Why won't my HD output or Atlas tcase speedometer not work?

[Yeller]

I saw this today in another thread. It looks like they got the problem solved but I wanted to make a specific thread about this issue that hopefully will help someone else, I've seen it many times.

Unless you are an old Mopar guy the speedometer gear and housing in an Atlas transfer case or HD Dana 20 output can be problematic to get the speedometer to function. It is really simple in design but not clear when no one tells you how to get it to work correctly.

I'll start with the design, which is really simple when explained how and why, it was copied not so much because the Advance Adapters parts were designed to copy a jeep, it goes much further back than that to Mopar/Dodge/Chrysler/Plymouth. When they developed the Torque Flight series of transmissions in the late 1950's they developed a speedometer drive that could accommodate a very large swing of gear ratios and tire sizes with a single drive gear on the output. To do this, it required that the driven gears be able to be different diameters to accommodate the range of teeth available. The tooth count has a wide range from 26-45 teeth. This design was carried all the way through to the mid 2000's when they were replaced with a speed sensor.

Now on to "why won't my speedometer work?". It is simple really, to accommodate the diameters of the gears they made the driven gear holder eccentric; it rotates to accommodate the different diameters of the driven gear, moving the axis of the driven gear closer or further away from the drive gear as the housing is rotated. This picture isn't super clear but you can see that it is eccentric. You can also read the numbers on the gear holder, the dot next to the numbers needs to be pointed at the 6 o'clock position for the tooth count range that your gear has. Do that and install the clamp and it will drive your speedometer or VSS adapter just like it is supposed to. The trouble arises when a 33-tooth gear is installed in the 39-45 tooth position and not in the 32-38 tooth position, the gears are not meshing together. I find it helpful to use a small screwdriver in the square end to turn the driven gear while in stalling so the gears mesh together and ease that installation.

Now if your speedometer is not correct, the tooth count needs to be more to make the speedometer read slower and less to read faster. So if your speedometer reads 66mph when you are traveling 60mph and you have a 33 tooth gear, going to a 36 tooth should get you within 2% of 60mph. Same if it reads 55 when traveling 60mph, going from a 33 tooth to a 30 tooth should get within 2%. FYI most OEM speedometers are only accurate within 5% so getting within 2% is very good.

Happy speedometer gear installing

 

[jamesroney]

I saw this today in another thread. It looks like they got the problem solved but I wanted to make a specific thread about this issue that hopefully will help someone else, I've seen it many times.

Unless you are an old Mopar guy the speedometer gear and housing in an Atlas transfer case or HD Dana 20 output can be problematic to get the speedometer to function. It is really simple in design but not clear when no one tells you how to get it to work correctly.

I'll start with the design, which is really simple when explained how and why, it was copied not so much because the Advance Adapters parts were designed to copy a jeep, it goes much further back than that to Mopar/Dodge/Chrysler/Plymouth. When they developed the Torque Flight series of transmissions in the late 1950's they developed a speedometer drive that could accommodate a very large swing of gear ratios and tire sizes with a single drive gear on the output. To do this, it required that the driven gears be able to be different diameters to accommodate the range of teeth available. The tooth count has a wide range from 26-45 teeth. This design was carried all the way through to the mid 2000's when they were replaced with a speed sensor.

Now on to "why won't my speedometer work?". It is simple really, to accommodate the diameters of the gears they made the driven gear holder eccentric; it rotates to accommodate the different diameters of the driven gear, moving the axis of the driven gear closer or further away from the drive gear as the housing is rotated. This picture isn't super clear but you can see that it is eccentric. You can also read the numbers on the gear holder, the dot next to the numbers needs to be pointed at the 6 o'clock position for the tooth count range that your gear has. Do that and install the clamp and it will drive your speedometer or VSS adapter just like it is supposed to. The trouble arises when a 33-tooth gear is installed in the 39-45 tooth position and not in the 32-38 tooth position, the gears are not meshing together. I find it helpful to use a small screwdriver in the square end to turn the driven gear while in stalling so the gears mesh together and ease that installation.

View attachment 932072

Now if your speedometer is not correct, the tooth count needs to be more to make the speedometer read slower and less to read faster. So if your speedometer reads 66mph when you are traveling 60mph and you have a 33 tooth gear, going to a 36 tooth should get you within 2% of 60mph. Same if it reads 55 when traveling 60mph, going from a 33 tooth to a 30 tooth should get within 2%. FYI most OEM speedometers are only accurate within 5% so getting within 2% is very good.

