Continuing Odometer Problem

[g59tester]

Hi Guys, I 've still been unable to resolve the inaccuracy in my Odometer. The cars been off the road for 10 months having major bodywork and a window's out respray... hence the timescale. My car is an Oct 87 220 turbo with a 180 MPH speedometer. I had the usual problem with the broken gear wheel which I replaced on various recommendations with a pink 20/23 wheel. I have a picture of the old wheel in place with the missing teeth which allows me to check albeit slightly inaccurately that the original was also 20/23. The odometer is recording about 38% high while the speedo is pretty well bang on correct. I sent the speedo head to a so called expert in Holland to get the instrument calibrated. He advised that some of the capacitors in the PCB had failed, [common problen with VDO electronics of that age] replaced them and then recalibrated the instrument. I believe he recalibrated the PCB and perhaps the speedo.... but not the Odometer. this cost in excess of £300 with customs carriage etc. All to no avail still recording 38% high.
As there is a single signal from the gearbox sender to the speedo head and the speedo is correct, I assume the sender is OK. if the guy in Holland did his job correctly, I can only assume the gearing is wrong. The 20/23 gives a 0.87:1 ratio and the next wheel down is 19/24 which is 0.79:1 still wouldn't correct the 38% error.
Where should I go from here?
Anyone got a spare turbo 180 MPH speedo head c/w turbo gauge? My car has 95000 miles on it
Eddie

87 944 Turbo
2007 Cayman S

 

[944Turbo]

I have a pink 20/23 wheel waiting to go in my 1991 cab however it is currently sorned so it might be a while before I can give you feedback! As I have had it for nearly a year I really should fit it (and use the car its on the same tank of fuel as last year). Will see if I can at least fit it this week.
Tony

 

[GregBarton78]

When the odo fails, does the speedo needle still work? Mine has come back from paint with a non functioning Odometer. Trip computer reset absolutely fine (whilst stationary) and the needle works.

Car is a late 90 S2 coupe so presume I need to pull it apart and find out what's in there before ordering the bits.

Only other niggle is the passenger side mirror adjustment no longer does anything. Not sure I can be arsed pulling everything apart for that.

 

[Eldavo]

Speedo drive is from an electronic sensor on the gearbox on series two cars so I’d expect the needle to continue to work.

Passenger mirror will just be a case of the bodyshop not plugging it back in (in my personal experience).

 

[g59tester]

Greg, as i understand it the sender in the gearbox sends a signal to the speedo head PCB. this operates the speedo itself and sends an additional signal to the odometer.. On my car the speedo is accurate and the odometer reads 40% high. It was like that before i sent it away to a specialist in Holland who replaced some components on the PCB, recalibrated it and did nothing about checking the odometer accuracy. You could try Julian Reap at 0208 8632305. he seems to be more of a 'dial' man than PCB's
Eddie
2007 Cayman S
1988 MY 944 Turbo

 

[944Turbo]

Hi,
I put in my 'pink' replacement wheel and now I have it back on the road and so far I believe it reads 5 percent out compared to GPS but the speedo also over reads by approx 5% relative to GPS so I am not surprised.
I used this video as a guide https://youtu.be/9E-2uAQ5I14
Eddie, I wonder if your gear should have a different number of teeth? 1 revolution of the worm drive moves it too far?

 

[g59tester]

Hi Tony, when I investigated the possibility of another 944 gear with different ratio's none of them seemed to offer a possible solution The guy Reap did have lots of alternative ratios for 911's and reckoned they would fit the 944 speedo. I traded the car in for the white one before I found a solution.
Since then the odometer in the white car packed in... one broken tooth. A new gear solved the problem and the odometer is reading bang on in relation to GPS.
So the car is going well ... one annoying gremlin is the a/c and drivers window seem to be powered from the same contact barrel on the ignition switch. Going over a bump is enough to make them inoperative... which I can remedy immediately with a touch of the key. it seems to be getting more reliable so hopefully some regular usage will cure it

Eddie