I have an F250 XLT Super Duty V10 with 150k miles. Never had a problem with it until Jan of this year. Initially I thought I was not getting some traction on an icy intersection light, but problem continued and I felt jerking and grabbing of my (assumed) transmission. I've only previously experienced a slipping clutch in a manual transmission but the symptoms I was experiencing FELT like it could be a tranny. Starts and runs fine cold, but when it got hotter as milage progressed, especially in town, I would feel like it couldn't catch gear from a stop sign or light, then it would catch and it would feel like I was getting rear ended. When idling it would barely catch a gear then slam into gear.

I took it to a well known transmission shop in OKC who has been around since 1949--so you'd think they'd know trannys. They do state and government accounts so I felt secure with them. I dropped it off and told them what I'd been experiencing and when they called back it was "yes Ma'am, you've got a bad tranny." Okay, what are my choices. Little did I know that transmissions are not NEW, but rebuilt. To the tune of $2400 with installation, I drive home in my 'new rebuilt' transmission.

On the way home I experiene SAME EXACT symptoms. Take it back in. They determine that it was a faulty rebuilt tranny so they install 2nd tranny. Take it home, and it runs fine for another 5 days. Take it back in with SAME symptoms. They say they take it on long test drive and "it's fixed." On one occasion they determine it's the MLPS and so they replace that and tell me I'm good to go. Same problems within days. Then they say it's the alternator and they put magnets in it for some reason to either enhance or d/c the sensor from sending signal to computer?? I'm in a fog at this point. They tell me the computer says my truck running but in idle is reading 25mph. Take it home after it's "fixed" again, later that night huge knocking noise coming from engine and it appears to be coming from the alternator. The guys from the shop come to my truck in the parking lot at my workplace and determine that the serpentine belt is fraying and that's the noise it's making. Coincidense? I don't have any idea. And apparently neither to they. They replace that at the cost of $125.

Took it to another transmission shop for a test drive and diagnostic. Come to find out their head tranny guy used to work for the initial tranny company. Nice. He's aware of the crap they do. He firmly believes it's a tranny problem but since it would void my (apparently useless) warranty I cannot have them take an inside look at the tranny.

To make a long story short, it has been in the shop 12 times/days, and in all, SAME SYMPTOMS to this day.

It is now at the Ford dealership with THEIR computer. Their mechanic has been filled in on all the stuff they've done to the truck at the tranny shop. He is convinced it's the alternator and has driven it til it gets hot and does the slipping/ramming and then d/c'd the alternator from the battery and the problem stops.

Has anyone ever heard about this?

To make a long story short, it has been in the shop 12 times/days, and in all, SAME SYMPTOMS to this day. I am at my wit's end.

Thank you!

 

Low voltage can make the trans do all sorts of bad things. The shift solenoids and pressure control solenoid are electronic and will misbehave when the voltage is too low.

 

Thank you Mark:

Wouldn't there be other issues with low voltage? I have a normal reading on the dash gauge and there are no power issues when I use a/c, no problems with elec windows, door locks etc....but I am no mechanic that's for sure.

I guess my biggest concern now is if the alternator HAS been the problem all along, then I paid $2400 for a transmission that I didn't need (at least yet) and 4 months worth of a pain in the A$$ not to mention 4 rental cars and the inconvenience....I am going to have to demand the $$ back from the transmission guys who clearly didn't diagnose the problem AT ALL and who cost me dearly in time and more cash. Good luck, right?

Thank you!
Lisa

 

The problem won't be low voltage from the alt, it will be a "dirty" output. If the alternator has an internal issue it can sometimes cause a wildly fluctuating output that isn't noticeable to humans looking at lights, etc., but the computer components will have a very hard time dealing with it. The alternator can be tested with an oscilloscope to see if this is the issue.

 

You can pick up a cheap alternator from a junk yard that has the Superduty to see if that clears it up. If it does, then you know that was the problem.

 

You could use an oscilloscope to see what the alternator output looks like. A good tech with the right tools can test if that's the problem instead of just swapping parts with a part that may be good or may also be bad.