Speedometer Is Out By 15 -18 Km/h

[mpython78]

hi folks,

my speedometer in my nissan hatch is out by something around 15 - 18 km/h according to my GPS.

so when I'm doing 100 km/h on the clock my GPS shows my 82 - 85 km/h...

(that is why I never got booked speeding, because I never had the GPS on...

and I was wondering why a truck can overtake me when I'm doing 110)

how could I fix this problem ? is there any chance that this is just a adjustment

of something ?

thanks guys,

zee-german

[Ghostrider]

Michael,

Where are you in Sydney?

There is a couple of reasons; 1. The speedo could be knackered. 2. Your tyre size might be wrong. 3. You could have a worn drive gear in the box and it is slipping. 4. The diff/drive gear combination is wrong.

This being said the service manual suggests only one (1) possible option and that is the speedo is faulty.

I'm in Sydney's south west (Campbelltown area) if you want another speedo, I'm sure I would have a spare laying around somewhere from when I had mine rebuilt by Jenesis.

Cheers, D

[blind_elk]

If the odometer is correct, then all the gearing (tyre sizes, diff ratios) are correct.

The speedo works off a magnet spinning inside a metal "cap". A spring controls the "cap" from just going on and on. With age, I reckon, the spring loses its tension, and lets the "cap" rotate further than it should, thus indicating a higher apparent speed.

[mpython78]

If the odometer is correct, then all the gearing (tyre sizes, diff ratios) are correct.

The speedo works off a magnet spinning inside a metal "cap". A spring controls the "cap" from just going on and on. With age, I reckon, the spring loses its tension, and lets the "cap" rotate further than it should, thus indicating a higher apparent speed.

hmmm, sounds good... but it shows me a slower speed... so the other way round.

I know that I have the right tyres on the car. right size ect... just changed them a few months ago.

and the gearing should be ok as well. it is an auto transmission, it works fine and solid.

[mpython78]

Michael,

Where are you in Sydney?

There is a couple of reasons; 1. The speedo could be knackered. 2. Your tyre size might be wrong. 3. You could have a worn drive gear in the box and it is slipping. 4. The diff/drive gear combination is wrong.

This being said the service manual suggests only one (1) possible option and that is the speedo is faulty.

I'm in Sydney's south west (Campbelltown area) if you want another speedo, I'm sure I would have a spare laying around somewhere from when I had mine rebuilt by Jenesis.

Cheers, D

hi,

I'm on the other side of the city (north sydney, neutral bay)

I bought this car of an old lady 16 months ago with only 116.000 km on it.

and it drives well... engine and auto sounds solid, just changed the injectors and the waterpump.

but my speedometer problem is since I have this car.

[Ghostrider]

You want another speedo?????

Cheers, D

[blind_elk]

hmmm, sounds good... but it shows me a slower speed... so the other way round.

No, it's not (the other way round).

You said the speedo shows 100 when you are actually - according to the GPS - doing 85. So the spring isn't retaining the speedo needle enough. The speedo is indicating a speed HIGHER than actual. (which is what I believe I said the first time, perhaps not so succintly)

[66yostagea]

I have always gone by gearbox ratio, diff ratio and tyre diameter with tacho reading. So in a manual you can work out exactly what speed you are doing, but in an auto you have to decide whether the torque converter has locked up.

There are places on the freeways where you can clock time against the actual tyre diameter will drive you at a predetermined tacho indication. But you must have an accurate tacho.

My new Ti hatch in 1984 was pretty close to 50 clicks per 1000. So about 2000

[Datto70]

Hi, To check if your speedo is working properly go find a 5km odometer check and record how far your odo shows over the 5k's (do the test at the posted speed limit as speed has no relevance with this test) - if the odo shows around 4.2 k's or even under 4.5k's then the problem is unlikely to be the speedo - if the odo shows between 4.9 & 5.1ks then the speedo is likely to be the problem. If the speedo checks out, then you are looking for a component in the gearing so the speedo cable is not spinning at the correct number of revs/km eg speedo drive, the diff changed to a lower ratio and the speedo drive not changed to suit, or wheels/tyres are not standard but i doubt that as the wheel/tyre combination would have to be a lot smaller than standard to make that much difference - most of us put wider & higher tyres on which reduces the revs per km and this causes the speedo to read slightly slower relevant to actual speed ie more accurately - which is why most speedos have a 5% fast read built in ex-factory. If you need help with correct speedo drive ratio i would need to know your diff ratio & tyre size. Cheers, Tel

