Speedometer Pinion Gear

[Silky_Johnson]

My speedometer's been off since I bought my goon. I swapped out the rear end for a 3.7 and the speedometer still reads about 5-6 mph too fast at an actual speed of 35 mph. Maybe I'm wrong, but I think I need an 18-tooth (Blue?) speedometer pinion gear? I'm running an early 280zx five speed, although I don't think this makes a difference.

[ggzilla]

Five mph fast at 35 mph is 35/5 or 14% -- that's a huge amount. Anything over 10% is out of spec.

 

Different speedo gears are not guaranteed to fix it, in case there is some fixed amount problem too (like 2 mph off regardless of speed).

 

I would go from the 17T to a 19T pinion. They 20T would be too much I think. They are around $15 at the Nissan dealer. The pinion assembly is about double that, but you only need the gear.

[darrel]

Blue is supposed to be for a 3.7 rearend.

 

The other thing you want to consider, clean your spdo cable and housing, then make sure there aren't any kinks in the housing.

[datzenmike]

My speedometer's been off since I bought my goon. I swapped out the rear end for a 3.7 and the speedometer still reads about 5-6 mph too fast at an actual speed of 35 mph. Maybe I'm wrong, but I think I need an 18-tooth (Blue?) speedometer pinion gear? I'm running an early 280zx five speed, although I don't think this makes a difference.

 

It's nor clear what tooth gear you have. Blue is what is in there now or what you want?

 

If Blue then yes it's an 18 tooth.

 

If you are 5mph out at 35 then this (as ggzilla says) 14.28% out.

Going from an 18 tooth to a WHITE 19 tooth is a 5.555% change

Going from an 18 tooth to a RED 20 tooth is a 11.111% change

Going from an 18 tooth to a PURPLE 21 tooth is a 16.666% change (close as you'll get and only 1.2MPH out at 50MPH)

 

If you are absolutely sure this is a later zx 5 speed then 32702-58S21 is the purple 21 tooth.

[Silky_Johnson]

I'm not sure what pinion gear is in the car now. I'm assuming that it's a 15- or 16-tooth gear. Like I said, the speed was off when I bought the car. The blue gear is what I want.

 

The only reason I know about how far off it is is from driving by radar speed signs which are in some school zones (and no, I'm not driving 35 through any school zones during school hours). I definitely have a 3.7 rear end (which I put in), and I think I have the 8/78-7/79 280zx 5 speed, based on the higher revs in fifth gear. I'm turning over around 3200 rpms going what I think is 67ish mph (again only a guess).

 

I tried getting the blue pinion gear through Nissanparts.cc, but I got a message back saying the part was NLA. Would the dealer be any different?

[datzenmike]

Without knowing what exactly is in there this is a shot in the dark. The '79 model year 5 speed had 16,17,18 and 19 tooth pinions in them depending on the model of the car, the rear ratio, and tire/rim options.

 

BTW I've discussed this with several people and have no clear answer but yes the plastic gear can be bought separate to replace. Swapping the gears only, I don't think will work. Here's why... more teeth on a plastic cog will change the diameter. A smaller diameter and the teeth won't mesh with the drive worm gear. To large and it will be crushed. Whenever I change the ratio I swap the complete pinion assy.

 

 

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[Silky_Johnson]

So does anyone have the part number that I should look up for the whole 18-tooth pinion gear assembly?

[datzenmike]

If this is the first year ('79) zx tranny then 32702-R5618 (18 tooth) should work. Later trannys changed the placement of the pinion.

 

Be sure to verify this number with Nissan. About $25-$30

[Silky_Johnson]

Thanks Datsunmike. Merry Christmas!

[datzenmike]

You too!

 

BTW you have to drain the 5 speed or it will pour out the pinion hole. My gift to you. :lol:

[ggzilla]

Bruno, ask the Nissan parts guy if you need the whole assembly or just the gear.

 

Note that the assembly has the gears concentric, not to one side, so I think there is no difference.