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240Z speedo is off


davek

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I recently installed an R200 with a 3.54 ratio gears in my 240Z. Ratio tested by counting drive shaft rotations per wheel rotation. It has the black plastic gear in the transmission but the speedo is reading faster than the car is moving. I will drive with a GPS later this week to get an accurate speed variation. The tranny is the BW T5. Both tranny and diff came out of a doner 1983 Turbo car.

Anyone have a known solution.

Everything I have read says the black gear in the one needed. The black gear was in the tranny unmolested when I bought it.

 

Stock 1973 240z speedometer.

Dave

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Tire size matters.  My gears work as expected to give an almost perect speedometer reading.  205-70-14.  25.3" diameter by calculator.  Smaller would read faster.  I've had a 3.54 and a 3.9 in it and the right gear gives the right speed.

 

http://tire-size-conversion.com/tire-size-calculator/

 

Does the BW use the same colors and numbers as the Nissan 71B and C transmissions?  Maybe that's the problem.

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If it was fine before maybe your diff got another gearing, pop cover and check. Or if your speedo shows to high(the same amount all the time) speed throw out the scale, you could just pop the speedo needle and put it back in pointing a bit lower. Iv done that many times when converting mph gauges to km/h gauges. Just give it a test drive before you put it back together.

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Wow, thanks for the quick replys.

It does have 3.54 gears easily checked by counting drive shaft rotations to wheel rotation. I did not drive the car before the tranny & diff swap I did with the donor car.

My tires are 195/70-14 very similar to stock 240Z tires so this is not the problem either.

Andreas I will check with a GPS are stated later this week if it is indeed a constant speed variation I will move the needle as you suggest. I hope it is that simple.

I'll reply Friday or sooner after my drive with GPS. Waiting on return of my fuel injectors. That's a whole other discussion.

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  • 2 weeks later...

I'm leaning toward a blue 18 tooth gear and see what happens. another $30 spent. I will try the rolling car/tire again to check diff gearing. 3.54 to 3.70 is pretty significant. Yes I know both wheel need to be on the ground or tuning the same.

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  • 2 years later...

I put a white gear in the tranny and gained a little ground. Reads 10-11 mph fast now.

Sorry I should have posted this a long time ago.

Been driving with GPS for a year or better. Time to start looking for a solution. I'm thinking swapping in the guts of an electric speedo and use the original face. Thanks what I did for my tach. I'm running. MS3X

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Not sure if it's the same as your problem or not, but my speedo seems to be fairly accurate up until I get up to highway speed (about 55) at which point the scaling seems to change and it jumps up 10-30mph faster than I'm going, essentially becoming useless. My intention is to take the speedo out and give it a thorough cleaning, but it hasn't happened yet so I don't know if that's the problem or not (for the record, I'm running a 3.7 rear with the cog for a 3.54)

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