Speedometer issue after AT545 to MT643 conversion

[NovaTRON]

So I'm having the speedometer issue after having my transmission upgraded (on a 5.9 12v) from an AT545 to a MT643. It's been quite an ordeal, but I'm (hopefully) down to the last couple issues....

The shop connected the sending unit of the 643 to my existing speedometer and now my speedometer and odometer are both reading double (x2).

I keep reading that the 545 speedometer output is electric, while the 643 has a mechanical output. Well the sending unit on the my 643 does not use a cable- it's a plug with 4 wires- though my bus's speedometer only uses 2 wires - one is power and one is signal. So 2 of the 4 wires are not connected.

Anyone have any insight into a fix for the issue?

 

[alpine44]

So I'm having the speedometer issue after having my transmission upgraded (on a 5.9 12v) from an AT545 to a MT643. It's been quite an ordeal, but I'm (hopefully) down to the last couple issues....

The shop connected the sending unit of the 643 to my existing speedometer and now my speedometer and odometer are both reading double (x2).

I keep reading that the 545 speedometer output is electric, while the 643 has a mechanical output. Well the sending unit on the my 643 does not use a cable- it's a plug with 4 wires- though my bus's speedometer only uses 2 wires - one is power and one is signal. So 2 of the 4 wires are not connected.

Anyone have any insight into a fix for the issue?

A speed sensor needs at least 3 wires. Supply voltage, ground, and output signal. The fourth wire may be signal ground.

Call Chris at UJoint Offroad. He uses a signal converter after installing 4WD transfer cases with different speed sensors. The company he gets the converters from (name escaped me) will know how to deal with your issue; it's their business.

Edit: Name is Abbott Enterprises Inc.

 

[cadillackid]

the MT643 is available 2 ways.. with a speedo GEAR and with a Tone ring.. the 545 was the same way also..



if you are using a gear to electric conversion on one or the other then the number of pulses would be off..



stock the tione ring pushes 16 pulses per rev .. the gear with a converter on it whould be made to do the same..



im assuming your speedometer itself is electric? (wire going to it and not a cable?)//


look at your old trans and see what type of sensor it had in it.. and then the new.. its Possible the speedo pickup is grabbing some sort of signal from the work gear but highly unlikely..



the Tone ring or gear can be extracted from the old AT545 and installed into the new 643.. the shaft sizes, lengths and such are identical on both..


-Christopher

 

[NovaTRON]

A speed sensor needs at least 3 wires. Supply voltage, ground, and output signal. The fourth wire may be signal ground.

Call Chris at UJoint Offroad. He uses a signal converter after installing 4WD transfer cases with different speed sensors. The company he gets the converters from (name escaped me) will know how to deal with your issue; it's their business.

Edit: Name is Abbott Enterprises Inc.

The speedometer in the bus only uses 2, so that's why only 2 were connected to the 643 sending unit... Are you saying I need to ground one of the remaining 2 wires?

I will give Ujoint Offroad a call (or Abbott)- thanks.

 

[NovaTRON]

the MT643 is available 2 ways.. with a speedo GEAR and with a Tone ring.. the 545 was the same way also..



if you are using a gear to electric conversion on one or the other then the number of pulses would be off..



stock the tione ring pushes 16 pulses per rev .. the gear with a converter on it whould be made to do the same..



im assuming your speedometer itself is electric? (wire going to it and not a cable?)//


look at your old trans and see what type of sensor it had in it.. and then the new.. its Possible the speedo pickup is grabbing some sort of signal from the work gear but highly unlikely..



the Tone ring or gear can be extracted from the old AT545 and installed into the new 643.. the shaft sizes, lengths and such are identical on both..


-Christopher

No Cable, the speedometer is electric.

Edit:I'll see about extracting the gear from the old 545, the shop is holding it for still,,, but from talking to the mechanic and he said the gears were different and weren't compatible.

 

[cadillackid]

OK.. yes 2 wires.. what i was asking is if the old trans had a 2 wire sensor in it screwed to a gear drive or was it a 2 wire sensor that goes directly into the trans?


and same with new trans?.. there are devices made to convert the gear drive to an electric signal.. its possible the 643 was shipped with a gear and not a tone ring.. and the shop installed a converter device that takes the rotation of the gear drive and converts to 2 wire electric...





like I say my NT643 I got from LKQ shipped with a gear and not a tone ring.. the allison speed sensor only needs 2 wires as it generates a Millivolt AC voltage and the dashboard speedo reads the frequency of the AC signal to get the speed..



the standard tone ring in an AT545 is a 16 tooth as it is if in an MT643.. its possible the chassis manufacturer used a different one..



to extract it and move it over..
order 2 brand new allison transmission rear seals..(you only need one.. but they are easy to FUBAR..)

obtain or make the tailshaft bearing extractor tool...

