Speedometer calibration after 4.11 swap

[joeaxial]

I've got my 4.11 trans and rear differential swapped into my 1992 SVX. Everything works great, but I've found that my speedometer now reads about 10% faster than my actual speed. Has anyone come up with a solution to this problem. I'm not so concerned about the inacurate reading on the speedo, but I don't like the idea of clocking up 1.10 mile on the odometer for every mile I drive! If any of you SVX geniuses has come up with a fix for this, I'd appreciate hearing about it.
Thanks A Lot
Steve

[Manarius]

Get bigger rims. The speedo on my car is 10% over and I'm running stock 14's on my 4.111 geared Legacy.

Swapping up to larger rims will fix the problem.

[oab_au]

I believe the fix is to swap out the speed sensor from the SVX box into the 4.11 box.

Harvey. ;)

[joeaxial]

I believe the fix is to swap out the speed sensor from the SVX box into the 4.11 box.

Harvey. ;)

Thanks Harvey, but I did use the SVX speed sensor when I did the swap.
Steve

[Beav]

We discussed this a while ago. A number of us have come to realize the SVX is usually 4mph slower than the speedo. Kinda goes along with the pessimistic gas gauge.

[bwb3]

Pessimistic gas guage. It down right lies. Drove on empty for 20 miles and still had 7 gallons left.

[Red SVX 92]

We discussed this a while ago. A number of us have come to realize the SVX is usually 4mph slower than the speedo. Kinda goes along with the pessimistic gas gauge.

You mean there's no way to calibrate the speedo properly? It would suck to have to run taller tires to offset the gearing change... You'd lose any benefits the shorter gear set would provide in acceleration, etc.

[Earthworm]

Well you could reposition the speedo needle using a GPS to calibrate your speed. I believe Lwin/Seraph does this with every SVX he goes through.

[joeaxial]

Well you could reposition the speedo needle using a GPS to calibrate your speed. I believe Lwin/Seraph does this with every SVX he goes through.


The problem with re-positioning the needle is that my speedo is about 10% off. The inacuracy is not linear with increased speed. So the difference between indicated speed and actual speed increases the faster you drive. For example 70 mph indicated = 63 mph actual or 7 mph off, 90 mph indicated = 81 mph actual or 9 mph off. If I were to simply re-position the needle, the speedo would only be truly accurate at one speed.

I think I've heard of an electronic box that can be wired in with your speed sensor that will allow corrections. Has anyone else heard of such a thing?

Steve

[Earthworm]

Yes that is correct. The difference is a percentage and moving the needle won't be perfect but it will be a little more accurate. I do not know of anyone here using an electronic device to calibrate their speedometer yet.

[svxcess]

Check out this link: http://www.terf.com/SpeedChangerPage.htm

There are others out there as well. Some don't work with AWD or ABS. This company has experience with Subarus and hasn't had any problems.

Are our speed sensors 2-wire or 3-wire?

You can also do a google search for "electronic speedometer calibration" or "electronic speedometer recalibrator"

.

[Earthworm]

Ours are 3 wire

[Beav]

^^^ a.k.a. 'Hall Effect'.

[pavanbabut]

The problem with re-positioning the needle is that my speedo is about 10% off. The inacuracy is not linear with increased speed. So the difference between indicated speed and actual speed increases the faster you drive. For example 70 mph indicated = 63 mph actual or 7 mph off, 90 mph indicated = 81 mph actual or 9 mph off. If I were to simply re-position the needle, the speedo would only be truly accurate at one speed.

I think I've heard of an electronic box that can be wired in with your speed sensor that will allow corrections. Has anyone else heard of such a thing?

Steve

I am also having the same exact problem with my speedo after my 4.44 swap, but i didn't get an exact or approximate remedy to correct it.

I would be more than happy if someone comes up with something to correct this.

-Pavan.

[lee]

Could someone explain how this error could happen by a swap?

My understanding of the speedo setup is that a gear is driven from the right side axle, which in turn does some magnetic signaling that gets decoded and sent on to the speedometer.

My point is the speedo, since it's driven by axle revolutions, should register exactly the same (good or bad) before & after, regardless of the ratio installed.

So, which automotive class do I need to take over again?

[pavanbabut]

Could someone explain how this error could happen by a swap?

My understanding of the speedo setup is that a gear is driven from the right side axle, which in turn does some magnetic signaling that gets decoded and sent on to the speedometer.

My point is the speedo, since it's driven by axle revolutions, should register exactly the same (good or bad) before & after, regardless of the ratio installed.

So, which automotive class do I need to take over again?
same here toooo... not able to understand... maybe Tom[svxfiles] can explain this clearly as he is the master in swaps 4.11 and 4.44.

