Today I took my truck to the Ford dealership and they couldn't even figure out what was going on. They didn't even charge me a diagnostic fee. So I'm going to give everybody the run down to see if yall might have a possible solution.

My truck: 2006 Stage 3 Roush F150, 3v 5.4(supercharged), 57k miles, 2WD, auto.

My problem: At speeds of 50+ if I let off the gas quickly i get a quick, strong vibration or shutter on the downshift. And if I give the truck a little gas it shutters also. The "shutter" feels like a transmission shutter and it shakes the entire truck. It's like driving over rumble strips. This happens on acceleration and deceleration.

What I've done so far: The first thing I thought of from reading on forums was to check the COPs. The ford dealership hooked it up to their computers and ran full diagnostics on the motor while driving it and they said the motor is operating at 100%. They said the coils, and spark plugs and injectors are fine and there are no misfires. Ford also said the u-joints are tight, the slip yoke is not dry or worn. They believe its a front end issue.

I don't know what else to think of besides the rear diff? Or even the transmission? From reading about this issue, I was almost positive COPs would be the issue but according to the dealership its not. Sorry for the long post but I'm getting tired of not being able to solve this. Any input is appreciated.

 

I'd buy a cop and move it around to each cylinder to see if it cures it

 

Almost sounds like a torque convertor lock/unlock issue via the electronic engagement .....just speculating

 

Has the fluid ever been changed?

 

Sounds like tq convertor symptoms.

 

I was thinking torque converter also. The tranny fluid is red and its not low. I'll possibly be taking this to a tranny shop to see if they can find anything.

 

@88racing: So would a flash of the tranny be a solution to that?

 

Jack the truck up, put the axle on stands set parking brake, put trans in N, try and turn driveshaft by hand each direction, if you have a lot of travel its ring and pinion clearance that needs to be adjusted.

Check the torque convertor, coast at 70, just tap the brakes and the convertor should unlock and RPMs flare up a little

 

Not a F-150 but I had a similar issue on my Lincoln LS. It would shudder into and out of third gear and bang 4th gear really hard. I did occasionally have a cyclic surging as I rolled on the gas over 50, and shifts were slow and sloppy. The main issue was a bad PCM which caused the banging and shudder. The slow shifts were caused by worn servo bores, and the surging was a worn torque converter.

The dealer told me the PCM was OK and wanted to keep going $100 farther into the trans. The first trans shop I went to knew the PCM was the main issue and didn't want to touch it. The next shop rebuilt the trans and replaced the PCM for $2200 ($400 for the PCM, $1800 for the trans.). It shifts great and no surge or slams. The trans probably didn't need the rebuild, but other issues were fixed in the process.

 

This ^ ... and checking the U-joints myself while under there would be my next steps.

 

@Patman:Tthanks ill give that a shot and get back with yall. Thanks for the input everbody.

 

If this just started to happen I'd be more inclined to say electrical/mechanical....

From 08' on back the tranny control is part of the pcm.....there is no seperate tcm to reflash.....

Also remember your truck 's pcm has a roush tune....

 

I possibly found the culprit. I changed the rear diff fluid because it was in pretty bad shape. While I was under there I noticed A LOT of play in the carrier bearing. So I plan on changing that and u-joints while I'm at it next week. I can't believe this slipped through the dealership and myself. I'll let yall know how it turns out.

 

A bad carrier bearing will do it too, just like universals almost. I don't have one on my '07 (just two universals) , but my '77 4X4 LB does .... and three universals in the rear shaft.