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Speedometer Gear Issues

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EDIT: READ THE END OF THIS THREAD FIRST.

 

So I searched, but couldn't find much on the subject. We all know you can remove the gear catridge from various Nissan/Datsun transmissions and match to whichever ratio you're using, but I've run into a snag. Mainly, I now have 4.11 rear gearing from a 90-94 Subaru Legacy R160 housing, and there are no more standard cars in pull and save to go yank a speedo gear cartridge out of.

 

One of my 510 buddies said to get a speedo gear reducer. I'm sure NAPA used to sell them, but I don't see anything available there or from Jegs or Summit, so I'm wondering if they died out due to not being needed, or I'm just not looking in the correct place.

 

The other thing I don't know is if the Subaru transmission gear cartridge even fits in the '77 goofy-shift trans I have. I think they do since Nissan made a lot of Subaru's diffs and trannies.

 

So far I can't find any other Nissan/Datsun with a 4.11 gear ratio. The '79 510 had a 3.45 or something, forgot to check on the '77 200sx. Most of the others had a 3.90 (stock 510). 620s usually got steeper gears IIRC.

 

The other option would be an aftermarket speedometer with an electronic pickup, but I'm still not sure how those units are calibrated? I would assume you have to enter your tire size as in a bike computer and then I would guess the magnetic sensor would read each time a full revolution was counted, and then report back to the computer inside the unit. Of course, these are kind of expensive units, from what I've seen.

 

I realize the car is going to be a race car, but I still need to have a speedometer that functions since it functions as a second vehicle right now, and even a race car needs to be able to measure speed on transit stages.

 

Anyone running different gears out there have any ideas?

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Holy shit, you don't say?! Mine had 4.375s but I'll take have Rick check the hollander tomorrow and see if they maybe have one of those. Hmm, those don't have tags on the diff though, I think they have them on the info plates on the door or under the hood don't they?

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This is information taken from a "Datsun competition parts manual, I do not know what year, but it has Items for the 620 truck, and L-20-B engines.

It is under "Speedometer Pinion" in the 240Z/260Z/280Z section

 

Available for a Z-car 4 speed, up to August, 1971, and all five speeds

32703-78100 16 Tooth yellow 3.364

32703-78101 17 Tooth Black 3.545

32703-78102 18 Tooth Blue 3.700

32703-78103 19 Tooth White 3.900

32703-78104 20 Tooth Red 4.111

32703-86401 21 Tooth Purple 4.375

32703-86402 22 Tooth Orange 4.625

32703-86403 23 Tooth Green 4.875

 

The manual also mentions that there is a different sleeve used to hold the pinion, depending on its size.

32707-78000 for speedometer pinions with 16 to 19 teeth

32707-86300 for speedometer pinions with 20 to 23 teeth

 

Available for a Z-car 4 speed, after September, 1971

32703-P2616 16 Tooth Yellow 3.364

32703-P2617 17 Tooth Black 3.545

32703-P2618 18 Tooth Blue 3.700

32703-P2619 19 Tooth White 3.900

32703-P2620 20 Tooth Red 4.111

32703-P2621 21 Tooth Purple 4.375

32703-P2622 22 Tooth Orange 4.625

32703-P2623 23 Tooth Green 4.875

 

The manual also mentions that there is a different sleeve used to hold the pinion, depending on its size.

32707-78000 for speedometer pinions with 16 to 19 teeth

32707-66300 for speedometer pinions with 20 to 22 teeth

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.....even fits in the '77 goofy-shift trans I have.

 

So this is a dogleg tranny????

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Yep, it is a dogleg/goofy shift, reverse in first gear position. It's a 6 speed. (5 forward, 1 reverse! :) )

 

DanielC, Jason, thanks for the info! This may help my choices at the local pull and save.

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datsun 79 620 had 4.11.... BAM! I need that one too... Ben?

 

 

The dogleg is a 63 series tranny, the '71B speedo drives won't fit. You need a gear from a 200sx or A10 tranny that had the dogleg. Dealer may be the only place to find one without a lot of bother.

