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4a speedo wobble


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Hi,

My car is a 1967 TR4a with overdrive. The speedo has always wobbled a bit and so I got it refurbished.

It now surges.

On looking through the Moss and Rimmer catalogues I see that both companies show the speedo on the left and the tach on the right; mine are the other way.

The former denotes a 78" cable for a RHD standard gearbox and the latter denotes a 69" cable for overdrive; I have fitted a 69" cable.

Is the wobble/surging caused by too short a cable or does it suggest a restriction in its curvature please?

Any advice would be welcomed.

Thanks

d2

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This is often caused by contact within the speedo itself.

If I recall right the needle is driven by a spinning magnet/magnetic disc which acts upon another which connects to the needle working against a spring. If there is any debris or oil causing physical rather than magnetic contact you get jerking.

A speedo cable not spinning smoothly can do the same as it "winds up" and then spins unevenly.

The 69" cable seems fine on mine. As did the old one until it mysteriously wrapped itself round the steering column and got mangled by me turning the wheel!

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22 hours ago, d2alfa said:

Hi,

My car is a 1967 TR4a with overdrive. The speedo has always wobbled a bit and so I got it refurbished.

It now surges.

On looking through the Moss and Rimmer catalogues I see that both companies show the speedo on the left and the tach on the right; mine are the other way.

The former denotes a 78" cable for a RHD standard gearbox and the latter denotes a 69" cable for overdrive; I have fitted a 69" cable.

Is the wobble/surging caused by too short a cable or does it suggest a restriction in its curvature please?

Any advice would be welcomed.

Thanks

d2

Speedo was positioned to the centre of the car for LH or RH drive cars.  Allegedly so the passenger could spot the road speed.

Have you lightly lubricated the speedo inner drive cable ?

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13 hours ago, BlueTR3A-5EKT said:

Speedo was positioned to the centre of the car for LH or RH drive cars.  Allegedly so the passenger could spot the road speed.

 

On early TR2 the speedo was on the right and rev counter on the left (Rhand drive cars) it was moved fairly soon when the cars began to be used in competition so the navigator could see it more easily and it remained in that position to the end of TR production.

Stuart.

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d2 I commend the checks recommended in an old Smiths Instruments booklet 'The Care of Instruments'. It is too large a file to attach here ( ~6mB) so if you PM me your email address I will send that way. Following thethr recommended checks and inner drive lubrication instructions on  my speedo resulted in a perfectly steady needle, which had perviously oscilated wildly around a mean reading at any speed up to an indicated 30mph.

Tim

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34 minutes ago, d2alfa said:

Tim - My email address is   ****** .com

Best wishes

David

Hi David,

A heads up, probably a good idea to click "edit" on the three horizontal dots at the top right corner of your post, and remove your private email address from a public forum. (Unless you're a fan of spam mail). :ph34r:

Also, the Smiths Instruments booklet 'The Care of Instruments' is available online as a free downloadable PDF document, here:

VeryBritishCables:Smiths Instruments booklet.pdf

Deggers

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Mine refers to a 5 but i guess the same.

up to 50 the needle is stable but after this it goes hay wire . is there a fix or where best to send for a rebuild if that is the answer.

Roy

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I have had the speedo checked and assume that the wobble/surging is caused by bends in the cable.

If I reposition both the speedo and the tach, it looks like the speedo cable would have a better alignment. However I assume that the tach cable will enter the cabin where it currently does near the glove box and need turn through two lengths of 90 degrees as it does now. Are I correct?

thanks d

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15 hours ago, d2alfa said:

I have had the speedo checked and assume that the wobble/surging is caused by bends in the cable.

If I reposition both the speedo and the tach, it looks like the speedo cable would have a better alignment. However I assume that the tach cable will enter the cabin where it currently does near the glove box and need turn through two lengths of 90 degrees as it does now. Are I correct?

thanks d

Tacho cable comes behind the engine along the front of the battery and into the bulkhead behind the master cylinders like this.

Stuart.

 

Steves4 003.jpg

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