My speedo reads incorrect

[Stan 24v 0]

Not sure where to post this, so feel free to move jailer :lol:

 

My speedo is reading incorrect. If Im doing 30MPH on the clock, Im actually ownly doing 25MPH, as I got the missus to drive next to me. This seems to be the same at all speeds.

 

I had the clocks out a few months back, but hadnt noticed any difference when I put them back together. Only really noticed it since the conversion, but The wiring for the speedo wasnt touched apparently.

 

Anyone got any advice? :?

[Supercharged 2]

Hi Stan, on my TDi there is a metal box with an adjustment screw that was set up using GPS to set the mk4 clocks up for the mk2 drivetrain etc... I don't know much apart from that but I think i have the name of it written down somewhere...

[Stan 24v 0]

Ive got the original C clocks mate, they werent changed.

[vr6storm 0]

whats to say that its not yer missus's motors speedo not reading true either tho??.........ive found the MFA's speed to be reasonably acurate(measured with a mates GPS)..........tho you have to have a nice long straight for it to work

[Stan 24v 0]

I noticed it at first when slowing down at speed cameras, the other cars were going quicker. Ive also just been away and my dad was driving next to me, and his speed was registering less than mine.

[A5 VRX 0]

Haven't had engine swap or owt but i have a feeling that my car is doing the same, when doing any speed feels like i'm going much slower. 80 feels like 70 etc?

[Supercharged 2]

Yeah - you need to do it by GPS - most old cars overread by a percentage but newer cars seem to do it by about 3-5mph across the range... you need to test yours at various speeds and decide what to do...

 

Yep, you have the corrado clocks but the drivetrain and rolling radius are still completly different to a mk4 so you may need to adjust it...

[colinstubbs 0]

My 1990 valver over-reads by 5mph across the board checked against GPS, as does my wife's about to be scrapped renault 19.

[Stan 24v 0]

Where does the car take the speed from? Is it from the wheels? If so, then it hasnt changed. The gearbox is also original VR.

[colinstubbs 0]

I always thought it was a siginal from the gearbox...somehow! :lol:

[Stan 24v 0]

I did too, but wasnt sure. In that case though, the engine swap shouldnt have affected it....right?

 

How can I adjust it?

[coolrado 0]

the signal is taken from final drive in the gear box so it shouldnt have changed, it is possible to adjust the clocks but you really need to check it with gps or something accurate when you do, have you checked the speed using the mfa or just the dials?

[Lippy 0]

did you take off the needle from your speedo? did you put it back on the same place?

[gradeAfailure 0]

aye, take the needle off, put it back on 5mph further round! mine over-reads by exactly 5mph all the way round (checked using a Road Angel), so that's what i plan to do!

[Stan 24v 0]

I did take it off, and it was resting against the little plastic stub at 0MPH, thats where I put it back on, well thats what it looked like anyway. May have to retry it.

 

How do you check the speed using the MFA? It doesnt have speed on it.

[gradeAfailure 0]

actually, the speedo doesn't sit against its stop - if you have never taken the needle off before, you can actually lift the needle over the stop and it will rotate a few more degrees anti-clockwise before it stops, hence the error when you put it back on... ;)

[Andi 2,147,483,647]

I did take it off, and it was resting against the little plastic stub at 0MPH, thats where I put it back on, well thats what it looked like anyway. May have to retry it.

 

Not quite right.

If you lift the needle over the stop - it should come to a rest pointing at the angle in the bottom corner of the dial.

That's about 5mph out, so there's your problem.

 

Put the needle on pointing to the angle in the metal of the dial face, then lift it over the needle rest.

 

Edit: Oops, missed the Page 2 ;)

[Stan 24v 0]

:oops: Might well be my problem then, I'll have a look this week. Cheers guys :thumbleft:

[ben16v 0]

you can check speed using the MFA by getting onto the average speed screen and resetting it while you stay at a constant speed, it`ll take a few seconds then it`ll pop up showing you how much your out (roughly)

 

and to check your rev counter in MFA position 2 turn ign on hold MFA button turn off ign still hold button then start the car still holding the buton i think 2 clicks on the mfa will give you a digital rev counter

[Stan 24v 0]

You learn something new every day, cheers Ben ;)

[Kevin Bacon 5]

The analogue speedo has a tolerance built in. Always set to over read. It's the same with most cars. It's

to allow for speed trap mph drifting as people should be concentrating on the road rather than studying the speedo.

 

The MFA is a direct representation of what the final drive sender is recording and is the accurate measurement as said already, but it's just slow at updating.

 

Most Corrados I've driven over read by 3-5mph at low speeds and by as much as 10mph by the time you exceed 130mph.

 

GPS isn't entirely accurate either, laser telemetary is the only measurement that is, but it's more truthful than the anologue speedo, that's for sure!

 

As you're using the VR box, the speedo is telling you what it should be, you can outrule the fact you're not using a MK4 box, which is expecting 215/45/16 tyres at each end.

 

Jaguar's are the only car I've seen that actually read exactly what the car is doing on the analogue guage.

[Stan 24v 0]

So what do I need to do then Kev?

[Kevin Bacon 5]

I've never tried the repositioning of the needle as the other guys suggested, that might work. I'm just loathe to fiddle about in there as I've done in it in the past with MK2s and made matters worse.

 

I just personally accept it and go through Gatsos at 35, 45, 55, 65 and 80 safe in the knowledge that the speedo is off :-)

[Stan 24v 0]

Think I'll try the needle, I dont like going through gatsos at that speed, just in case :(

[Kevin Bacon 5]

Nah you're safe mate. Certainly true of the gatsos I go through, they have high thresholds. I've been through a motorway Truvelo (forward facing one) at 90 before (on the speedo) and it didn't go off!