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Location:
Brisbane
Registered:
May 2002
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Speedo drive gears
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Fri, 05 December 2003 00:26
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Hi all,
Now that I've installed my new diff, my speedo is going to read completely wrong. I now have a non-standard gearbox (Mk4 W58) and a non-standard diff ratio (was 4.1:1, now 3.5:1), so it's anyone's guess what the speedo is going to do!
Clearly I'll have to change one or both of the gears inside the gearbox which drive the speedo cable. What I'd like to know is, how do I calculate the gear ratio I need to make the speedo read correctly? Apparently Toyota speedo's are set up to read 100km/h at X rpm of the speedo cable, so if I can find out what X is I can figure out the rest! Can anyone help me out here?
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I supported Toymods
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I renounced punctuation
Registered:
May 2002
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Location:
Menai area of Sydney
Registered:
June 2003
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Re: Speedo drive gears
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Fri, 05 December 2003 02:36
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All I did with mine is, I know that I have a 33 toothed gear in there at the moment, and my speedo reads about 9% high (I know what it should read from before I did the conversion
so 33 + 9% is 36 teeth !!
The problem is that toyota only make 32, 33 and 34 toothed cogs for the w58 
And I *think* the cogs between w50, w58 and auto are all different sizes, but I could be wrong
Norbie, tell us all the specs you can think of
Diff ratio
Speedo Drive teeth
revs in 4th @ 100km/h
both before AND after
It will help us decypher the code
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Speedo drive gears
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Fri, 05 December 2003 02:59
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you might be lucky and have the rev/km printed on your speedo dial (or mechanism)
iirc, a KE30 one is something like 600rev/km. (the KE10 one is 1000rev/mile 
for the K boxes the ratios available are 5/19, 6/20, and 6/22
the 5 and 6 tooth worm drive gears are different diameters, but the 20 and 22 teeth driven gears are same and can be swapped.
if you pull out the driven gear, it will probably have the ratio printed on the plastic gear, or on it's shaft. if the drive gears are same number of teeth, i would guess that they are same diameter....
Cya, Stewart
edit: oh yeah, so pull out your instrument cluster, pull out the speedo, and the revs/km should be printed on it somewhere.
[Updated on: Fri, 05 December 2003 03:02]
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Location:
Brisbane
Registered:
May 2002
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Re: Speedo drive gears
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Fri, 05 December 2003 03:05
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Cruzsida: The worm gear on the output shaft comes in 10 and 11 tooth varieties, so if you swap this as well you should be able to get the ratio you need.
I don't know how many teeth my current speedo gear has, but I'll check it out this weekend. It's not really relevant though because the speedo wasn't accurate before I changed the diff ratio! That's why I'm trying to find the actual formula to calculate the gear sizes you need.
I'll try my luck with the local Toyota parts dealer, but I doubt I'll get anywhere...
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Re: Speedo drive gears
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Fri, 05 December 2003 03:18
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OK then, if someone can tell me the ORIGINAL ma61 manual teeth (32 i think), and what diff it went to, and how many revs it pulls, I should be able to figure it out
And regarding my gear, the number of teeth on the output shaft doesnt matter a shit, its the physical diametre of the worm gear, and they different pitch of thread that makes the difference
But in saying that, I suppose the more teeth you have, the closer they are together, and hence a smaller pitch.
I just plan on taking my speedo cog somewhere, and getting someone to machine up a 36 toothed gear, OR, when I get my odometer fixed, get them to recalibrate the speedo to read 9% less (if this is possible, it will be ten times easier).
They will have to recalibrate the tacho for an 8 anyway
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Speedo drive gears
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Fri, 05 December 2003 03:27
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| Norbie wrote on Fri, 05 December 2003 14:05 |
That's why I'm trying to find the actual formula to calculate the gear sizes you need.
