Dodgy speedo readings on Stag powered Estate

[flying farmer]

I used the estate to go to Stonleigh today (it is tax exempt, unlike the Stag), and despite it being on the road for two years, I think this is the first time I have used it on the motorway. I had an feeling something might not be right when I realised I was passing most things on the motorway at an indicated 75mph. It was only when I got to the A45 with its 60mph speed limit I realised that I was only doing an indicated 52 when following other cars. I was down to 32mph in the 40 zone, and just to confirm things on the way back I was doing 42 in the 50mph variable speed limit on the M6
It appeared to be 6-8mph out right through the speed range, so tonight I disembowled the speedo, and firmly gripping the internals I tweaked the needle round 7mph.
Hopefully this will prevent any future speed ticket embarassment
I had to do the same thing with the stag after its MOD conversion though that was only about 3-4 mph out
I don't think I have ever had a Triumph speedo over read, unlike all moderns, but at least there were no speed cameras when they were built. I am glad I was able to miss spend my youth when I did!
Neil

[GDPR]

Had a similar issue after fitting the 3.45 diff - 63 reading at gps 70. Changed the speedo to one from a 2500S with 840 turns per mile marked on the face instead of 1000, and now I have a speedo that reads just 3% fast.....reads 72 at gps 70 and 31 at 30....

[Westfaling]

I've had this issue a number of times when fitting overdrives to Hillman Hunter's, MGBs and Stag conversion to MOD. I've had the speedos re-calibrated. You have to measure the rolling circumference of the rear wheels and the number of turns of the speedo cable to the rear wheels and send it away and you can get a hopefully 100% acurate speedo - until tyre wear upsets it. I've used Speedograph Richfield but there must be other companies.
Nick

[flying farmer]

Part of the problem is the oversize wheels and tyres, but that makes the over read worse with increasing speed, a lot of this problem was simply the needle needed turning on the spindle. I used the original A type overdrive from the estate mounted on the back of an originally non overdrive stag box (£30 off ebay) as the correct speedo drive gears are a tad expensive, this was the cheapest way of getting an overdrive stag box with the right speedo drive gears to suit the estate. Unfortunately it wasn't reading quite right to begin with.
Neil

[Mike J]

Neil Have the same problem with by 3.45diff. Is it easy an easy job to adjust the speedo? Mike

[GDPR]

Just get the speedo from a 2500s ....