I see this mentioned in the forum but I don't know what a diode transmission is? Can some one enlighten me?

 

The only thing I have ever read about this is something about a diode in the alternator that somehow effects the trans if it goes bad. This may be something completely different than what you're looking for but just thought I'd put in my 2 cents. lol

 

Many of the 2001 4R100's had a mechanical diode (switch - EDIT: See Mark K's correct evisceration of this term below. Clutch is the correct term.) ) that was prone to fail. Ford stopped using them in the middle of the model year, so later '01's didn't have them. My '01 X (Build in 12/00) did, and it's original tranny failed at 17K. The most common initial symptom is an unwillingness to shift from first to second gear.

Mark

 

Some 2001 trucks and excursions had transmissions that used a mechanical diode. It was/is prone to sudden failure. I just saw the build dates on another forum a day or so ago.
By now most of the 99-03's have had their trannys rebuilt anyways, mechanical diode or not.

 

It's not a switch, and it's not anything electrical. Mechanical Diode is a brand name for a type of one way clutch. Here is everything you would ever want to know about it: Epilogics Mechanical Diode Website Homepage

They were in the 2001 diesel transmissions from the start of 2001 production in July, 2000, until March, 2001.

 

You know Mark, the explanations of what parts are get crazier and crazier the longer these forums are around, huh?

 

Old thread I know, but sometimes thats what you get when you search...

I doubt thats true.

Im looking at a truck with a 03/01 build date. Any way to tell whether it has the diode or not?

 

You have to look at the build date on the transmission itself. The reason I know that is my transmission has a build date later than the truck build date, meaning a different transmission was installed after it rolled off the assembly line, presumably because the original one was defective. Regardless, the build date on my transmission is a diode model. Here's some information from past threads on build date decoding:

Mechanical Diode Tranny Build Dates2001 vehicles equipped with 4R100 transmission, having a transmission build date between
7/27/2000 and 3/23/2001.
Roland (mueckster) 04-15-2008
The trans does have its own build date located on the tag on the trans case (left side ,rear).
4th line down should show BD- #Letter##. This is the build date year/ month/ day.
Example : BD-1D28 1=2001 D=April (A=Jan, B=Feb...12=Dec) 28=Day of Month.
Using his example tranny Build Date is Jan 28, 2001
　
Mark Kovalsky 01-03-2009
The mechanical diode was in the diesels from the start of 2001 model year (July, 2000) and left production in March, 2001.

Cody (cleatus12r) 01-03-2009
If anyone is still interested, the "mechanical diode" was the replacement for the one way roller clutch previously (Intermediate one way clutch) used in the E4OD and 4R100s. After Ford found out that the diode wouldn't work in the gasser trucks (they exploded when shifted at 5300 RPM), they decided that they should stick with the proven and slightly more robust design. It is a mechanical device that allows rotation in one direction but not the other. It is used for the 1-2 shift when in drive range. When the "diode" was used, it replaced the roller clutch with a sprag that is inherently weaker. High power/high RPM 1-2 shifts are what kills the intermediate one way in the diesels.

Mark Kovalsky 01-03-2009
The gas engine trucks blew up the diode at 4600 RPM if the driver lifted his right foot just as the WOT 1-2 shift started, then put it right back on the floor. The person that discovered this was able to do it on 100% of the trucks he tried it on. That's why they left it in the diesels, they couldn't run 4600 RPM.