Odometer Dilemma

[kiwi]

Does anyone want to figure this out for me?

Last month I was inspired to take my BX 19TZS down to a calibration specialist to confirm a error which I had long suspected.

Heres the results (bearing in mind this is Kilometres)

Car reading - Dyno Reading (actual speed)
30 - 28
50 - 50
80 - 82
100 - 105
120 - 125

100 Kph is the Legal open road speedlimit in NZ which is also 99% of the roads I most commonly use. So the effects are noticed o Distance Travelled as well.

Thing is I have not a clue how to fix this problem.

[Way2go]

The odometer is likely correct even if your speeds are not. The odometer is directly geared to the speedo input shaft whereas the speedo uses a magnetic coupling.
Possibly the magnets have lost some of their field strength so are less efficient than they once were on their influence at higher speeds.

Only remedy is probably to change the speedo head as the mechanism is non-adjustable and not designed to be easily dismantled/reasembled.

[kiwi]

The odometer is out as well. That much has become clear running with the GPS over set distances. This has been evident for some time with Fuel consumption figures that I put down originally to having Aircon.

But when both my wife and I travelled in convoy with the GPS and the BXTRS behind me. My wife commented on the "moving quicker" but what was more apparent was the distance coverd my BX effectively losing 40 kms over the trip.

Before you ask Both BXs have identical tyre sizes, I have also noted that since the TRS was put to the correct spec tyre that the TRS is now travelling slower than indicated speed which is consistant with smaller profile tyres.

I tried changing speedometer heads and that made it even worse.

Yes it has me completly foxed

[MULLEY]

Very strange, unusual to under read the correct speed, mine over reads by quite a large margin, which hopefully means i wont be caught speeding but then also has the unusual effect that everyone else appears to be blasting past me, speedo say's 70, actually doing 63mph Never mind, good fuel consumption

Could it be the speedo cables themselves that have stretched or gotten damaged somehow?

[khan]

I suspect that the speedo gear inside the gearbox (next to the right driveshaft exit) is different, maybe somebody changed it with a diesel or a Peugeot one. check it out and compare with the one in the other car u have, it has to be the same

[kiwi]

Very strange, unusual to under read the correct speed, mine over reads by quite a large margin, which hopefully means i wont be caught speeding but then also has the unusual effect that everyone else appears to be blasting past me, speedo say's 70, actually doing 63mph Never mind, good fuel consumption

Could it be the speedo cables themselves that have stretched or gotten damaged somehow?

I thought that so when the cable had to be repaired when the cable broke at the join I thought problem solved. But nope this "official" calibration check was done after that.

If you notice the readings over read at 30 kph (thats NZ Road works speed ) but is spot on at 50kph (normal Urban speedlimit) the problem seems to go out by 5kph at 100 and curiously stay out by 5kph to 120kph.

Only thing I can think of is the drive at the head of the gearbox? I am wondering if I do not have a standard gearbox?

I did consider seeing if I could find a speedometer with Miles Per hour on it so if I was doing 60mph I would be doing 96kph which given the error would be 101kph The logic being that using 30,40,50,60 mph readings would be lower than the NZ speedlimits.

Only snag is that if the gearing is differant and like I have found with swapping speedo heads is this would probably not work either.

Since the Laser Gun Armed Gestapo Revenue Collectors have pretty much a zero tolerance policy on speed with the Quota system the Police Follow in this country (NZ) it is all to easy to swap between the BXs and forget the error of 8kph between them.

I have rapidly, OK already knew that this BX19TZS I have here is one heck of a mystery beast. No wonder it sat for 2 years before being registered on the road.

[kiwi]

I suspect that the speedo gear inside the gearbox (next to the right driveshaft exit) is different, maybe somebody changed it with a diesel or a Peugeot one. check it out and compare with the one in the other car u have, it has to be the same

Sorry was writing last reply so missed this.

I agree with you on that it was what I was starting to think. The only snag is comparing them means removing a drive shaft. I have taken on off the BX16 Gearbox would you think they would be the same?

The only problem I can see though is that maybe the speedo head has been calibrated with a smaller error for what is currently fitted. Although I would have a speedo head from said 16 anyways.

[kiwi]

Anyone able to confirm if the Gearbox head of the BX1600 will be the same as the BX1900?