Happy speedometer gear installing

The speedometer output on the Torqueflite, as well as, Jeep, and GM is 7/8-18 male thread. The Ford passenger car uses an o-ring sealed push in type. So you still need some kind of adapter, or replace the cable. I will never understand why Advance doesn't make the adapter. I have had to build a few dozen for friends. I use a piece of aluminum hex stock, and thread one end 7/8-18, and bore the other end for the Ford drive. There are many other ways to do it, but this allows the use of the factory speedo cable, or the Ford VSS.
Send me a PM, with an e-mail address, and I can send you a pic of the one in my Bronco.

I'm not paying $200 to post pictures. (Been here since 2007, and at $12.00 per year, I've reached my limit.)

 

[Yeller]

I use a speedometer cable for a 78 Cheverolet K30 with cruise control. The cable is 83" long, has the correct 7/8-18 thread for the speedometer drive, and the 5/8-18 thread for the speedometer head. Today's cost on Rockauto is $7.24. If 83" is too long, there are shorter options for 67-72 chevy trucks, they have the correct ends as well and have similar price points.

 

[Yeller]

@jamesroney sent me the pic of his adapter that he uses to drive the Ford VSS. He bottoms the treads and pins the VSS through the o-ring slot. I'll let him expand on that if he wishes.

This brings up another question. Does anyone know the pulse rate of the Ford VSS? Maybe a question for @EFI Guy .

 

[jamesroney]

EEC-4 is looking for 8 pulse per revolution, 8000 pulse per mile. Odometer looking for 1000 revs per mile.

 

[jamesroney]

I use a speedometer cable for a 78 Cheverolet K30 with cruise control. The cable is 83" long, has the correct 7/8-18 thread for the speedometer drive, and the 5/8-18 thread for the speedometer head. Today's cost on Rockauto is $7.24. If 83" is too long, there are shorter options for 67-72 chevy trucks, they have the correct ends as well and have similar price points.

This needs to be a sticky. 67-72 k10 pickup. Got it!

 

[Yeller]

8k/mile, that makes sense, and why AA does not make an adapter. Dakota digital makes an 8k generator that connects directly to the speedometer drive, just needs wired in place of the ford VSS. I do get wanting to keep the Ford VSS though. I need to do more research, it appears Dakota Digital may have a solution that retains the Ford VSS, probably wishful thinking, but will dig.

There are easy solutions if we just talk about it, they are out there. For whatever reason speedometer drives are like black magic, really aren’t, just needs to be some information shared.


Here's an image of the Dakota part with part number.

They also have a pass through to drive a mechanical speedo and run the VSS. Dakota Digital pass through VSS

 

[toddz69]

I saw this today in another thread. It looks like they got the problem solved but I wanted to make a specific thread about this issue that hopefully will help someone else, I've seen it many times.

Unless you are an old Mopar guy the speedometer gear and housing in an Atlas transfer case or HD Dana 20 output can be problematic to get the speedometer to function. It is really simple in design but not clear when no one tells you how to get it to work correctly.

I'll start with the design, which is really simple when explained how and why, it was copied not so much because the Advance Adapters parts were designed to copy a jeep, it goes much further back than that to Mopar/Dodge/Chrysler/Plymouth. When they developed the Torque Flight series of transmissions in the late 1950's they developed a speedometer drive that could accommodate a very large swing of gear ratios and tire sizes with a single drive gear on the output. To do this, it required that the driven gears be able to be different diameters to accommodate the range of teeth available. The tooth count has a wide range from 26-45 teeth. This design was carried all the way through to the mid 2000's when they were replaced with a speed sensor.

Now on to "why won't my speedometer work?". It is simple really, to accommodate the diameters of the gears they made the driven gear holder eccentric; it rotates to accommodate the different diameters of the driven gear, moving the axis of the driven gear closer or further away from the drive gear as the housing is rotated. This picture isn't super clear but you can see that it is eccentric. You can also read the numbers on the gear holder, the dot next to the numbers needs to be pointed at the 6 o'clock position for the tooth count range that your gear has. Do that and install the clamp and it will drive your speedometer or VSS adapter just like it is supposed to. The trouble arises when a 33-tooth gear is installed in the 39-45 tooth position and not in the 32-38 tooth position, the gears are not meshing together. I find it helpful to use a small screwdriver in the square end to turn the driven gear while in stalling so the gears mesh together and ease that installation.

