tops out at 50mphs when I shift to 3rd and then takes a good 3-5 seconds to catch up to my consistent speed after that. On the other side when stopping at a red light from 45mph to 0mph it can take the needle a good 8-10 seconds to catch up.

I've had the speedo checked by North Hollywood Speedo and it is functioning fine, so it needs to be in a speed sensor or somewhere else. My shop asked me to check a couple of things and I did - the cruise controls still works and will accel/decel quickly, the rear spoiler still comes up at the right speed, and the ABS still works under hard braking.

So - anyone dealt with this or have an idea of what could be causing this? I have the club race this weekend - is there any safety issue that could stem from these symptoms?

Thanks a bunch,
-Skip

[Dr K]

Skip,

This problem is not fixable, in my experience. but you're in luck. I happen to have a very clean 1986 Targa (with, I might add, a speedometer that functions perfectly), which I could trade for your flawed 993.

Peter

[BobNovas]

Maybe the speedo is indicating road speed and the tacho is indicating motor speed. (Like, Is your clutch slipping?)

[Dr K]

Originally Posted by BobNovas

Maybe the speedo is indicating road speed and the tacho is indicating motor speed. (Like, Is your clutch slipping?)

His brakes would have to be slipping, too. He says he comes to a stop and it takes 8-10 seconds for the speedometer to get back to zero.

[swftiii]

Peter - thanks for the offer...

Bob - there is no clutch slippage

Any ideas please chime in otherwise I guess the shop will get a chance at it.

-Skip

[HoodPin]

Not sure how the 993 is rigged. But been working on speedo on my 86 944. Since your's in a 97, I have to believe its also an electric variety, instead of cable driven.

On the 944, there's a small shaft with gear on end that goes into tranny. It connects at top to a electronic convertor/sending unit that translates the shaft rotation to electrical signals. Wires plug into sending unit that then send signal to the speedo. My guesses (and that's all they are....):

1) Something wrong with speedo itself
2) Something wrong with sending unit (if like 944, easy to unscrew and replace)
3) The shaft into tranny may be broken or gears stripped which causes inconsistent connection/rotation.

Hope you figure it out.

[Vicegrip]

Check if it is mechanical or electrical. Find a clear straight section of road. Take the car out of gear and turn the key all the way off off a second. The speedo should drop to 0 right away. If not I would be inclined to think it was mechanical stiction in the speedo. From the sound of you post it sounds like there is friction in the speedo itself regardless of the pass from the guage shop. There is more power to move the indicator up the range but only a spring to return to 0.

A sending unit fail would most offten give a 0 speed as it is looking for an on/off pulse. No pulse of messed up pulse would make 0 or random speeds indicated. IIRC on 962 and later cars the speed is taken from the drivers front wheel ABS sensor. If the sensor was messed up the ABS light will come on as well. Could also be completly wrong too.

[flatsixcrazy]

Originally Posted by pkaufman

Skip,

This problem is not fixable, in my experience. but you're in luck. I happen to have a very clean 1986 Targa (with, I might add, a speedometer that functions perfectly), which I could trade for your flawed 993.

Peter

Can't comment on how to fix the problem but I can comment on the incompatibility of the 86 speedo on a 97. Can't use it, different wiring connectors. It is even different than the 964s connectors.

[VaSteve]

Originally Posted by swftiii

So - anyone dealt with this or have an idea of what could be causing this? I have the club race this weekend - is there any safety issue that could stem from these symptoms?

I thought real racers used thier tach to indicate track speed.


Sorry...I'm useless. Good luck in the race.

[Manny Alban]

Only time I use the speedo is on pit lane during club races. I guess I could be like the NASCAR guys and just find what RPM in 2nd gear is the pit lane limit.