Crazy Speedo sounds coming from dash

[Fordum]

The problem is that the VSS sends a signal to the speedo, ECM, and the cruise control and each requires a different signal. The pieces you need from the t-case are easy to remove and swap. You'll need to remove 4 bolts on the tail housing, then remove a snap ring holding the rear output bearing, then remove 4 more bolts holding the rear bearing housing, then remove another snap ring to remove the 40 tooth tone ring (IIRC there is another snap ring behind the tone ring and I would take that also just in case). The reassembly is the reverse order just swapping the speedo gear for the tone ring. Use RTV on the rear bearing retainer to t-case and once again on the tail housing to the bearing retainer.

Scott, and Jeff. I have watching this thread, some of your project, Scott. And others, and I think I see something.

What you are trying to do, Scott, is the whole conversion, and I think what you are doing is necessary.

But, if all someone wanted to do was swap in just a new electronic speedo for a mechanical one, there seems to be a simpler way.
Bearing in mind, you are looking at the actual parts, I'm just reading stuff on a computer screen.

From what I have read, the speedo takes 4000 pulses per mile for correct reading.
And the mechanical cables turned at 1000 revs per mile.

If that is true, then electronically, its so simple its pitiful. I could whip up a pulse generator that puts out 4 pulses per rev with stuff I have in my junkbox in about an hour.
Commercial encoders that will do that are available from hundreds of sources.

It then boils down to mechanics. You need some way to hook one to the cable or the transmission. Plus, if there is anything else that used the cable input, cruise control for example, then you need to retain the cable.

With all that in mind, I find two products that seem to solve the problem.
This one, scroll down:
http://www.abbott-tach.com/Other Products.html

And this one on that site I mentioned before. Scroll down about halfway to #54MG

http://www.transmissioncenter.net/speedometer_calibration_______va.htm#Cable

Before I ordered either one, I would call or E-mail and ask if it will do what is wanted.
I note the second one mentions 8 pulses. Might work if you have really large tires........

 

[4X4HIGH]

If all he was concerned about was making an electric speedo work you are correct that it would be easy BUT if he is using cruise control and also wants the vehicle to operate properly (not die when coming off of cruise speedo or when coming to a stop) the ECM needs to see a VSS signal also.

 

[Fordum]

If all he was concerned about was making an electric speedo work you are correct that it would be easy BUT if he is using cruise control and also wants the vehicle to operate properly (not die when coming off of cruise speedo or when coming to a stop) the ECM needs to see a VSS signal also.

Ok, glad to hear I still make sense sometimes. At my age I like to keep checking.


But, this just revealed a large hole in my otherwise voluminous bank of knowledge.
What does the cruise control and the ECM use for information with a mechanical speedometer?

On my Ford, there is a pulse generator about 6 inches down from the speedometer in the shaft. Do K5s have a similar setup?

If so, I wonder how many pulses per mile it puts out?
And I wonder if a second one could be added to run a speedometer.
I would be worried that trying to use it to drive cruise control and speedometer might be too much, and one or the other might not get signals that are high enough for them to work.

 

[4X4HIGH]

Ok, glad to hear I still make sense sometimes. At my age I like to keep checking.


But, this just revealed a large hole in my otherwise voluminous bank of knowledge.
What does the cruise control and the ECM use for information with a mechanical speedometer?

On my Ford, there is a pulse generator about 6 inches down from the speedometer in the shaft. Do K5s have a similar setup?

If so, I wonder how many pulses per mile it puts out?
And I wonder if a second one could be added to run a speedometer.
I would be worried that trying to use it to drive cruise control and speedometer might be too much, and one or the other might not get signals that are high enough for them to work.

They use the optic eye (little green box behind the cluster) that attaches to the rear of the mechanical speedo. There are 4 wires going to the optic eye, one is a keyed 12 volt, one is a ground, one goes to the ECM A10 pin and the last one goes to the cruise control module.

 

[Fordum]

They use the optic eye (little green box behind the cluster) that attaches to the rear of the mechanical speedo. There are 4 wires going to the optic eye, one is a keyed 12 volt, one is a ground, one goes to the ECM A10 pin and the last one goes to the cruise control module.

Cool, I never knew that.

Next time I'm in a Pick and Pull, I'm going to watch out for a truck that has the dash mostly out and see if I can snag one of those boxes.
I don't have any use for it that I know of, but I like learning new stuff.

Its probably just a LED/Phototransistor pair with a little interrupter wheel between them.
I wonder how many pulses per rev it puts out.

Either way, if he wants to swap just the speedo, he is still going to have to duplicate those pulses.

Which, of course, makes me wonder if those pulses would drive an electronic speedo....

Either way, its 3:30 in the morning, and I should have been in bed 5 hours ago. Got to get up in 2.....

Sometimes I hate this forum.....

 

[Blue85]

The little optical pick-up was used at least as far back as the early 80's. It is monitoring the spinning of the speedometer itself, which should come out to 2000 pulses per mile.

 

[jeff in co]

I did head out to the junk yard yesterday to start my investigation.

I pulled two speedos (86’ and a 91’). The 86’ is identical to mine but has the “dual” high beam holes at the top instead of one, and it also does NOT have the trip odometer. Everything else, pretty much the same. For $5 each, I figured I could play with them and see how they “tick”.

For the 86’, if I took the needle off correctly, it’s pretty straight forward if I want to just fix my “whining sound”. I used the face plate to apply pressure to the needle evenly and then it popped off. I originally thought I broke the needle but I tried putting it back on and it stayed seated pretty well.

