I have a 99 PSD with Auto. The other day the OD light was flashing and I traced that to a wiring harness disconnect for the the trailer towing harness. Light went out but my shifting problems started. Now it shifts in forward gears very softly and overdrive early, but not all of the time. When you go to reverse it acts as if it is a higher gear and bogs the enging mementarily. I reloaded the factory program from my predator and it has made no diference. The fluid is not burnt and is actually slightly over full. Does anyone know what is causing this? I really do not want to go to a transmission shop.

 

Mine was doing sort of the same thing. I put in a Sonnax kit and it took care of the problem. Then the tranny went out and I had to put a new one in, but I kept the sonnax kit in it. It is great now.

 

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rharp,

Don't forget that the Vehicle Speed Sensor (VSS) that's located on the upper left part of the differential center section, will also cause the OD light to flash and cause erratic shifting. It also causes the speedometer to be somewhat erratic, too. It's a pretty common problem with these trucks.

It's easy to find, easy to R&R, and pretty cheap to buy if you actually need a new one, even at your friendly Ford dealer.

You may find it only needs cleaning, too, as it is a magnetic device that reads a "tone wheel" attached to the ring gear, and it has a tendency to collect the black magnetic "soot" that gets suspended in the differential gear oil.

On the chance that this is what's causing these symptoms, clean all around the sensor with a wire brush to knock off all the dirt and grime, remove the connector to the truck's chassis harness, remove the single bolt that holds it in place, and gently pry it loose and out of the housing. Clean it with a clean cloth, inspect the o-ring for damage, lightly lube the o-ring, and reinstall it in the housing. Make sure the connectors are VERY clean, as they are pretty exposed to the elements under there, and a slight corrosion on them can cause these symptoms, too.

It's a shot in the dark, but it it solves your problems, you will have learned something, and all it cost you was about twenty minutes.

Pop

 

It was not the speed sensor or the SONNAX kit that came in the mail. I pulled the pan to install the new shift kit and there was a lot of metal. Changed the filter and fluid, headed to the trans shop. Did not make it. Picking up new transmission from TPS monday and I will be $1800 poorer. Thanks for the suggestions.

 

SpringerPop -

I bought my 99 F250 SD 4X4 auto over Thanksgiving and drove it from Vermont to FL just fine. But the other day the speedo started to not register until at least 40 MPH was achieved. This morning I was in slow traffic and the tranny tried but wouldn't upshift 1st to 2nd unless I accelerated hard; it keep trying to but stayed in low, kind of rocking the truck. Are these the symptoms you refer to? Also the OD light flashes while accelerating until it shifts to OD. Is this normal or the same problem?

Thanks.

 

Same symptoms. Drain the trans fluid pull the 20 pan bolts and you will know pretty quick. Inspect the bottom of the pan for metal. If there is not much metal in the pan then next look inside the filter for a lot of metal. If your really lucky you will not find a lot of metal and it will be a different cause than internal component failure. What happens as I have recently learned is that the filter clogs withte the shavings over a period of time. This slows down the circulation of fluid back to the pan and deprives the pump fresh fluid to supply back to the trasmission. The more she clogs, the less fluid the fluid, temp increses, thus friction increses, then parts wear more causing more metal until the filter completly clogs and strats dumping it out the front of the trany through the flywheel inspection plate onto your driveway giving your wife another reason to complain about the oil stains on the concrete not realizing that your whole world has been set back to the tune of at leats $2000. Also check the speed sensor at the rear axle housing as described earlier in this thread it can cause some of the same symptoms and I hope that is the case here.

 

Sorry to ask for simplification, but I haven't even been under the truck yet. Where exactly do I look for the VSS (is it on a center diff. between the axles or on the rear diff. [in the center of it])? What does it look like?

 

On top of and drivers side of the diff center. It has a wire running to it.

 

I had the same symptoms and cleaning the vss didn't help but a new one was the cure. Good luck

 

Well, I finally got under the truck today since I had some time available. I replaced the VSS with a new one and wa-la (sp?), no more shift problems, no more OD OFF light flashing, no more erratic speedo below 40 MPH, even no more ABS light on and the cruise control works again. $20.65 and about 10 minutes to accomplish my first repair. If this is what I can expect for repair experiences with these trucks, I'm in heaven. Thanks for the tip SpringerPop

 

Well, we don't always get 'em right the first time, but collectively, we're likely more concerned with actually finding the root cause of your problems than your local dealer's tech and his service department in general.

We're motivated by a different thing. ;-)))

Pop

 

I changed the vss on the truck and I did not help? Do you think I have to do anything else like clear the computer?

 

It could be your pcm I had the same trouble with my 99 and it was traced back to my pcm it was spiking and kicking OD light on and would start blinking. It also was hard to start.

 

Oh by the way a PCM cost about $400 from ford.. I found that out the hard way..