(I made my own then an old allison guy gave me the real one)
I can post pics of the tool later


obtain or make a allison rear bearing installer.. may be able to rent this from auto zone.. it should be similar to allison 1000 used in duramaxx 2 wheel drive trucks.



on the 545

1. remove the yoke.
2. remove the rear seal
3. remove the LARGE snap ring that holds the rear bearing in.

4. using tool above, pull the rear bearing carefully..

5. spacer and tone ring just pull off of tailshaft.


on the 643. perform the steps 1-5 to pull the old ring or gear from 643..



now install..
insert spacer and bearing onto 643 shaft.
install the 643 bearing(not 545 bearing)(you will know its in all the way when the snap ring groove is revealed fully).
install the snap ring
install a brand new rear seal
install the yoke
install the sensor..


a bit of a PITA tools wise.. your trans shop if they service allisons should have the tools..



ill post pics if you want of the special tools..


-Christopher

 

[alpine44]

OK.. yes 2 wires.. what i was asking is if the old trans had a 2 wire sensor in it screwed to a gear drive or was it a 2 wire sensor that goes directly into the trans?


and same with new trans?.. there are devices made to convert the gear drive to an electric signal.. its possible the 643 was shipped with a gear and not a tone ring.. and the shop installed a converter device that takes the rotation of the gear drive and converts to 2 wire electric...





like I say my NT643 I got from LKQ shipped with a gear and not a tone ring.. the allison speed sensor only needs 2 wires as it generates a Millivolt AC voltage and the dashboard speedo reads the frequency of the AC signal to get the speed..



the standard tone ring in an AT545 is a 16 tooth as it is if in an MT643.. its possible the chassis manufacturer used a different one..



to extract it and move it over..
order 2 brand new allison transmission rear seals..(you only need one.. but they are easy to FUBAR..)

obtain or make the tailshaft bearing extractor tool...

(I made my own then an old allison guy gave me the real one)
I can post pics of the tool later


obtain or make a allison rear bearing installer.. may be able to rent this from auto zone.. it should be similar to allison 1000 used in duramaxx 2 wheel drive trucks.



on the 545

1. remove the yoke.
2. remove the rear seal
3. remove the LARGE snap ring that holds the rear bearing in.

4. using tool above, pull the rear bearing carefully..

5. spacer and tone ring just pull off of tailshaft.


on the 643. perform the steps 1-5 to pull the old ring or gear from 643..



now install..
insert spacer and bearing onto 643 shaft.
install the 643 bearing(not 545 bearing)(you will know its in all the way when the snap ring groove is revealed fully).
install the snap ring
install a brand new rear seal
install the yoke
install the sensor..


a bit of a PITA tools wise.. your trans shop if they service allisons should have the tools..



ill post pics if you want of the special tools..


-Christopher

The way I understand your comments is that the correct sensors for both transmissions have only two wires (i.e. no signal amplifier) but that the number of teeth on the tone ring is different on the MT643 compared to the AT545.

Why does the sensor in the OP's photo of his MT643 have four wires? Wrong sensor?

 

[cadillackid]

the photo isnt showing up on my end..



the way I understand it is the followingL
the Standard Tone ring for the AT545 and MT643 is always supposed to be 16 teeth...

its Possible an OEM Spec'd a different tone ring for their application.. allison did a lot of custom stuff for OEM's..


BOTH AT545 and MT643 were available as a mechanical or an electronic output..


the difference between electronic and mechanical output is a tone ring vs a Gear


the Same Tone ring or gear fits both AT545 and MT643 as the output shaft size on both is the same..



in my opinion the correct way to fix this is to extract the tone ring and spacer from the original AT545 and install them on the new MT643. this would ensure having the correct number of teeth..


an OEM can specify a sensor with 4 wires even though the standard was 2... the sensor can be different from the standard as long as it threads in and poicks up the signal..



the procedure I described can be done with a transmission in a bus or on the ground..

fluid loss will be minimal so you dont even need to drain the pan.

