Speedo differences 83-84, 85-88

GTSSportCoupe · Post by **GTSSportCoupe** » Thu Jan 20, 2005 10:56 am

Just a couple questions for you folks regarding the tercel speedometer:

I have known for a while that my 86 tercel speedo is quite a bit out. It reads about 10% faster than I am actually traveling. I think I know why this might be happening. Before I bought the car, the previous owner swapped the original 86 transmission out with one from an 83 tercel's transmission. He did NOT change the front and rear diffs though. As you know the 83 tercel had diffs that had a ratio of 3.73:1 and the 86 had diffs that had a ratio of 4.10:1. So, I am assuming that the speedo gearing must be different between the 83 transmission and the 86 transmission. This would account perfectly for my 10% error.

So my question is, how do I fix this? Where are the gears that drive the speedo? They must be in the trans somewere, because the previous owner didn't change the cable or gauge cluster.

Thanks for any suggestions on fixing this problem. It's sort of irritating having a speedo that is out by 10%. Heh, does keep me from getting speeding tickets tho!

3A-C Power · Post by **3A-C Power** » Thu Jan 20, 2005 11:41 am

If you have the driven gear from the 86 then you should be okay. I have the same combination of tranny and axle ratios and the speedometer seems to be correct at least relative to the tachometer. The driven gears have one tooth difference and from comparing them side to side it looks like the angle of the teeth is the same which would mean the pitch of the worm gear that drives them is the same. Since they are plastic and pretty close in size, you can get away with using a bigger driven gear and while the fit between gears will not be quite right, the ratio will be correct. The real right way to do it would be to change both gears, and that involves taking the transfer adapter off.

GTSSportCoupe · Post by **GTSSportCoupe** » Thu Jan 20, 2005 1:06 pm

Thanks for the info! I sorta follow you. I have not actually ever looked at how a speedo cable is connected and driven, so I'm trying to picture things I have not opened up before. So basically I can change out the driven gear without too much trouble, but to change both out is a serious PITA? Is removing the transfer adapter pretty tough? (I can't picture this part right now either.) I've never really don much with transmissions before except drop 'em and put 'em back in.

How many rpms are you at on the highway when your speedo says 100kms/h? What size of tires is this with? I'll check on the way home today and let you know what mine says. Or you can tell me how fast you are going when your tach reads 3000rpm. Whatever is easiest for you.

Thanks.

2wagons · Post by **2wagons** » Thu Jan 20, 2005 1:52 pm

GTS Sport coupe,
My 87 speedometer is also about 10% - discovered using milage markers on the highway- made my mpg come up! I run 175-70R-13 at about 35 psi. How did you soundproof your car?

GTSSportCoupe · Post by **GTSSportCoupe** » Thu Jan 20, 2005 1:59 pm

2wagons wrote: GTS Sport coupe,
My 87 speedometer is also about 10% - discovered using milage markers on the highway- made my mpg come up! I run 175-70R-13 at about 35 psi. How did you soundproof your car?

Interesting about your speedo...maybe mine is just WAY out of calibration. Yours must be out the opposite way as mine. Mine makes it look like I'm getting better mileage than I actually am.

I swapped an entire interior over from an 87 tercel 4wd that I owned before my 86. While I had the entire interior out of my 86 I bought a big piece of 1" sound proofing material. I cut it to fit under the carpet basically everywhere where the carpet is (whole floor of car except under the rear seats). I had to cut holes for the ebrake, shifter, and bolting points for the seats and seat belts etc. It is quite a lot of work to remove the interior to the point that I did, there are way more pieces than you might think.

Typrus · Post by **Typrus** » Thu Jan 20, 2005 10:40 pm

I think my speedo is out as well. I can't truly tell whether its right or a bit off, but sometimes those little radar speed limit signs tell me I'm moving 37-39 when my speedo says 40-41. Could just be wacky.
Is that little thing that comes out of the bottom of the tranny and goes up into the dash the speedo cable? I was wondering about that....

