As I start to get used to my Sprint auto, I notice that the speedometer is underreading.. Or it feels it!
I'm pretty sure it's the correct unit for the car (see pic) but looking through my parts catalogue I can see there were different units for the engine ranges. Anyone know if autos had a specific unit? I wouldn't think so.
I guess a different speedo drive may have been fitted at somepoint... I haven't got much long term history with the car.
Not a big issue but one I would like to add to the list of jobs over winter!
Any advice appreciated.
Regards MC
Matt Cotton
TDC Oxfordshire Area Organiser.
TDC/TSSC group meeting - 3rd Tuesday of the month
AFAIK all Dolomite speedos are calibrated the same, ie 1000 Turns per Mile (TPM) The different part numbers are due to to the number of different fonts and scales on the various models. discrepancies from differing diff ratios is made up for by different gearing in the gearbox drive.
As the same trans is used on all auto Dolomites, the gearbox driven gear governs accuracy, it's entirely possible that an 1850 auto gear could have been fitted in ignorance by a previous owner (the 1850 auto being the ONLY one with a taller diff)
It's also possible to just have a lazy instrument, but the first thing i'd do is take it out with a satnav and check it against that in a number of constant speed conditions to determine what the error (if any) is!
The speedo will also under read if the nut is not completely tight on the rear trans/prop drive flange as this locks the drive gear in place on the tailshaft by friction alone (no keyway) I've actually seen this 2 or 3 times on auto cars.
Steve
'73 2 door Toledo with Vauxhall Carlton 2.0 8v engine (The Carledo)
'78 Sprint Auto with Vauxhall Omega 2.2 16v engine (The Dolomega)
'72 Triumph 1500FWD in Slate Grey, Now with RWD and Carledo powertrain!
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My 1850 auto is the same Matt, i did what Steve suggests and went out with a satnav and found at 25mph on the speedo i was doing 30mph As it's not a daily driver i have just put some tiny marks on the glass at 30 40 and 50mph. Strangely the trip and milometer are correct.
Hi Matt, The Sprint Auto speedo driven gear should be a 219002 which according to my chart has 21 teeth and is coded green. Availability wise it is NLA but I reckon an auto transmission specialist might be able to help.
I have a note that the Early 1850 auto-box has the same driven gear as well. Strange that as the 1850 diff; is not the same.
Use an activity tracker app to check the trip meter and odometer. If they are reading correctly as per dollyman's experience then the speedo is getting the correct 1000 revolutions per mile. Incorrect speed reading is then just a lazy unit. They can be recalibrated by specialists.
There is a company called Speedy Cables who can refurbish and recalibrate speedo's. Check the website for info although basically you find a flat bit of road or drive, undo the cable at the clock and have the end poking out below the dash or through the speedo hole. Stick a strip of paper on the cable pointing to 12 o'clock. Likewise a chalk mark on the rear tyre. Push the car one complete revolution of the tyre and have an assistant count the turns of the speedo cable. Thats all they need to recalibrate the clocks. Handy if you change wheel sizes or as my friend does quite often, is fit 5 speed gearboxes to MGA's. Beware it might be more than 1 turn of the wheels and it is surprising how far the car can travel.
Hello folks.
As it's not a daily driver i have just put some tiny marks on the glass at 30 40 and 50mph. Strangely the trip and milometer are correct.