-Pavan.

[joeaxial]

Could someone explain how this error could happen by a swap?

My understanding of the speedo setup is that a gear is driven from the right side axle, which in turn does some magnetic signaling that gets decoded and sent on to the speedometer.

My point is the speedo, since it's driven by axle revolutions, should register exactly the same (good or bad) before & after, regardless of the ratio installed.

You got me thinking on this 'cause on a typical Front engine/rear drive car, the speed sensor senses transmission rotations and is independent of the final drive ratio. I did some research and found a copy of a tech document concerning our 4eat transmissions published by Subaru at this site http://www.ravensblade-impreza.com/techdocs/pdf/transmission/4eat.pdf I'm now quoting from this document:

Vehicle Speed Sensor #1
Vehicle speed sensor #1 is mounted to the transmission and is basically electrical governor pressure. It is used to detect vehicle speed and it effects shift points, lock-up, and line pressure. In FWD transmissions the speed sensor reads parking gear rotation at the front output shaft. In AWD transmissions it senses the transfer clutch drum rotation at the rear output shaft.

Vehicle Speed Sensor #2
Vehicle speed sensor #2 is built into the combination meter. In FWD units, it is used as a back-up for speed sensor #1. In AWD units, it is used as the front output shaft speed sensor.

If I'm reading this doc correctly, #1 takes a reading from the rear output shaft while #2 takes a reading from the front output shaft before the front differential. I took a look at the wiring diagram for my 1992 SVX and it shows that the speedometer is driven by Vehicle Speed Sensor #2. Neither speed sensor would be affected by final drive ratio, so speedometer readings would naturally be inacurate after changing the final drive ratios.

I emailed the tech guy at http://www.terf.com/SpeedChangerPage.htm. He indicated that the SpeedChanger box would work with the Subaru electrical system, but I'm concerned that if it wasn't wired into the correct spot on the harness it could cause the TCU to think that the front wheels would be turning at a different speed than the rear and cause a whole pile of problems.

Any Thoughts?
Steve

[pavanbabut]

You got me thinking on this 'cause on a typical Front engine/rear drive car, the speed sensor senses transmission rotations and is independent of the final drive ratio. I did some research and found a copy of a tech document concerning our 4eat transmissions published by Subaru at this site http://www.ravensblade-impreza.com/techdocs/pdf/transmission/4eat.pdf I'm now quoting from this document:

Vehicle Speed Sensor #1
Vehicle speed sensor #1 is mounted to the transmission and is basically electrical governor pressure. It is used to detect vehicle speed and it effects shift points, lock-up, and line pressure. In FWD transmissions the speed sensor reads parking gear rotation at the front output shaft. In AWD transmissions it senses the transfer clutch drum rotation at the rear output shaft.

Vehicle Speed Sensor #2
Vehicle speed sensor #2 is built into the combination meter. In FWD units, it is used as a back-up for speed sensor #1. In AWD units, it is used as the front output shaft speed sensor.

If I'm reading this doc correctly, #1 takes a reading from the rear output shaft while #2 takes a reading from the front output shaft before the front differential. I took a look at the wiring diagram for my 1992 SVX and it shows that the speedometer is driven by Vehicle Speed Sensor #2. Neither speed sensor would be affected by final drive ratio, so speedometer readings would naturally be inacurate after changing the final drive ratios.

I emailed the tech guy at http://www.terf.com/SpeedChangerPage.htm. He indicated that the SpeedChanger box would work with the Subaru electrical system, but I'm concerned that if it wasn't wired into the correct spot on the harness it could cause the TCU to think that the front wheels would be turning at a different speed than the rear and cause a whole pile of problems.

Any Thoughts?
Steve

Well Well... makes sense, but if we replace everything related to transmission (i mean along with rear differential that is matched to it); how come the front and rear wheels run at different speeds? I didn't get how this goes wrong with the swap. Come on SVX gurus, give us ur ideas on how to rectify this problem. I dont like putting more virtual miles on my speedo, as it makes me to think that my car is becoming older :p :p.

I need to know in first place wht causes this problem and secondly how to rectify it.

-Pavan.

[joeaxial]

Well Well... makes sense, but if we replace everything related to transmission (i mean along with rear differential that is matched to it); how come the front and rear wheels run at different speeds? I didn't get how this goes wrong with the swap. Come on SVX gurus, give us ur ideas on how to rectify this problem. I dont like putting more virtual miles on my speedo, as it makes me to think that my car is becoming older :p :p.

I need to know in first place wht causes this problem and secondly how to rectify it.

