Another but slightly different speedo problem

[Daz.]

Occasionally a while back the speedo would drop to zero for a while, then would pop back on. One day it did it and didn't come back, give the dash a wallop and voila!

Been doing this on every occasion until it started working perfectly last Nov. Then last week it started acting up again, hitting the dash has no effect now lol.

What I noticed though is I can park at my house with it not working, do the dash test and it works everytime, start the car to drive away and it still doesn't work!

This to me tells me its not the dash connections at all, and that the car isn't telling the dials what to do, so what am I looking at? the abs has ALWAYS worked even when the speedo dies so does that mean its not the rear wheel pickup?

I'm confused where to start now!

 

[Rob]

Gearbox sensor dude, about 30£.

If the needle itself works then that indicates its just the signal isn't being sent to the clocks.

 

[Daz.]

Well thats where I'm confused as I thought the ph2 172's got their feed from the abs rings on the rear wheels? I thought it was only ph1's and cups that had gearbox sensors?

 

[Rob]

Really? I wasn't aware of that, and thought they all had GB sensors.... I'll return to my hole now.

Unless its just the sensor at the ABS ring or whatever?

 

[Daz.]

Just been out and if its this...

Then I do lol.

Better take if off and have a look!

Pic is stolen, mine seems to have a heatshield around it

 

[Rob]

Yes indeed that is it, and yes indeed it has a heat shield, easy to remove, twist and pull, if you twist pull, clean and re-fit, and it works for min, then you'll just need to get another, I always found when mine was fubar'd it'd still work if you took it out for a bit and cleaned it etc.