Odd problem with dancing speedo!

[Sam Gamgee]

I know this problem has been covered before and I have just lived with it for a couple of years but today I noticed something else....

most of the time speedo dances around usually indicating greater speeds than is so I have little idea wot speed i`m doing often, except when acceleraing. However I noticed as, I was at traffic lights, that if I blipped the throttle the speedo "bounced" back toward zero then returned to doing its little boogie...can anyone out there suggest wot can be the cause of this? Car is early 1994 500 preserp/T5 `box. I have cleaned all (I think) of the earths except for those under the centre console abd cleaned up the sensor adjecent to the diff ( it is a fixed type, no adjustment seems possible).


Hope somebody has an idea or experience of, would like to put this little baby to bed after 2.5 yers of putting up with...

Thanks all

Dave.

[Ballistic Banana]

If the Transducer has been damaged then it may casue the speedo to bounce all over the place.
I think you can check it at the ecu with a mulimeter and lifting the wheels of the ground and getting someone to spin them You should then see some resistance at the ecu..... or if you have an oscilloscope you get a better results.

BB

[spend]

Can you bypass the 'blackbox splitter' on these to see if that is causing the problem (temporarily having no roadspeed to ECU)?

Dave

[Seasider]

spend said:

Can you bypass the 'blackbox splitter' on these to see if that is causing the problem (temporarily having no roadspeed to ECU)?

Dave

Where is it Spendy ?

[davetherave1970]

Mine has done this from when I bought it.
It only happens sometimes and I can change the way it acts if I turn on/off electrical items. The biggest change is when the fans kick in!
I too have cleaned earths and even added an extra earth strap without joy.
I'd be very interested in a fix for this.

[Ozstyle]

Hi,
had exactly these symptoms also. First thing to do is to make sure the gap between speed sensor and toothed wheel is as small as you can get it with out sensor and wheel touching. Check wire connections are clean and tight also.

Ozstyle

[spend]

The 'black boxes' are stowed behind the dash I reckon Del.

If it has the GKN diff, so the toothed wheel is more like a 'spinning turret', the gapping doesn't seem to be very critical unlike the BTR ABS type.

Dave

[Seasider]

spend said:

The 'black boxes' are stowed behind the dash I reckon Del.

Easy to find then

spend said:

If it has the GKN diff, so the toothed wheel is more like a 'spinning turret', the gapping doesn't seem to be very critical unlike the BTR ABS type.

Dave

My BTR works out to about 10 thou more than that it kicks in from about 20mph

[dnb]

If you remove the black box then you have to short 2 of the pins together in the loom to make the speedo work. (I forget which 2 )

I have a spare black box if you wish to test the thing. I don't use one in my car since my ECU doesn't really care about road speed. I'll make sure it's packed for the Growl...

[spend]

I don't know if the black boxes for GKN & BTR speed transducers are the same, or even wired similarly?

Its quite possible that the T5/GKN combination is the rarest combination..

Dave

ETA: Duplicate deleted (twice now - both acked!).. Seems like the NT hamsters are revolting and dropping connections today, or is there something rank lurking behind a BigIP

Edited by spend on Monday 30th July 13:31

Edited by spend on Monday 30th July 14:56

[dnb]

So rare you had to say it twice

I expect they are different, but only as far as the expected frequency of pulses for a given speed. If this is the case, then there's no problem in testing with this box as IIRC the Lucas ECU only uses the signal to do things with idle...

And the speedo doesn't use the box for anything at all, other than a simple pass-through. (Initially, I thought it was acting as an amplifier, but I was wrong there)

[Toffer]

davetherave1970 said:

Mine has done this from when I bought it.
It only happens sometimes and I can change the way it acts if I turn on/off electrical items. The biggest change is when the fans kick in!
I too have cleaned earths and even added an extra earth strap without joy.
I'd be very interested in a fix for this.

I was interested to learn that some Griffs are factory fitted with an extra earth strap, some have provision for one (none fitted though) and some just don't have teh "extra strap feature"?

