Howling noise and vibration.

[fast1990gt]

I had a friend of mine who has done dozens of gear swaps before put in my 3.55's. Everything was in spec. Good pattern, .008" backlash, and perfect drag on the bearing preload. When I had it on the freeway yesterday at about 75mph or so I had a vibration and droning sound when I was on the throttle. At first I thought it was the gears but after doing some research on the corral I found that I could be an imbalance in my stock steel drive shaft. I also found a link to this article on drive shafts and gears. What do you guys think? It only happens around 70 mph and up.

http://www.tccoa.com/articles/tranny/transmission/page17.shtml

[upngo50]

Was there any evidence of the vibration before the gears? If not then I would suspect the crush sleeve. Did you use a new one or the old one? If you used the old one, tear it all back apart and put in a new one or will be constantly retorquing your pinion. If you used a new one what did you use to crush it? Impact or did you just try a big bar for leverage? Does it only do it under load and not when cruizin' a steady rpm? What happens when just let off the gas at the speed, do you hear the same thing or something different? Driveline vibrations sometimes can be tricky to find, but if you didn't have any problems before the install, obviously that is where you should start.

[fast1990gt]

Everything and I mean everything is new except for the carrier itself. A guy here at work said he's had howling gears before but nothing that ever caused a vibration. That is why I'm leaning toward the drive shaft.

[upngo50]

How do the u-joints feel? Another trouble area is the bushing in the tail of your t5 trans. Pull your driveshaft off and check the condition of the yoke. If it is worn then chances are the bushing is bad. You have to pull the tail cover off the trans to replace it. Axle bearings were new also?
Uh...oh! Did you rebuild your t-lok @ the same time? If so did you add any extra clutch paks? That can sometimes make the axles rub on the center pin causing vibrations. I had to shave down the end of my axles.
I personally have a hard time believing it is the driveshaft out of balance. You would have noticed it before the gears went it. Maybe not as much or in the exact same way you do now, but in someway you would have.

[fast1990gt]

U-joints are solid, axle bearings are new, and yes I did rebuild the t-lok but I didn't add an extra clutch. I already had to shave down my moser axles because they didn't fit though which I read is a common issue. Did you get a chance to read the link I posted? This is what is leading me to believe it is the drive shaft.

[markstang]

I agree on the crush sleeve issue, also .008 back lash is tight. it should be .011 to .014. that could cause the droning sound. also look at the flange yoke & see if the pinnion seal is on the same spot as before the gear swap. If not then the crush sleeve is not crushed all the way down were it should be.
I'm shure your buddy did a good job, but could have missed a small detail.

mark

[upngo50]

If you can tighten your pinion nut, chances are the sleeve never really crushed. As far as the .008 back lash, that is the bottom of the recommend spec from Ford (.008-.015). That is where I always put it.

[fast1990gt]

The set of gears that I put in was already used and broken in. They had a couple thousand miles on them and had a perfect wear pattern. They were off of a fairly new F150. I talked to the guy who did it and he reminded me that we set it at .012", not .008" since they were already broken in. My mistake. Anyways, I remembered that my slip yoke was kind of worn down in the middle when I put it in. I decided to order a FMS aluminum d.s. today since I'd rather do that right away than just dump the money on a new slip yoke. Hopefully this will fix the problem. I'm going to check the bushing too.

[upngo50]

Yep if you have wear on your yoke then it is a safe bet your trans will have to come down to get at that bushing. It has to be changed from the inside.
I wouldn't drive on the new DS too long before doing it or you will have the same result in no time.

[Jesse James]

Just my $.02 here. 3.55's out of an F150? I do know that some 3.55's have what may be called a "flat" spot. My 03 Cobra had a roar at 45-50mph, then again at 75-80ishmph. I had a couple of other issues though, the driveshaft was replaced, rear end assembly replaced. Even after that I still had some vibration at the upper end 75-80mph but not as bad. They ended up re-indexing the driveshaft "on the IRS there were like 6 different possibilities/combos. The master mech at Ford said that quite a few batches of the newer 3.55's were known to cause a little vibration. Just being informative here and trying to be helpful. You still got the big weight "dampener" on there too? j/c.