Speedometer problem

[SeanF]

Having restored my brakes following 24 hours under calibrated stick (ask RogerH!) I took her out this morning for a run to take advantage of the lovely sunshine here and to continue my troubleshooting. Anyway drove over to Sevenoaks on the A25 and then thought I'd try the M25 back from Jn5 to Jn6 to see how she would do.

Well she did very well and coped with speed changes from lane to lane etc perfectly......however, as I was pushing up past 70 mph the speedometer needle suddenly shot all the way around to the high speed end and sat there pushing against the needle stop for a minute or so before popping off the stem and falling to the bottom of the glass. The mileometer (is that what you call it?) continues to work fine. I refurbished all the gauges as part of the restoration and didn't notice anything untoward in the speedo, but am not really qualified to notice anything amiss really.

Anyone seen this before and any advice as to what might be the problem and what to do?

Many thanks,

Sean

 

 

[Paul Hill]

Flippin heck did you go into Hyperdrive Warpspeed.

Never heard of that happening ever

[ed_h]

The internal magnet has likely fouled the induction cup.  It can happen when internal parts wear beyond limits.  The instrument can probably be rebuilt.

Ed

[Charlie D]

Sean,

There is a spring that is attached to the needle spindle and to the speedo chassis. It’s shaped in spiral and I think it is called the hairspring. (Possibly because the wire it is made of is as thin as a hair… but possibly not…)

Its function is to try to keep the needle at zero. As the speed builds up there is a magnetic coupling that tries to turn the needle around and the hairspring tries to pull it back.

If the hairspring breaks or comes undone at one end there is nothing to fight against the magnetic coupling and so the needle will wiz around until it hits the max speed end stop. I would guess that eventually the force of the magnetic coupling is too much for the push-on needle to take, and so it falls off.

Not an easy repair for the amateur. I guess you need to send it off for a rebuild. Speedy cables or such like, other will be better experienced as to who is best to go to.

Charlie

PS

Just read what Ed said. Also quite possible. End result the same though. More money out I'm afraid.

[SeanF]

Thanks all for the replies so far.

Does anyone have a good usable speedo for a CR?

Cheers,

Sean

[Paul J]

Hi Sean

I had a similar problem on my 4A, the reason for the failure was lube travelling into the back of the speedo from the over lubricated speedo drive. Cured by a removing the speedo and cleaning the clutch mechanism with electric cleaner. Lesson do not oil the speedo drive with oil.

Paul

[Mike C]

I cleaned and lubricated my tacho with silicon lubricant  and it did the same thing after about an hour's running it  started reading roughly double actual rpm's.  I was lucky enough to find  another good replacement tacho as I didn't fancy delving into the tacho's internals .

I'm glad this came up as I now have some ideas on how to repair my original tacho - I was considering sending it to a UK specialist

[SeanF]

Thanks all so far.

As an update, I have taken the speedo apart. It does not appear to have any oil or grease fouling like Paul's, but there is a stray spoon like spring lodged in the spinning disk and held by the magnet. I have circled it in the pic below. Any ideas on where it should be or if its easy to fix? The magnetic disc does not appear to be sprung. In other words, when it spins and the needle moves, it does not return to zero on its own

Many thanks,

Sean

[ed_h]

I believe that stray piece is the keeper spring for the odometer (mileometer) ratchet pawl.  They can be prone to popping off.  The actual pawl must still be in place if the odometer is working.

Ed

Edited January 9, 2019 by ed_h

[SeanF]

Thanks for that Ed. I've also worked out that the hair spring is broken so I think this one is off to speedy cables or some such for repair.

Many thanks all.

Sean

[RogerH]

Hi Sean,

                 you could try JDO. John does reasonably quick and economical repairs.

 

Roger  - thank you Rockie

Edited January 9, 2019 by RogerH
Typo

[Rockie51]

"Roer?" Saving on email ink?

[SeanF]

Thanks for the tip Ro(g)er.

[SeanF]

Hello all,

Just to close this one off and report excellent service.

I discovered that the Gauge Shop was only 3 miles down the road from me and got in touch with Alan Davis, the owner. Alan repairs and reconditions all Smiths and Jaeger gauges and also reconditions carburettors. See website:

http://thegaugeshop.com/

I dropped my speedo off yesterday morning (Monday) and was told it would be fixed by Friday. Got a text lunch time today - a full 24 hours later - that it was ready with a new hair spring, replaced drive dog (which was incorrect apparently) and re- calibrated….all for £50.

Alan is based in Edenbridge Kent so for anyone in the South East, particularly the Surrey/Kent/Sussex areas he is easily accessible and does what it says on the tin.

He can't promise 24 hour service every time, but as a very happy customer, he gets my recommendation.

Cheers,

Sean

 

 

[Mk2 Chopper]

Thanks for letting us know, I'm in the South East and not that far from Edenbridge, when I eventually get the gauges out to refurb the bezels, at least I know somewhere local if they need anything else (my needle bounces above 40 and the trip is stuck).