-Christopher

 

[cadillackid]

I should also mention it may be possible to "program" the speedometer without replacing any parts. I dont klnow much about this bus but I knoiw that most either had dip switches or if the bus is electronic engine the ECM can be adjusted for different gear ratios and provisions..



im not sure if that year thomas used the ametek speedo or not which has a dip switch on it.. some of the freightliners did..

-Christopher

 

[NovaTRON]

I did link a photo in my original post - but it's not showing on my end either,

This bus has the 12-valve mechanical engine. I'm not sure about the dip switches, if I have them would they be on the back of the speedometer?

I'm making a plan to go back to the shop and see about removing the original Tone Ring from the AT545 -

Thanks for all the insights

nova~

 

[NovaTRON]

Here is the sensor/sending unit from the AT545

(try this again- sorry still learning to use this site)
Here is the sending unit/sensor on the MT643

I haven't pulled the sensor out of the MT643 yet to compare, but the mechanic says they are "2 different types of sensors" , so I'm not sure if pulling the Tone Ring gear off of the AT545 is the way to go or not..

 

[alpine44]

Here is the sensor/sending unit from the AT545

(try this again- sorry still learning to use this site)
Here is the sending unit/sensor on the MT643

I haven't pulled the sensor out of the MT643 yet to compare, but the mechanic says they are "2 different types of sensors" , so I'm not sure if pulling the Tone Ring gear off of the AT545 is the way to go or not..

There is no tone ring in your AT545 show in the picture. It uses a gear that meshes with the gear of the transducer you are holding in your hand. This transducer adapts transmissions that originally had a mechanical speedometer cable to an electronic speedometer.

A tone ring has very coarse, square teeth that are not meant to mesh with anything. It is a non-contact solution that relies on changes of a magnetic field (or more precisely, reluctance). That's what your mechanic tried to convey; two completely different principles. You would have to get the correct AT545 tone ring from somewhere else like fleabay or a junkyard.

BTW, that conversion box I was talking about is called ERA and costs $180.

 

[NovaTRON]

.....

BTW, that conversion box I was talking about is called ERA and costs $180.

Thank you! I'll look into this solution, which may be the best bet, including if I ever end up changing my rear end gear ratio.

 

[alpine44]

Thank you! I'll look into this solution, which may be the best bet, including if I ever end up changing my rear end gear ratio.

To answer your previous question: The adjustable Thomas/Ametek speedometers have the dip switches visible from the rear in a cut-out. I have the instructions for the adjustment if you need them.

 

[cadillackid]

Ok .that was the device I tried to describe previous was a gear to electric conversion.. now take the sensor out of your 643 and how down the hole? Is that a worm gear like the hole shown or is it the course gear alpine talks of which is a tone ring..

So right now how is it set up? The moved the sensor from your 545 and screwed it into your new 643 and your speedo reads double speed?

The 4 wire sensor is what was OEM on your bus correct? I’d the 2 wire that’s in the at545?
Any part numbers on that 2 wire sensor or where it came from?

What I’m trying to figure out is what was on the bus originLly and which one was new with the new trans?
Reason I ask about it is if he cobbled together wiring to make the 4 wire sensor work when the 2 wire sensor was oem that could explain issues..

Sounds like alpine has you covered better than I at this point.

Although that 2 wire sensor intrigued me as I am working on another bus project where one just like that would be the ticket so if it has any numbers or where you got it from please do tell

 

[NovaTRON]

Ok .that was the device I tried to describe previous was a gear to electric conversion.. now take the sensor out of your 643 and how down the hole? Is that a worm gear like the hole shown or is it the course gear alpine talks of which is a tone ring..

So right now how is it set up? The moved the sensor from your 545 and screwed it into your new 643 and your speedo reads double speed?

The 4 wire sensor is what was OEM on your bus correct? I’d the 2 wire that’s in the at545?
Any part numbers on that 2 wire sensor or where it came from?

What I’m trying to figure out is what was on the bus originLly and which one was new with the new trans?
Reason I ask about it is if he cobbled together wiring to make the 4 wire sensor work when the 2 wire sensor was oem that could explain issues..

Sounds like alpine has you covered better than I at this point.

