Speedo Issue... Balls

[Northernchimp]

I put my car up for sale on Monday, shortly afterwards it developed a speedo fault (basically works 80% of the time). I immediately ordered a new transducer from Racing Green and had it fitted by a local garage today (have no time to take it anywhere 'proper').

Anyway, still doesn't work properly. I still don't have time to take it anywhere, so I have had to drop the price in the hope that somebody is willing to take it on. Is there anything obvious I can check?

I work through the week and am away most weekends, I don't have time for this st. Such bad timing too.

Edited by Northernchimp on Friday 7th June 17:18

[QBee]

Did the odometer stop working too?

[Northernchimp]

Not sure, I will check. It's gone from working intermittently before the new sensor was fitted, to now intermittetly working above 30mph only. Maybe the sensor hasn't been fitted correctly, it was done by a sports car place but they are more Japanese focused.

I've mentioned it in the ad and knocked a few quid off, not a lot more I can do.

Edited by Northernchimp on Friday 7th June 21:57

[QBee]

Look, I am not an expert, just an owner.

Last summer I kept finding I had no speedo at all. And I noticed when I had no speedo I had no odometer either.

My TVR indie replaced the widget that sits on top of the diff. Problem solved.

If the gap between the widget and the diff isn't correct I believe that this causes it not to work correctly......see pages 249-251 of the bible. If you don't have it, email me via my profile and I will email you back the pages. My best guess is that your non-TVR garage didn't know the correct gap between the sensor (widget) and the toothed wheel that triggers it. Time for a TVR indie?

[zacherynuk]

QBee said:

My TVR indie replaced the widget that sits on top of the diff. Problem solved.

From what I know the widget on the diff is the leading cause - it's all very mechanical. if only drops at high speed, then I would say is likely that it is loose or worn.
I'm no expert, but if your car person refers to it as an ABS sensor.. raise an eyebrow and go elsewhere....

[Northernchimp]

I've had the diff widget replaced, still broken but in a different way now. I think it's on wrong, but the people who fitted it won't hear of it.

No specialists within a reasonable distance (not one I still trust anyway).

[QBee]

Northernchimp said:

No specialists within a reasonable distance (not one I still trust anyway).

Where are you?

[EGB]

11-12 thou clearance and a good cleanup of the dirty exposed electrical connections including the serrated wheel. Hope no damage done to sensor and it does not work because the japs have set the clearance too wide.

[ewan221]

Speedo on my old car did not work under 15 mph even with new sensor set to correct gap. Problem was apparantly with the Speedo its self.

[QBee]

ewan221 said:

Speedo on my old car did not work under 15 mph even with new sensor set to correct gap. Problem was apparantly with the Speedo its self.

I think the "no speedo under 20 mph" is something to do with the changes made by TVR during the production run. Cannot remember what it was now, t mine does it too.

Now you know the correct gap between sensor and toothed wheel I think you have the answer.... So go down to your local indie tyre place when they are quiet, get it up on the ramp, and check with a feeler gauge. IIRC the sensor is on top of the diff. If you cannot see it, find the wire coming down through the bodywork above the diff and follow it.

[Northernchimp]

QBee said:

Where are you?

South Herts / North London

Thanks for all the tips.

[jonnyZ]

The sensor will probably be a variable reluctance pole face pickup.
The induced emf is directly proportional to speed hence the drop out at low revs.
The air gap also influences the sensor output so this needs to be as close as possibly without the tooth wheel touching the pole face.

Hope this helps

[SILICONEKID350HP]

jonnyZ said:

The sensor will probably be a variable reluctance pole face pickup.
The induced emf is directly proportional to speed hence the drop out at low revs.
The air gap also influences the sensor output so this needs to be as close as possibly without the tooth wheel touching the pole face.

Hope this helps

Is that why my speedo reads a few mph out at 30 and it reads 90 when I`m doing 73 on the Tom Tom

This is since the diff came out .

[QBee]

SILICONEKID350HP said:

jonnyZ said:

The sensor will probably be a variable reluctance pole face pickup.
The induced emf is directly proportional to speed hence the drop out at low revs.
The air gap also influences the sensor output so this needs to be as close as possibly without the tooth wheel touching the pole face.

Hope this helps

Is that why my speedo reads a few mph out at 30 and it reads 90 when I`m doing 73 on the Tom Tom

This is since the diff came out .

There is a 10 tooth cog that passes close to the sensor. The sensor counts the teeth as they go past. If you change the diff to a different ratio, then the speedo will read incorrectly unless you change the speed sensor to match.