Sorry to hear of your speedo problems. Guess the instruments are still the Caerbont Caterham Branded instruments. I had this problem and you need to do 2 things. 1) check what the gearing is in top for your car with Caterham i.e. 22 MPH per 1000 revs. 2) borrow a Tomtom or other GPS and note down what your speedo is showing against the GPS and also what revs. as both instruments could be wrong. If you find that you are doing 50 when Tomtom is showing 45 you need to adjust the speedo. To do this at home just put car on axle stands with rear wheels off the ground. With ignition off. remove the speedo and obviously pull off the wiring connector block. Examine the back of the speedo and there should be a rubber grommet behind which there should be a slot for a small "jewellers" size screwdriver. Carefully ease down the connector block and there should be enough slack to reconnect the speedo below the dashboard where you can get to the adjustment slot and see the speed at the same time.
Then keep the revs steady at 50 MPH in top gear and turn screwdriver to get the speedo to show 45 MPH.. Providing you kept the revs steady you should find that 50 is correct with the TOMTOM. However is the Rev counter correct for your new 50? You can calculate what it should be at the new 50 from the revs Caterham have provided per 1000 revs. If the revs are wrong from your base MPH per 1000 revs then you will have to do the same exercise with the Revcounter.
It will vital to chock up the front wheels to prevent the car moving when doing this as you don't want the car to fall off the axle stands with the wheels doing 50 MPH !!!.
Don't worry if you find that the speedo readings are slightly out at set multiples of 1000 revs you always want the speedo to be a little fast say 68 correct at an indicated 70 MPH so you don't get caught on cameras. My speed shows correct reading and revs at about 40 ,but slowly shows higher speeds against actual the faster you go. Remember Caterham has a great range of gearing combinations due to wheel sizes and axle ratios so one speedo does all will always need adjustment depending on the model.. Mine has claimed top speed of 122, but speedo goes to 160 to allow for R500's and the latest 310 BHP models.
But surely he has a programmable speedo? If so, calibrating it is simply a matter of entering the correct 6-digit code to match the number of pulses/mile generated by the sender. Once that's done, the accuracy of the readings (speed and/or trip) can be refined by small changes to the code.
Yes, I'd have thought it was the electronic one with the code I putted.
Mine was 10% fast against my satnav, on delivery. I had some details that told you how to access the code and adjust it. I adjusted it by 7% to leave the speedo about 3% fast.
Yep, adjusted. 30 second job with a code. Just used the one for my tyre size from Johns link. May elect to adjust further after I've checked against sat nav at steady speed.
then a gearbox that doesn't fit,
"...although the image in the guide shows a flange that sticks out of the bottom of the box and potentially this rests on the mount. My gearbox does not have this."
leads me to ask if you have correct gearbox?
Do you have the gearbox serial number/format of the serial number so that you can check that you have the correct gearbox and not variant of the gearbox destined for another part of the world?
a one off wrong variant would explain why it appears that only you have a problem.
It might be unlikely but worth checking.
1988 1700 Supersprint
From what I know the speedo calibration is a very common issue. It's easily sorted once you know how but not mentioned in the handbook or manual.
I don't think the gearbox is a one off issue either.
I've driven 450 miles this weekend whilst away in Yorkshire. Before I left I'd raised the gearbox on 2-3mm thick spacers and I do believe that this has reduced the vibrations a little. However, the problem is not fixed. The vibrations are really annoying and I still believe the clearance tolerances on the Mazda 5 speed are too tight. I have spoken to a few others who describe similar issues. If you don't know what Caterhams are supposed to be like then my additional assumption is that there are many folk who think that this is normal. I beg to differ and need to get to the bottom of the issue.
I drove Caterhams 420 demonstrator on Friday and it had no more "vibration" than my supersport. Does sound like something is amiss. Can you get it to CC to get it up on a ramp and do a direct comparison with another?
I had a close look at my 6 speed whilst it was up on stands for a spanner check last week. It is adjustable laterally, a little and I remember taking quite a bit of time getting it exactly central. It's well clear of any rails; there is a bulge, forward on the left side of the box that is very close to the insulation, possibly touching, but I can't say I've noticed any undue vibration.
Is your box clear of the insulation? Is the vibration still high frequency?
Not sure how well it will work on the whole body / chassis unit but I've got an engine stethoscope you can borrow to give it a try if you want? Works well for finding engine vibration noises and vibrations, there's a long metal rod you touch to the part you want to listen to. You may find you can hear the buzzing getting louder as you get closer if you are lucky. Worth a try?
SV VVC 170 - 170.4 bhp @ 7100 rpm - 142.4 ft.lb. @ 4900 rpm