Speedo reads + 10%

[AMMO]

Other than sending the speedo to be recalibrated is there any way of changing the speedo drive gearing? Are there alternative speedo drives available for the gearbox? If so, can they be changed with gearbox in situ?

 

13" wheels, type 9 five speed box.

 

Thanks.

 

 

AMMO

[Taran Las]

Ammo,

 

I have the same problem - interested to hear what responses you get.

 

Phil Owen.

[F355GTS]

Me too I have a bike computer fitted which gives me the true readings but it would be good to find a 'proper' solution

 

Mark

[Dave H]

I had that problem with my old 4 speed box. Gave Caterhams a ring and they sent out a new speedo drive gear, standard Ford part. The bad news is the gearbox had to come out to change it, so it didn't get done straight away.

The other ways to change it is to replace the diff, or wheel/tyre diameter, which I guess you won't want to dosmile.gif

 

Dave H

[Toby]

I have the same problem with mine - presumably it also means that the milometer is clocking up +10% as well.

[V7 SLR]

Inside the back of the gearbox is a plastic gear driven wheel. There are a number of different gears for different wheel/tyre/diff combos. From new mine reads 70mph at 60mph (I found this out on a rolling road on Saturday) so I'm in the process of reviewing the options.

 

I am not sure how the plastic gears are distinguished. I have a feeling they are colour coded but that could be wishful thinking. I have a brown gear with a Caterham 6 speed box, 3.62 diff and 22 inch rolling diameter wheels.

 

To change the plastic gear, you have to take the box out as access is impossible otherwise. There's an indented plate, something like a core plug but bigger that you have to lever out gently with a screwdriver. Then disconnect the speedo angle-drive and you should be able to pull the plastic gear out.

 

Some people would advise you not to bother with this, and to go for either a hall effect transmitted (with a corresponding electric and calibratable speedo, which Caterham now sell) or go for the much more accurate pulse driven speedo mechansism which work off a sensor-probe pointing at the bolt heads inside one front wheel's brake disc.

 

The milometer will read over by the same percentage that the speedo reads over by.

[Pierre Gillet]

There is a VDO electronic speedometer fitted by Tony Martyr if I remember well. Does anyone know from where I can order it?

[Allan Haighton]

Merlin Motorsport at Castle Combe.

[AMMO]

My gear box has a small leak so may have to take it out this winter to fix (possibly upgrade the engine at the same time?). Could change the speedo drive then. Was hoping someone would say it could be done with the box in the car. Who knows for sure what speedo drive gears I need?

 

AMMO

[paul jacobs]

No one has mentioned using a larger tyre yet.

 

For example, instead of using 204/45/16 tyres, I used 205/50/16 and my speedo was as near perfect as it is likely to get, up to 90mph it was true, according to the RR that I was using, at 100 mph it was under 2 mph fast.

 

Of course that brings other factors into play, but personally I needed the extra ground clearance, so all I can say is it worked for me.

[AMMO]

Paul

 

Thanks for the suggestion but I like my 13" wheels and tyres. I'm not willing to raise the gearing 10% so my speedo reads correctly. . The setup I currently have is to my liking on my road car with a 3.92 diff.

 

AMMO

[Tony Martyr]

The VDO unit I fitted enables your to change wheel sizes and reset the calibration via adjustment on the display and it fitted in the original 4 inch hole.

I used a GPS unit to calibrate at 40 and 80 mph and it has worked consistantly in fine and foul weather on road and track. Contary to fears expressed the magnets have not come off the prop-shaft. It has a nice clear kilometer and mph display which is good for France. Down side is the LCD odometer is very difficult to read from normal driving position

[AMMO]

Tony

 

Does it match the older style VDO istruments? Mine has black face with white numbering and illuminates green at night. Where did you get it and how much did it cost you?

 

People like Speedy Cables will charge around £50.00 to recalibrate a speedo. Might as well put the money towards something a bit better.

 

AMMO

[NickD]

VDO used to make (& Caterham used to stock) 2 different speedos. These were geared at 1000 or 1100 revs/mile. The 1000 rev/mile unit was normally supplied with cars fitted with a 3.92 diff. Changing to the 1100 unit would therefore give you a 10% slower reading.

There are also several different speedo gears for the type 9 5-speed box. The drive gears on the gearbox mainshaft are available with 6, 7 or 8 teeth and the plastic driven gears with 22, 23, 24 & 25 teeth. The usual Caterham fitment was 7/24 with a 3.92 diff. Fitting the 25-tooth gear (Ford p/n 6011057) would slow the speedo down 5%. Otherwise the only useful combinations are the 6/22 & 6/23. Changing the plastic driven gear can be done without taking the box apart but is almost impossible to do with the box in the car. Changing the steel drive gear requires the tailshaft to be removed from the box.