[mpython78]

Hi, To check if your speedo is working properly go find a 5km odometer check and record how far your odo shows over the 5k's (do the test at the posted speed limit as speed has no relevance with this test) - if the odo shows around 4.2 k's or even under 4.5k's then the problem is unlikely to be the speedo - if the odo shows between 4.9 & 5.1ks then the speedo is likely to be the problem. If the speedo checks out, then you are looking for a component in the gearing so the speedo cable is not spinning at the correct number of revs/km eg speedo drive, the diff changed to a lower ratio and the speedo drive not changed to suit, or wheels/tyres are not standard but i doubt that as the wheel/tyre combination would have to be a lot smaller than standard to make that much difference - most of us put wider & higher tyres on which reduces the revs per km and this causes the speedo to read slightly slower relevant to actual speed ie more accurately - which is why most speedos have a 5% fast read built in ex-factory. If you need help with correct speedo drive ratio i would need to know your diff ratio & tyre size. Cheers, Tel

thank you guys for all the answers ! I will check it with the 5 km test..... :-)

[Ghostrider]

"My new Ti hatch in 1984 was pretty close to 50 clicks per 1000. So about 2000"

What a hoot old man, my new 180B SSS in 1973 used to get 20mph/1000rpm in top (4th) so when I was sailing across Mooney Mooney bridge on F3 at 6750rpm, I sorta understood the fowl looks I got from the boys in blue doing radar duty. lol

Cheers, D

Sorry for hijacking your thread temporarily

[skybt1]

my speedo is stuffed with the vl gearbox.

the speedo drive is for 3.45 gears and i have 3.9.

i just work out how fast i am going from the RPM's.

100kmh is 2500rpm in 5th and every 500rpm is 20kmh.

speedos are always wrong from factory.

[skybt1]

only shit thing is it clocks up klms quicker on the odo

but who cares. just buy another dash.

[66yostagea]

only shit thing is it clocks up klms quicker on the odo

but who cares. just buy another dash.

My first RMR30Ti had 600 on it when I gave her a decent burial. Changing the speedo is (illegal) a bit of a waste.

[skybt1]

there are many illegal things that we do.

boosting your car is illegal. you are not going to jail for it.

[skybt1]

if its cheaper to change the dash then to repair one im not going to be repairing it.

[Ghostrider]

"Changing the speedo is (illegal) a bit of a waste".

Not if your old one is broke, it's not.

In NSW the annual rego checks require an odometer reading on the inspection slip, so the RTA knows wether the speedo has changed and or been repaired.

My PNV when it goes on the road will have a Jenesis 260kph speedo with ZERO on the clock & a 9000rpm tacho and that wont be illegal.

I suppose it's a bit diferent for these backward states that don't have regular inspections eh?

Cheers, D

[noddle]

I suppose it's a bit diferent for these backward states that don't have regular inspections eh?

Shhhhh, I like these backward states that don't have regular inspections.

otherwise my turbo conversion may never get done, or my aftermarket ECU, wouldn't past muster (emissions), but then again, I have never looked into what is or is not illegal.

Nigel

[skybt1]

"Changing the speedo is (illegal) a bit of a waste".

Not if your old one is broke, it's not.

In NSW the annual rego checks require an odometer reading on the inspection slip, so the RTA knows wether the speedo has changed and or been repaired.

My PNV when it goes on the road will have a Jenesis 260kph speedo with ZERO on the clock & a 9000rpm tacho and that wont be illegal.

I suppose it's a bit diferent for these backward states that don't have regular inspections eh?

Cheers, D

I thought as much, its more illegal to have an odo that is not working.

I think we should have regular inspections. Get all the shit heaps off the road.

Maybe not every year but every three or five years. You see cars driving around

with smashed lights, rust everywhere, some real junk boxes.

[BensDR30]

skybt1, might I suggest you change the drive in your gearbox to the correct one - the RB30E gearbox should take the same pinions as the old FS5W71B/3N71B/4N71B that the car came with.

Dennis, if you were doing 6750rpm (as indicated on a 1973-accuracy tacho!) in a stock 610 SSS in 4th, then it must have been downhill

(and you must have been out of your mind)

I've got a 4.375:1 LSD in my DR30, but in order to get the speedo correct (within ~5%) I've had to fit the 4.625:1 speedo drive. A combination of slightly shorter tyres (225/50/16) and a 25-year old speedo have resulted in extra compensation being required to get things right.