VDO Electronic Speedo

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rmel
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VDO Electronic Speedo

Post by rmel » Sat Jul 08, 2017 4:33 pm

Just had to replace my VDO eSpeedo due to a very temperamental LCD display. Need a trustworthy Odometer on the trail,
not to mention to know when to change the oil.

Although it is easy to program a new one using mile markers, I wanted to pre-set the new one with the old setting which
has proven to be accurate for my tire size and HWY air pressure.

Got the old one on the bench, used a heat gun to get a the LCD to work long enough to read the old value of 12,190 pulses/mile.
That value is different by 1/2 from a prior thread on this subject so I decided to find out why.
viewtopic.php?f=14&t=9783

Comes down to what Hall Effect sender you have. VDO has several that fit ranging from 4, 8, and 16 pulses per revolution
of the Hall sender. Mine is 8 pulses, the prior thread must be 16. FYI the formula to calculate a ballpark setting is simple.

Pulses/Tire revolution = Diff * Axle * Hall / SpedGear = 19.01
Diff = 2.846 (37/13), Axle = 2.66 (34/15), SpeedGear = 19/7, Hall (mine) = 8
Pulses/Mile = (5280 * 19.01) / Distance traveled/tire rev = 12,167, pretty close to my setting.
Distance traveled/tire rev = 8.25' based on 285/75-16 and the loaded effective radius.

So depending upon your Hall senders pulses out per revolution 4,8, or 16, ballpark values are; 6,100, 12,200, 24,400.
Last edited by rmel on Tue Jul 11, 2017 1:09 pm, edited 1 time in total.
Puller: 710K 2.7L EFI
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4x4Pinz
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Re: VDO Electronic Speedo

Post by 4x4Pinz » Sat Jul 08, 2017 6:00 pm

I noticed a huge difference in both my pinz VDO speedo installs. Currently, the one in my 712 has finally given up the ghost. It used to read out whenever it felt like it but did keep track of the mileage (which would display from time to time) Now the mileage never displays and the speedo does not work. It goes through the test mode when powered up but that is it. Have checked all wiring and everything looks in order. The lighting side works just fine, it is just no speedo reading and no lcd display of mileage. In all fairness the speedo has been in my truck since '06 and had 42,000+ miles on it. For a VDO product that is not bad.

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rmel
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Re: VDO Electronic Speedo

Post by rmel » Sat Jul 08, 2017 7:03 pm

Well you did better than me! The one I just replaced lasted only 6 years and clocked only 24,600 miles :(
I have it completely gutted on the bench, was hoping to replace the LCD but it's pretty clear this was a
build for purpose LCD and not a standard. Frankly, I'd expect more from VDO.

BTW, if your looking for a replacement I have found eGauges to have the best prices, and since these
puppies are >$100 a pop -- free shipping.
Puller: 710K 2.7L EFI
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Re: VDO Electronic Speedo

Post by 4x4Pinz » Sat Jul 08, 2017 7:57 pm

thanks for the heads up. I am definitely going to be replacing. likewise I use it to keep track of mileage for service. Pretty good at gauging frequency by now but it is always good to be sure.

My son in law now has my 710. He has been doing a lot of modifications to it. One of them includes a gauge cluster that has a speedo along with a few other indicators. Hoping he resolves the install issues soon so I can steal his idea.

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Re: VDO Electronic Speedo

Post by GadgetPhreak » Mon Jul 10, 2017 12:07 am

Following this thread... My VDO gauge is starting to get temperamental and I'm curious to see what others come up with.

Do we have any info on what causes the failure?


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rmel
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Re: VDO Electronic Speedo

Post by rmel » Mon Jul 10, 2017 12:22 am

How is it behaving? Is the LCD flaking out or is the miles/hour needle the problem.
Based on some Google'n I have done, I have seen a few complaints about the LCD,
some have noted that damp wet days seem to effect the LCD.
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Jimm391730
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Re: VDO Electronic Speedo

Post by Jimm391730 » Mon Jul 10, 2017 10:53 am

Do we have any info on what causes the failure?
Numerous reports here, over years, show the VDO LCD display contacts fail over time. Unfortunately there does not appear to be any solution to this problem. Generally the needle still works but the display gradually dies.
Jim M.
712W and 710M

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Re: VDO Electronic Speedo

Post by rmel » Mon Jul 10, 2017 11:43 am

Ya, the LCD seems to be the weak underbelly with these gauges.
Having ripped apart the old one (and that was not easy as the brass rim on these are crimped on),
the LCD is mounted on a separate bezel and has a very tiny connector to the main housing. All
looked to be in good conduction. I was hoping the LCD was a standard through-hole mount that I
could source and replace but it's a unique custom built for VDO.