Once the needle and face plate were removed, I could gain access to two small bolts that connect the “speedo cogs” with the spinning magnet. It looks like I can swap the spinning magnet unit to my old speedo and still preserve my mileage and also fix the “whining sound”. I don’t know this for sure (superbowl came) but will try out next weekend. Might be an easy fix.

The number cogs have individual clips in them and at first attempt, could get them out or to move. I think if I go electronic, I may bring it to the speedo shop and have them dial in the correct mileage.

The 91’ is significantly different on the backside. This one is run by the circuit board on the instrument cluster and nothing else. I traced the 3 inputs…..two of them go to several other gauges so I’m assuming that was the positive and negative leads. The third went to the plug harness (and was isolated). I then traced this third wire to a box mounted just under the factory radio on the inside of the dash. I assume this was the DRAC.

I tried tracing the wires from there but couldn’t determine it for sure. There were about 6 wires that headed in the direction of the ECM and another few wires heading towards the fuse block/or toward sensor on t-case. I clipped the wires from there and took the box.

On the T-case, I unscrewed the sensor and started taking apart the rear section of the t-case itself. The driveshaft was already removed so that made it easy….however a heat shield was in the way for the 4th bolt so I couldn’t get it off. I also grabbed the wire connector from the sensor to the other side of t-case. Still need to find another donor truck for the rest of the wires that go up to the DRAC.

I did find a 90’ Blazer….but all those pieces were gone, including the speedo and steering column. I guess someone else has the same idea around here.

 

[cuervo]

It won't get hard or stiffen up in the cold.

See your doctor about that, and if stays stiff for more then 4 hours see him again.

 

[jeff in co]

Which is the "T-case housing?" In Red circle or Blue circle? Would the 40 tooth ring be in there too as an assembly?

If so, I think I can go and get that off the 91' suburban still in the yard. Any concern with 200k on it's speedometer (wear and tear)?

 

[Fordum]

Look at the legend. Number 11 is the speedometer gear on the shaft, and number 9 is the sensor.

They are both in number 8.
They would not be in the red circle, but should be in the blue.

 

[jeff in co]

Look at the legend. Number 11 is the speedometer gear on the shaft, and number 9 is the sensor.

They are both in number 8.
They would not be in the red circle, but should be in the blue.

That's what I though. So I guess I need to pull the whole thing all together......makes sense now.

On another note, I did swing by our local Speedo shop (on a few blocks away). I asked him the different options, cable or electric. He did say that because the truck is so old, adjusting the odometer numbers to match the existing mileage isn't really that big a deal. Especially if my intent was to be legal and just trying to be more accurate with a 7 digit odometer vs. teh 6 digit one. He said I could probably get it set in Denver for about $40 or $50 bucks. Said he needed a special bench to do it and Denver already has it. So good news.


Pretty interesting really......

 

[4X4HIGH]

If you want to convert to the electric speedo you need to remove item #4, then snap ring #5, then unbolt #8, then gently pry #8 away from #17, and #6 will come off with #8, then remove #10 and slide the tone ring off. Basically you need #8, 9, and 11.

 

[jeff in co]

If you want to convert to the electric speedo you need to remove item #4, then snap ring #5, then unbolt #8, then gently pry #8 away from #17, and #6 will come off with #8, then remove #10 and slide the tone ring off. Basically you need #8, 9, and 11.

That helps a ton, thanks.

I did dig into my cable speedo to try and temporarily fix it. I tried turning the needle and it DOES NOT work. Obviously it's vehicle specific. On the Junkyard speedo, I did 3 full revolution and it really never stopped....just twisted the spring inside.

So, I went back to the idea of prying it off evenly using the faceplate...it worked. This was my second needle removal and both did not break so I'm getting more comfortable this is the proper way of removing it.

I did have to grind down a socket to access one of the screws but I was able to swap over the magnet base assembly to my speedo and put it all back together. I just re-installed it and it works like a charm! Short term problem fixed for now.

So next weekend, I'll hit the junk yard again and try and get the tail pieces....thanks 4x4.

 

[Fordum]

Could you tell what was wrong with the original magnet?
On my Jeep, the magnet was one of the flexible brown ones like on car signs, and it kept coming unglued from the hub it was attached to.

 

[jeff in co]

From what I can tell, the speedo cable is attached to housing "A". At the end of housing "A" there is a spinning magnet that spins inside a cup which makes the speedo needle move (no mechanical connection here). The speedo needle is resting on a twisted spring so the magnet field creates the needle to rotate against this spring. This would be considered the assembly "B".

When I went to the speedo shop, he said that probably the bearings were getting a little play creating the noise (on assembly "A"). I replaced the whole assembly "A" and no more noise.

So, obviously the loose bearings were creating the magnet to move around ever so slightly tapping the magnet cup.....or something close anyways. I did take some pics if you want to see anything.

Hope this makes sense....

 

[British Slave]

It is a federal offense for any used car place to alter the odometer but it is ok if a private citizen alters one AS LONG AS when the vehicle is sold it is noted that the odometer IS NOT the actual mileage.

Back before it was illegal, I reset hundreds of odometers for the dealership I worked at. It was esay, and after I left, I used that knowledge for rebuilding gas pump and pipeline meters registers. They all work the same way.

 

[Fordum]

Oh, OK, I did not think about the bearings.
Mine had the same setup with the aluminum cup, needle and spring.

But on mine, the magnet was a flexible one which was wrapped around and glued to a hub which was spun by the cable.
This spun inside the cup and the magnetic field turned it against the spring.

Mine would go bad after about two or three months.
The original one ran for years, but the replacements only lasted a short while.

Finally I took one of the new ones apart and found the glue was not holding the ends of the magnet solidly.

I prised the ends up, cleaned off the old glue and re-glued it with epoxy.
That fixed it.

I was thinking your magnet might be coming loose also.