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Discussion Starter #21
I'm not very good at reading your spread sheet. I have a 5 speed out of a 82 supra which came with a 3.73. I put the transmission in my 84 after auto swap but the rear end is still the 4.10. Could you tell me what I would need to do to get the speed right. Or would I need to get either a 3.73 rear end or a 4.10 transmission?
You would either have to swap to a 3.73 rear end, or install the appropriate 4.10 transmission speedo gears into your transmission.
 

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I always that i was going about 5 miles under the speed limit. That all started when little old white haired ladies would drive by me and flip me off...
 

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Just for clarification if I wanted to go with the 4.10 I would have to change both gears in my trans that came with a 3.73 rear end or could I just change the gears out on the side of the transmission?
 

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The plastic outer gear will have two numbers printed on it. ...36 and 10... or something to that effect. So long as the small number is the same between the two outer gears, you're set. (The OD's will be the same as well.) Otherwise, welcome to splitting a tranny. (hold pressure on the output shaft while you pop ONLY the rear portion off and you will halve your chances of leaks once you put it together again.

--billyM
 

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The link is down :(

Any chance this can be accessed some other way? Or is there a new link, Dean?

Thanks,
 

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For those who don't have Microsoft Office (or don't want it), look into OpenOffice.org. It's a free open source office suite available for Microsoft Windows and most Unix-like operating systems. It will read and write to Microsoft's proprietary Office formats and the ISO approved open document format.

Sorry if that sounds like an infomercial/shameless plug. Just figured I'd try and help the people who aren't able to check out the spreadsheet you made.

Thanks for that, by the way!
 

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http://kmfdmk.com/tirespeedocalc.xls 21KB
http://kmfdmk.com/w58_rpm_mph.xls 32KB

http://spudguns.org/tirespeedocalc.xls
http://spudguns.org/w58_rpm_mph.xls

http://akarally.com/incoming/rusty/tirespeedocalc.xls
http://akarally.com/incoming/rusty/w58_rpm_mph.xls


All three tested and working. Thanks Donn. I own the first two hosts and contribute to the third. Should be up from here on out.

If people want I can burn them to CD and mail them out.

Also I have a mirror of the revised TSRM manual from elsewhere in this forum.

http://kmfdmk.com/TSRM,_Celica_Supra,_Toyota,_1986_v1.1.zip 35.4MB
 

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Does the R154 use the same part numbers?
Yes.

SOOOOOOO, has anyone else actually used this thing to try and correct their speedo yet? I've just gone through all of this, used the calculator to find the right ratio for my shorter then stock tires and my new 3.72 diff (car was originally 4.3), and I must say, we have a bit of work left to do here.

Ok, first off, all of these speedo side shaft gears are stamped with 10 or 11 as well as the number of teeth on the gear (30-35). Those numbers listed in the excell sheet are NOT foriegn part numbers, we just don't understand how this all works yet. My first conclusion was that you could not match a gear stamped with 10-3X with an 11 tooth output shaft gear and vice-a-versa, and that most of the side shaft gears were available in 10 and 11 tooth versions and thats what those secondary part numbers are for. Now that could still be true, but I'm afraid the confusion doesn't end there. Turns out theres 2 different diameters of 10 tooth gears in use just in the w58s in our mk2s! Maybe in 11 tooth too. Theres side shaft gears in 10-3X and 11-3X gears in two different diameters, and you can't mix and match them! I'm probably confusing you all so here's the numbers from my findings so far and maybe some of you can help me figure this out (I still have some more research to do on my own). Luckily I have a plethora of trannies sitting around in my shop, here's what I've found so far...

w58 from what I thought was an 83 5spd mk2 (might not be), should be a 4.1 rear end: Has a 28.8mm OD 10-31 side shaft gear.
w58 from an 84 Celica GTS with a 3.42 rear end: 11-31 with a 28.8mm OD
w58 from an 84 Supra and another from an 85, both 4.3 cars: 10-35 with a 31.4mm OD
r154 from an 88 Supra Turbo with a 3.9 rear end: 10-32 with a 28.8mm OD

In addition there appears to be 2 different styles of the actual side shaft in use though they seem to be directly interchangable, even the r154 could take a mk2 w58 side shaft and 28.8mm gear. Of course the car I'm trying to adjust the speedo on has the larger 31.4mm gears and none of my 28.8 actually contact the 10 tooth gear on my output shaft. Before when I was under the assumption that you had to have a side gear marked 10 if you had a 10 tooth output shaft gear, I ordered the 10-32 gear with the pn 33403-29125 since the 33403-19255 32 gear was more common in the EPC so I figured it was the 11-32 one. Well I ended up with a 28.8 OD 10-32 gear, exactly the same one as was in my r154 and then I discovered the diameter difference and now I can't use the damn thing (and probably can't return or exchange it, special order from CA through the dealer). So now I'm thinking\hoping the 19255 number is for a 31.4 diameter 10-32 gear. I did stick my 11-31 gear into a tranny with a 10 tooth gear and it seemed to rotate just fine.

