2001 7.3 Diesel Excursion with 4R100 Trans.

Here's the story - All of a sudden the truck wouldn't shift from 1st to 2nd without holding at/near redline for several seconds. After it eventually shifts to 2nd, the trans then shifts through the other gears without a problem. Hooked up the code reader and no codes were thrown. I was playing with it and romped on it trying to get it to shift. Well it shifted real hard with a noticable thump like I'd broke something. Limped back home and could hear some grinding when going slow.

Hooked up the code reader and there were still no codes thrown. Did some searching aound on the internet and was fairly confident I had broken the mechanical diode. Had the transmission torn apart and the mechanical diode was broken. Replaced it and had it rebuilt with beefed up parts and a triple clutch torque converter (Performance Automotive and Transmission Center - Enforcer 4 transmission kit). Reinstalled the trans and test drove. Noise is gone but still have the 1 to 2 shift problem. No codes present.

Hooked up a diagnostic tool and test drove it. With shift selector in DRIVE, the SSA solenoid reads ON and the SSB solenoid reads OFF while in first gear. Once the truck reaches 12 MPH (normal shift speed), both solenoids read ON which is normal. The PCM is commanding the solenoids to shift from 1st to 2nd, but the trans is not shifting. I suspected a bad solenoid and replaced the solenoid pack, but the problem is still there.

I'm about to replace the manual lever position sensor and the input/output speed sensors, but I don't think they are the problem. Seems to me they are inputs to the PCM and the output of the PCM to the trans is telling the trans to shift, telling me something's wrong after the signal leaves the PCM. I guess I should wring out the wiring from the PCM to the trans.

Any thoughts on what the hell to do next??? Thanks for your help.

 

I would suspect a sticky intermediate clutch regulator valve in the accumulator valve body, which was most likely the original problem before you broke it trying to make it shift.

I use a TransGo shift kit when I rebuild these things, it makes them shift great and it gives you a steel 1-2 regulator valve to help with this problem.

The MLPS and speed sensors are not your problem.

 

A Transgo shift kit was installed during the rebuild. Any other thoughts on what might be the problem? Thanks.

 

I had the same issue. I replaced the whole valve body with a John Wood unit. Came with a TransGo plate. I got mine here: Riffraff Diesel: John Wood 4R100 Valve Body

 

Update: I replaced the valve body and still had the 1-2 shift problem. I finally broke down and pulled the trans and tore it down again. Found the sprag gear that was installed to replace the mechanical diode was ground down on the inside. The kit that I used to replace the mech diode was designed to re-use the same intermediate clutch drum but with a race installed on it to make it mate with the new sprag gear. The race looked good so I don't know what caused the sprag to grind down. I talked to a ford trans mech and he said he's not a fan of the kits that reuse the drum by installing a race on them - he says a lot of them are junk. Other ideas he had were the sprag may have been installed backwards (the outer band should rotate CCW and it should lock CW) or the wrong valve body gasket may have been installed and was blocking one of the hyd ports (he said to only use the gasket with the white stripe). I bought a new intermediate clutch drum and sprag that are designed to mate with each other without a race. I also checked the valve body gasket to make sure it had the white strip. Trans is now reassembled and ready to go back in the truck. I will probably throw it back in the truck this weekend and see what happens.

 

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For years, most Ford dealers have been selling remanned transmissions built with re-used clutches due to Ford Motor Company closing many of their regional facilities for training dealer technicians. You’re lucky to have found a Ford dealer with an actual transmission tech. A transmission tech that actually does rebuilds at a Ford dealer is rare today. Many just have tranny removers and installers with some diagnostic skills. The one you found was very rare because Ford techs that are trained today only gain stock rebuilding experience and knowledge.

We don't use those diode kits period. They shouldn't be sold as performance parts by dealers or by performance rebuilders either. Those diode retrofit kits were designed for stock vehicles only. They definitely shouldn't be used in any 4R100 that will be in any vehicle with the smallest of horsepower modifications. The Teflon pump gear gang should know that, but then again why you only use plastic utensils in Teflon coated cooking pans was missed too...

The diode retrofit kit won't grind up the sprag if it is installed backwards. If the wrong gasket was used, many more parts than the sprag alone would have been ground up and others would have been damaged severely when you test drove. You'd have an expensive mess similar to what's in the photo below. Different steel parts are shown, but the result would be the same from the diode kit back to many of the parts behind it.

 

I put the transmission back in the truck last night. Problem solved. It's shifting great now. Lesson learned - if you need to replace the intermediate clutch mechanical diode, replace the drum as well. Don't buy one of those kits that lets you reuse the drum with a race adapter to make the new sprag fit or else you may be pulling and tearing down the transmission twice. I learned the hard way, but at least I'm back on the road now.