Mechanical driven speedo cable to electronic cluster? - PeachParts Mercedes-Benz Forum

rwd4evr · #1 02-24-2021, 04:56 AM

Any ideas on a simple(ish?) Way to run my stock speedo in a 85 w126 300sd with a mechanical speedo 4 speed trans from a 240d? How many pulses per revolution(I'm sure I can figure that out after I pull the drivetrain)? Maybe rig a tone wheel with screws into the flex disc perimeter? Maybe a tone wheel that bolts to the drive flange facing the trans ? Would the sensor live on a bracket exposed? Abs sensors aren't sealed and are almost identical. Hmm lots of ideas now just writing this. Anyone done anything like this?

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Roncallo · #2 02-25-2021, 10:56 PM

Quote:

Originally Posted by rwd4evr

Any ideas on a simple(ish?) Way to run my stock speedo in a 85 w126 300sd with a mechanical speedo 4 speed trans from a 240d? How many pulses per revolution(I'm sure I can figure that out after I pull the drivetrain)? Maybe rig a tone wheel with screws into the flex disc perimeter? Maybe a tone wheel that bolts to the drive flange facing the trans ? Would the sensor live on a bracket exposed? Abs sensors aren't sealed and are almost identical. Hmm lots of ideas now just writing this. Anyone done anything like this?

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does your 4 speed use a 110mm bolt circle 3 lobed flange. If yes, I have tone wheels.

Roncallo · #3 02-26-2021, 12:35 AM

See this thread.

Connect 722.6 Transmission to Electronic Speedometer

rwd4evr · #4 02-26-2021, 06:21 AM

Quote:

Originally Posted by Roncallo

does your 4 speed use a 110mm bolt circle 3 lobed flange. If yes, I have tone wheels.

If that is the v8 auto size then no. All the 4 speeds are the small 6cyl size. Even the v8 107 and w116. Is that the same count as a stock 722.3? If it's just 4 windows I can make something pretty easy I'm sure.

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Roncallo · #5 02-26-2021, 11:57 AM

Yes that's the V8 size. Your the second guy asking about the 6 cyl size. I believe they are 100mm bolt circle.

I made two proto types myself. First one took me 40 hr. The second one took me 20hr. I would guess a really good machinist could get that down to 10hr on my manual machines. But I cant do heat treating. As one of our ME told me at work its 15 minute job on todays high speed CNC machining centers once the programing is done.

Tony H · #6 02-26-2021, 12:50 PM

Not sure if interested but there is a GPS spedo driver available. I will probably use that on mine since any other option would be difficult with the WC S10 tailhousing.

rwd4evr · #7 02-26-2021, 03:01 PM

Quote:

Originally Posted by Roncallo

Yes that's the V8 size. Your the second guy asking about the 6 cyl size. I believe they are 100mm bolt circle.

I made two proto types myself. First one took me 40 hr. The second one took me 20hr. I would guess a really good machinist could get that down to 10hr on my manual machines. But I cant do heat treating. As one of our ME told me at work its 15 minute job on todays high speed CNC machining centers once the programing is done.

I was thinking simple like reading the heads of screws in the flex disc or a sheet metal piece something like what you made. Maybe a delrin locking collar on the output flange with bolt heads. I'm really just curious about how many teeth it needs. I do like the GPS sender idea. It really boils down to how cheap or easy it is since my phone/GPS has a speedo on it plus it's manual and the tach works so I'll know how fast I'm going after a couple days anyway.

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rwd4evr · #8 02-26-2021, 03:01 PM

Quote:

Originally Posted by Tony H

Not sure if interested but there is a GPS spedo driver available. I will probably use that on mine since any other option would be difficult with the WC S10 tailhousing.

What's the info on that?

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Roncallo · #9 02-26-2021, 03:35 PM

Quote:

Originally Posted by rwd4evr

I was thinking simple like reading the heads of screws in the flex disc or a sheet metal piece something like what you made. Maybe a delrin locking collar on the output flange with bolt heads. I'm really just curious about how many teeth it needs. I do like the GPS sender idea. It really boils down to how cheap or easy it is since my phone/GPS has a speedo on it plus it's manual and the tach works so I'll know how fast I'm going after a couple days anyway.

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It's not as easy as it looks. Your really need a clean signal. The first one I made used nuts and bolts to hold it on. I tested it on the lathe with a scope and all looked great. But on the car I would get to about 50 MPH and the speed would jump to 70 MPH. The was due to the signal from the heads of the nuts would start to be picked up even though they were far (I thought) away from the pickup.

I retested it on the lathe with bolts installed and you could see a second wave starting to form from the heads of the nuts. It was a very low amplitude but VRS sensors put out a stronger signal with higher speeds. Once I got to about 50MPH the second wave was strong enough trigger the speedometer circuit and make it erratic. That is why the ones I showed you a link to don't use retaining nuts. They are threaded holes and consequently need to be made of 4140 steel and heat treated to the equivalent of a 10.9 metric nut.

Using the head of a bolt may work fine because there would be nothing near it that would be operating at a different frequency. In my case I was picking up 4 pulses per rev from the tone wheel and 3 pulses per rev from the bolts once the speed got high enough.

A hall effect sensor alleviates a lot of problems, but I don't know if that will work on a bolt and it requires a separate circuit. They are also cheaper and the circuit is real simple.

Tony H · #10 02-26-2021, 04:41 PM

Jason, do a web search for GPS speedometer and you will find some options/info on different variations. Been a while since I looked but i remember a few different options.

Quote:

Originally Posted by rwd4evr

What's the info on that?

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rwd4evr · #11 02-26-2021, 09:03 PM

Quote:

Originally Posted by Roncallo

It's not as easy as it looks. Your really need a clean signal. The first one I made used nuts and bolts to hold it on. I tested it on the lathe with a scope and all looked great. But on the car I would get to about 50 MPH and the speed would jump to 70 MPH. The was due to the signal from the heads of the nuts would start to be picked up even though they were far (I thought) away from the pickup.

I retested it on the lathe with bolts installed and you could see a second wave starting to form from the heads of the nuts. It was a very low amplitude but VRS sensors put out a stronger signal with higher speeds. Once I got to about 50MPH the second wave was strong enough trigger the speedometer circuit and make it erratic. That is why the ones I showed you a link to don't use retaining nuts. They are threaded holes and consequently need to be made of 4140 steel and heat treated to the equivalent of a 10.9 metric nut.

Using the head of a bolt may work fine because there would be nothing near it that would be operating at a different frequency. In my case I was picking up 4 pulses per rev from the tone wheel and 3 pulses per rev from the bolts once the speed got high enough.

A hall effect sensor alleviates a lot of problems, but I don't know if that will work on a bolt and it requires a separate circuit. They are also cheaper and the circuit is real simple.

Maybe just make the abs ring 4 large teeth instead of a ****load of tiny ones. ? I disable abs in my cars anyway so I can use the wheel sensor spot.

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Roncallo · #12 02-28-2021, 05:57 PM

Quote:

Originally Posted by rwd4evr

Maybe just make the abs ring 4 large teeth instead of a ****load of tiny ones. ? I disable abs in my cars anyway so I can use the wheel sensor spot.

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That should work. You will need about 3 times as many teeth to compensate for diff ratio. So use 12 teeth of the wheel. Fortunately both the 48 tooth and 96 tooth wheels MB uses divide by 12 nicely.

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