View attachment 932072

Now if your speedometer is not correct, the tooth count needs to be more to make the speedometer read slower and less to read faster. So if your speedometer reads 66mph when you are traveling 60mph and you have a 33 tooth gear, going to a 36 tooth should get you within 2% of 60mph. Same if it reads 55 when traveling 60mph, going from a 33 tooth to a 30 tooth should get within 2%. FYI most OEM speedometers are only accurate within 5% so getting within 2% is very good.

Happy speedometer gear installing

Thanks for the info on this! I'll likely be doing this soon when I change my diff gears. I figured I would be changing the speedo gear but wasn't aware of the alignment tips.

Todd Z.

 

[Yeller]

Thanks for the info on this! I'll likely be doing this soon when I change my diff gears. I figured I would be changing the speedo gear but wasn't aware of the alignment tips.

Todd Z.

You are most welcome! Hopefully through the course of this thread we can give points to solve other speedometer drive issues with cables and VSS

 

[jamesroney]

8k/mile, that makes sense, and why AA does not make an adapter. Dakota digital makes an 8k generator that connects directly to the speedometer drive, just needs wired in place of the ford VSS. I do get wanting to keep the Ford VSS though. I need to do more research, it appears Dakota Digital may have a solution that retains the Ford VSS, probably wishful thinking, but will dig.

There are easy solutions if we just talk about it, they are out there. For whatever reason speedometer drives are like black magic, really aren’t, just needs to be some information shared.


Here's an image of the Dakota part with part number.
View attachment 932083

They also have a pass through to drive a mechanical speedo and run the VSS. Dakota Digital pass through VSS
View attachment 932084

View attachment 932085

I have purchased this in the past. (and others like it) In each case you end up buying a speedometer cable. Also, the plug in connector from the RJM EFI harness does not fit. The plug is looking for a Ford VSS.

The one from Wild Horses is similar, but instead of the double nut...it uses a short speedo cable to remote mount the universal VSS. It's actually a decent solution, because it gets the VSS away from the transfer case. But of course you still have to buy 2 speedo cables, and hard wire the VSS.

Tom's has a nice speedo to Ford VSS cable, But you can also machine the end of the factory ford speedo pencil, and shove it into the VSS.

 

[Yeller]

@jamesroney very true about still needing to purchase a speedometer cable, the GM solution mentioned above at least removes the cost roadblock, yes there is still a cost, but typically under $20 even from the local parts pusher. I've seen those "conversion cables" go for well over $100 that do nothing more than the off the shelf GM cable that is cheap, when I looked on RA this morning, they were less than $10.

 

[jamesroney]

@jamesroney very true about still needing to purchase a speedometer cable, the GM solution mentioned above at least removes the cost roadblock, yes there is still a cost, but typically under $20 even from the local parts pusher. I've seen those "conversion cables" go for well over $100 that do nothing more than the off the shelf GM cable that is cheap, when I looked on RA this morning, they were less than $10.

Pioneer CA3004 for the 1970 K10 Pickup should get it done. I wish I knew that info 20 years ago!

Also available locally at Oreilly Auto. $12.99. THANKS!!!

 

[bigmuddy]

I wish I had known this a few years ago when I bought a new and expensive GPS speedo due to my atlas II.

 

[Soylent]

You can also read the numbers on the gear holder, the dot next to the numbers needs to be pointed at the 6 o'clock position for the tooth count range that your gear has. Do that and install the clamp and it will drive your speedometer or VSS adapter just like it is supposed to. The trouble arises when a 33-tooth gear is installed in the 39-45 tooth position and not in the 32-38 tooth position, the gears are not meshing together. I find it helpful to use a small screwdriver in the square end to turn the driven gear while in stalling so the gears mesh together and ease that installation.

View attachment 932072

This would have been a nice fact for WH to include with the output shaft assembly instructions. I just assumed you line up the dot with the clamp bolt hole. Luckily I haven’t driven it yet.

 

[Yeller]

This would have been a nice fact for WH to include with the output shaft assembly instructions. I just assumed you line up the dot with the clamp bolt hole. Luckily I haven’t driven it yet.

This is what I find interesting, it is not in anyone’s instructions that I can find. This design is sold by many companies and produced by several manufacturers.

