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Speedometer Gear Issues


HRH

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Now we have the trifecta! I started digging through my old Nismo catalog, and I found the following page. The speedometer pinions listed on the first page are only for the Z car long tail transmission.

 

But here are all the part numbers needed for the short tail F4W63L transmission! I still may try and just make another groove in mine as I'm guessing the sleeve is fairly expensive. We shall see.

 

speedogeartable.jpg

 

http://www.youtube.com/watch?v=tMQa1-mToN8

 

I think I should put a big Ratt logo on the back window of the 510!

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Well, bad news. Just got back from Jaremko Nissan and I brought most of those part numbers, had him check up to 20 tooth and for the sleeve. They're all good part numbers, but NLA.

 

Anyone up in the Great White North have a line on those? I'm looking specifically for the 19 tooth (32703-78600)and 20 tooth (32703-14816).

 

The next step is taking my speedo stems down to my Datsun guru, chopping, welding, lathing, re-inserting! At least there's a way, but was hoping just to be able to get one.

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Well, bad news. Just got back from Jaremko Nissan and I brought most of those part numbers, had him check up to 20 tooth and for the sleeve. They're all good part numbers, but NLA.

 

Anyone up in the Great White North have a line on those? I'm looking specifically for the 19 tooth (32703-78600)and 20 tooth (32703-14816).

 

The next step is taking my speedo stems down to my Datsun guru, chopping, welding, lathing, re-inserting! At least there's a way, but was hoping just to be able to get one.

 

I shall telephone my guy today, which one do you want?

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One of the 19 and one of the 20 if they're available, part numbers two posts above. Provided they're not more than $20 each.

 

Available for order out of Japan only, no knowing wether or not the order will be filled until it arrives or is rejected by Japan. 6 weeks for shipping to Canada. Prices are high on these bits, 19 tooth $35, 20 tooth $18, sleeve $33, subject to fluctuations with currency, wind etc .... Oh yeah, subject to prepay to Nissan because JDM order :huh: !

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I dropped off the two gears at my Datsun guru/machinist's shop tonight, we'll see how it turns out. I'm optimistic it can be done without too much effort, just hope the 20 tooth is the right gear. I think it will be pretty close. I'll post some pictures if it turns out correct, then I suppose Owen will want me to make one for him too! :)

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Okay ladies and germs, are you ready for the next installment?! Learned a few things. Got the gear back today, it wasn't my Datsun guru's best work, but it's trial and error right now anyway.

 

So it's welded back together at the long length. I had to go over it with some sandpaper to smooth it out, and as I was looking at the sleeve for fitment, I realized there's a little tiny seal in there! So considering my Datsun guru had just done a little grinding with the air sander, the shaft isn't perfectly round anymore. Something I didn't think would matter. And actually, so far, it doesn't seem to matter too much so long as your speedometer cable seal is decent. I only took it for a 10 mile drive though, not a long trip in summer, so we'll see if it starts leaking in a while.

 

The remedy for that would be welding it, then lathing it as opposed to just hitting it with the 2" air sander.

 

As for the opposite notch, took care of that with the cutting wheel, then went back over it with a bastard file. Came out pretty nice, seemed to fit in fine. When I first took it around the block, I seemed to hear a little gear noise from it, but it may have been my imagination. And since it was either work or don't, I started rallying the piss out of it, and eventually it quieted down. It may have been the differential too, as I just changed out the conventional oil for Royal Purple and I hadn't driven it around yet.

 

Anyway, got it back to the garage and ran it up on the ramps and it doesn't appear to be leaking any worse than the little bit of oozing it did before.

 

The only thing you have to be careful about is cleaning off the cartridge. I put a few dinks in it while clamped in the vise grips, and they made it hang up on the case when I tried to reinstall. Quick hit on the grinder and they were gone, but just something to note. It's a really tight fit in the transmission. The slightest burr makes it a bitch.

 

As for actual speedometer usage, I think it's about 5-10 mph higher than actual speed, which is reasonable. Speedo says 60 when I'm at the top of 2nd gear shifting to 3rd, and realistically with 4.11 gears, I'd say it's closer to 50. The tranny is fairly close ratio and with the stock 3.90s I think I could barely get 55ish out of 2nd. I was going to take it out and time it against the mile markers but it was 11:30 and kind of dark. So I settled for screwing around and pissing off slow vehicles. :) The 4.11s really shit and git!

 

So that's about it. I'm using the 20 tooth red gear, and here are the pics. Oh, also the speedo shaft isn't hollow all the way down like I thought. It's solid, just hollow for the slit for the cable end.

 

speedogears7.jpg

 

speedogears8.jpg

 

speedogears9.jpg

 

speedogears10.jpg

 

speedogears11.jpg

 

speedogears12.jpg

 

speedogears13.jpg

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Alright, so guess what? I lied! Sort of. I did some mile marking today with the stopwatch and have it all figured out on my excel sheet.

 

The speedo is 5-10 mph off up to 51 mph as indicated on the speedo, which is actually 40.035 mph. Past that, it gets a lot worse. 60 is actually reached at an indicated 77 mph. 75 mph is a whopping 96 indicated. 100 mph is at 129 indicated.

 

YUCK!

 

Did 8 mile marking sessions at various speeds, averaged that out for a common multiplier, and found that if I limit 5th gear to 6500 rpm, I top out at 114 mph. If I go to 7000 it's 122. It's actually pretty good as I'm unlikely to be able to use that kind of speed while rallying given the power I have. I am probably getting a free 300ZX to strip soon, so I may have a VG30, in which case I'll need a longer trans gearing because that would have the hp to push the higher speeds.