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oohh, you want actual numbers yayy...
okay
find the rolling diameter of your tyres in m. (RD?)
find number of revolutions per km of the tyres (TR?),
TR=1000/RD
then multiply by the diff ratio (DR) to get driveshaft revs/km (DSR)
DSR=TR x DR
the speedo driven gear will be running at driveshaft revs.
now, to find speedo cable speed (SCS) you need to facter in the worm gear teeth (WGT) and driven gear teeth (DGT)
SCS = (DSR x WGT)/DGT
the SCS will be in revs/km, which should be printed on your speedo.
hth 
Cya, Stewart
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Speedo drive gears
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Fri, 05 December 2003 03:38
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| CrUZsida wrote on Fri, 05 December 2003 14:18 |
And regarding my gear, the number of teeth on the output shaft doesnt matter a shit, its the physical diametre of the worm gear, and they different pitch of thread that makes the difference
But in saying that, I suppose the more teeth you have, the closer they are together, and hence a smaller pitch.
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how do you figure that the number of teeth on a gear don't matter? the whole point of a gear as that the teeth engage and you can work out the gear ratio. the same applies for worm gears, which are just "very very helical cut" (tm) compared to a straight cut gear.
Cya, Stewart
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Re: Speedo drive gears
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Fri, 05 December 2003 03:44
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Coz the worm gear is rotating ALONG the teeth, not perpendicular to their orientation, as is the case in all other gears.
Its the pitch that matters, not the number of teeth
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Location:
Brisbane
Registered:
May 2002
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Re: Speedo drive gears
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Fri, 05 December 2003 03:48
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It's not really valid to say the pitch matters and the tooth count doesn't, because they're both closely related! For a gear of any given diameter, an increase in pitch must result in a decreased tooth count.
Oldcorollas: thanks for that, I already know how to figure everything out right up to the output shaft speed, but it's the part from there which has me stumped. If I know the revs/km figure I'd be right, but I can't see it printed anywhere on my digital speedo...
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Re: Speedo drive gears
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Fri, 05 December 2003 03:54
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| Norbie wrote on Fri, 05 December 2003 11:48 |
It's not really valid to say the pitch matters and the tooth count doesn't, because they're both closely related! For a gear of any given diameter, an increase in pitch must result in a decreased tooth count.
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This is why is stated this after
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But in saying that, I suppose the more teeth you have, the closer they are together, and hence a smaller pitch.
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| Norbie wrote on Fri, 05 December 2003 11:48 |
but I can't see it printed anywhere on my digital speedo...
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I got a spare Analogue lying around if ya wanna trade??
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I supported Toymods
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Location:
Sydney
Registered:
May 2002
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Re: Speedo drive gears
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Fri, 05 December 2003 03:58
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try working that out by using the figures that came with the arristo gear.. arristo RD diff ration gear count etc.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Speedo drive gears
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Fri, 05 December 2003 04:04
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| Norbie wrote on Fri, 05 December 2003 14:48 |
I already know how to figure everything out right up to the output shaft speed, but it's the part from there which has me stumped. If I know the revs/km figure I'd be right, but I can't see it printed anywhere on my digital speedo...
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well, use the original measurements of the car, ie wheel diameter and speedo gears.
| Quote: |
the speedo driven gear will be running at driveshaft revs.
now, to find speedo cable speed (SCS) you need to facter in the worm gear teeth (WGT) and driven gear teeth (DGT)
SCS = (DSR x WGT)/DGT
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using the original measurements will tell you how many speedo cable revs per km there are for the factory specs.
if can you tell me what the stock wheel diameter, diff ratio and gear teeth count are, i will tell you what the speedo is rated at.
CrUZsida: oki, whichever way you wanna look at it. i just find it easier to calculate the movement ratios in terms of teeth, which are directly proportional, rather than the angles of the teeth which are a little harder to measure.
both sets of teeth are rotating round their respective shafts, the same as happens in a gearbox with helical cut teeth, just having a very helical cut allows you increase the drive:driven ratio, and also allows you to rotate the gears orientation with respect to one another.
Cya, Stewart
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Re: Speedo drive gears
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Fri, 05 December 2003 04:04
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| gianttomato wrote on Fri, 05 December 2003 11:55 |
The number of teeth is the whole point so that you can work out the gear ratio. The pitch is only relevant insofar as gear meshing is concerned.
