Speedo/Speedo Cable question

[peterako]

Hi there,

I couldn't find any guidance for this in the archives so here goes:

My Speedo has become a bit unreliable....(was very good)

After the car warms up a bit the read speed will drop on the
speedo (about 10 to 20 mph below actual).

If I lift the pedal off the throttle the speedo will jump to the
correct reading.

Throttle on again, speedo needle drops, and stays steady.

Any guesses as to what could be the cause.

Also....is there any easy way to get at the speedo drive on the
gearbox.

I have a 5 speed (Lotus box). The drive appears to be on top
of the gearbox rear and access is extremely tight. REALLY tight.

Thanks in advance,
Peter 1973 +2S 130/5

[types26/36]

After the car warms up a bit the read speed will drop on the speedo (about 10 to 20 mph below actual).
If I lift the pedal off the throttle the speedo will jump to the
correct reading.
Throttle on again, speedo needle drops, and stays steady.
Any guesses as to what could be the cause.

Also....is there any easy way to get at the speedo drive on the
gearbox. I have a 5 speed (Lotus box).

Well as no one else has replied I'll take a guess...but it is only a guess.
It would seem that while torque is being applied to the speedo via the cable (while under power) there is some resistance in the speedo, under freewheeling the amount of torque is reduced and the speedo works O.K.
Now that would indicate to me that there is some sort of problem with the speedo mechanism.....draging.... seizing....very tight? I dont think the cable or anything is slipping or the speedo would be eratic and jumping.
Try disconnecting the cable off the clock and turning with a piece of old speedo cable or a small screwdriver that will fit in the square hole, there should be some resistance but it should not be excessive.
As for getting to the speedo drive, I did once hear that you have to remove the gearbox on a 5 speed but I do not know, surely even Lotus wouldn't make it that difficult
What does the workshop manual say on the subject?

[john.p.clegg]

Well seeing that only Brian has replied here's my twopenneth

Seems to me that torque is the problem but my idea is that under acceleration the g/box is twisting slightly altering the drive angle whatsit and throughput,under idle/decelleration it regains its normal configuration?

Any other takers?

John

[peterako]

Hi Brian,

Workshop manual:

Disconnect the cable from behind the speedometer.
Disconnect from gearbox.
Remove cable through the dash....

Easy.....

No specific info (as far as I've seen) on the drive.

All pics with the drive seem to be of the 4 speed.
Teh 4 sped drive appears to be on the side of the gearbox.

I'll start with the speedo and see if it's a problem at that
end. I live in hope!

Thanks to both you and John for your replies!
(I was leaning towards John's analysis, but hoping...hoping...
that I do not have to touch the drive)

Take care,
Peter ... 1973 +2S 130/5....today 40mph in 5th at 3,300 rpm!!!

[alaric]

I can't see how this can be due to the speedo itself. To test the speedo, if you can get the drive end out of the gearbox, hook it up to an electric drill...

My guess is that the drive gear in the back of the gearbox is worn or the speedo cable is worn. The difference under load may be a slight fore and aft movement of the drive gears under load - again a guess - that means that some of the teeth are not engaging properly. Or maybe the position of the cable moves a bit and doesn't engage as well at the gearbox end - maybe it's loose.

I have a 5 speed box sat on the floor of the garage, and have the speedo right angle drive removed etc - would it help if I took some photos to illustrate how it works?

Sean.

[types26/36]

. To test the speedo, if you can get the drive end out of the gearbox, hook it up to an electric drill....

Well I wouldn't spin it with an electric drill, its considered bad practice by some people. Speedo heads have gears,shafts and other parts made from plastic, brass and other delicate material...a bit like a watch.
If the parts need lubrication and it is dry,tight or starting to seize spinning it at an imediate 2500 rpm plus may damage the internals beyond repair. When a speedo is driven from the car it is a gradual take up of the drive and less likely to damage anything even though it may be dry.
The choice is yours.

[stuartgb100]

Providing the 'user' has a variable drive drill, I see no problems.
Ok, user must also be gentle in their approach as the drill starts, and keep revs to a minimum.

Regards,
Stuart.

[types26/36]

Providing the 'user' has a variable drive drill, I see no problems..

True, but not everybody has a variable drive drill and I think that even less people would consider the consequences befor attacking it with a drill.

[stuartgb100]

Where necessary, we've now alerted them.

And on the same point, the drill needs to drive the gearbox end of the speedo drive in an anticlockwise direction (SLOWLY)

Yes, initially, I went clockwise too (Northern Hemisphere down the plughole).

Regards,
Stuart.

[stuartgb100]

If Sean can get you pictures ............ brilliant. I can do nothing until after the holiday.

However, am about to swop Lotus 4 speed for Lotus 5 speed gearbox. Well, sometime in the New Year.

Just had problems with my Speedo. Turned out to be the drive unit, and removed it okay (on the 4 speed, mounted on the side of the box).

Looking at my replacement 5 speed Lotus box (the speedo drive is missing)..... it's clear that it would be a vertical fitting, approx 3 - 4 inches behind the gearlever. And that IS a challenge !

Would dropping the gearbox support bracket (with support) give enough access?

Regards,
Stuart.

[alaric]

I was meaning the gentle application of a variable speed drill - I certainly wouldn't use a high speed drill - I'd start it rotating very slowly, with the torque setting low - I have a battery powered drill with a torque setting that would be quite safe to use for this, and that's what I had in mind. I'll endeavour to be clearer next time.

Sean.

[M100]

From memory (and it is hazy on this!) the speedo is something like 1000 revs per mile. So 1000rpm = 1 mile per minute = 60mph. Ramp it up over 6 or 7 seconds and it's no worse than driving on the road.

If you get steady readings at the speedo head with the electric drill then I'd check the speedo cable has no kinks and is not getting trapped somewhere. Bit of a bugger if it turns out to be a gearbox problem though.

[peterako]

Hi Guys!

Many thanks for all your replies.

Sean is going to post some pics for me, which will be
most helpful.

I'm going to try some of the suggestions out, hoping that it's a
speedo problem! But mentally prepared for a gearbox one....

I'd naturally revert to reading the Rev counter as a Speedo
except that a previous owner put a stupid 12 inch steering wheel
in and I can't see from 2000 to 3000....hopefully will be sorted
soon if that steering wheel IO bought on eBay ever arrives!

Happy Christmas to you all.....not too much time on the Elans
now!!! Relax!

Peter 1973 +2S 130/5

[ppnelan]

It IS possible to remove & replace the speedo drive gear on the 5-speed gearbox without removing the gearbox or it's mounting - at least it was on mine. You need small hands, a lot of patience (you need that for most jobs anyway ), and probably a cut-out in the fibreglass just behind the gear lever aperture (thanks to a previous owner for that...).

Matthew

[alaric]

I finally managed to get out to the garage and take some photos - all presents are now wrapped and ready to go - always seems to be a last minute effort...

Hope the pics help.

Sean.