 

The only thing I didn't do was check the mile markers against the odometer. My Datsun guru suggested that. I didn't realize how the speedo worked, even after looking at one torn apart in the junkyard. While the odometer is attached to the speedo cable drive via worm gears, the speedometer needle is actually a spinning magnet. You can (very slightly) adjust the distance between the pickup to slow or speed up the speedometer. He mentioned it's really, really sensitive. I may crack that open and see if I can't fix it that way. If not, it's either find another gear or just go with an aftermarket magnetic pickup electronic speedometer, which seem to be expensive, and HOMIE DON'T PLAY THAT! :D This is Ratsun, if there's a cheap way I'll find it.

 

On the plus side, I finally chopped up the juniper bush I yanked out of the yard. Think I'm going to sell the camper shell too. Looks better without. And damn, when I went to the dump, with me and the dog in the car and probably 40 pound of stump they wouldn't take, I cleared the scales at 4000 pounds. No wonder my mileage sucks!

 

datsunjuniper.jpg

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Remember when I said the speedometer is just a tachometer, for the speedometer cable? That is all it does, it is just marked in miles per hour, instead of RPM.

 

The odometer is just a counter, marked in miles. It counts the number of times your speedometer cable has turned, and it does not care if you went a mile in 30 seconds, or three minutes. (120 MPH, or 20 MPH)

Obviously, they are both getting their information from the same thing, the speedometer cable.

 

If you want them both to be correct, you have to get the speedometer cable turning the right RPM for the rear axle ratio, and tire diameter of your car.

 

You should still try to get the correct speedometer pinion first, before you try to make the speedometer accurate. It is probably possible to "adjust" or correct the speedometer a slight amount, but trying to make up for the wrong pinion might be out of the range of adjustment that is possible, but I do not know.

 

Adjusting the speedometer without getting the correct pinion will leave the odometer incorrect, because the odometer is just a set of gears, that convert 1024 RPM at 60 MPH to only 1 RPM, for the tenth of a mile wheel inside the odometer.

 

There is a very good possibility that once the odometer is correct, the speedometer will be also.

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I have a theory. Since I'm only going from 3.90s to 4.11s, the speedometer shouldn't have been far off at all. What I'm thinking happened is a combination of things. One could be the excessive vibration in the car due to jumping, harsh suspension, etc. has fluffled the speedometer.

 

Two, and I think this is more likely: I tweaked the magnet accidentally when I was changing out the speedometer cable. I also had a sealing issue at the back of the speedo cluster so I was reefing on the end to tighten it. I'm wondering if I pushed the back of the housing one way or the other, thus making the speedo off. When I examined the speedometer in the wrecking yard, it's a fairly fragile little thing. It would be pretty easy to bend it.

 

To have the speedo off by .785 is pretty huge. I calculated I would need 29" tires to make it correct as of right now. Going one size down in gear ratio, and a tire size up with the tires I'm running now should have been very close to accurate.

 

I'm at work now, but after I'll go check the odometer against the mile markers and see what happens. I wouldn't be too surprised if it's on, and just the speedo portion is off.

 

Who's Icehouse's hero? The Russian cosmonaut?

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So here's something interesting. Don't know why I didn't do this before. Went to 4lo.com, it has wonderful gear calculators. I backward solved for the new gear ratio, and with the tire size I'm running now vs the stock 155/80/13, the ratio would have been 3.84:1, which is darn near 3.90.

 

So the original speedo gear should have been fine to use in the first place, leading me to think either I screwed up the speedometer, or it just got old and maybe the magnet isn't working as well as it should. Rather interesting.

 

I'll check the odo, but I'm betting it's going to be off now that I'm taking into account the larger tire size.

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Yeah, basically that's about right, smartass! :D Never thought about the speedo just being wrong, but it sure makes sense now. Either that or the speedometers were never very accurate to begin with? I suspect me monkeying with the backing while attaching the speedo cable and 40 years of speedoing might have compromised it's integrity. Good thing I have another spare gear cartridge left with a black 17 tooth.

 

I'll try the odo thing with this gear and then with the 17 tooth if the odo is off.

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Yep, the odo is off. I read 1.1 ~ 1.2 miles at a regular mile. So looks like I'm going to stick the 17 tooth back in, then screw around with the speedometer magnet to try and tweak it back to normal.

 

Then went to some back roads and did some 0-60 tests. Best I came up with was 8.8 seconds, with my stopwatch, and roughly 77 mph on our crappy speedo, which I think I could have gotten in 2nd, but for some reason there's some lag time past 75, so I have to hit third, then it zips past on the needle.

 

0-75 was 13.9 seconds.

 

Or basically, my car is slow. :)

 

I tried to weigh it at the dump tonight, but they closed at 4:30, same time I got off work. Bummer.

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right now i can picture matt hitting his head on his refridgerator while holding a gps in one hand and keys in the other... haha Ill help you get all this figured out when i get back there in a couple weeks If you dont have a GPS i have a couple that are really accurate.

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HAHA! Lol! Totally. I'm way behind on tech stuff. Unless it pertains to carburetor tuning, then I'm pretty decent. :D Heck I just bought a book on EFI tuning since I'm going to be doing that when I convert the 510 over. Don't know much about it, hence the book. All the EFI cars I ever had, I just drove.

 

I've decided to fix the problem a different way. I'm going to stick in a VG30 and corresponding 5 speed, and I'll probably graft the guage cluster into the 510 dash. Or maybe just attach it with zip ties if I get lazy.

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