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Actually GT, if you think about it for a sec, pitch=number, as Norbs stated, they are directly related when you limit the length of the gear.
A 5cm gear with 50 teeth has a smaller pitch than a 5cm gear with 10 teeth.
But a 25cm gear with 50 teeth has the same pitch as a 5cm gear with 10 teeth.
So its actually pitch that makes the different, number of teeth only matters when the length of the gear is fixed.
But back to topic. Some manual ma61 stats PLEASE
Oh yeah, Norbs, is the MK4 W58 speedo gear the same physical size (diametre) as the MK2 W58?
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Speedo drive gears
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Fri, 05 December 2003 04:18
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| CrUZsida wrote on Fri, 05 December 2003 15:04 |
A 5cm gear with 50 teeth has a smaller pitch than a 5cm gear with 10 teeth.
But a 25cm gear with 50 teeth has the same pitch as a 5cm gear with 10 teeth.
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oki, say you have two worm drive gears, one with 50 teeth, and one with 10 teeth, both with the diameters you said.
now rotate them one revolution.
how many revolutions of the DRIVEN gear will occur? ie how many teeth will the driven gear turn by?
50 teeth and 10 teeth respectively.
pitch makes a difference for same diameter gears, but it is still the tooth count that is important.
if you have 2 5cm gears, but one is 1cm wide, and one is 10cm wide, you have different pitch, but same teeth count. the 10cm wide gear cannot have as large an angle between gears as the 1cm wide one, but the ratio of gear movement is still the same...
with a gearbox, if you give the gears a helical cut of sayy, 5 deg, it doesn't change the ratios just because there is an angle.. same goes for diff, which is exactly halfway between gearbox and speedo drive situation...
all i can say is (apart from the theory being correct) is that i have manually tested the 5/19, 6/20 and 6/22 ratios on the K boxes, and i know this to be true.
Cya, Stewart
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I supported Toymods
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I renounced punctuation
Registered:
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Re: Speedo drive gears
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Fri, 05 December 2003 04:38
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Peewee, you're just complicating a relatively straight forward problem by talking about pitch. No offence.
Anyway, as it turns out, Norbie you are shit out of luck anyway.
For the W5x boxes, output shaft gear has 10 teeth, and the speedo drive gears come in 30, 31 or 32 teeth (just got off the phone to Rod Hadfield at CRS). The maximum amount of correction you can get is 6%.
Speedo corrector box for you!
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Location:
Brisbane
Registered:
May 2002
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Re: Speedo drive gears
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Fri, 05 December 2003 05:19
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Thanks. I'll go with the speedo correction device if I have to, but I was kinda hoping to do it the "right" way. 
GT: the output shaft gear is available in 10 and 11 tooth varieties according to this thread. I refuse to believe the correct gears aren't available; I pulled my 3.5:1 diff out of an RA65 Celica which originally had a W58 in it! I suppose one approach is to find another RA65 and steal the speedo gears out of it, but that would probably involve purchasing the entire gearbox...
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I supported Toymods
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I renounced punctuation
Registered:
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Re: Speedo drive gears
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Fri, 05 December 2003 05:31
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That was what I suggested right at the start Norbs! 
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Location:
Brisbane
Registered:
May 2002
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Re: Speedo drive gears
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Fri, 05 December 2003 05:34
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I know I know, I'd just rather get new parts! Besides, the RA65 gears may not be quite what I want since they have a different tyre size.
Anyway, it's all much too hard. Maybe I'll just disconnect the speedo and pretend it was never there.
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I supported Toymods
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I renounced punctuation
Registered:
May 2002
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Re: Speedo drive gears
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Fri, 05 December 2003 05:46
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As a side issue, do you know what gears you have in your Mk4 W58? What diff ratio do the NA JZA80s actually run? You may be in some luck!
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Re: Speedo drive gears
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Fri, 05 December 2003 05:48
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| gianttomato wrote on Fri, 05 December 2003 12:38 |
Peewee, you're just complicating a relatively straight forward problem by talking about pitch. No offence.
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Yeah, I know, but I'm bored at work (can ya tell!?!!)
