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?
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?
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?
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.
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.
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?
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.
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.
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!
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…).
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…
Just noticed I never responded with the fix for this!
In the end it was caused by the worm gear on the gearbox output shaft being a little loose.
So nothing to do with right angle drives, cables, speedo etc…
This worm gear is held in place purely with a friction joint that is tightended by a bolt (from memory) on the end of the output shaft.
When my engine was out (about 16,000 miles ago) we did a minor maintenace overhaul on the gearbox too and found this joint loose.
Was just about to reply with the same answer and then realised how old the thread was - I had a similar thing happen with my 5 speed box (reported on another thread ages ago) jumping speedo then nothing at all. Careful use of a variable speed drill showed that the speedo and cable were fine so it was the drive gear on the output shaft of the gearbox…
Over a weekend, my father and I then took the engine and gearbox out, tightened up the nut on the end of the output shaft and then put it all back together. Fixed. (we did sort a few other things out at the same time mind!)
I have replaced my speedo drive on my 5 speed gearbox, I did it from inside the cab, mats out insulation off then cut a small triangle of glassfibre away from in front of the gearstick then with a long socket extention you can remove the 1/4" whit hex head screw that holds the fork clamp. Then with a coat hanger suitable bent the speedo drive will lift out. Easy!!
Yes, that bit is relatively easy, however, if the drive gear that’s on the gearbox output shaft comes loose (i.e. the gear in the gearbox that drives the speedo drive) you’ve got no other way of fixing it than taking the engine out…
It’s very frustrating as it’s a very simple fix (you just re-torque the big nut in the propshaft flange on the output drive shaft from the gearbox) once you’ve you’ve got the engine and gearbox out.
I have a new one (+2 speedo cable) I bought by mistake for my S4. Its a little longer than the baby elan. Any one needs it they can have it for 75% of what RD charges.
Matthew
