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Very neat solution.

The Smiths instruments in my Esprit don't bounce around at all, but the VDO ones in my Excel, well that's another matter. I fitted a HUD to get over that issue.

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thanks for the post. I have had exactly the same problem as you. The speedo has now been rebuilt twice, as has the angle drive at the gearbox end. I even took the back of the gearbox off to check the internal drive gear. Have replaced the cable as well. The only thing I have not changed is the sleeve but I just can't believe its that. As you say its pretty irritating as otherwise my car is well sorted. I may try your solution.

cheers

C43

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I’ll post some pictures of the sensor setup in the back as soon as I find some time to crawl under it again. As outlined in the post; best would be a tone ring + passive sensor setup. The inboard brakes don’t make that easy. I bought a spare rear disk to experiment with to find a more sturdy solution. The current setup works fine for now. 

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Simple VSS for an older G car- Hall sensor on an angle bracket reading 6 magnets epoxied to outer CV joint. 

VSS small (2).jpg

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8 hours ago, snowrx said:

Simple VSS for an older G car- Hall sensor on an angle bracket reading 6 magnets epoxied to outer CV joint. 

VSS small (2).jpg

That’s exactly the same hall sensor I’m using. I weatherproofed mine a bit more with shrink tape. How long have you been running this setup Thomas? Any feedback on reliability?

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BTW like you I have changed nearly everything in terms of the speedo. The only part I have not changed is the outer speedo cable. I am not sure how this can make the speedo wobble but was wondering if this could have an effect, did you try changing yours? Also did you try grease on the cable? I am using graphite lubricant but its quite dry and therefore no damping effect. I was wondering if grease on the cable would add some damping? I know but long shots but it is strange that we are having this problem. 

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  • Gold FFM

Mine has always bounced all over the shop... anyone else managed to sort this without fitting an electric version?

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On my 1990 SE (VDO gauges) it was a loose/slipping magnet inside the speedo. Had it repaired a looooooooooooooooooooooong time ago (worked perfectly after) but recently it started to bounce again. 

Esprit Freak

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6 hours ago, Christian43 said:

BTW like you I have changed nearly everything in terms of the speedo. The only part I have not changed is the outer speedo cable. I am not sure how this can make the speedo wobble but was wondering if this could have an effect, did you try changing yours? Also did you try grease on the cable? I am using graphite lubricant but its quite dry and therefore no damping effect. I was wondering if grease on the cable would add some damping? I know but long shots but it is strange that we are having this problem. 

I changed the  complete cable inner and outer Christian. It improved it a bit but didn’t cure it. Greasing also didn’t make a difference. 

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Almost all car speedo cable outers since the 1970's have been nylon lined. I've not cut an Esprit one in two to check, but there is no reason to assume it's unlined. (Motorbike ones are often unlined)

Nylon lined cables should never be greased. The grease swells the nylon causing binding. I don't know about the effect of a dry graphite lubricant, but the cables are designed to operate dry. The second effect of grease on a cable is that it can work it's way into the speedo which can damage the speedo.

With heavy use or tight bends the nylon liner can wear through in places which also causes binding. So it's never a good idea to put a new inner in an old outer even if it works ok to start with, it won't have the life of a new inner in a new outer.

The most likely cause of a bouncing needle is too tight a bend in the route of the cable, and the longer the cable the less tolerant of tight bends the inner cable is. It winds itself up and then releases. It's always worth checking your full cable route and making sure all bends are as big a radius as possible.

Bouncing most of the time is caused by the cable. Occasionally you get damage to the drive gear teeth which then slip causing bouncing, but if the teeth look ok they usually are. If the gauge becomes stiff (usually because of grease contamination) that can cause the cable to wind up causing bouncing, normally the cable doesn't last long if that's the case. It's easy to check the speedo with it out. Use a match stick or similar to turn the speedo with your fingers. It should be smooth and almost effortless.

Speedograph Richfield http://www.speedograph-richfield.com/ repair Smiths Speedos and instruments at a very competitive price. I don't know if they do VDO ones though. They also repair speedo angle drives. I've used them a few times with excellent results.

Speedos don't bounce for no reason. It's got to be the drive, cable or instrument, there is nothing else.

 

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One other issue I've just remembered. It's possible sometimes not to seat the drive cable properly into to drive or instrument when attaching the cable. (quite common on old mini's where access to either end is difficult)

You would think 1/4 turn of the cable in use and it would seat, but it never seems to, just drives using end friction. The inner compresses into slack space in the outer and binds causing bouncing

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13 hours ago, Gis said:

That’s exactly the same hall sensor I’m using. I weatherproofed mine a bit more with shrink tape. How long have you been running this setup Thomas? Any feedback on reliability?

I think this went on as a quick and dirty test setup to give speed info to my Megasquirt ECU for boost by gear and datalogging, but I can't remember when. Photo meta data says 2014. It's been dead reliable for me, although I used a metal-filled epoxy (JB weld) to attach the magnets and it was quite messy when the iron in the epoxy mounded up over the neodymium magnets. Someday I'll clean it off and redo it.

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Here’s the setup on the inner CV joint. Works well. Love the steady needle 😀

4EA604ED-F258-4BA7-8CA0-4F800C4C243B.jpeg

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Those magnets look neat, did you make the brackets and heatshrink magnets to them?

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Brackets are from a local hardware store and modified. The thin neodymium magnets are glued on with loctite 638. 2 layers of shrink tube provide some protection against the elements since they can corrode. 

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