Intermittent speedo cut out

[mad in general]

Another issue with the 172. Non cup.

Quite regularly my speedo will drop to 0 when moving. It can stay there for mile after mile then randomly readjust.

Thing is. I can feel when it kicks back in. There is 100% a minute change in the pickup feel through the accelerator.

If it's at 0 and I feel this blip through the throttle it immediately returns to reading correct speed.

Any ideas?

 

[JamesBryan]

Could be the speedo sensor in the gearbox if you have an early ph2 172 with the jc5-129 box in.

 

[PP200t]

I had this with my 52 plate 172 (non cup) and it was the Speedo sensor in the gearbox as said above. Easy enough to replace and didn’t cost too much. Worth a shot first for what it costs.

 

[mad in general]

I do have the 129.

What exactly do they read?

Any idea why this fluctuation can be felt through the pedal?

 

[mad in general]

I have fitted a brand new sensor and unfortunately this makes the problem worse!

Speedo now bounces around and can feel each movement through the pedal, engine almost stutters.

Put my original back in and again it's either reading perfect or changing to 0. No engine issues.

I believed the sensor had no input on how the car drives but my symptoms say otherwise.

Any help?

 

[hopgop1]

Strange hunting at speed

So I've got an issues with my 02 172 cup 1st and 2nd gear are fine pulling off is fine but when in 3rd/4th following other cars it won't hold a steady rev it dips and then jolts forward under power it's fine runs fine and pulls fine but as soon as you are following behind somebody in a queue I...

cliosport.net

Sounds a lot like the above thread, new speed sensor resolved.
I'd be tempted to try another geneuine speedo sensor tbh, otherwise maybe wiring?