Rev counter

I’ve just been browsing through the old threads and it looks like we’ve discussed to death problems with speedos / odometers not working and the possible causes.
However, what about the rev counter ? Mine occasionally decides to either stay on zero and not move at all. Or it moves albeit very slowly and doesn’t react quickly to changes in engine speed. Also, it has been know to stay stuck on , say, 2000 RPM even when the engine is switch off !

Initially I thought something must be preventing it from moving freely – physical, such as the backing board touching the needle. But no, this doesn’t appear to be the case.
I’ve even dropped a spot of oil on the spindle in case it was fouling inside. Again, no difference.

It can occur in hot weather, cold weather, go months without being a problem and then decide to play up.

It’s doubly annoying when the speedo has just died and I ‘was’ relying on the rev counter to give me an idea on speed !!!

Any ideas ?

Hi Paul,

I think you are right to think that the rev counter is sticking. I have checked the circuit and see that the only voltage applied to the rev counter is swtched by the ign. So it is not a voltage causing the problem.
As you most probably read, I have a spare clockset supplied by our friendly dodgy colour blind breaker (his words, not mine ) which I have been able to check out, and I find that mine is marked Atmo, so I suspect the turbo one is slightly different, however I dont think by much. The Atmo picks up its pulses from the ign coil which produces 3 pulses per rev, but I suspect the Turbo gets it pulses from the ECU which could be 1 pulse per rev. Unfortunately although the Atmo diag shows the pulse path, the Turbo one does not. However irrespective of the pulses, the 225 degree meters should be the same.
The way we used to check for sticky meter movements was to blow the needle around the dial, doing it this way will not cause damage to the movement. That should show if the movement is sticking. If it is, there is a rear bearing adjustment on the back of the rev counter. I have found that over time they can become tight due to wear. If you turn the adjustment a midge...and I mean a midge, anticlockwise, this should just take the pressure off and by blowing the needle you should see it clear.
You will have to remove the clockset completely to do this adjustment, and remove the holding bracket across the back of the clockset to uncover the adjustment. See pic below:-



It might be an idea to mark the alignement of the slot so you know exactly where the adjustment is before you start.
You could kill two birds with one stone if you do this.....I note you have speedo probs as well.....so there is another job for you, and with a bit of luck all your problems will be solved
I took a couple of other pics of the rev counter which are below...just for interest. The first one shows the actual meter movement and the other shows a general view of the back of the clockset with the white connector which is the 12v + & - (red and black) and the pulse input (yellow)




I hope this helps

Many thanks John.
I took the instrument cluster off the car today, changed the illumination bulb (main reason for removal of the cluster) and then decided to do as you suggested and ever-so-slightly moved the rear screw at the rear of the rev counter. Hopefully this will help to resolve sticky needle syndrome - time will tell.
The only annoying part is that I sprayed all connectors with switch cleaner (standard practice for me when removing cluster) and after I reassembled and took it for a run, the speedo decided not to work

I've experienced this many many times before, and its always been a case of spray everything and put it back (including the rear connector behind offside wheel. Only this time it's made no difference.
I have done a continuity check between the big connector block (LHS) and the pcb on the RHS, and that reads fine.

I can only imagine it is yet again poor connections somewhere!
I've taken it all apart once again and take it for a run tomorrow to see if it's solved itself !

Rgds
Paul

............and it hasnt, still no joy.

JohnC, am I correct in assuming that the three screws securing the speedo clock to rear holding bracket are there just as support ?
I'm wondering if removal of this bracket has caused something to play up.

I've since taken the whole cluster out again to check no wires or connectors are visibly caught or not seated correctly.

Speedo woes, dont you just love um...

JohnC, am I correct in assuming that the three screws securing the speedo clock to rear holding bracket are there just as support ?...........Speedo woes, dont you just love um...

Yes Paul, if you think about it, without the rear supporting (x3) screws, the weight of the whole speedo assembly would be held by the two small screws through the dial. The rev counter has one support screw....the one also holding the earth for the computer illumination. I would check again for a trapped or nipped wire/s under the bracket, and I would tighten up all the female connector pins by reducing the gap in the slot in them...if you know what I mean...with, say, a watchmakers screwdriver or something similar...starting with the speed sensor connector in the engin bay, then the large connector LHS of clockset, and the smaller flylead one for the computer. Also remove the speedo board connectors and retension the contacts one by one by removing them from their housings. If that still does not work.....see members area for board makeover.
PM also being sent

John

SPEEDO FIXED !!!!!!!! ..........after doing a spot of continuity, detective work, I've manged to fix the blasted thing. In this instance, it was the big connector block RHS of the dash that was playing up (again). Fooled me for a while because previously I'd just undo, spray with switch cleaner and reconnect. This time the pins must have stretched a tad and were not making a connection. Thanks to Andrew for suggesting the obvious - which was to short out the terminals at the connector behind the rear wheel and then check continuity at the front of the car. This showed up the problem at the connector end.
JohnC, thank you for the kind offer re. refurbing the speedo board.
As it appears to be behaving itself I'll leave it alone for the time being.

Apologies for dragging up an old post.
Decided to remove cluster and attempt to solve my sticking rev counter again....
The screw on the rear housing of the rev counter was already loosen off - as I had played with this some while back. But I was wondering what the other two screws purpose are on the side of the mechanism - shown in John's photo above.
Also, I see the rear screw has a small hole in the middle. Thinking this is a lub hole? If so, then maybe the bearing is sticking due to lack / no oil present.

Comments anyone ?

But I was wondering what the other two screws purpose are on the side of the mechanism - shown in John's photo above.

Paul ..... if you mean the screws (one shown in center of pic below) the other about 90 degrees around the mechanism unseen in the pic ...... these are balance adjustments for the movement and should not be touched.

With regard to applying oil to this movement ..... again this is a not advised. The only lubricant that should be used is watch makers oil as this is a very delicate movement. Any available light oil will only go sticky and attract dust. If you think about this movement, it is not like a motor which is spinning continuously, this movement only moves a maximum of 225 degrees and comparatively slowly so does not need lubricating as such, the bearings do not wear like normal bearings. In fact, if they have ever been "oiled" at all, then I suggest that is the cause of the sticking.
We did speak briefly the other evening about this and my comments were in fact, the same as my first post on this thread ie:- with the front clear panel removed, blow the meter needle gently to the position where it sticks, then carefully turn the screw anticlockwise in the center of the rear of the revcounter, but stop the moment the needle returns to zero ..... keep repeating until you have eliminated any other sticky points in the meters sweep. Lets say it sticks at 2000 rpm, blow gently till it is passed that point then reduce you "blow" so the needle drops very slowly ..... that is the best way to find its sticking points.
I have done this many times over my working life .... this was long before digital readouts were invented, and it does work but it is quite fiddly, and takes a lot of patience.
If you can mount the instruments with their dials horizontal on a pile of books or similar at each end on a table so the assembly does not move, high enough to get your screwdriver up from under to the rear bearing adjustment without moving the assembly so much the better ..... anyway, that's how I would do it.
Let us know what you think.

John

Thanks for the comments John.

The rear screw does have a hole in the centre, hence the question on oil.

The problem I have (and have done ever since owning the car) is that it is an intermittent problem.
I can take it all apart and loosen off the rear screw slightly, put it back together and it will work fine for a couple of weeks before sticking again. Also, it doesn't always stick in the same spot - sometimes 1500 rpm mark, other times 800 rpm etc..

Wondering if it's heat related and perhaps not to the rear bearing ?

So, on the plus side it's working fine at the moment

....... However, what about the rev counter ? Mine occasionally decides to either stay on zero and not move at all. Or it moves albeit very slowly and doesn’t react quickly to changes in engine speed. Also, it has been know to stay stuck on , say, 2000 RPM even when the engine is switch off !

Paul ...... I have just read back on your original post about this. If it sometimes stays on zero, that could indicate a bad connection of the signal from your ECU, however it could also indicate a stiff bearing ..... you take your pick.
But then you say it sometimes stays reading 2000 rpm or other rpm's, even when you have switched off ..... that must indicate a mechanical sticking.
There is little more I can help you on this. Only by blowing lightly then increasing your blow to move the needle slowly up scale will you see where it is sticking.
There is a small electronic board converting the pulse rate from the ECU to a variable voltage which is applied to the meter movement, but that would not account for the needle reading rpm when the engine stops and no pulses produced. That is why I feel it is a sticking movement.
Sorry ..... but I can't suggest anything else.

John