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MG MGB Technical - Wobbly speedo despite new cables!

Hi all,

After having lived with a wobbly speedo needle for around 8 years, I bit the bullet and replaced the speedo cable last year. What a result- a steady needle and me wishing I'd done it long ago...

But that was last year- now, less than 600 miles later it's all gone wobbly again! Thinking it could have been due to a cheapo 'well-known auction site' part, I've replaced it with one from the MGOC. But now I'm merely the proud owner of two speedo cables and one wobbly speedometer nedle.

What are the possible actions for me now? Without wanting to pre-judge things, I'm worried some excess lube has got into the speedo head- I didn't grease the final few cm of the inner cable, but it seems to have done well at going uphill nonetheless.

If there is indeed greasy kack in the speedo head, can I do any harm squirting in something like brake cleaner or carb cleaner? (having removed the speedo from the car, naturally).

Or is there some other option that I've missed?

Thanks for your thoughts, in advance.

Ian Geeza
I F

Hi Ian,

Several points:

To check if grease has got to the speedo, disconnect the cable and inspect the union area. Any grease working its way up the cable would need to also be present in here.

Maybe the input shaft bearing of the speedo is dry.

Maybe the problem is at the gearbox end, a damaged or missing tooth on the drive gear.

If you have the speedo out you could check its operation by running it with an variable speed electric drill, with and without the cable.

Here's a link to an article on speedo repair.

http://home.comcast.net/~rhodes/speedo.pdf

Herb
Herb Adler

Depends on the rate of wobble. If it is occurring at the same time the trip odo tenths wheel moves, then the problem is dryness inside the speedo. I had this and a drop of oil on the input shaft (in my case) cured it. But if it trembles at a faster rate than that then the cable itself is the issue, in part at least.

From what I have been able to glean all MGBs originally had a right-angle drive at the gearbox end of the cable. Left-hand drive cars may have had one at the speedo end as well, *if* the came came across behind the dash and doen the same hole in the firewall as for RHD, but many LHD seem to have the cable exiting through the firewall on the LHS and so don't need the right-angle drive at the speedo. If you don't have a gearbox right-angle drive, and you try to fit an original length cable, you will probably end up with too tight a turn in the cable at the gearbox, and you need a longer cable.
Paul Hunt 2010

Fellas, thanks very much for the link and pointers. I'll remove the speedo from the dash and try a drill on the end, to try and get a handle on which part is actually at fault. I'll get a drip of oil on that spindle too, while I'm about it, can't do any harm. the confusing thing for me is how replacing the cable last year made things fine, suggesting it was a cable rather than a speedo fault, and yet now I'm back at sqaure one (in fact square minus one, as it's now wobblier than 2 years ago!)

I'll report back on how I get on, but things sometimes move slowly round here...

Ian
I F

Given the increasing problems with rubbish manufacture of replacement components these days it's potentially not confusing at all. For fifteen years or more the general watch-word was "if you buy cheap you get cheap" and buying off reputable suppliers was good enough. In the last few years even the reputable suppliers are ending up with rubbish stuff. Whether that is because the cheap copies have destroyed the manufacturers of the decent stuff and that is all they can get, or whether suppliers are having to buy cheap to 'stay in business' I don't know. It's happened with hoses, points, rotors in the past but there are now decent parts available again from certain specialists. They are expensive, but if they work that is cheap.
Paul Hunt 2010

Paul, I was very interested in your coment below,
( but there are now decent parts available again from certain specialists. They are expensive, but if they work that is cheap.) could you please tell us more, as like a lot of owners I am not very happy with most of the parts i buy, many thanks. A.T
andy tilney

I've got a V8 and a roadster and when changing the V8 hoses some years ago my supplier warned me that they would only last a couple of years but they were the best he could get at the time. More recently he has sourced decent rubber (at a higher price) and silicone rubber (at an even higher price). Also rotors have been causing a lot or problems lately, but again some suppliers have red bodied ones which so far seem to be much better. The suspect ones have a visible rivet on top of the rotor arm inside the base circle of the rotor (see http://www.mgb-stuff.org.uk/rotors.htm), which puts it very close to the distributor shaft and at risk of breaking down (especially with the higher plug gaps that many like to run it has to be said), as well as the material used for the body being suspect - having too high a carbon content. At least one supplier of these red rotors also has points and caps etc. available, claimed to be of a higher quality, and even original advance spring sets for 25D4s! http://www.distributordoctor.com/red-rotor-arms.html.
Paul Hunt 2010

Paul thanks for that, A.T
andy tilney

Update time...

A little further investigation, and I'm inclined to blame the speedo unti itself rather than either of the two replaced cables. From what I could tell, the needle was still wavy with a drill connected directly.

I did partially dismantle the unit itself, but didn't get any furtehr as (a) I need a teeny tiny allen key to release the trip reset knob; and (b) I was frightened of really screwing things up with kack-handed repair efforts. I did get a spot of oil on the needle pivot jobbie though.

Back in the car, no improvement, in fact a propensity to sweep even higher around the dial than before...

