LostSoul Posted November 12, 2023 Share Posted November 12, 2023 Hi there On a '73 Manta, how is the speedo driven please? How do I change/recalibrate/similar to make the speedo accurate for larger diameter wheel/tyre combination or lower final drive, if I decide to, please? Thank you LS Quote Link to comment Share on other sites More sharing options...
cam.in.head Posted November 12, 2023 Share Posted November 12, 2023 you have 3 basic speedo drive nylon cogs that are interchangeable for basic setting but any fine tuning for greater accuracy will probably have to be done with thespeedo head itself.never done it myself but may need to move the needle or adjust the spring tension ? ? or maybee different speedo head i THINK possibly the "W" marking ? ? Quote Link to comment Share on other sites More sharing options...
LostSoul Posted November 12, 2023 Author Share Posted November 12, 2023 Thank you! Where is the cog located please? (Hoping easy access at g'box end of speedo drive...) Can you help with a part number for whichever one of the three suits the lower final drive please? Thanks again. LS Quote Link to comment Share on other sites More sharing options...
Mickfrad Posted November 12, 2023 Share Posted November 12, 2023 (edited) Easy to change on the B series not sure about the A. Just on the side of the gearbox the speedo cable plugs into it. Edelschmiede has them, but not cheap. Best to take yours out and see what colour it is. Someone may have a different one you could try. https://www.edelschmiede.com/shop/#bms_q=Speedo drive Edited November 12, 2023 by Mickfrad Quote Link to comment Share on other sites More sharing options...
LostSoul Posted November 12, 2023 Author Share Posted November 12, 2023 Thank you, Mick They have a lot of great stuff! Based on zero knowledge or skills, I'm thinking more teeth on the cog equals slower drive to speedo so best for lower final drive...? All the best LS Quote Link to comment Share on other sites More sharing options...
cam.in.head Posted November 13, 2023 Share Posted November 13, 2023 yes as mentioned above .the b series ( and most other vauxhalls of the era) have the same setup. it will be obvious when you look at it. the red drive cog is the lowest on std models (used on 2 litre mantas) for the 3.44:1 diff. if the A uses the same idea you will see it on the side of the gearbox. maybee google some pics. undo cable to see colour. Quote Link to comment Share on other sites More sharing options...
Mickfrad Posted November 13, 2023 Share Posted November 13, 2023 If the cars on the road download one of the gps speedo’s onto your phone and take it for a spin. You never know it might not be that far out. Here’s a photo borrowed from the internet. Quote Link to comment Share on other sites More sharing options...
LostSoul Posted November 13, 2023 Author Share Posted November 13, 2023 Thank you both! Right now, on standard wheels and tyres, the speedo is uncannily accurate. If I prolong engine life by reducing revs at higher speeds - either with wheel & tyre combination or by changing the final drive - it will be too far adrift. I hope that changing this cog will get me back into the correct ball park at least...sounds like some trial and error will be needed between the three cog options. Good excuse to go for a drive! Thanks again LS Quote Link to comment Share on other sites More sharing options...
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