-Pavan.
You're right, the only thing that stayed the same after the swap is the speed sensor. You have to remove the sensor that came with the 4.11 donor trans and replace it with the SVX sensor because the donor trans used a two wire sensor while the svx uses a three wire. I wonder what gives?
Steve

[pavanbabut]

You're right, the only thing that stayed the same after the swap is the speed sensor. You have to remove the sensor that came with the 4.11 donor trans and replace it with the SVX sensor because the donor trans used a two wire sensor while the svx uses a three wire. I wonder what gives?
Steve

of course we have to swap the sensors tooo.. since we can't fix our speedo wiring harness which is 3pin to anyother sensor. But the only work it does is to change the mechanical rotations to electrical pulses. But i dont know how it effects in the speedo error. thts seems to be wiered for me.. :confused:

-Pavan.

[svxfiles]

Gentlemen,
The speedometer sensor is driven by a gear on the passenger side of the front differential.
The amount of rotations of the gear is determined by the tire diameter, and the coefficent of friction, of the tire, controling the amount of rotations, of the axles, in relationship to the ring gear.
THE INTERNAL GEAR RATIOS HAVE NOTHING TO DO WITH THE SPEEDOMETER ACCURACY!
It is only the sensor accuracy, the speedometer accuracy, the wireing, tire diameter, and the ability of the splined shafts to transfer power, that can show inaccuracies!
That said, I would "be really interested" in joeaxial's new transmission # on the bell housing, by the starter.
If the trans came from a 1996 2.5 Legacy, then it should be a 4.44 ratio trans, and his 72 mph at 3000 rpm is correct.
If the trans is a 4.111, and the rpm is 3000 at 72, rather than 77 mph, there is some problem, like its not locking up the torque converter?

Think about this, in first, second, third and forth, the speedometer reads the speed of the car, without reguard to the gears inside the transmission unit.
The reason for this is, it only reads the speed/rotations of the front ring gear.

All cars to some degree have a speedometer error.
The internal ratios are not a factor. Tom

[pavanbabut]

Gentlemen,
The speedometer sensor is driven by a gear on the passenger side of the front differential.
The amount of rotations of the gear is determined by the tire diameter, and the coefficent of friction, of the tire, controling the amount of rotations, of the axles, in relationship to the ring gear.
THE INTERNAL GEAR RATIOS HAVE NOTHING TO DO WITH THE SPEEDOMETER ACCURACY!
It is only the sensor accuracy, the speedometer accuracy, the wireing, tire diameter, and the ability of the splined shafts to transfer power, that can show inaccuracies!
That said, I would "be really interested" in joeaxial's new transmission # on the bell housing, by the starter.
If the trans came from a 1996 2.5 Legacy, then it should be a 4.44 ratio trans, and his 72 mph at 3000 rpm is correct.
If the trans is a 4.111, and the rpm is 3000 at 72, rather than 77 mph, there is some problem, like its not locking up the torque converter?

Think about this, in first, second, third and forth, the speedometer reads the speed of the car, without reguard to the gears inside the transmission unit.
The reason for this is, it only reads the speed/rotations of the front ring gear.

All cars to some degree have a speedometer error.
The internal ratios are not a factor. Tom

Yep!.. i too agree with your statement, that transmission has nothing to do with speedometer reading. But what we are not able to understand is, why this inaccuracy is showing up in such a noticeable level only when we are swapping the trannies of different ratios other than the stock ratio. Afterall we are using the same stock sensor, if our stock one reads 4mph less as someone above stated, why is it now reading more than 7mph (i mean in percentage increase) when we are using the same sensor, same tires and all that is going to change is transmission. I hope now you got what we are worrying about. In my case it doeasnt matter for me untill I am able to make my speedo show me atleast or approximate to accurate reading.

-Pavan.

[lee]

Gentlemen,
The speedometer sensor is driven by a gear on the passenger side of the front differential.
The amount of rotations of the gear is determined by the tire diameter, and the coefficent of friction, of the tire, controling the amount of rotations, of the axles, in relationship to the ring gear.
...snip... Tom

thanks Tom, I've had the unit apart and just couldn't see any way a gear ratio swap could affect speedo readings, but then I'm a bit challenged and so I thought maybe I was over looking something in the electronics.

[Manarius]

If the trans came from a 1996 2.5 Legacy, then it should be a 4.44 ratio trans, and his 72 mph at 3000 rpm is correct.
If the trans is a 4.111, and the rpm is 3000 at 72, rather than 77 mph, there is some problem, like its not locking up the torque converter?
My 4.111 geared Legacy turns 70 (acutally 63) mph @ 3000 RPM. (70 on the gauge, 63 for the 10% allowed for small wheels)

And as I recall, on Legacy 4EAT's, the speedo is a cable, not a gear. I may be mistaken however.

