speedometer occilations

[Ian7]

Hi Guys

Anyone else out there with a Caterham brand mechanical drive speedo that occilates +/- 5 mph while driving at a steady speed?

Mine was fine when new, but occilations started at maybe the 500 miles-from-new point, now does it continuously regardless of what constant speed I'm doing.

 

Anyone else experienced this, and more hopefully, found a fix?

 

As I write this, I realize I've never looked at it during hard accel to see what its doing; stay tuned...

[yellowss7]

My Caterham speedo gave up the ghost after 582 miles, 8 years ago. I fitted a bike speedo that performs well.

 

But last week I finally got around to fixing the stock one, and found that although the quill that fits into the right angle drive was not broken, it did not turn the right angle drive. Fitted a new quill and presto, the speedo works. (quill was about $3)

 

Can't see much difference between the old and new quill, but possibly the old quill was worn a bit?

 

We'll see how long this one lasts. The Caterham speedo is notoriously prone to failure. Tom

[homebrew]

Ian - Sounds to me like something is binding up. Could be anything from the speedo head to the drive gear at the trans.

 

First thing I'd check is to make sure the cable isn't kinked. Speedo cables like to have long gentle bends.

 

If the cable isn't kinked, I'd disconnect the cable from the back of the speedo head and make sure the speedo head is free and not notchy or binding. Sometimes you can use the tip of your finger to turn the speedo, if not a very small flat blade screwdriver can be inserted into the speedo. You should be able to turn it enough to make the needle move. If it's hard to turn the speedo head will have to come out and taken to speedometer repair shop.

 

If the head looks ok then you'll need to look at the drive gear. If you have a right angle drive those things can bind up as well. Again remove the cable from the right angle drive and the drive from the trans. Just like the speedo head it should turn without any binding or notchy feel. The British made angle drives I've seen had a tendency to get pretty sloppy and work themselves apart. A speedo shop should be able to help you out with an angle drive if that turns out to be the problem.

 

Now check to make sure the inner cable turns in its sheathing. It shouldn't turn as easily as the speedo head because of the long run from the trans to the speedo and it should be lubed with grease therefore increasing it's resistance to spinning. If it's almost impossible to turn pull the inner cable out, wipe it down then relube with grease and try it again. Also check to see if the sheathing may have gotten pinched or burned from being to close to an exhaust pipe or such. This could cause the inner cable to bind.

 

Good luck. Hope this helps.

 

Jim

[Ian7]

Thanks guys.

 

Binding was my first thought as well, but at 1000 miles from new? I guess anything's possible.

 

More info:

 

Should have added that the occilation is very smooth, almost a perfect 'sine wave' effect. If its binding, its doing it very 'smoothly', as contradictory as that sounds.

 

Also noted that contrary to my initial post, the magnitude of the occilation seems to be proportional to speed, and while accelerating hard, it does still occilate.

[11Budlite]

Ian,

 

I worked for a Ford dealer back in the early 80's and 90% of speedo problems such as yours could be corrected by lubing the cable. A lot were new cars that hadn't been properly lubed from the factory. Ford even had a special speedometer cable grease which was lighter than wheel bearing grease. Not sure if there isn't something else causing your problem, but lubing the cable would be an easy first fix.

 

Bruce :7drive:

[Cherik]

I've had some troubles like this a few times and learned of potential causes:

 

1. cold weather - stiffens the cable and causes it to "jump". It's a square spring coiled cable, thus it is predisposed to this kind of studdering motion.

2. reverse installation - one end of the cable has a collar around it, make sure this is at the speedo side, not at the gearbox. It prevents the inner cable from sinking down, in which case it'll bottom out in the right angle drive and eventually loose touch with the speedo, it'll jump before failing

3. the cable is too long.. check this at the gearbox, by removing the cable from the right-angle drive and spinning it by hand, and have someone watch the speedo. Also, get a feel for how it spins.

If it's too long at the speedo side, it'll eventually take out the speedo. Check how deep it goes when the collar touches the speedo and make sure it'll still run free. It's best to take out the speedo and the cable for this test.

4. don't use ty-raps anywhere on the cable. It needs a large smooth arc. If it's kinked anywhere it'll bind up and eventually take out the short 1" cable segment between the drive and the right angle gearbox.

 

Probably more things, but that's what I could think off

 

Cherik

 

[Ian7]

" 2. reverse installation...

3. the cable is too long.. "

 

I started to type "...but they are stock Caterham parts installed by Caterham... "

 

then caught myself laughing out loud. I'll go check

[Cherik]

..one more thing, If you do find that the cable is too long e.g. 1/16" or 1/8", make sure to grind it off, as cutting leaves a messy end.

 

Cherik