GTSSportCoupe · Post by **GTSSportCoupe** » Fri Jan 21, 2005 9:51 am

Typrus wrote: I think my speedo is out as well. I can't truly tell whether its right or a bit off, but sometimes those little radar speed limit signs tell me I'm moving 37-39 when my speedo says 40-41. Could just be wacky.
Is that little thing that comes out of the bottom of the tranny and goes up into the dash the speedo cable? I was wondering about that....

Yup, thats the speedo cable.

GTSSportCoupe · Post by **GTSSportCoupe** » Fri Jan 21, 2005 9:55 am

OK, I did some testing this morning:

At 3000 rpm I was traveling approx 106-107km/h.

At 100km/h the engine was at approx 2800rpm.

Oh yeah, this was in 5th gear. I have 90% tread 155/80R13s on right now.

3AC-Power, since you have the same gearing as me, can you do this test on your car sometime? I'd like to see if mine is similar, or way off. Thanks.

3A-C Power · Post by **3A-C Power** » Fri Jan 21, 2005 4:57 pm

Do you mean actual speed or indicated speed? At 3000 rpm my speedometer reads just under 100.

GTSSportCoupe · Post by **GTSSportCoupe** » Fri Jan 21, 2005 5:08 pm

3A-C Power wrote: Do you mean actual speed or indicated speed? At 3000 rpm my speedometer reads just under 100.

Indicated speed.

So assuming yours is roughly accurate, my car is at least 6% out. Guess I'll just ignore it for a while longer. I don't have a shop to work in anymore, so can't do much about it anyhow.

waynehoc · Post by **waynehoc** » Wed Dec 14, 2005 7:53 pm

Last week I installed a 1987 SR5 4WD wagon instrument cluster in my 1987 2WD wagon. So, I wanted to check the accuracy of the speedometer/odometer, but there are no mileage markers close to where I live (in B.C., same as GTSSportCoupe).

So I found a nice straight, level section of road, and drove exactly 8.4 indicated km. Today, I drove the identical stretch of road with my wife's 2001 CR-V, and the odometer indicated 8.15 km.

Her (stock sizing) tires are about 60% worn, so that would mean that the 8.15 km is actually a bit less than indicated (smaller tires, i.e., worn, should mean that the odometer reads a bit higher - am I correct in this assumption?). Tires on my wagon are near new (few months old 175 70's - stock tires are 155 80's, and the page takza had a link to in his tire size post http://350zx.com/tire-wheel.html shows zero speedometer error if changing from 155 80 to 175 70 tires).

So, I don't think my tires should bring in any speedometer/odometer error. dcn and 3A-C Power both indicate almost exactly 100 kph at 3000 rpm, but my 2WD wagon indicates 108 kph at 3000 rpm.

I wondered if maybe the gearing in 5th is a bit higher for my AL21 wagon vs the gearing in 5th for the AL25 4WD wagons. I have scoured the Internet for specs on the AL21 5-speed trannys, but have come up empty - all I found was others asking for the same specs I was trying to find.

So, either my gearing is a bit higher in 5th, or my speedo and odometer are out somewhere in the range of 5% or so.

Does anyone know of a source for gear ratio specs for the AL21 5-speed trannys?

waynehoc · Post by **waynehoc** » Wed Dec 21, 2005 10:22 pm

Well, I've discovered (more on-line searching) that my trans code and axle code are right in front of my nose on a little plate in the engine compartment. Turns out that my diff has 3.58/1 gears and that the trans is a Z53 - for which trans I can find nothing about gear ratios anywhere. Even emailed Toyota Canada and talked to the local Toyota service and parts dept's. Neither had any info.

So, I'm now going to assume that the speedo is reading fairly accurately showing 108 kph @ 3000 rpm, and that 5th gear is likely 0.825/1.