Although that 2 wire sensor intrigued me as I am working on another bus project where one just like that would be the ticket so if it has any numbers or where you got it from please do tell

No sensors were moved. The 2 wire transducer/sending unit with the pencil gear (pictured) was the original on the AT545.

The 4 wire sensor/sending unit came with the MT643 and was straight connected right to speedometer, though with just 2 wires, and is now giving me the doubled speed & distance.

Without pulling it out to look, I'm assuming this 4 wire sensor on the MT643 is the type that uses a Tone Ring (but that's also what I assumed about the 545 -which contradicts every thing I had read up until now)

Sounds like the Electronic Ratio Adapter (ERA) is the easiest fix for this job.

Oh and here is a pic of speedometer - if that helps anything

 

[cadillackid]

Ok now I’m understanding. That 4 wire sensor may not give a signal compatible with your speedo also. I’d love to see a pinout of it as I’ve only ever seen 3 wire not 4.
So that 2 wire is what was originally in the bus as OEM.
So yours may be opposite of my issue. My 545 had a tone ring my 643 a gear.
And the new endeavor I’m working on has a gear and needs a tone ring. I need a sensor like your 2 wire.

You could swap the gear and ring from trans to trans.. I’m not sure what that box posted is, I couldn’t find it, I’ll have to scroll back through the thread to see if it is special.

This is the speedo cal unit I use and it works great.
https://www.summitracing.com/parts/...MIv76G5pDL5AIVNP_jBx01eg0DEAQYASABEgLeR_D_BwE

 

[NovaTRON]

Which unit should I go with???

Ok now I’m understanding. That 4 wire sensor may not give a signal compatible with your speedo also. I’d love to see a pinout of it as I’ve only ever seen 3 wire not 4.
So that 2 wire is what was originally in the bus as OEM.
So yours may be opposite of my issue. My 545 had a tone ring my 643 a gear.
And the new endeavor I’m working on has a gear and needs a tone ring. I need a sensor like your 2 wire.

You could swap the gear and ring from trans to trans.. I’m not sure what that box posted is, I couldn’t find it, I’ll have to scroll back through the thread to see if it is special.

This is the speedo cal unit I use and it works great.
https://www.summitracing.com/parts/...MIv76G5pDL5AIVNP_jBx01eg0DEAQYASABEgLeR_D_BwE

I could swap the gear and ring from trans to trans, but it seems using a calibration unit would be much easier/faster- though does requires another purchase.

The Abbott unit cost $180
ERA (Electronic Ratio Adapter)Â* Your Speedometer Solution

While the Dakota Digital unit is $80
https://www.summitracing.com/parts/dak-sgi-5e?seid=srese1&gclid=EAIaIQobChMIv76G5pDL5AIVNP_jBx01eg0DEAQYASABEgLeR_D_BwE

Are these both going to accomplish the exact same thing? that is- re-calibrate/ adjust the ratio of the speedometer signal.

Anyone have an opinion on which unit to go with?

:Thanx:

 

[cadillackid]

I am using the dakota Digital unit on my red bus.. it can take in and custom adjust about any type of speed signal into any type.... it has a mode where you can drive a known speed... ie a GPS or follow other vehicle with calibrated speedometer.. and you can live-adjust the signal ratio up and down till your speedo matches..





your 2 pin adapter with a gear on the end? is there any part number on that? i really Need to buy one Just like that but have been googling and cant find that beast... where did you get that? was it OEM to your Bus?

 

[NovaTRON]

I am using the dakota Digital unit on my red bus.. it can take in and custom adjust about any type of speed signal into any type.... it has a mode where you can drive a known speed... ie a GPS or follow other vehicle with calibrated speedometer.. and you can live-adjust the signal ratio up and down till your speedo matches..





your 2 pin adapter with a gear on the end? is there any part number on that? i really Need to buy one Just like that but have been googling and cant find that beast... where did you get that? was it OEM to your Bus?

Sounds fairly simple to install/adjust. And it saves $100 over the Abbott unit.

That 2 pin adapter is the OEM to the bus (as far as I know) . You can see some numbers in that picture, but they look too worn-out to be readable.

It's certainly possible that I could get that part back, though it is a bit of a drive for me.. I left the AT545 at the shop that did the swap/conversion- they are holding it for me for a short time until I determine if I can sell it for any core value, if not, they are just going sent it to scrap.. I've just had too much other things going on to even want to look into it.