Anyway, is it possible to get your speedo reconfigured?
Is it a magnetic drive, or a direct drive?
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Re: Speedo drive gears
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Fri, 05 December 2003 05:52
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| Norbie wrote on Fri, 05 December 2003 13:34 |
I know I know, I'd just rather get new parts! Besides, the RA65 gears may not be quite what I want since they have a different tyre size.
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Well, you getting new rims/tyres soon right?
Then get your speedo as accurate as possible, then change the profile of your tyres to get it perfect
Maybe
*Disclaimer: I have no idea how this will impact on any other physics the car is put through*
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Location:
Brisbane
Registered:
May 2002
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Re: Speedo drive gears
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Fri, 05 December 2003 06:20
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| gianttomato wrote on Fri, 05 December 2003 15:46 |
As a side issue, do you know what gears you have in your Mk4 W58?
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I haven't checked out the output shaft gear, but the gear on the speedo cable gear came out of an MA61 so it should be about right for a 3.9:1 or 4.1:1 ratio. I think.
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What diff ratio do the NA JZA80s actually run? You may be in some luck!
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4.0:1, which is why the speedo was "sort of" accurate with the old diff ratio.
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Location:
Brisbane
Registered:
May 2002
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Re: Speedo drive gears
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Fri, 05 December 2003 06:27
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UPDATE: I've spent half the afternoon on the phone trying to get some actual answers.
First call was to the parts division of a local Toyota dealer. They refuse to talk to you if you're not ordering a specific part (and can quote a chassis number) so they were no help at all. They suggested I call the Toyota Motor Corporation customer service line, which I did.
After being put on hold for about half an hour, I spoke to a female call-centre type who obviously didn't know a thing about cars. I asked to be put through to someone with some sort of technical knowledge, but she refused so I tried to explain the situation to her as best I could. Of course she completely misunderstood the situation, and when the answer eventually came back she actually chastised me for attempting to illegally tamper with my speedo! I tried to tell her I wasn't actually modifying the speedo itself, but it was clearly beyond her comprehension and she refused to provide any further information.
Next I tried a Toyota service centre and spoke to one of the technicians there. He at least understood what I was talking about, but couldn't provide me with any information because they never deal with modified vehicles - if the speedo gears need replacing, they just look up the standard part number and install them! Kind of what I expected from a place like that.
Anyway I'm out of ideas. Who should I try next??
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Re: Speedo drive gears
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Fri, 05 December 2003 06:32
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| Norbie wrote on Fri, 05 December 2003 14:27 |
Anyway I'm out of ideas. Who should I try next??
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Tried VDO?
They usually deal with speedo mods and shit.
Failing that, fuck nose!!
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Location:
Launceston, Tasmania
Registered:
October 2003
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Re: Speedo drive gears
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Fri, 05 December 2003 08:35
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Okay Norbie try these guys they specialize in this stuff. Gauge Works Australia 03 5277 9296 id they can't help maybe they can put you onto someone who can.
Rich
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Location:
Finland
Registered:
November 2002
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Re: Speedo drive gears
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Fri, 05 December 2003 23:27
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Norbie! cheapest option might be to get custom made gears. Most machine shops could do gears of your wish.
Even cheaper: vocational schools takes orders from clients, at least here. Very cheap.
Just something to consider.
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Registered:
May 2002
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Re: Speedo drive gears
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Sat, 06 December 2003 11:30
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Why not just get the chassis number of the vehicle the diff was in (or one the same) and order the gears to suit that?
I think I just reworded GT's answer.
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I supported Toymods
Location:
Perth
Registered:
May 2002
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Re: Speedo drive gears
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Sat, 06 December 2003 11:39
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Get a decent Toyota dealer who will actually spend the time to help you
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Location:
Brisbane
Registered:
May 2002
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Re: Speedo drive gears
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Sat, 06 December 2003 16:03
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OK, where do I find one of them?
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Location:
Melbourne
Registered:
November 2003
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Re: Speedo drive gears
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Sat, 06 December 2003 17:16
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Pah! Why dont they just put some convinient twisty thing on the back to adjust the speedo?! Stupid... unadjustable cars.