[svxfiles]

I am going to pull a 4EAT apart later this week, and post pictures of the speedometer drive gear in the front differential.
Just for the record every 4EAT SVx has a three wire front speed sensor, and every Legacy 4EAT, that I have seen, has had a two wire speed sensor.

[oab_au]

I am going to pull a 4EAT apart later this week, and post pictures of the speedometer drive gear in the front differential.
Just for the record every 4EAT SVx has a three wire front speed sensor, and every Legacy 4EAT, that I have seen, has had a two wire speed sensor.

The three wires on the SVX unit, are the two normal wires, with a shield wire, to stop any interferance getting in. The Legacy may not have the shield on the wires.

I wonder if the drive gear has a different tooth angle?

Harvey. ;)

[michael]

Not sure if I misssed something or am ovresimplifying but. Couldn't you follow a friend going say 60 according to their accurate speedometer, set your cruise control and properly reposition the needle at 60mph. A passenger might be helpful,along with a nice straight empty road.

[pavanbabut]

Not sure if I misssed something or am ovresimplifying but. Couldn't you follow a friend going say 60 according to their accurate speedometer, set your cruise control and properly reposition the needle at 60mph. A passenger might be helpful,along with a nice straight empty road.

Yeh.. of course that is one way to check the speedo accuracy, but not all speedos are accurate and i myself checked with a radar meter on the road and I personally can feel the inaccuracy and can tell for sure my speedo shows over reading than the actual speed.

Coming to repositioning, this variation is not by a fixed value. But its a proportionate difference depending upon the speed of ur vehicle and changes according to it.

-Pavan.

[svxfiles]

The three wires on the SVX unit, are the two normal wires, with a shield wire, to stop any interferance getting in. The Legacy may not have the shield on the wires.

I wonder if the drive gear has a different tooth angle?

Harvey. ;)
Since all the transmissions I have looked at were WV and MD transmissions, there is NO UNIFORMITY TO THE TEETH!!!






OK, that was fun.... :rolleyes:



As long as the teeth were of the same #, and they drove each other, the angle is not important.
However, the HAL effect speedometer sensor COULD be affected by the distance when seated. I do not know this for certain, but it "sounds logical" ;)
Harvey, can the third wire be a shielding wire if it does not surrond the two pulse carring wires?

[pavanbabut]

Guys, come on, some one help us what we can do to rectify this. We are not saying that the speedo off is due to transmission faults or someother. Just we don't know what's causing this. Give us your ideas on what we can do. As far as we can say-

1) There is no mismatch of tire sizes and they are all of stock size and are same as they are on old tranny.
2) Stock speed sensor is installed

we are trying to say tht the only ones that are been changed are the tranny and the rear end. Hope now you can get what we are trying to say.

-Pavan.

[lee]

Guys, come on, some one help us what we can do to rectify this. We are not saying that the speedo off is due to transmission faults or someother. Just we don't know what's causing this. Give us your ideas on what we can do. As far as we can say-

1) There is no mismatch of tire sizes and they are all of stock size and are same as they are on old tranny.
2) Stock speed sensor is installed

we are trying to say tht the only ones that are been changed are the tranny and the rear end. Hope now you can get what we are trying to say.

-Pavan.

the problem with answering this (I predict) is there won't be a single answer. I can tell you that most every day I pass one (sometimes 2, even 3 on rare occasions) of those unmanned radar trailers on the side of the road (the police around here really like them, every little town up & down Highway A1A uses them). I presume they show you your speed in the hope you will slow down (pretty rare to see traffic flow at/below the limit during the morning rush). Anyway, I saw exactly zero difference in speedo readings at any given indicated speed from before, to after the swap going from OEM SVX transaxle to 4.111 using a '98 Imprezza transaxle (and matching 4.111 from a '97 Legacy).

[blacknite]

i did notice a 10 mile difference between what my speedometer read and what the radar said (with the 5 speed 4.11). after i put the knew rims a get an empty gas at about 240 miles and before it was at around 340. so what ever it is i really don't think is accurate...

