I am going to try and cut to the chase and keep this somewhat short for everyone's benefit. Anyway, some time ago a problem developed with my 99 F350. My OD light would flash and suddenly the transmission would start shifting funny until I got moving. It became increasingly worse over time, to the point that I had to manual shift or the truck would die at a stop.

I had a new transmission put in maybe 6 months before this all happened. It was a Certified tranny, I opted to upgrade when I did this and got the Road Ripper 1000. I took it back to Certified and they said it wasn't the transmission that was the problem. They gave me a list of codes they had pulled and I was on my way. None of the codes helped or were associated with my issue.

Over time I had taken my truck to several shops and no one could figure out what the problem was. I had replaced all 3 of the speed sensors with zero luck. So I just dealt with it and manually shifted at stops.

About a week ago I was leaving the in-laws and I heard a bang and there was no more forward motion. None of the gears would engage and park wouldn't even hold my truck in place. I had to sit for 45 min with my foot on the brake while I waited for the tow truck.

Luckily it was still under warranty so it was off to Certified to get replaced. So here is the bread and butter of those post and I really hope it helps someone else who might be experiencing this problem. with the tranny replaced they test drove and encountered the issue I was having. They began hunting the issue and after 2 days they found it. It turns out that there was a diode in the alternator that had been causing the problem. I have no idea why it was causing the issue and honestly I don't care. Its fixed and I am so incredibly happy to finally not have to see that light flashing every time I stop. I apologize for the long post but I wanted to include some detail. BTW, my experience with Certified Transmission was awesome, they are now on my go to list if I need work done.

If anyone needs any additional detail feel free to ask. Finally, something worked in my favor with that beast.

 

A diode in the alternator ? Did they give you have any details as to how it affected the trans. Glad you got it fixed

 

Yeah, that seems improbable, not impossible, but I want to know more details please.

 

more info and details on this mysterious diode in the alternator please, curious minds need to be fed food of knowledge!!!

 

The voltage regulator in the alternator uses diodes to create a full or half wave rectifier. But your battery light would illuminate if those failed. Didn't those trucks have a mechanical diode in the transmission that kept torque going in one direction?

https://www.ford-trucks.com/forums/9...nsmission.html

Some pictures of MD's:

http://www.idmsvcs.com/2vmod/tranny/...res/index.html

 

It will be interesting to hear what Mark has to say on this subject...

 

He may need to be summoned, without 'transmission' in the header it might not get his attention.

 

@Mark Kovalsky

Stewart

 

He is on one of those white sand tropical beaches in Florida relaxing. You need to send a "message in a bottle."

 

I need to hear more about this.

 

Mark- glad you got it figured out, however I would also like to hear more on this.

 

Just some surmising thoughts. . . Alternators produce AC. The diodes in the Alt. covert it to DC. Diodes can short like a wire and AC leaks into the DC. The AC effects the DC in a way that causes the DC to vary in value. A varying DC could affect electronically controlled transmissions in a way that you experienced.

 

It's a bit cold today for me to be on the beach, so I'll tackle this instead.

I'll bet they would have been useful.

That indicates the transfer case (it is a 4x4, right?) went to neutral.

A bad diode in the alternator will put an AC component in what is supposed to be a DC circuit. The PCM sees this on the signal from the speed sensors, and it looks just like input from the sensors, so it reads too high of a signal. I've seen this happen before, and it didn't turn on the light on the dash, either.

There is NO WAY that it caused the bang an no movement. I'll be that was something with the transfer case that they took care of for you.

Those were only in the first half of 2001, and only in the diesels. It was never in a 1999, and if a rebuilder put one in, they are incompetent.

 

Diode in the alternator, eh? This sounds suspiciously like something went sideways with the transmission install, and the diode thing was a way to save face. I could be wrong.

If the alternator really had a diode problem, good luck charging the battery properly - how were the battery volts? One obscure possibility - if it really was a diode allowing AC to pass through, reference voltages for key sensors and controls would run amok. This would cause many more issues than a transmission malfunction - the whole truck would seem possessed by a Powerstroke poltergeist.

 

I've seen a bad diode in an alternator only cause problems with the speed signals. Everything else worked fine, including charging the batteries.

So we have your thoughts compared to what I've measured in a vehicle with an oscilloscope. But I respect your decision to ignore the data I've collected over the years.