I did find a potential alternative from Speedhut.
http://www.speedhut.com/gauge/GR338-SPE ... ogrammable
Programmable to the Pulse/mile from a VDO Sender, also settable functions for maintenance; Hey bud,
time to change your Oil :)

The interesting bit is that these gauges are guaranteed for Life ! The challenge is that some adapting would
be required as these are 12V gauges. Would need a pair of low power 24V-12V DCDC converters. Also these
gauges source the Hall effect output (Pulse and GND) but do not provide the power to the VDO sender. I'd
have to dig into that if anyone is interested, I don't know if it is 24V switched or some intermediate voltage.
Devil in the details, and VDO isn't all that great at publishing detailed Tech notes :(

Well since I went with a new VDO speedo I'll just hope it lasts, but keep this Speedhut one in mind for the
future.
Puller: 710K 2.7L EFI
Follower: Sankey MK 3, 3/4 Tonne
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Re: VDO Electronic Speedo

Post by Jimm391730 » Mon Jul 10, 2017 8:47 pm

Now that Ron mentioned it, I used the Speedhut speedo to replace the VDO on our 710M. I have a 24-12V converter and used it to power both the speedo and the original (VDO?) hall sender power, no need for "a pair" of converters. IIRC I used the 24V illumination bulbs to light the unit, no need for 12V for that. I may be able to look up how I connected the sender, but I may not be able to do that for a few weeks (away from the truck, unfortunately). Final answer: I really like the Speedhut unit! Since I didn't have the pulse/mile data from the VDO, I just set the Speedhut to 60mph, ran the truck up to 60mph on the GPS, and pushed the button to set it. Works like a charm.
Jim M.
712W and 710M

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rmel
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Re: VDO Electronic Speedo

Post by rmel » Tue Jul 11, 2017 12:13 am

In a way I wish I had looked further and thought about a Speedhut Speedo rather than just replacing the VDO.
I like the looks of the VDO and when it works no complaints, I just think there's a quality problem here they
have not addressed so I may be on borrowed time again, hopefully I go more than 6 years.

These Speedhut Speedo's look like a new generation, they are only 25mm deep! Dial is driven by a steeper
motor but all else is electronic and LED illuminated. Here's where I was going with the low power converters,
there are 3 power inputs; Keyed, Dash, and Dial illumination - -you could connect all these to a 12V source if
you have one under the dash. Or you could use LM431 converters which are the size of your pinky finder, and
shrink wrap them in a harness as a bump in the wire. Then you have Illumination working properly and then
power on the Gauge when keyed on. It would take 2 converters, they are check and low power.

The big mystery is what do you do with the RED wire on the Hall sensor. when you are VDO all around, the
VDO Speedo has an output to drive the VDO sender. I'm betting it's a 12V output even though the Speedo
is 12V/24V. That makes sense as the Hall-sender is typically used on GM products and they are definitely
not a 24V system. So if I am right, one would connect the Hall sensor RED wire to Keyed +12V.
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Re: VDO Electronic Speedo

Post by Jimm391730 » Tue Jul 11, 2017 12:49 am

there are 3 power inputs; Keyed, Dash, and Dial illumination
Dial illumination can be on all the time, day or night (only on with the key on). No need to have it tied to the light switch, unless you need to be able to turn the backlighting off at night. Keyed and dash can be tied together (my converter only comes on with the key on). This way the speedo doesn't draw any power with the key off. But all three can be powered by the same converter (I did).
The big mystery is what do you do with the RED wire on the Hall sensor. when you are VDO all around, the VDO Speedo has an output to drive the VDO sender.
I can't quite remember, but I think I did +12V to one lead, ground to another, and had to add a 10k ohm pull up resistor between the output and +12V since the output is common emitter (pulls the output to ground, so the resistor is needed to pull the output back up between pulses). No joy until I got the pull up resistor in place, then it all worked like a charm. IIRC most of this was in the Speedhut instructions. Again, I'm using the same 12V converter output for the sender.
Jim M.
712W and 710M

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