[svxfiles]

I have driven 12 different SVXi that have either 4.44s or 4.11s, and some of them are exactly right on, some are very close.
It seems to me it would have to be the sensor in the bell housing, or the speedometer itself.
Since it is so much easier to trade out the sensor, I would try that first.
Pavan, pm me your mailing address and I will send a sensor for you to try.
Please send me your old one.
When you install the new sensor, make sure it seats properly.
Or stop by at the shop and I'll install it. Tom

[pavanbabut]

I have driven 12 different SVXi that have either 4.44s or 4.11s, and some of them are exactly right on, some are very close.
It seems to me it would have to be the sensor in the bell housing, or the speedometer itself.
Since it is so much easier to trade out the sensor, I would try that first.
Pavan, pm me your mailing address and I will send a sensor for you to try.
Please send me your old one.
When you install the new sensor, make sure it seats properly.
Or stop by at the shop and I'll install it. Tom

Thanks Tom for your reply. Please dont misunderstand me, we are just trying to know why this is happening. At present my car is not with me, but I tested it many times while I drove it and even talk about this many times with Mark too. As soon as i ship my car to my place, I will let you know. At present I am using Mark's sensor. I think stopping by your shop will not happen again as I moved to west coast :)

-Pavan

[benebob]

[QUOTE=svxfiles]Since all the transmissions I have looked at were WV and MD transmissions, there is NO UNIFORMITY TO THE TEETH!!!

QUOTE]

HEE HAW!!! :D

[Chiketkd]

HEE HAW!!! :D
Nice one Ben! :D :D :D

-Chike

[svxfiles]

Here is a picture of the inside of the front differential.
You can see the green plastic gear on the right side.
http://www.subaru-svx.net/photos/files/svxfiles/30259.jpg
There are moore pictures i my locker.
http://www.subaru-svx.net/photos/user.php?svxfiles|30258

[oab_au]

Since all the transmissions I have looked at were WV and MD transmissions, there is NO UNIFORMITY TO THE TEETH!!!

OK, that was fun.... :rolleyes:

As long as the teeth were of the same #, and they drove each other, the angle is not important.
However, the HAL effect speedometer sensor COULD be affected by the distance when seated. I do not know this for certain, but it "sounds logical" ;)
Harvey, can the third wire be a shielding wire if it does not surrond the two pulse carring wires?

As the Euro version does not have the speed sensor in the front diff, it is driven by the parking gear in the box, I am only guessing. :) It is showen in my book as a sheild.

Which model has a Hall effect pick-up?. Hall and magnetic pick-ups are not compatable. The Hall gives a 0 to 5Volt square wave sig. The magnetic gives a zero crossing sine wave.

Harvey. ;)

[drivfour]

I bought a 96 legacy 4eat to put in theee svx. The speed drives at the rh axle are different one is square one drive is a slot- so it does not appear I can put the 3 wire svx into the 96 legacy housing. Any ideas?
thanks

[AJ4U2]

Could someone explain how this error could happen by a swap?

My understanding of the speedo setup is that a gear is driven from the right side axle, which in turn does some magnetic signaling that gets decoded and sent on to the speedometer.

My point is the speedo, since it's driven by axle revolutions, should register exactly the same (good or bad) before & after, regardless of the ratio installed.

So, which automotive class do I need to take over again?

The speed sensor is doing what it is surpose to do,need to slow down the speed sensor< it is messuring the speed of the alxe that is turning, say the svx was turing 50 times and now it is turning 60 times because of the smaller gears, so you will have to change the speedo gears, say4:11 has 40 splines and the svx has 60 that means the speed sensor is counting revolotion per alxe, it is not the sensor it is the speedo gears itself, because the axle is turning faster,your right it is decoding the signal but it is for the 4:11 not the 3:54, The samller the gear the faster it turns, the speed sensor is desisgn to work with the 3:54,not the 4:11, I have not got into this yet since i am still in the process but somehow it has all got to match from one tranny to the other, The speedo gears are spline with more or less and the speed sensor has got to signal it has 4:11 or 4:44, you might have to change the gears on the axle shaft to match the speed sensor, If i am not mistaken the speedo on the axle has 41 spline while the sensor has 10 and the stock has 35 while the sensor has 10 so big difference in ratio, don't know if speedo gears are interchaneable or not, You can take to the speedo shop where they calabrate them buy moving the spring on the dial behind the speedometer they either tighten it up or back, it just like the old time clocks when they were fast you move the spring tension one way or the other about 60 bucks here in NC, best way to go, Just some thoughts on this, it does fix the mileage to
I might be all wrong on the SVX but i know on GM you have to match all the speedo gears to be correct, you got to change the speedo gears in the trans and the sensor gears to be correct, when you change out 3:55 to 4:10

[pavanbabut]

Hi all,
Any updates on this issue??

I am having a doubt, even if we adjust the needle to exact position (say while crusing at 60mph using GPS as reference), the total miles reading will still have wrong miles on it (I mean more miles than it actual had on it), right??

thanks,
-Pavan.