Lotus Elan

Wobbly speedo.

PostPost by: Keith Scarfe » Wed Apr 24, 2013 9:43 am

My speedo is really unstable. It varies about 10 mph, constantly oscillating. I guess the solution is to strip out the cable and angle box and check and clean as it is probably sticking as it rotates. I just thought I would ask in case anyone has any other suggestions. It is likely to be the cable or angle box? Can the box be serviced? Cable would be a new one if suspect I assume. Any comments?
Thanks.
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PostPost by: Keith Scarfe » Wed Apr 24, 2013 10:00 am

Do other peoples wobble a bit or a lot or is yours really steady?
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PostPost by: elanfan1 » Wed Apr 24, 2013 10:15 am

I'd suspect that either the end of the 'square' cable has rounded or the fitting in the speedo itself has rounded and the cable is slipping as it spins i.e so not every revolution is getting 'recorded'.
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PostPost by: peterako » Wed Apr 24, 2013 11:25 am

Hi Keith,

A long while ago I spent AGES trying to fix a wobble speedo in my +2 (Lotus 5 speed).

Serviced Speedo, bought new speedos, cables, angle box.....still wobbly and beginning to drop to 0 above (eg.) 60mph.

In the end it turned out to to be the rear 'nut' in the gearbox driveshaft.

The worm gear on the shaft in the gearbox that drives the angle drive is only a friction fit and if not fully tight on the shaft symptoms can be as above.

Having said all that.......

I would be 90% sure that a cable change will fix your problem.

10% is on the Speedo, gearbox and angle drive in that order :)

Bets of luck,
Peter

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PostPost by: vernon.taylor » Wed Apr 24, 2013 11:58 am

Salut Keith

Mine wobbles a bit, too - and that's with a new angle drive.

Read on here recently that the speedo cable doesn't like sharp bends and that it should be dressed carefully - even if it looks a bit untidy. Might be a the thing to try before buying another.

@+

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PostPost by: elanner » Wed Apr 24, 2013 1:04 pm

My speedo bounces around too and I suspect it's the cable, on the scientific basis that the cable was at fault for the same problem on the Elan I had back in the 70s.

However, in this case the cable also seems to be routed wrong. From the speedo (LHD car) it dives behind the heater and is next seen appearing between the chassis and the body, coming though one of the large holes in the side of the chassis, into the angle drive from the top.

I went over to Gary's a few weekends ago and he mentioned that the cable should run from the speedo through the bulkhead into the engine bay and then somehow down to the angle drive on the other side of the gearbox - passing very close to the exhaust, presumably.

Could somebody with a LHD Elan tell me how the cable should run? Is it possible that a LHD cable needs to be longer than a RHD cable? I've looked at RDEnt's parts list and there only seems to be one part number. But the only reason for my routing I can think of is that the cable is too short to go via the engine bay, so it takes a short cut around the heater. Put another way, how long should the cable be?

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PostPost by: jeff jackson » Wed Apr 24, 2013 7:51 pm

I agree with all of the above, but in the case of my wobbly speedo, it was a simple case of a tiny bit of muck stuck in the internal gears of the speedo itself. I cleaned all of the old tired grease off, applied some new, and re-assembled the speedo. That cured it for me.
I would check that the gears are clean before going down the expensive cable, right angled drive .
Hope it helps.
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PostPost by: AHM » Wed Apr 24, 2013 8:24 pm

I have have had a wobbly spedo from
- Kinked cable
- cable not inserted to gauge correctly

peterako wrote:The worm gear on the shaft in the gearbox that drives the angle drive is only a friction fit and if not fully tight on the shaft symptoms can be as above.


I think it is prevented from rotating by a small ball in the shaft and a keyway in the gear.
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PostPost by: Keith Scarfe » Thu Apr 25, 2013 8:13 am

Wow thanks every one for the replies. Doubt I will do anything immediately but will have a look next time I jack it up and get under there. One thing I thought of doing to narrow it down is to disconnect the cable at the gb end and put the inner into an electric drill and run it. That would tell me if the problem lies in the cable/ spedo or the angle/gear box.
If the problem is worn square drives in the angle box or speedo, it there any fix or are they scrap and find a new ones (along with some hens teeth).
Ta.
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PostPost by: gjz30075 » Thu Apr 25, 2013 10:20 am

Nick, my speedo cable exits the bulkhead as shown: just above the heater hose and below the wires. I then is routed behind the engine, above the bellhousing, on its way to the gearbox. It's really nowhere near the exhaust. I got the cable from, I think, Dave Bean and it is quite long. Once reaching the gearbox, it continues to the rear of the car and is gently looped back to connect to its gearbox. Very little wobble in my speedo.

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PostPost by: elanner » Thu Apr 25, 2013 8:43 pm

Great. Thanks Greg.

Another item on the to-do list!

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PostPost by: StressCraxx » Fri Apr 26, 2013 2:06 am

Ever since I used some #2 bearing grease on the speedo cable 20 years ago, it has been smooth and steady. Good point on routing the cable. The fewer and most gentle bends are best.
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PostPost by: JJDraper » Sat Apr 27, 2013 5:39 pm

I have a theory.

If you dissect a broken speedo cable you will note that the inner is a very long spring. Kinks in the cable run cause friction between inner and outer. The rotation at the gearbox is constant, but a sharp bend will cause the inner to momentarily slow down as friction causes a twist in the length of the cable. Acting as a torsional spring, it stores a little energy as the gearbox end continues to turn until the friction/stiction is overcome by the build up in torsional energy and the rotation rate of the inner, past the kink speeds up until it 'catches up' with the rotation rate of the gearbox end and the whole process repeats. Very wordy, I know, but its worth trying to understand the process.

The upshot is that the speedo end sees a cable constantly speeding up and slowing down and this is reflected in a wobbly speedo needle. In my experience with both cars and bikes, most cable breaks seem to occur at the driven end (gearbox). Better lubrication also overcomes the friction, eliminating the needle wobble, but at the risk of grease or oil getting into the speedo head. A wobbly speedo needle is a symptom of a problem in the cable, not the speedo head. An older auto storesman mentioned to me some years ago that it was not uncommon to sell a cable and then another to the same punter a few weeks later - he reckoned it was poor routing of the new cable.

Muck in the speedo will (in all probability) only affect the accuracy - being a constant drag on the speedo disc.

Just my tuppence..

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