 

I think the 510/521/610 and 710 4 speed drives will fit but I doubt they had 4:11s in them. My 710 has 4:11 but is an automatic.

 

I'll check some #s when I get home tonight.

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You know I was wondering about that, would the speedo drive be different if the car was automatic vs. manual trans? I was thinking they would be, but maybe not?

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The rear gear ratio alone doesn't determine the speedo cog, because tire size also has to be taken into account. Truck and Z cars used bigger tires than 510s.

 

Unfortunately finding a speedo drive for a 4.11 in a car is going to be next to impossible, since that ratio never existed stock with the 63A transmission. It was something you used to be able to order from Nissan Motorsports, but probably NLA.

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Hmm, that was something I was thinking of, but what about the Z car trans? I wonder if the guts of the gear cartridge are interchangeable? Might be able to cannibalize one and make it work. I don't worry about the tires so much, because that I can calculate a percentage off, as long as the speedometer is linearly incorrect.

 

I wonder about the standard trans. 4.11 geared Subis though. I would think they would have used the same gear cartridge. Going to do a Pull and Save mission tomorrow along with Pick and Pull up north, see if I find anything.

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The rear gear ratio alone doesn't determine the speedo cog, because tire size also has to be taken into account. Truck and Z cars used bigger tires than 510s.

 

Unfortunately finding a speedo drive for a 4.11 in a car is going to be next to impossible, since that ratio never existed stock with the 63A transmission. It was something you used to be able to order from Nissan Motorsports, but probably NLA.

 

The speedo drives where available for the dogleg through Nissan last year when I ordered them, I'll have to check again as I will need a new one again for the 4 door project to correct the speedo error.

 

I'll have a look around for the invoice, I seem to "lose" them frequently so my wife doesn't see them :cool: !

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How much was it I wonder? I'm working on a budget, hence the trying to find one cheap at a jy.

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In the competition manuals I have, (I have three) the speedometer information is only listed in two of them. In the two it is listed in, it is only in the Z-car section. I am guessing that Nissan thought if you were buying competition parts, you were smart enough to know a Z-car transmission would fit a 510, or a truck.

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I don't worry about the tires so much, because that I can calculate a percentage off, as long as the speedometer is linearly incorrect.

 

 

 

The same applies to tire size or gears. That's why the speedometer in my '74 620 reads almost right (less than 5MPH off @60, or around 8%) even though the speedo cog isn't in remotely the right application. The speedo cog is the one from a car that had 3.7~ rear gears and P175/70R13 tires, installed in a truck with 4.375 rear gears and 225/70R14 tires.

 

The speedometer will always be off by the same percentage across the sweep, the percentage is derived from rear end gear and tire size.

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I assume that with 4:11s you are reading higher than you are actually going. The gear you have is for a 3.889 diff so go up one tooth size this will slow the speedo about 6-7%.

 

32703 N9017 is the part number (>$15) for the 17 tooth pinion that fits the 200sx speedo drive for a standard with 3.889 diff.

 

You need an 18 or maybe even a 19 tooth pinion (if they exist) depending on the % over speed you are.

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Yeah I'm a badass. I cruise at 120 now. I go up to 140 if I want to pass people! :D It's actually really annoying. I marked some points on the tach in 5th gear to figure approximate "not get pulled over" speed.

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The same applies to tire size or gears. That's why the speedometer in my '74 620 reads almost right (less than 5MPH off @60, or around 8%) even though the speedo cog isn't in remotely the right application. The speedo cog is the one from a car that had 3.7~ rear gears and P175/70R13 tires, installed in a truck with 4.375 rear gears and 225/70R14 tires.

 

The speedometer will always be off by the same percentage across the sweep, the percentage is derived from rear end gear and tire size.

 

You know it's funny, that makes sense now, but the wagon I used to have had a 5 speed trans from a 79 510 and stock rear end gears, but the speedo wasn't linearly off. It was accurate around 30, then jumped out and was accurate close to 65ish, and then not after that. I was thinking the rear end gears and the speedo cog have to be matched, but if they're not matched, wouldn't that be two instances of being off, thus the non-linear offness of the speedometer?