So my next question is- who are the UK professionals to entrust with a repair, and would anyone know how many GBP £££ I can expect to pay?

Thanks all!

Ian

I F

Flicking down then up is usually the cable, but flicking up to a higher speed than you are actually travelling is the spinning disc catching on the needle disc.
Paul Hunt 2010

As Paul said, the disc may be "catching". Some newer cables have a slightly-too-long inner cable end... the square bit. You can add a washer or 2 where the outer cable butts up to the speedo to space the inner cable away from the disc, thus relieving pressure on the disc bearing.

Peter
Peter Caldwell

Paul, Peter thanks. I feel as if I have both of the symptoms Paul describes, which I can see makes an at-a-distance diagnosis somewhat of a challenge. I can see some mileage in the idea of a cable inner protuding by different lengths, which could explain why multiple re-insertions have contributed to a variety of 'issues'.

I do like the washer idea, and will give that a go hopefully tomorrow.

Thanks again fellas, Ian.
I F

I tried the washer insertion tip, but no dice, sadly. It waves round still, higher than the true speed.

I think it may be time to call in professional help- who in the UK would do a good fix at reasonable cost, does anyone know?

Ian
I F

Hi Ian,

My speedo did weird things, like taking a long time to get to its reading, then staying a speed when stopped.

What the problem turned out to be was that the needle axle has an adjustment for axial play, which was a bit too tight. Loosened it off and everything OK now.

Herb
Herb Adler

G'day Herb, thanks for that.

I'm keen to have a go at fixing it myself, if poss, but have fallen at the stage of getting the screw out that attaches the rod to the trip reset mechanism. I can't for the life of me discern if it's held on in such a way that removal needs a regular (albeit tiny) screwdriver, or a teen-tiny allen key. Does anyone know at all?

Ian

I F

The answer lies in the speedo drive shaft which is most probably very slightly out of true inside the speedo itself if all else has failed to correct the fault. I wrote a RV8 workshop note on this theme a while back. If you get into www.v8register and click into RV8 workshop notes Vol 9 note no. 306 you will see what I'm refering to with pictures. I don't konw who the speedo. manufacturer is for the MGB but I found out the RV8 VDO people were in Germany and so they could completely repair my speedo.defect.
Peter Garton

Hi Ian,

I can't recall the exact method for removing the trip reset thingy, but I didn't have any problems with it. A vague feeling that it might be a small roll pin and can be removed with a thin nail as a drift.

I will see if I can discern the method a bit later today and report back.

Herb
Herb Adler

Hi Ian,

I checked the speedo repair note and this paragraph describes the removal.
As I didn't have any hassles in removing the works I assume that the screw mentioned can be removed with "standard" tools, such as jeweler's screwdriver. Also called precision screwdrivers. Cheap at any auto parts or hardware shop.

A couple of other hints when removing the works, take out the highbeam warning light first, it might be a bit tight, but leaving it in makes the whole job more difficult, as it jams when the innards are tilted to extract. To remove the bezek twist it, as it is attached by a bayonet style fitting, don't bend the tabs.

Herb

SPEEDOMETER: Inspection
To remove the speedometer works, first remove the metal bezel and the glass. Remove the two screws on the back and, if necessary, the tiny screw holding the reset cable
(TR2-4). Then press the reset shaft (TR2-4) into the case and then push the threaded end
(where the speedometer cable attaches) inward. The works should slide forward out of the
case. There may be some adhesion to the rubber gasket inside the case, If the works do
not move freely check the reset shaft and be sure that it is not catching on the case. Use a
screwdriver to press it free.
Herb Adler

Ian, I doubt any 'professional' would know any more than the knowledge and information you could get here, unless they were very exceptional.

Many years ago I could never see how to get my trip reset twiddler disconnected. Managed to get the innards out anyway, but the needle pinged off on replacement. Fortunately it hadn't broken the spindle, so I propped up one rear wheel, set the engine to the appropriate revs to give 30mph in top gear, and popped the needle back on in that position.
Paul Hunt 2010

Hi,

I found that replacing the pointer wasn't difficult at all. There is a tiny mark on the speedo dial, just below the zero stop. locating the pointer to this at rest and then retracting the spring loaded end stop to allow the pointer to be moved onto the scale gave a very accurate speed reading.

Herb
Herb Adler

True, but I had no idea how accurate my speedo was after all these years, making sure it was accurate at 30 seemed the most sensible option.
Paul Hunt 2010

Similar problems to Ian's.

Following speedo failure in February, I had it reconditioned and all was fine. In April, the cable broke. After fitting a new cable, the wobbling started. I tried the "washer trick" but it didn't work.

Just the other day, I noticed Paul's post of 2nd July
and on checking noticed that the wobbles were in phase
with the tenths counter in the odometer. At about
70mph, the needle was swinging from 70 to 78 two or
three times a second.

Anyway, I took the speedo out again yesterday, opened it
up and gave it a couple of hopeful squirts of WD40.
While this may not be the *exact* recommended way of
doing things, it worked for me. On a test drive today,
the wobble had totally gone, so thanks for the
suggestion Paul!
Geoff Everitt

My pleasure Geoff, mine is still working and wobble free maybe fifteen years later :o)
PaulH Solihull

A quick update,(or rather, a slow update).

