D21 Datsun speedo reading 20-30kms fast

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rxsmiddy
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D21 Datsun speedo reading 20-30kms fast

Postby rxsmiddy » Sat Nov 26, 2016 9:29 pm

My speedo on my d21 Datsun is reading fast
It's had a td27t put in at some stage and unsure if the box they used was original or one from a terrano...... My speedo drive has 20 teeth ... I would need one with more teeth to slow the speedo down.... Has 30in tyres ..... Any ideas??
I'm struggling to find speedo drives

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Crash bandicoot
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Re: D21 Datsun speedo reading 20-30kms fast

Postby Crash bandicoot » Sun Nov 27, 2016 8:04 am

Margin of error is +/- 9kph so I don't think another factory drive will compensate enough to drop 20kms without changing the diff/s as well.

Jus buy a 100 dollar GPS and use that.
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Re: D21 Datsun speedo reading 20-30kms fast

Postby sirLachlan » Sun Nov 27, 2016 11:14 am

Can you be more specific with the margin of error . Eg it's 20 kph fast at 100 . Or tell us in a %

Get bigger wheels ha ha

I don't know anything Terrano specific . But one solution is just to move the needle so it reads right at 100 .
Thats all i did for 33s etc say the needle is 15 mm in the wrong place . Ping the needle over the 0 stop pin so it rests neutrally where ever it wants . Pull needle off . Move it 15mm push it back on . Ping it back over the 0 stop pin

Although you're still over paying on ruc if it over reads .


Depending on the mismatch you
Could also get a speedo converter from imperial to metric . It's a 1.6 :1 reduction box you put in the speedo cable . Eg it makes a kph speedo correct for mph or the opposite . Believe they are pretty cheap n cheerfully off the Internet

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Crash bandicoot
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Re: D21 Datsun speedo reading 20-30kms fast

Postby Crash bandicoot » Sun Nov 27, 2016 12:51 pm

There isn't a speedo that reads bang on that was made in the 80's and 90's. And Nissan is proof of that. Depending on what gear box transfer differential final drive and tyre size the vehicle was fitted with depends on which of three different speedo drives it was fitted with.

An example.......

So two Nissan navaras made one behind the other on the assembly line might have the same block, box ,transfer, diff's but one might be turbo the other non turbo...the turbo one gets bigger brakes due to being turbocharged so requires 16 inch rims to clear the brakes and ends up with a smaller rolling diameter on metric tires .....as apposed to the non turbo fitted with smaller brakes gets a set of 15 inch rims and 31x10.5's.

That as example...and creates a variation in road speed but not enough to warrant Nissan making a specific speedo calibrated to the differences in the same line of production.

In your case you could retro fit the donor vehicles odometer into your instrument cluster attempt to find a speedo drive that will fit, however I suspect if the speed reading difference is that great the speed drives will be completely different as well and will involve pulling the tail shaft to swap the worm as well.

Google speedo correction for a bit of kit that will reduce the speed of the cable from the box to speedo by 25%.....which leads to the last thing diff ratios...if the difference at a true 100kph is 25kp(speedo reads 125) then you need to go from 5.1 4.8 down to 4.1 at least to compensate. Which tells me the engine and box combo came from a truck with a h233b rear axle and r180 front diff and you'rs is a c200 rear axle and corresponding front.
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Re: D21 Datsun speedo reading 20-30kms fast

Postby rxsmiddy » Sun Nov 27, 2016 9:51 pm

The problem with the correction kits that I have found is they are for speeding up your speedo not for slowing it down,
I'm gonna ring Nissan on Tuesday and see what different options there are teeth wise......
I'm sure last time I gpsd it was reading 125km/h and I was doing 100km/h

rxsmiddy
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Re: D21 Datsun speedo reading 20-30kms fast

Postby rxsmiddy » Sun Nov 27, 2016 10:39 pm

Edit that, found some on eBay that slow it down ..... Just have to work out what will fit

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