[spend]

dnb said:

..I expect they are different, but only as far as the expected frequency of pulses for a given speed. If this is the case, then there's no problem in testing with this box...

So the different boxes are plug compatible, or is this just conjecture?

Dave

[dnb]

Conjecture based on the fact TVR have always been unwilling to change anything that worked...

The part no on my box is MO 559 or ETi 1812 2A96 (It has to be one or the other of these.)

[Sam Gamgee]

Hi all, thanx for replies (super site this!)...forgot to add that, yes, it has GKN diff/T5 `box and unable to close the gap on the sensor due to fact it is/seems to be fixed.
bit more to go on, though....really must try to get to growl on one day but struggling (and also having domestic issues with her indoors! thats another story...)

Wonder has anyone else got exactly this combo? Agree it seems a bit rare....BTW, davethrave, yeah, similar goings on...!


Dave.

Edited by Sam Gamgee on Monday 30th July 18:12

[Bluebottle]

Sam Gamgee said:

Hi all, thanx for replies (super site this!)...forgot to add that, yes, it has GKN diff/T5 `box and unable to close the gap on the sensor due to fact it is/seems to be fixed.
bit more to go on, though....really must try to get to growl on one day but struggling (and also having domestic issues with her indoors! thats another story...)

Wonder has anyone else got exactly this combo? Agree it seems a bit rare....BTW, davethrave, yeah, similar goings on...!


Dave.

Edited by Sam Gamgee on Monday 30th July 18:12

Yes same combo and the same speedo fault which curiously is affected by the heater fan (turn fan on and I am doing 30mph when I was doing 50mph) also have a very bouncy rev needle as well, that also lies.
I was told that the speedo and rev. guage feeds wire from the ecu could be twisted in the loom causing magnetic field interference, which was the cause in another Griff.

[Sam Gamgee]

Bluebottle said:

Sam Gamgee said:

Hi all, thanx for replies (super site this!)...forgot to add that, yes, it has GKN diff/T5 `box and unable to close the gap on the sensor due to fact it is/seems to be fixed.
bit more to go on, though....really must try to get to growl on one day but struggling (and also having domestic issues with her indoors! thats another story...)

Wonder has anyone else got exactly this combo? Agree it seems a bit rare....BTW, davethrave, yeah, similar goings on...!


Dave.

Edited by Sam Gamgee on Monday 30th July 18:12

Yes same combo and the same speedo fault which curiously is affected by the heater fan (turn fan on and I am doing 30mph when I was doing 50mph) also have a very bouncy rev needle as well, that also lies.
I was told that the speedo and rev. guage feeds wire from the ecu could be twisted in the loom causing magnetic field interference, which was the cause in another Griff.

Gawd!! Griffs...dont ya just love `em?
Sounds like a bit of a job to sort but determined to get to the bottom of this one.....like those wheels BTW, Hamish!

[Bluebottle]

Thanks, If you manage to get to the bottom of the fault let us know what it was as it would be good to get mine fixed to.

[Ozstyle]

Sam,
I have the same set up (T5 GKN diff)and had the same problem. I also found my sensor was about 3 mm from the toothed wheel but no more adjustment as it was fully screwed into the bracket. The speed sensor bracket is attached via the two top front diff bolts. I fixed the problem by simply bending the bracket down to move the sensor closer to the toothed wheel(I did this off the car as I had the diff out). I'm sure you would be able to bend the bracket down with a stout screw driver by levering off a chassis rail.

Ozstyle

[Sam Gamgee]

Ozstyle said:

Sam,
I have the same set up (T5 GKN diff)and had the same problem. I also found my sensor was about 3 mm from the toothed wheel but no more adjustment as it was fully screwed into the bracket. The speed sensor bracket is attached via the two top front diff bolts. I fixed the problem by simply bending the bracket down to move the sensor closer to the toothed wheel(I did this off the car as I had the diff out). I'm sure you would be able to bend the bracket down with a stout screw driver by levering off a chassis rail.

Ozstyle

Sorry for late reply-been away with work!

Thanks ozstyle, will see if I can give this a go at weekend....

Dave.