I have an 05 Ex V10 with the 4R100 trans. Recently I have added a 5 Star SCT X4 tuner and started running an 89 tow tune. The tune makes the truck hold gears a little longer between shifting and seems to have a much crisper feeling shift. Only thing I've noticed now is then when under moderate to heavy acceleration (not towing anything ) I hear what I can best describe as a screeching sound when it shifts from 2nd to 3rd gear. It's very brief and does not happen under light acceleration. I assumed athat first it was a transmission noise but now after some online searching I am seeing that some are saying it's the serpentine belt slipping briefly. It could be as the noise certainly sounds like a belt screech. I can't tell whether it's coming from the engine bay or transmission. It's odd if it's the belt as I have replaced the belt, tensioner and idler pullies maybe 6 months ago. I want to try setting the tune back to stock today to see if it goes away but that won't necessarily tell me if it's the transmission or belt. Has anyone else experienced this?
Thanks,
Matt

 

Do this: Got to the parts store or Walmart and get some CRC Belt Conditioner. (Do not get dresser!) Spray it on as directed and see if the noise goes away. If it does go away, recheck the belt and tensioner. With all the crappy Chinese parts anymore, it could be a weak tensioner. if it does not get rid of the noise, start thinking of the bearings in idle pulleys, alternator, and other bearings. I really doubt that it could be the trans under any circumstance.

 

Maybe, maybe not. I had a new Trans installed on my Excursion in January and in two days I got a massive squeal. People would point as I drove by. The transmission shop said no way... must be breaks. Wasn't breaks... it was coming from the rubber coupling that the drive shaft yoke went through to engage the transmission. I tried to slide the rubber up a bit and smeared a little high temp grease on the shaft and the noise stopped. It did sound like a belt slipping.

 

BTW, how old are the tires? IF they are old, they could be slipping on the rim when the shift happens and all that torque hits. As far as it being a seal, that would be squealing almost all the time, not just under a major torque and speed change.

 

Thanks for the suggestion housedad, I'll try it. As for the tires they are relatively new as are the wheels, purchased all new back in about April.

 

 

 

I can't imagine anything in the trans squealing, I also think belt slip. When the engine suddenly decelerates because of a quick shift the accessories also have to quickly decelerate. The belt tensioner and belt outing is designed to give max grip in the direction of rotation, when the force is reversed the grip is less.

 

Thanks all. It was the belt. Sprayed down with some CRC belt conditioner and the noise completely went away, even under hard acceleration. If it comes back I can spray again or just switch to the Motorcraft belt. The belt I put on a few months back was a NAPA belt.

 

MIne does the same thing using the tunes. It's the belt chirping during the fast engine speed change.