Volvo RWD 120-130 Forum

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Finished installing m46 Need help with speedo 120-130

Just installed my m46 into my 122s with a b20 and I'm wondering how can I fix the speedo for it to measure the speed correctly? Thanks








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Finished installing m46 Need help with speedo 120-130

You can crack open the speedometer and adjust the clock spring inside. Tighten the spring, the speedometer will go slower. Loosen the spring, the speedometer will go faster.

The factory uses a little drop of paint to keep the spring from moving after they calibrate it. I used a drop of fingernail polish.

The way I calibrate my speedometer (my odometer was reading about right-> within 3% or so, and the speedometer was reading way to fast), remove instrument box (I built an electric temperature gauage, so I didn't need to remove the mechanical one, also be careful of the live wires touching ground-> tape them up), open up instrument box (the chrome is pinched on both sides, so pry open the box and remove the speedometer face -> some tiny screws), set the instrument box up so you can get to the clock spring ( I posted pictures of the clock spring a while ago, I can repost them if you want to go this route) and be able to put the speedometer face back on to see were the "ribbon" is reading. Ideally, three people and two cars would be the best way to do this-> One person/car (with an accurate speedometer) driving a certain speed next to the car you are setting the speedometer, the car you are setting the speedometer -> one person driving, and the other person adjusting the speedometer. After you think the speedometer is set, check it against different speeds with your pace car. This take a while, but I got my speedometer within 5% of right speed.

Paul








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Finished installing m46 Need help with speedo 120-130

An easier and more accutate method to check against while adjusting the speedo would be to use a GPS. This then will become a two man job.








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Finished installing m46 Need help with speedo 120-130

Any speedometer shop will be able to put your car on the dyno, measure your speedometer error, and custom build a little gearbox that will get you within 1 or 2 percent of true speed. Be sure to have the tires that you are going to use for the rear on the car when you take the car to the shop as well...hope this helps.







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