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Discussion Starter · #1 ·
Searched and searched on this topic but couldn't find many people who had actually DONE the speedo gear swap.

I recently acquired a good set of lower mileage 3.73s with a good working stock LSD. Looking to swap the diff with my 4.30 very soon but really want to get much more accurate speedometer than the one I'm currently running. (It now reads ~7mph fast)

Set up will be as follows:
stock 85 supra w58
225/50/15s
3.73

I know I'll need 3.14/1 ratio with this set-up which leaves me with either the 35/11 tooth set-up or the 31/10 tooth set-up.

I've read that most w58s came with the internal 11 tooth gear, however the 85s were equipped with a 10 tooth internal gear? Can anyone confirm this? Also, are the external gears interchangeable or are they specific to their 10/11 tooth counterparts? I'm basically trying to avoid splitting the transmission and trying to determine which outer gear I'll need. Any help would be appreciated.

Thanks,
David
 

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10 tooth inner needs matching outer. How sure are you tranny is OE? Edit-current Outer gear style will tell you inner gear type-Just pull small gear.
 

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Discussion Starter · #3 ·
100% sure that the trans is OE. Car was completely stock when I bought it. Should I pull the outter gear to be safe?

I found this through a rigorous search:

I've found some description on my EPC..

33403-29145 31 teeth (for 31:10)
33403-29125 32 teeth (for 32:10)
33403-29135 33 teeth (for 33:10)
33403-39075 34 teeth (for 34:10)
33403-19235 35 teeth (for 35:10) (MK2 with 4.3 diff)

33403-29105 30 teeth (for 30:11)
33403-19245 31 teeth (for 31:11)
33403-19255 32 teeth (for 32:11)
33403-29115 33 teeth (for 33:11)

..and asked Mark if he could add USDM & CDN applications.
I'm thinking of ordering 33403-29145 31 teeth (for 31:10) . Thoughts?
 

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If you want the speedo to read correctly, you are going to have to split the trans. It is not just the number of teeth that are different, it is the size of the gears. The one on the output shaft gets larger or smaller depending on the diff ratio, and the driven gear has to change size in a reverse relationship for it to work. I have seen many destroyed driven gears due to people just swapping that part and thinking there are GTG.
 

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Discussion Starter · #5 ·
If you want the speedo to read correctly, you are going to have to split the trans. It is not just the number of teeth that are different, it is the size of the gears. The one on the output shaft gets larger or smaller depending on the diff ratio, and the driven gear has to change size in a reverse relationship for it to work. I have seen many destroyed driven gears due to people just swapping that part and thinking there are GTG.
If this is the case, why are there only 2 part numbers (from what I can find) for the output shaft gear? One for the 10 tooth and one for the 11. I'm not saying you're wrong, I've just never heard of this before.
 

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what years uses the 10 tooth n what years uses the 11 tooth?

i swap mine, got one off an 82 and put it in my 85 w58, my speedo works great,
 

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Discussion Starter · #7 ·
what years uses the 10 tooth n what years uses the 11 tooth?

i swap mine, got one off an 82 and put it in my 85 w58, my speedo works great,
Not sure. I read somewere that the 85+ uses the 10 tooth and 82-84 uses the 11. What exactly did you swap?
 

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the 45 degrees elbow with the gear , my 85 5mge n w58 are in my 84 chassis,
 

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Chris and I are talking about same thing. Gears are matched sets. If you pull outer gear, and compare it to new gear, the wrong one will be physically different-length and tooth pitch-than the correct one. BEST way to tell is to pull housing, but you should be able to tell from outer gear. Personally, Ive had 4.30s, 4.10s, 3.58s, and now 3.91s in my car. Ive never swapped gears, I just do the conversions for odo and speedo. The speedos in these cars are never correct, and Im more concerned with odo for MPG calcs, anyway.
 

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If this is the case, why are there only 2 part numbers (from what I can find) for the output shaft gear? One for the 10 tooth and one for the 11. I'm not saying you're wrong, I've just never heard of this before.
If I can dig up the pics, I have some comparing a 3.42, 3.73, 4.10 and 4.30 and all the drive gears are a different size.
 

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Discussion Starter · #11 ·
Chris, Freak, we're on the same page now. I'm gonna first install my gears and see how far I am out, if It's less than 5mph, I probably won't worry with it. Still doesn't explain why theres only one part number for the inner gear thought.
 