 

[jamesroney]

This is what I find interesting, it is not in anyone’s instructions that I can find. This design is sold by many companies and produced by several manufacturers.

The engineers at Mopar (torqueflight) and GM (hydramatic) were kind enough to cast in a little dot pointer to aim at the corresponding mark on the drive pencil.

For whatever reason, New Process, Dana Spicer, and Advance Adapters did not get that memo. So the NP231 housing points somewhere (?) and the Advance Adapters SYE conversion housing, as well as the Upgraded Dana 300 / Dana 20 / Atlas output do not have the pointer.

So you get to play the "try this location and see if the speedometer works" game. Then roll it to the next notch. It's annoying enough to drive you crazy, but not annoying enough to learn that it is always the 6:00 position. So I get to learn it over again and again.

Thanks.

 

[Yeller]

The engineers at Mopar (torqueflight) and GM (hydramatic) were kind enough to cast in a little dot pointer to aim at the corresponding mark on the drive pencil.

For whatever reason, New Process, Dana Spicer, and Advance Adapters did not get that memo. So the NP231 housing points somewhere (?) and the Advance Adapters SYE conversion housing, as well as the Upgraded Dana 300 / Dana 20 / Atlas output do not have the pointer.

So you get to play the "try this location and see if the speedometer works" game. Then roll it to the next notch. It's annoying enough to drive you crazy, but not annoying enough to learn that it is always the 6:00 position. So I get to learn it over again and again.

Thanks.

I spent 8 years as a transmission tech In the 90’s, I didn’t learn the 6:00 thing until recently. I always used my pocket screw driver to wiggle the gear while I installed the gear housing, rotated the housing counter clockwise until it stopped then rotate it back enough to get the clamp on, it always worked. A trick I learned from an old timer.

 

[jamesroney]

I spent 8 years as a transmission tech In the 90’s, I didn’t learn the 6:00 thing until recently. I always used my pocket screw driver to wiggle the gear while I installed the gear housing, rotated the housing counter clockwise until it stopped then rotate it back enough to get the clamp on, it always worked. A trick I learned from an old timer.

Ok. But do you start from the clockwise direction, and rotate the Eccentric until it engages, or do you go counter-clockwise? Because unless you are at the apogee or perigee…you will enter the worm gear from a different direction, and the speedo pencil gear centerline will be off axis, and the stupid teeth of the retainer will be in the wrong place. Because the retainer bolt is not at the 3:00 position. It is near the 2:00 position, Which makes it errror proof. Unless you do it backwards, and then actually either strips, or shears off the teeth. So again…do you engage it with the pencil to the rear of center, or front?

 

[Yeller]

Ok. But do you start from the clockwise direction, and rotate the Eccentric until it engages, or do you go counter-clockwise? Because unless you are at the apogee or perigee…you will enter the worm gear from a different direction, and the speedo pencil gear centerline will be off axis, and the stupid teeth of the retainer will be in the wrong place. Because the retainer bolt is not at the 3:00 position. It is near the 2:00 position, Which makes it errror proof. Unless you do it backwards, and then actually either strips, or shears off the teeth. So again…do you engage it with the pencil to the rear of center, or front?

I follow what you’re saying. I start with the eccentric as far away as possible from the drive gear, so the thinnest part of the eccentric is at the bottom. At that point, I’ve yet to find a pencil gear that engages the drive gear on the output, not saying it can’t happen, I’ve just not experienced it. At that point rotate counter clockwise wiggling the pencil gear so as it turns it engages the drive gear instead If crashing into it. Rotate until it stops, turn back clockwise until the retainer will bolt in place engaging the slots on the pencil gear holder.

A bit of oil or RTV can be used to lubricate it so it rotates easier. Not necessary but I prefer RTV. If it leaks I want to know it is the inner seal on the pencil gear not the o-ring that got scratched during the installation process.

Some of the older units the etching is much lighter than the ones we get today and often were illegible so this method always works. If you can read the numbers and see the dot, the correct dot at 6:00 position works too.

 

[Yeller]

I decided that I needed to correct the speedometer on my J Truck. It read 8% fast, finally had enough of doing the math and driving so I went from a 34 tooth gear to a 37 tooth, spot on now. Also tested the dot at 6:00 theory, works perfectly. 32-38 tooth dot at 6:00 and like magic it works