1970T - common speedo fails?

[RobFrost]

Speed on my 1970T registers as zero on the speedo, regardless of actual speed travelling. Is there a common fault, first place to look or logical order - broken cable, dial, cable disconnected, sender broken, gauge broken etc.?

[neilbardsley]

Check that the cable is connected into the back of the Speedo. Sometimes the blade doesn't sit probably in the receiver. Also sometimes it becomes disconnected or broken at the gear box end. One way to test this is to remove the cable from back of the Speedo then drive a short distance and feel if the blade in the end of your cable is turning.

If you do these checks and still think it's the Speedo then £110 for a rebuild at jdo instruments

Sent from my M2004J19C using Tapatalk

[RobFrost]

Check that the cable is connected into the back of the Speedo. Sometimes the blade doesn't sit probably in the receiver. Also sometimes it becomes disconnected or broken at the gear box end. One way to test this is to remove the cable from back of the Speedo then drive a short distance and feel if the blade in the end of your cable is turning.

If you do these checks and still think it's the Speedo then £110 for a rebuild at jdo instruments

Sent from my M2004J19C using Tapatalk

Is access via the boot, under the dash, or remove the speedo?

[neilbardsley]

I think you can just pull the Speedo towards you but the cable, from the gearbox, will prevent you moving it too much. However, on my 912, I think the 911 is the same, I think you access the back of the gauges from the bonnet? You might have it lift up some carpet to see them

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[Berny]

Yes you should be able to pull the spedoup from the dash the cable is long enough to move it up to unscrew it disconect the bulbs note where they go! and just about get the spedo out.

[RobFrost]

I think you can just pull the Speedo towards you but the cable, from the gearbox, will prevent you moving it too much. However, on my 912, I think the 911 is the same, I think you access the back of the gauges from the bonnet? You might have it lift up some carpet to see them

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I'm hoping it's not via under the bonnet. I've avoided taking out the blower and wiper motor so far. Will look in the morning.

[RobFrost]

Yes you should be able to pull the spedoup from the dash the cable is long enough to move it up to unscrew it disconect the bulbs note where they go! and just about get the spedo out.

It does indeed just pull out. Is it easy to access the needle / face for cleaning etc. e.g. by removing the glass? Or is that inadvisable?

[Sam]

The gauge rings are crimped on and once removed the glass just falls out. It’s easy to get them off with a little patience. You work round from the rear prying a little bit at a time. A small screwdriver will do the job but you can get pry tools for not much money which will make it easier and less likely that you’ll make a kink by prying too much.

The needles are delicate, I’d avoid disturbing them if you can.

Once you’ve cleaned the glass face a quick sand down and squirt of satin black on the bezel makes the world of difference.

[RobFrost]

The gauge rings are crimped on and once removed the glass just falls out. It’s easy to get them off with a little patience. You work round from the rear prying a little bit at a time. A small screwdriver will do the job but you can get pry tools for not much money which will make it easier and less likely that you’ll make a kink by prying too much.

The needles are delicate, I’d avoid disturbing them if you can.

Once you’ve cleaned the glass face a quick sand down and squirt of satin black on the bezel makes the world of difference.

Thanks. A rather sad situation exists in respect of the silver centre as you can see here: https://photos.app.goo.gl/CYWeThA6Ecy34NJE7

[Sam]

That’ll be an easy and very satisfying DIY job.

[RobFrost]

That’ll be an easy and very satisfying DIY job.

I've entered into many a job on an old car thinking that...

[911hillclimber]

Mine broke, no odometer at all some years ago.
Sent it to Julian Reep Instruments who changed the broken plastic gears inside, cost about £80 then, a week turn-round as promised.
I believe the gears break or can do, if you press the reset button while on the move.

There are ratios to suit some cars over another, but won't hamper Reep at all.

http://reapautomotivedesign.com/

As said, the speed just pulls out once you have broken the (considerable) grip of the rubber fitting ring. You can be mistaken and think the gauges are screwed in the grip is so tight. Good fingernails!

Once out the cable can be unscrewed and you will see/feel the flat tang that Neil has described.
Take the car for a short drive and you will have a chance to see/feel the tang rotating (concentrate on the road!)
Access is far from easy.
If it is not rotating then cable broken or disengaged at the gearbox end.

It is a stout cable, so I would suspect the speedo gears.

[RobFrost]

Righto, went for a drive with the cable in hand, and the inner is not turning within its sleeve. Anyone know what the commonest cause is? I assume it's a multiple choice from; broken cable, cable disconnected the other end, drive gear within gearbox broken.

[deano]

The speedo connection on the back of my 915 sheared off when I disconnected it for an engine/gearbox drop years ago. Not sure if that's a common cause

[RobFrost]

The speedo connection on the back of my 915 sheared off when I disconnected it for an engine/gearbox drop years ago. Not sure if that's a common cause

Well at the moment that makes it the commonest cause I know of. Need to get the car up in the air I guess as it looked pretty inaccessible last time I was under there.