Hello, I have been experiencing a unique situation this year. Back in late March, a lightning strike took out my PCM, IDM, the line-in function of my stereo, and several relays. There is a thread about that if you search for the word lightning.

Once a good shop with a good scanner helped sort out the complete list of missing parts, the truck has been running great ever since.

Except for one thing - the speedometer wasn't working. The shop told me to get that going, I would basically have to put in a new instrument module, and that the best solution there would be to use one from a junkyard. But neither of us had the time to track one down, and away I went.

Then about three weeks later the speedometer suddenly started working again. Some weeks are better than others, and the VSS (new) still doesn't seem to like a wet day at all.

I had the truck in with a shade-tree mechanic friend for some other items, and while he was on a test drive he told me the speedometer only starts to work at 37 miles per hour.

I had not noticed that, but it is true. As soon as I reach 37 or so, the speedometer pegs right up like a drag racer RPM needle. When I slow down below 37, it slowly dies it's way down to zero.

Just wondering if anyone else has lived with a dead / dying speedometer, and whether 37 mph was any kind of break point for it. I guess a capacitor in there got only partially damaged somehow by the lighting.

Overall I know I will just continue living with the situation. I've put about 400K on trucks with 7.3s in them, and I have never yet been pulled over in one. It is of course possible to go over the sped limit in one, but you have to work at that a little bit more than other vehicles, and I drive conservatively, particularly in terms of acceleration and building momentum.

I probably shouldn't type this, but I kind of doubt I ever will be pulled over in a 7.3, because hardly any folks on the shadier side of life are ever going to drive one. They seem almost exclusively used to earn a living, or by people retired from earning an honest living, and I think cops know that about these trucks.

 

Because 37 is 5 less than 42, and as everyone knows 42 is the Answer to the Ultimate Question of Life, The Universe, and Everything.

5 cuz that's the number of letters in blitz, the German word for lightning.

But seriously, I think you nailed it. The instrument cluster is a pretty elaborate electronic assembly and no surprise that it took damage from a lightning strike. Replacing it properly might cost more than a nice night out with your two best GFs, but that silly speedo would drive me nuts and I'd get a good one. OTOH I'd rather have no speedo at all than a malfunctioning one.

Does the odometer work when the speedo is dead?

 

The speedo likely works with "steps" in a digital to analog converter. It's possible the first step has a blown component. You can use a work-around until you replace the dash:

I have Torque Pro with an OBDII adaptor in the cab when I drive - and I can put the vehicle speed on the screen.

 

^ Can you elaborate?

If you can use Torque Pro or a scanner and monitor mph then that pretty much nails the cluster as mentioned.

I have a speedo cluster from my doner 03 E350. It doesn't have a Tach but I wonder if the guts for the speedo are the same? If you think/confirm the issue is the cluster and that the parts could be interchangeable I'll ship it to you.

Here is a pic: