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Post by dhb5610 on Jun 5, 2021 10:11:20 GMT
Morning everyone, Iv'e got a problem with the speedometer on my P5B it fluctuates a lot more so the faster I drive. What is the main cause of this, is it in the head it's self or more to do with the inner cable and drive. Is it completely curable or will it always do this to a certain extent.
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Post by Sam Bee on Jun 5, 2021 10:59:28 GMT
I should be curable. It may be the cable, or wear in the cable drive unit on the gearbox, replacement being the cure. But could well be wear in the speedo instrument itself as these seem susceptible to that. There are companies who will renovate instruments - one who charges a set fee per job and which I have used is JDO Instruments, Keithly, and they are quick.
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Post by harvey on Jun 5, 2021 16:15:26 GMT
It can also be caused by the gearbox rear flange bolt loose.
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Post by p5andrew on Jun 5, 2021 21:09:37 GMT
Another possibility is that lubricant has worked its way into the head unit between the disc driven by the cable and the disc attached to the needle. This was the problem with mine, the lubricant picking up on the needle disc and causing the needle to flick wildly round the dial. I very carefully dismantled the head unit sufficiently to gain access to this area and was able to clean out the lubricant using cotton buds and small quantities of WD40 which I used to dissolve the lubricant. The discs should be absolutely clean with no need for any lubricant. Do take great care not to in any way damage the hair spring. I suspect that a previous owner may have tried lubricating the speedo cable and the lubricant worked its way up and into the head unit - this is NOT a good idea!
In order to gain access you will need to temporarily remove the needle from its spindle and then remove the dial; the needle is a fairly tight friction fit on the spindle. When refitting you will need to ensure the needle is correctly positioned on the spindle in order to register speeds accurately - in other words that it is correctly calibrated. I used a long, straight and quiet stretch of road and a satnav to give me accurate true speeds at 30, 40, 50, 60 and 70 by holding the car at steady speeds for about 1/4 mile to allow the speed indicated by the satnav to settle, and a helper (my long-suffering wife!) noted the speeds indicated on the speedo as I read them out to her. It was then a simple matter to reposition the needle on its spindle as appropriate. I subsequently checked the accuracy again and at 30 it is spot on and at 60 it over reads by about 2mph so pretty good. I am sure this method could be improved upon but it seems to have worked for me!
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Post by 3litrekiwi on Jun 5, 2021 23:02:24 GMT
I would start with a new cable. My speedo(s) have been in and out more times than I can remember trying to cure this. The heads have been apart and cleaned several times and although the cable inner seemed fine, the inner strands must have been broken to some extent allowing the cable to twist and release leading to a wobbly needle. I finally bought a new cable from JRW and the needles in both heads are steady. Unfortunately in the process the car's original head was damaged and now reads very slow. A small sacrifice to my learning. At some point I will see if it can be repaired but in the meantime the spare is working fine and has been set to the correct mileage.
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Post by enigmas on Jun 5, 2021 23:23:17 GMT
I haven't read all the post so apologies if I'm repeating something here. The cause of a fluctuating/wavering speedo needle is often due to an "oily or oiled" inner drive cable. Obviously this doesn't solve the problem if the cable is frayed or damaged.
The Fix. The fix is to remove the cable, clean it with lacquer thinner or similar solvent, then coat it with dry black graphite powder.
The Process. If you've not done this before. Place the black graphite powder in the palm of your hand and pull the cable slowly through it whilst rotating the cable. Your hand will be very blackened by the process. Wearing a thin latex food handling glove assists here.
This generally fixes a fluctuating/wavering speedo needle with the reading being very stable after this.
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Post by 3litrekiwi on Jun 6, 2021 7:25:05 GMT
My cable looked perfect, the outer layer of the inner cable had no wear or shiny spots and even after following the process Vince describes I still had a wobbly needle. I would suggest pulling the speedo out and seeing if it is possible to twist the inner cable. A new one will have virtually no twist possible. Mine would twist through 20 degrees or so.
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Post by johnwp5bcoupe on Jun 6, 2021 12:07:34 GMT
Another culprit is the Angle Drive
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Post by dhb5610 on Jun 6, 2021 12:20:23 GMT
Thank you all for your helpful advice, this is a job that needs doing as it's getting a little worse these days I'll let you know how I get on
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Post by dhb5610 on Jun 6, 2021 12:20:58 GMT
Thank you all for your helpful advice, this is a job that needs doing as it's getting a little worse these days I'll let you know how I get on
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Post by lagain on Jun 6, 2021 19:49:21 GMT
mine did that.I had it overhauled by Speedograph Richfield, who also made it more accurate. It is now as steady as a rock !
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Post by Welsh Warlock on Jun 8, 2021 12:07:59 GMT
The speedo heads dry out and gradually seize until they break the weakest link: the 90deg angle drive. Yu can ask me how I know if you like.
I wrote an article for Take Five in about 2001 I think.
Take the speedo out - not too difficult and insert a suitable square drive in the back and feel how easily or otherwise it turns with your fingers. Probably sticks a bit? You could put a small drop of oil in the right place (don't get it on the magnetic disc or as already mentioned you'll end up with a hydraulically driven speedo that shoots up to maximum even at slow speed - again- aske me how I know.
IME cable is unlikely as is the 90deg drive.
It's all about small amounts of the right lubricant in the right place and none where there shouldn't be any.
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