# How to know everything about your D21 including axle/ gear ratio?



## timidev (Aug 31, 2017)

So I just got a 1986.5 D21 v6 2wd M/T king cab SRW SE, sounds like it's a great truck that a lot of people love, but I'd like to know more about it. 

I'm currently swapping out a blown fusible link and a bad ecu due to it being hooked up for a jump backwards. I found a great thread about that on here, thanks for the help everyone! That same thread had a mention about finding the rear gear ratio and axle on the door. Said to look for a HG for limited slip and HF if not, and 46 after it would mean a 4.6:1. Dude said he was at 3k RPM at 55mph with his HG46, both him and the OP were in 5th gear by 30mph, same year v6. I found a HD16 as part of the vin? not sure if that's it or what it would mean, 1.6:1 wouldn't make sense right?


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## smj999smj (Jan 1, 2006)

If you want to know "everything" about your truck, then get a Nissan factory service manual. It's worth its weight in gold for information! Nico Club's site has free, downloadable manuals, but I don't know if they go back that far. You can sometimes find the Nissan factory service manuals on Ebay for sale for around $25-$35 and they are well worth it! 87-88 Hardbody manuals will be pretty much the same. In the meantime, here's a link to a VIN decoder:

Nissan | Vehicle Identification Number


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## jp2code (Jun 2, 2011)

I've got the HG46 axle in mine, and I turn about 3000 RPM at 60. You may have read my comment to that effect.










Your truck has a metal plaque, I think in the engine bay on the battery side up against the firewall.

Here's a comparison photo I made showing a buddy's truck with the HG41 on the LEFT and mine with the HG46 on the RIGHT.










Both engines running about the same RPM in 5th gear.


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