[Browning01]

I have a 2001 F250 4x4 that I have had for a few months now. The transmition has always shifted hard but that maybe how they are Im not sure, its an automatic. Just recently when shifting from first to second , it started to have a little bit of a lag then would pop into second. Last night I was driving and all of the sudden it did that, only much worse and wouldnt go into second at all. I limped it back home and today tried to drive it again and it wont shift into second unless I get it to high rpm's and then let off the gas really quick, it then shifts and the other gears seem ok after that. Downshifting also seems to be ok. Any ideas on what my problem is? I have read something about a mechanical diode failing, if its that or not, am I looking at a new tranny now?

 

[Mark Kovalsky]

It's the mechanical diode. It takes either a complete rebuild with a lot of new hard parts or a new trans to fix this. Sorry.

 

[Gooch]

Yep. You may want to contact Ford Motor Company. They paid for almost half of my HD factory replacement, even after 100K miles and 7 years.

Tell them you are aware that they knew this transmission had a defective mechanical diode, and that while they addressed the defect on vehicles with higher-revving gasoline engines, they did not address it on some of the lower-revving diesels. You have one of those, and now your transmission has failed, and you can't afford to pay for their defect. Your dealer can help you work with them. It's worth a shot. They had to tear mine down and verify the defective diode before authorizing repair. But it saved me $1500 and it seems to be a tough transmission.

 

[trailready]

Mark, please check your PM.

Larry

 

[trailready]

Thanks a ton Mark.

Larry

 

[sparvin]

Mine did the same thing--you're revving up high and skipping 2nd going into 3rd (drive). I drove it like that for about 6 weeks then made it to BTS for his tranny. I don't think its the diode--when he tore my tranny apart you could see broken 2nd gear sitting in it--impressive, but disgusting sight.

 

[sparvin]

Sorry, mark, didn't see your credentials, guess it is the diode.

 

[61uni]

What years had the bad diode?

 

[Mark Kovalsky]

The mechanical diode was introduced at the start of the 2001 model year. After a few thousand trucks were built all the gas engine trucks had new transmissions installed with the older, more reliable sprag one way clutch. Every gas truck was supposed to get a new transmission before being shipped to dealers.

Since the problem with the diode only showed up at speeds above 4500 RPM it was thought that the diesels wouldn't have a problem. In March, 2001, even the diesels dropped the mechanical diode. We were told that no gas engine trucks were shipped with the mechanical diode in the transmission.

 

[Mark Kovalsky]

I don't think its the diode--when he tore my tranny apart you could see broken 2nd gear sitting in it--impressive, but disgusting sight.

No, you couldn't. There is no "2nd gear" in an automatic transmission. These have planetary gearsets. There is no specific gear for any of the ratios. You can't identify a specific gear as being 2nd gear. All gears are engaged all the time. The various clutches hold different parts of the planetaries to produce different ratios.

You probably saw a broken mechanical diode. It's engaged to make second gear ratio.

 

[sparvin]

Is the diode one of the round plates? That's what I remember it looking like. I took a pic and I'll see if I still have it and can post it later. I like to be educated on this stuff. Ya know, just enough to be dangerous.

 

[Mark Kovalsky]

The round plates are probably the clutch plates.

Here's a photo of a mechanical diode from Epilogics, the company that makes mechanical diodes. Automotive Transmission MD Part #100806

 

[Browning01]

Thanks for the replies guys, it is in the tranny shop now so I will keep you posted on what happens, I should know some things by tomorrow.

 

[sparvin]

Ahhh, that pic does remind me of what I saw. Just learning.