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Location:
1st street on the right
Registered:
November 2002
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Re: Speedo drive gears
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Sat, 06 December 2003 22:51
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Go to an instrument shop, they can tell you what the rpm/km ratio is with a drive box they can plug into the cable. Next find out if it's direct drive or magnetic pulse. It should be magnetic, then tell them the gears available, and ask how far they can adjust the speedo. This is done by moving the magnets inside the speedo drive in or out.
This can be done as I've had it done in a Range Rover, same magnetic type. Went from 205/75/16 to 44 x 15 tyres and it wasn't a problem. General Auto Instruments in Sydney did the work (actually done all my speedo work) ad they also do the calibration for the NSW police cars from new and every 10,000 k's.
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Location:
1st street on the right
Registered:
November 2002
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Re: Speedo drive gears
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Sat, 06 December 2003 22:54
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Go to an instrument shop, they can tell you what the rpm/km ratio is with a drive box they can plug into the cable. Next find out if it's direct drive or magnetic pulse. It should be magnetic, then tell them the gears available, and ask how far they can adjust the speedo. This is done by moving the magnets inside the speedo drive in or out.
This can be done as I've had it done in a Range Rover, same magnetic type. Went from 205/75/16 to 44 x 15 tyres and it wasn't a problem. General Auto Instruments in Sydney did the work (actually done all my speedo work) ad they also do the calibration for the NSW police cars from new and every 10,000 k's.
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Location:
Albany WA
Registered:
October 2003
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Re: Speedo drive gears
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Fri, 19 December 2003 02:10
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Is there some sort of digital, GPS based speed meters out there? Thats what I'm going to be looking for.
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Re: Speedo drive gears
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Fri, 19 December 2003 02:15
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Yes, its called hand held GPS, but they only work in a straight line, as soon as you take a corner, the speed will go waaaay out
GPS tracks nicely in a straight line, but not around corners
Any why do you want GPS speedo?
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Location:
Albany WA
Registered:
October 2003
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Re: Speedo drive gears
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Fri, 19 December 2003 02:23
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Har har bloody har har. At first I thought you could use a G-Tech as a speedo, but apperently not.. if I can get a little device that will give me the correct speed without needing a hookup to the car, I can go for whatever tyre sizes / diff ratios that I want, and I don't have to figure out the speedo ratio on the box I'm using.
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Re: Speedo drive gears
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Fri, 19 December 2003 02:30
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Maybe you could install on of those speedos that a plane has, that pointy needle thingy
Or install a Microsoft Intelli-eye mouse sensor, that would give you an accurate reading when properly configured
(I am actually being semi-serious here, they both may work)
But A laser reading the road speed would be the way to go
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Location:
Albany WA
Registered:
October 2003
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Re: Speedo drive gears
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Fri, 19 December 2003 02:37
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Aircraft are a little out of my depth... Intelli-mouse is interesting, but I don't think the sensor has enough stonk to hit the road, and Microsoft is lying when they say its plug-and-play compatible  pity there doesn't seem to be any off the shelf stuff for this sorta thing, but maybe I'm not looking hard enough.
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Re: Speedo drive gears
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Fri, 19 December 2003 02:48
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Hmmm, you should be able to find some semi off the shelf laser speed sensors. Tried Jaycar/Altronics?
Failing that, pop a halleffect sensor inside the rim, and when you put bigger rims/tyres on, you just have to move the sensor towards/away from the centre
This is the same way a pushbike speedo works
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Location:
Albany WA
Registered:
October 2003
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Re: Speedo drive gears
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Fri, 19 December 2003 02:52
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Good thinking 99. I'll talk to my uncle, he's pretty full bottle on electronics.
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Location:
Perth
Registered:
July 2003
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Re: Speedo drive gears
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Fri, 19 December 2003 12:17
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Wraith,
Jaycar sell a digital speedo kit based on hall effect sensors. Looks like it is relatively easy to calibrate.
BTW - how often do you visit Perth? There is a wrecked Supra down your way I might be trying to get some bits off.
Regards
Peter
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