A very interesting day.

[1 Bravo 6]

The car club I belong to, (The All Classic Motor Club), ran a speedo check for the members today. My participation called for a 100 km round trip but it was worth it as my little "Precious" was in bad need of a good run. (For a change, the rear carby didn't flood once):classic:

The club used a hand held speed gun and large digital readout so drivers could see for themselves what speed they were doing. We do the speedo check once a year on a usually quiet stretch of road on the south side of Rockhampton (Central Queensland).

There were quite a few surprised drivers, including me. I knew "Precious" was travelling slower than the speedo read but I was sure surprised just how much slower. When the speedo read 60kph, the readout was 51kph. At 80kph, the readout was 70kph and at 100kph it was 86kph. So the old girl is really 10kph slower than the speedo indicates. No wonder so many cars overtake me.

Rick.

:devious::devious:

[Fun_in_my_z]

Are you sure people don't pass you because you drive like an old man?

[1 Bravo 6]

Billy my lad,

OLD MAN ??????????

Mate, ... in actual fact, I'm the oldest 25 year old there is.

Rick.

:devious::devious:

[BRE-240Z]

Mate, ... in actual fact, I'm the oldest 25 year old there is.

Ha!

That's a nice looking Z, BTW.

My car also is traveling slower than what's indicated on the speedo. I haven't had the opportunity to see what a radar gun would measure, but by gauging the speed of the traffic around me, I figure that my speedo is off by about ten percent.

[JimmyZ]

I have recently had the same problem. Took apart the speedo and sprayed/soaked teflon lube in everything. It reported actual speed for about a week then went back to what it was doing. (Used my GPS to check speed)

I suspect it's slop in the bearing assembly where the drive goes into. It's a very simple arrangement which uses two drums. On drum on the driven side has a magnet and the other drum is spring loaded and is attached to the speedo needle.

What I think it is is that the drums are not in close enough proximity to each other causing the spinning magnetized drum to have less of an effect. The good thing is that odometer numbers are not affected since they are "upstream" of the rotating drum thingys.

Someday I'll take apart the speedo bearing assembly and see what it takes to replace/rebush the bearing hub. There is a calibration statement on the face of the speedo which says something like 1024rpm= 60 mph.

2c

Jim

[Pop's Z]

Rick, That's a really beautiful Zed. Now, who's the old fart you got to stand next to it? Cheers, Mike (another old fart...takes one to know one)

[Carl Beck]

Rick:

What size wheels/tires are you running?

Stock transmission and rear end? (5spd with the 3.9??)

FWIW,

Carl

[Bruce Palmer]

So to get back to "correct", figuring 100 is 86, you need to go find a speedo drive gear for the tranny that is 14% smaller then the one you have, correct? Tha smaller gear will speed up the speedo while a larger gear will slow it down.

[xray]

It may be just me, but those tires look a little small, not quite filling the wheelwell in the way stock Zs do, which would certainly make your speedo off. Like Carl said, are they stock width/aspect ratio?

[Jeff G 78]

So to get back to "correct", figuring 100 is 86, you need to go find a speedo drive gear for the tranny that is 14% smaller then the one you have, correct? Tha smaller gear will speed up the speedo while a larger gear will slow it down.

Not really. Like Jim said, the odometer is likely correct (assuming the tire OD is stock). If he were to swap speedo gears, then his speedo will read closer to where it should, but his odometer will read off by 14%. :stupid:

I did the same test as Jim with a GPS and my speedo was way off, but the odo was pretty close. The problem lies with the speedo itself, not the gearing.

[Bruce Palmer]

Rick, In any event get back to us with the solution.....

Anyone on here ever take one of these units into a speedo shop?

[JimmyZ]

My speedo was reading accurately (per GPS) at one point. One day it started bouncing and then it would stay stuck on occasion. It also began reading wilder (higher) speeds and was eventually doubling my indicated speed. When I took it apart I found that a very small "counterweight" under the needle's hub had dislodged and was keeping it stuck. After glueing the CW back in place and teflon lubing everything it showed the correct speed for about a week. Now it's back to where it started except that it's not sticking. I'm thinking bearings/bushings being replaced will fix it. There's a speedo repair shop in town which I might give a try or at least consult with.

Hopefully your problem is a simple speedo gear issue.