Said roll pin holding the trip reset has been dispatched by drilling it out. It wouldn't budge with less destructive encouragemnent. Only when it was out was I sure it was a roll pin rather than a screw. So now I should be able to dismantle further, having got over that particular hurdle.

I shall report back when I know more. (=When I have my next 'what on Earth do I do now?' question!)

Ian
I F

Hi Ian,
I have a '69 BGT and for several years I had a bounce in my speedo. I finally cured it by replacing the cable & sheath with the longer overdrive type and rerouting it to eliminate a fairly tight bend. I kept the ninety degree fittings on each end. It's very stable now. Paul
S Canup

Hi Paul, thanks for your thoughts. I do have (I believe) the longer overdrive cable, but don't have the right-angle fittings. I'm still inclined to blame the speedo unit itself rather than the cable, as I can't see how a replacement cable should go bad within such a relatively short time

Anyhow, I had a try at extracting the works from the speedo casing and have failed. I have undone the two screws and the roll pin that holds the trip reset, and I can't manage to manoeuvre the innards out. Tilting the innards to clear the drive cable socket makes the trip reset rod foul things, and I'm frightened on using too much brute force and ignorance! It's like a version of getting an awkwardly shaped sofa round a bencd in the stairwell!

Am I missing something? Can anyone who has manged this extraction share their tips n tricks?

Cheers, Ian
I F

Hi Ian,

I can share your frustration, having been there myself.
Things to look for

have you removed the hi lo beam indicator lamp? It may seem to be inconsequential, but it does tend to foul the works when trying to remove them.

If the lamp has been removed, pull harder, it does come out.

Herb
Herb Adler

Hiya Herb, thanks again for your thoughts- no I haven't removed the lamp, although I got the feeling peering through the gap at teh edge of the dial that the front (where the blue lens is) had become detached from the back. Do I need to remove the back, bulb holder part- if so do you recall how to detach it from the rear of the speedo? As I mentioned before, I'm treading very carefully where force is required, until I'm reassured that what I'm trying to force apart, *will* actually come apart, without destruction!

Ian
I F

Hi Ian,

Yes it is necessary to remove this lamp, it is about 2" long, being a light tube . This interferes with some of the works, stopping you being able to cant them enough to remove.
I can't remember exactly how it is inserted, my gut feeling is that it was a tight push fit, but it could be a bayonet. Try twisting it to see if it is a bayonet, then pull.

Herb
Herb Adler

Yay! Removal of the light fitting helped (as did fairly severe persuasion with a hammer on the cable entry bit at the rear).

Nothing obviously seemed loose but there was an excessive amount of what looked like liquified graphite grease (if that makes sense). I've cleaned up the magnet disc faces and will re-intall and see if that's been the problem, causing dragging.

I'll be both pleased and annoyed if so- pleased it's fixed, and annoyed that I may have casued the problem with over-lubrication, despite obeying the rule about not greaseing the final few cm of the inner cable.

Mind you, next I have to get the speedo unit back togther- stand by for more cries of help!

Ian
I F

The speedo actually went back together without too much grief. Removing the light tube was certainly helpful, even if only to aid better viewing of the innards.

Running a drill on the cable insertion point seems to give a steady reading, but it'll take a run out to check things are better for sure. Shame that rain is a comin'!
I F

I tried a trial fit of the speedo and took the car for a run. The needle was rock steady for around 6 miles (hooray), and then had a wobbly fit, before becoming rock steady once more for the final mile of the journey.

I wonder if when warm some of the acculumated gloop temorarily caused drag before being spun off somewhere less annoying? Or maybe it's all coincidence and the 'gloopy theory' is a red herring? Anyhow, I'll not fit it permanently in the dash until I've had another run or three. Perhaps I can live with wobbliness for 1 mile every 10.

Don't you just love intermittent faults?

Ian
I F

Is there any way you can reroute the cable without going to too much trouble? I think making a more gradual bend is was what helped steady my needle the most. I believe what happens is the cable is binding at a certain point as it turns (its basically a tight spring) and then when it slips loose it spins faster. It then repeats that cycle. Straightening the cable somewhat, keeps the cable from 'winding up and turning loose' as it goes around.

Paul
Paul S Canup

Not much chance of getting more gradual bends in an RHD unless you fit a right-angle drive at the gearbox, which the parts catalogue shows all cars had, or fit a longer cable. Neither of mine have the right-angle drive, and neither wobble, unfortunately I can't tell you how long they are, there were about 14 different cables over the years, models and markets.
PaulH Solihull

Just reporting back after the speedo has been re-installed a while and it seems fine (hope that's not tempting fate!)

A top tip for anyone removing and taking apart a speedo in future - attach the reset knob before reinstalling it back in the dash. I didn't and will need to remove it again sometime- doh!

I F

This thread was discussed between 01/07/2010 and 02/09/2010

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