 

To clarify, I'm thinking three circles. Speedo circle, rear end circle, and tire circle. If tire circle is changed, there's a set percentage of difference. But if the speedo is a 3.5 inch circle and the rear end is a 4.5 inch circle, then that relation is off, and the tires throw it off.

 

EDIT: Actually, now that I'm remembering looking at the speedo cartridges, some had a different gear, but also a different shaft diameter that turned on the gear, which would certainly cause different speeds if the there are two circles at the speedo cartridge.

 

Or am I misthinking?

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I think I figured out the speedo thing. I was incorrect on the cartridge having tow circles, because unless it has a gear reduction built in, the end size (speedo cable) will always be the same, so only the outer gear can change. Apparently took my unconscious mind to figure that one out! Anyway, I'll take a sample with me and go hunting for cartridges at Pull and save today. If I find one that looks promising, I'll try and get two. That way 510er will have one!

 

Okay, now I'm getting it. Grabbed my two old speedo cartridges from the previous and current 5 speeds. Both were 17 tooth, which should be 3.54 gearing according to the Z chart (they are both black gears), which is probably close regardless of sleeve difference. I'm just supposing here.

 

According to that chart, 3.90s would be a 19 tooth, and 4.11s a 20 tooth. So I think that's about right, because I have the 3.90 gear cartridge in now, and it reads high, but one tooth wouldn't make that much difference. BUT, one tooth with Z sized tires large tires, vs. 185/65/14s would be enough to make a substantial difference. I think a Z stock tire is 215/ something 14 isn't it?

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So right now, I'm 3/4 " taller than the original tire size with the 3.90 ratio. So I may need to go to a 21 tooth 4.375 to offset the tire size. I think I'll try and get a gear out of a 620 even though they're supposed to be different, that way I can at least figure out what the difference is. Plus a lot of 620s had 4.375 gears, or at least the last two I owned did. Actually so does my hardbody now. I wonder if I could use that cartridge?! :)

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Think of this problem this way. The speedometer is actually a tachometer, that is showing you what rpm the speedometer cable is turning. On the inside of a speedometer for a 1970 521 there is a note saying 1024 RPM=60 MPH.

You put a higher geared ring and pinion on your differential. Your driveshaft now spins faster for any given speed, and your speedometer reads too high, because all the speedometer knows is actually how fast the driveshaft is turning.

So you need a speedometer pinion with more teeth than what you have currently. That will slow down the speedometer cable.

The chart of speedometer pinions to gear ratios is not cast in stone, it could vary depending on the rear tires. If your tires are bigger than the tires used to make the chart, (that came out of something published around 1978) you may need a speedometer pinion for a lower rear axle ratio than you actually have.

In your case you may not need a red 20 tooth speedometer pinion for the 4.11 rear axle ratio you are running. You might get away with a purple 21 tooth speedometer pinion that is for a 4.375 rear axle ratio. This is a very common truck ratio. That may actually cause your speedometer to read a little too fast, but that is not an entirely bad thing, it might cause your actual speed to drop just enough to avoid a speeding ticket.

For what it is worth, a very handy way you can check speedometer calibration now, is to get a hand held GPS unit.

 

On a slight tangent, I got stopped for speeding in my 521, when I had a speedometer pinion for a 4.88 rear end, and my truck has a 4.375 rear end.

At the time I was stopped, the officer suggested I get my speedometer calibration checked. I took the truck to a place in Portland that does that, and got a slip on paper with actual speeds vs. indicated speeds on it.

When I got to court, the arresting officer asked if I had gotten my speedometer calibration checked, I told him I had, and he asked to look at the calibration slip. I handed it to him, and he looked at it, and then handed it back, and said "thank you".

When the judge called my name, the officer asked to address the court. The judge asked me if that was OK, and I said it was. The arresting officer then said that I had gotten my speedometer calibration checked, and it was reading about 11% low, and he then asked the judge to dismiss the case. The judge asked me if I had a problem whit that, I said "no", and the case was dropped. I thanked the officer in the hall outside the courtroom.

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