The speedometer on my P5B fluctuates 5-10 mph range but the rev counter is steady. My 3-litre was worse, like a windscreen wiper. The cable was replaced with new but it shows 15-10 mph when my portable sat nav might reads 50 mph. Any remedy suggestions please?
Post by johnwp5bcoupe on Aug 10, 2016 15:56:30 GMT
Could be the Angle connector on the box if not the head could have a problem I did Cyf's a while back lack of lube plus the disk was fouling due bearing being worn you can see it on the pic below! it had a broken spring as well.
Another area to investigate if the odometer is believed to be mechanically ok is the inner drive cable. The inner drive cable should be removed and cleaned of all dried and embedded lubricant with a suitable solvent. Once clean and dry, lubricate the cable with powdered graphite...nothing other, (place a quantity in your palm and pull the cable through the powder several times.) This also works well in erradicating fluctuations in the speedo.
PS. Do not oil or grease the cable. These lubricants eventually dry out and cause stiction between the inner and outer drive cables resulting in erratic drive to the attached instrument.
The 3-litre cable was replaced new a few years ago in an effort to rectify and opinions expressed afterwards was that a new cable was more likely to fail then the old one especially kinking. Someone mentioned also that there was a small magnet near the head which might be a cause but i dropped the matter until my recent P5B acquisition showed a similar problem which prompted me to raise the matter again.
Originally the needle swung between say 10 and 2 on a clock face. I was advised to replace it with a new cable which I dd from Classeparts. The needle is now between 7 and 8 even when i know i am running at around 50 mph.
they renovated it and also made it more accurate, it had been wildly optimistic. The needle does not wave at all now. If you have yours done you need to check it with a sat nav so that you can tell them how far out it is at 70mph
Is it a question of re-calibration? I guess different tyre sizes will make a difference too. I'm told that sat nav info is not reliable because it measures in straight horizontal lines without taking mountains and valleys into account - even my modern Volvo shows a difference. Just avoiding speeding tickets will be enough!
Eric : if by reading between 7 and 8 on the clockface you mean perhaps 10-15 mph at all speeds, then it is clear that there is slippage in the drive somewhere. First check that the cable inner is properly inserted into the speedo head. If that is ok, then the next thing to check is that the cable is rotating when the car is drive i.e. disconnect the cable outer and see that the inner rotates when the car is driven . If that shows no rotation at speed then either you have a broken cable or the angle drive at the gearbox end is faulty and you will have either to repair it ( not that difficult ) or replace it
Speedo head drying out. I wrote an article on it on Take Five about 15 years ago.
I meant to mention that if the head seizes it will break the drive at the weakest point.
I had a wavey speedo. It stopped working. I found the 90deg drive had broken so I replaced it. That one broke immediately so I tested the cable which was fine. Then as a last resort checked the head and it was seized solid.I managed to get it freed off and after making a hash of it initially got it fully functioning properly with a few drops of oil.
I can't find the article I wrote but I think John Wallet wrote something more technical on the board sometime later. Have a search around and you might find it.
resurrecting this speedo enquiry. If I didn't say the cable now installed was new I had meant to. The 3-litre speedo gave up and died to zero on the return from the recent photo shoot and I think the odometerhas too. Stopped for some miles but need to check again to see it was temporary exhaustion! In 2016 John you posted some images on Photobucket - now disabled. Can you offer them again in a different format or are they lost to you?
the angled drive might be a cause of the speedo fluctuating. The parts book for a Mk1 p299 describes a right-angled drive part 277741 but states Mk1 with overdrive. Will this be the same for a non-overdrive?
The Mk1 has a DG gearbox and as you say the P5B has the BW35. Are these gadgets identical (ie both slanted angles or 90 degs)? The Mk1 is the worst condition and has no overdrive. The other one has minor fluctuating is next to the rev counter which is steady.