'87 924S Speedometer question

[djkoke18]

The speedometer reads incorrectly (about 10-15% higher than I am actually going). Will replacing just the speedometer cable fix this, or will I have to also purchase the speedometer in the instrument panel as well?
Also, the Odometer does not work, is that also tied into the same problem?

Thank You!
-Steve

[944 Ecology]

Replacing the cable will not fix a speedo that it reading high.

Only replacing the speedo, or putting larger tires on the front of the car will change the reading of the speedo.

Replacing the speedo will also fix the odometer, but it's not related to the speedo reading high.

[Justin S]

I would just replace the speedometer. This auction is pretty Cheap so far

http://cgi.ebay.com/ebaymotors/VDO-PORSCHE-944-YELLOW-SPEEDOMETER_W0QQcmdZViewItemQQcategoryZ6763QQihZ01 8QQitemZ280228949466QQrdZ1QQsspagenameZWDVW

[bholmes]

What size of tires do you have on the car? Maybe they aren't stock....maybe they are 10% smaller LOL, never know.

[djkoke18]

Thanks for all the help. I am assuming that once I replace the speedometer, I should not change wheel size?

[mikepellegrini]

I fixed mine (an early 944, which I think is the same). It was actually pretty easy.

I had to take my speedometer apart to fix the odometer (a gear was slipping). As part of the disassembly, you have to take the needle off.

I have lower profile tires than normal on my car, so the speedometer was off already. I put the speedometer back in, and then drove at a range of speeds - all while I checked the actual speed against a GPS.

Doing this, I came up with an average amount of error (in my case, it read about 10 MPH higher at 70-80 MPH than it actually was).

So then I took the speedometer out again, and simply took the needle off, and re-mounted the needle so it read 10 MPH less at zero (zero is now actually about -10 MPH). There's a pin that works as a stop at zero - you have to break that off, if you need to recalibrate the dial to less than zero.

I found that the higher the speed, the higher the error. (It was maybe 3-4 MPH at 35 MPH, but was closer to 10 MPH at 70 MPH - so I recalibrated it to the higher speed.

I slapped the speedometer back in then tested it against the GPS again and it's very close at all speeds (closer at the high end, which is good). At 35 I'm probably doing 33 MPH, but at 70, I'm actually doing 70.

No, this doesn't do anything for the error rate in the odometer. But I'm less worried about that than I am about getting speeding tickets...

[ike229]

The speedo in my 88 924S also reads about 10 MPH higher after I get above 60. I just factor this in every time i look at the speedo.

[djkoke18]

Thats a pretty clever idea. So it does sound like wheel and tire size differances will have an affect on the speedometer reading. Then the question is, can the dash be taken out without damage? I read a tutorial on clarks garage a few years ago on it, but i believe it required some cutting near the windshield. . .something that might be difficult for me

[pokey]

You just need to remove the cluster, not the whole dash. Not a big deal to pull it. When I had my '24S, I swapped the speedo and tach so my tach was in the center spot. I also was going to mount a gps in the speaker grill in the dash.

[ERAU944]

Originally Posted by pokey

When I had my '24S, I swapped the speedo and tach so my tach was in the center spot.

my 944 is sporting this setup right now

[mikepellegrini]

I had a long, protracted fight with my odometer, and can now get the instrument cluster out in less than 5 minutes.

Here's the Clark's procedure for early cars: http://www.clarks-garage.com/shop-manual/elect-06.htm

Here's a calculator to determine how your tire size affects your speedometer accuracy. You input the OEM tire size, then the new size; it shows you the error in MPH. http://www.discounttire.com/dtcs/infoTireMath.dos

The car is designed to have wheels/tire combinations that are of a certain specific overall circumference. If you decrease the total circumference, the speedometer reads higher than it is; if you increase it, the speedometer reads low.

[djkoke18]

Mike, Pokey, Thats exactly what I was looking for!! Awesome insight. Whats wierd is that the speaker in the center is actually hooked up to the cd player, and it actually works, lol. My old 924s' didnt. But I was planning on taking it out and putting a holster for my phone in there, because my phone has gps. Very cool stuff guys. Not to change directions, but my oil drain pan gasket is leaking oil...I couldn't find a tutorial on clarks...any suggestions?

Thanks Again!

[mikepellegrini]

Naw, it's there: http://www.clarks-garage.com/shop-manual/lube-06.htm

It's a real PITA. My son replaced the pan gasket on his 84 NA. But it was worth it because it was leaking gallons.

[HondaDustR]

I think these cars call for 195/65 for 15 inch rims. I got 195/60's on the front and the speedometer reads exactly 10% faster. I know how fast I'm going by taking the speed readout on the guage and subtracting the value of whatever the tens digit is to get my real speed. I figured it out timing distance markers on the highway and doing the math.

[djkoke18]

I heard a rattling noise behind that cover on the center of the dash. Thinking it was that crappy original speaker, I popped off the cover. Too my shock, I found this, lol