Anyways, I can't find any rhyme or reason to why theres 2 different diameters in use here as I have early and later styles in the small diameters in both 10 and 11 teeth variants. If anyone has any insights or has another size of gear in a tranny kicking around that they can measure, please pipe up! I will get back to you all after some more digging in the epc and hopefully exchanging this speedo gear I bought for the other number.
 

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Good stuff there. I've got a quick question though. In my 85, I swapped out the 4.3 with a 3.73 and I'm using the W58 from my old 82 as well. Now, technically I should be getting the correct speed, right? But it seems like my speedo is reading a little fast (speedo says I'm going 65 but it feels like 60, that sort of thing). I've got stock 225/60/R14s on it. Was there something I missed that directly interfaces with the speedo that could be giving me my false readings like the cable itself? Another reason that I doubt its accurate is that when I'm at 2250rpms in 5th, I know that I should be going 60mph (at least thats what it was in both of my 82s), but my speedo reads 65mph. Hope that contributes somewhat.
 

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yeah I don't think so, theres no gears in the cable. I would chalk it up to tach and speedo error/variation.
 

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Done a little more digging in the EPC and theres only two 32 tooth gears in use in vehicles that share drivetrain parts with our car so I'm going to try exchanging the gear I bought for the 19255 gear instead of the 29125 I got already. Should be interesting to see if its a 31.4mm 10-32 or if its a 11-32 gear. I may have some brand new spare speedo gears available for sale soon lol.
 

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Ugh, 33403-19255 is a 11-31 28.4mm OD speedo gear too. I had to return both gears I bought from Toyota, couldn't use either of them. I have the right gears at home needed to correct my speedo as I have a 3.9 equiped 85 Celica gts growing in the back yard but I was hoping to not have to switch out the shaft gear on my beater, sigh.

So its looking like a couple of my assumptions are about correct but I will post up again in a new thread and here once I've swaped out the shaft gear as well as the speedo gear on my car as I will compare the shaft gear diameters first. Its also looking like you can't, or at least shouldn't mix and match speedo gears with the wrong shaft gear. I got a good look at Toyota's current EPC at the dealership (mine's from 1995) and the new one actually tells you if its a 10:3x gear or an 11:3x gear now in the notes section, handy.

As it stands, it appears almost all of the speedo part numbers listed in Slip's tire speed calculator are for 28.4mm OD gears (one of the 10:35 ones are the larger diameter). Everything I've seen so far suggests that the only trannies that came with speedo gears with 32.4mm OD gears are Celica Supras that came with 4.3 diffs. And that would mean if your tranny is out of a car that originally had a 4.3 diff and you want to change your speedo gears to correct your speedometer, you're stuck changing out both gears. shitty. More info on this soon.
 

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Discussion Starter #38
lol posting.

someone should probably take a good look at my math before they start spending money. I remember a lot of numbers and formulas. Could be an error somewhere.

edited the original post. you can download it again wooooo
 

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this is SO COOL, great job building that! I bought my Supra with non original tire sizes and its about 10mph off, going thru radar signs its maybe 9.5 to 10mph faster than what its really going. so 75 on the speedo is 65.

Can the gears be changed on an 85?

Question why is the % Error on the correct setup listed at 100.63 ? that sounds more like a correction factor? like its 1.0063 for the right one and 1.1376 when its off by a bit?

so speed x corr fac = speed ?


Well, in a fit of boredom I rebuilt a spreadsheet I made a couple years ago and inadvertently deleted. Using data gleaned from the forum I have compiled a one-stop calculator for changing tire sizes, speedometer gears, and differentials.

The excel sheet will tell you how far off your speedo is based on tire, differential, and speedometer gear combination. It will calculate and recommend the best speedo gear combination to use for your given tire/wheel/differential setup. While we aren't all changing tires and differentials all the time, it should be a nice thing to have around.

Instructions are included in the spreadsheet, although it's pretty straightforward.

Part numbers are good to go!

I am looking for you guys to test it out and see if there are any questions or suggestions you guys have for improving the sheet. Have fun!

http://www.northofnowhere.ca/deanfun/tirespeedocalc.xls

URL updated Sept 7th 2008
 

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Hey Dean! I really appreciate your effort with the spreadsheet and I hope it's accurate. Here's what I have:

- W58 from a Celica that was mated with a 3.90 geared differential
- The driven gear in the transmission is a 10/32
- I'm switching to a 3.73 geared differential

The spreadsheet indicates that if I go with 245/50/16 tires, then all I have to do is switch the driven gear to 11/32.

Awesome.
 
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