Escort mk2 speedo reads wrong

[muzzy]

Hi I drove my rebuilt RS today for the first time, and the speedo reads way out which surprised me as it runs factory wheels, std diff ratio and orginal green speedo drive ( now fitted to a 5 speed)
the reading are below
GPS Speedo
60 45
80 60
110 80
This works out reading low by 25%,
Has anyone have ideas on the possible problem
thanks

[wicko]

Factory wheels - but what size tyres?

[shepv8]

you did allow for the 5 speeds change in gearing?

[muzzy]

Factory vollante Mags with 185/65/13
As to the 5 speed bit, output shaft /diff ratio /tyre sets up speedo ,doesn't matter how many gears changing up to 5 th gear simply drops engine rpm

[foxtrot3]

Hi. even though you changed the gear on the end of the cable to your old one did you check how many teeth on the output shaft compared to your old gearbox? Start with a gear on the end of the cable with 2 less teeth and see what happens. Cheers MD

[muzzy]

The problem is the number of driver (spiral gear) teeth not the driven gear the 4 speed and 5 speed have different driver gears and they don't interchange, well not on my box! I have ordered a 33%step up ratio box that will fit under the dash

[Starlightblue]

where do you get the step up box from and how do they work?

[muzzy]

Originally Posted by Starlightblue

where do you get the step up box from and how do they work?

Most instruments places sell them , they are common fitment to Trucks, because of diff ratios
About the size of a box of matches, with 3 gears inside to provide the ratio you desire
I tested mine with a GPS and worked it out
They cut your cable( where you tell them and fit 2 new ends) so you can put the box in line
whole job $238 inc GST and delivery

[allanv6gt]

Whilst wasting some time on eBay....
I noticed two sets of Escort Mk2 instruments (2-dial only type), with speedo's having max value of 200 (100kmh at 12 o'clock) and 220km/h (vs 110-ish at 12 o'clock).
Dumb question, .....but you do have the right 5-dial RS instruments for your standard engine/diff don't you?

Unlike my first Capri v6, where with needle at 12 o'clock / indicated 60mph felt a bit fast. Determined later that it came with 1600GT instruments. It was actually 70mph with the right V6 instruments.

[muzzy]

Yes I have the factory dashboard for the RS the issue came about with the number of driver teeth in the 5 speed, there is 2 different types, bit random when you buy a 2nd hand box, the driven cant be changed, it would need to be 16th Burton's only sell 22-25

[muzzy]

I fitted it today , fixed up the speedo, same as the GPS up to 100K's (I didnt go any faster) all good
Brian