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Discoelk,

I calculated your required speedo ratio at 3.15, when using 225 x 50 x 15 and 3.73:1 gears.

This leaves you with a few options in terms of drive and driven gears. While the 35/11 combo would give you a 3.18 ratio (= -0.5 MPH at 55 MPH speed), I am not sure that this working combo exists.

You can use a 32/10 combo for a 3.20 ratio, which will result in a -0.8 MPH speed at 55 MPH.

Another combo is the 31/10 combo for a 3.10 ratio, which will result in a +0.9 MPH speed at 55 MPH.

When I switched to my 3.90:1 gears I swapped my 35-tooth driven gear out for a 32-tooth gear, but it did not work. Although both gears required a 10-tooth drive gear, they would not both work with the same 10-tooth gear.

So, I purchased a drive/driven gear set from Toyota. The drive gear is imprinted "10 x 31-33." The 34-35 driven gears actually use a smaller diameter 10-tooth drive gear. My Part No. is 33481-22030. This may be a part number from a 5-speed Cressida.

Let us know how you turn out!

Regards,

Carlos
 

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Discussion Starter · #13 ·
Thanks for the info everyone. I'll be swapping the diff this weekend so I'll see how much its off then go from there I suppose... If I need to swap the gears, I'll do so when I install my next clutch. (It should be pretty soon sense the current clutch has at least 65k miles on it.)
 

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David,

Which speedo gears do you currently have (or have you purchased)? Let me know and I will tell you exactly what kind of speedo error to expect.

Regards,

Carlos
 

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Discussion Starter · #15 ·
Carlos,

Currently is all stock 85 5mge 5-speed drivetrain. Thus, I'm assuming a 35/10 drive gear. With the current wheel tire set-up, the speedometer reads ~6mph fast. Even with 225/60/14s, the OE speedo read ~3mph fast IIRC. With this new set-up, I'm expecting a reading anywhere from 3 to 7mph slower than my actual speed. Because of this, and the possibility that I'll be upgrading to 16s or 17s(depending on how big of brakes I can get behind the 15s) in the next year or so, I'm thinking more and more it may not be the best idea to do a drive gear swap at the moment.

Thanks,
David
 

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i'm interested to find out as well since i will also be installing a 3.73 rear and 16's. what is the actual math that you use carlos in calculating the ratio and stuff? because instead of messing with tranny gears, you could also make up some or all of the difference with the tire size.
 

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David,

I went through some of your info today and came up with a few conclusions, which I listed below:

  • The 225/60/14 tire has an OD of 24.63"
  • The 225/50/15 tire has an OD of 23.86"
If you are infact running a 4.30:1 rear gear with a 35/10 speedo drive set, your speedometer reading should be as follows:

  • With 225/60/14 tires the speedo will read +0.3 MPH faster than actual speed. You are going 54.7 MPH in a 55 MPH zone...
  • With 225/50/15 tires the speedo will read +2.0 MPH faster than actual speed. You are going 53 MPH in a 55 MPH zone.

The only way that I come up with the speeds that you listed was by mixing 4.30 and 4.10 components. I think I ran a 4.30 gear with a speedo gear set for a 4.10, to come up with 5 MPH speedo discrepancies.

  • With 4.30 gears + 4.10 speedo gears (33/10) + 225/60/14 = +3.5 MPH speedo reading.
  • With 4.30 gears + 4.10 speedo gears (33/10) + 225/50/15 = +5.1 MPH speedo reading.

If you do maintain a 4.30 or 4.10 speedo gearset with a 3.70 rear gear, this is what you can expect:

  • With 3.70 gears + 4.10 speedo gears (33/10) + 225/60/14 = -4.9 MPH speedo reading. This means that you are speeding - doing 59.9 MPH in a 55 MPH zone!
  • With 3.70 gears + 4.30 speedo gears (35/10) + 225/60/14 = -8.5 MPH speedo reading. This means that you are really speeding - doing 63.5 MPH in a 55 MPH zone!
  • As you increase your tire diameter your speedo discrepancy will increase in this direction...

The calculations are listed in the following post: http://forums.celicasupra.com/showthread.php?t=10668&highlight=3.90+speedo&page=2

I would pull the driven gear "elbow" from the tranny and see what numbers are etched on the face of it (if you have not already). I think this will tell the tale...

Regards,

Carlos
 
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