vibration at 30km (18mph) to 40km (25mph)

i now have a vibration at 30kms to 40kms per hour. here is what has been changed.
i had a new exhaust system put on. when they did it, it was hitting the axle going over bumps. i put different leaf packs in hoping to raise the ride height a little, but that didnt work. i cant say i notice anything bringing it there (for them to fix the exhaust, which they did), but on the way home thats when i noticed it. here is the weird thing. no matter if i am on, or off the gas i have this vibration, then in magically disappears after 40km. if i coast in neutral, its there. if i rev the motor up to the same speed as it would be at that speed, it doesn't vibrate. i have a double cardon rear drive shaft in this truck, and it is also lowered. i just put a track lock in it last night, and while the rear part of the driveshaft was unbolted, i spun the u joint, and it felt fine. i havent checked the front two, but i cant see it being u joints because it doesnt act like one. anyone have ideas? it is also stumping my buddy who is also a ford certified tec for over 20 years.

The vibration was there before the trac loc was installed, obviously.
Does it also happen when braking?
Does it feel like your ass shakes? How about the steering wheel?
maybe eliminate tires and rims by swapping them out quickly? I know of a set of 4 on a certain black truck that I know for a fact are smooth as silk.

My rear drive shaft wont work for you to try, but you are welcome to your front.
Let me know what I can do to help.

I have a feeling we are going to have to use a process of elimination so we can find out what it isn't.

vibration is there when braking in that speed zone, and yup, was there before the track lock.
my ass is big, but not that.....oh, you mean the trucks ass! no, it goes threw the entire truck when it dose that. thats why its hard to pinpoint.
i dont have a front shaft in at the moment, but it was there when the front was in.

Wow,
Would you loose a lot of fluid pulling the rear drive shaft and drive in 4x4 with the front shaft in?

If its still vibrating, I say try tires and rims.
A quick google says pent rim, or bad tire.
http://www.ericthecarguy.com/faq/determining-the-causes-of-vehicle-vibrations?start=1

we will have to rule out tires. the summer rims have been on it for a bit now.

in 2wd raise the rear wheels off the ground, and set chocks.
take off the rear tires, start the engine and shift to 1st gear.

while the brakes are rotating watch for a slight in and out movement of the calipers indicating a bent axle shaft

Like this, on my driver side

i remember when you had that problem jon. my problem (to my knowledge) only happened after the exhaust was put on, and i changed the leafs.
btw, the leaf pack is out of a 03 sport. i changed the rear bushings in both packs. on the old leafs, the rear bushings were good, but the front bushings were toast

It just doesn't make sense to me that leafs or bushings could do that. I could see your truck not tracking right if the dif wasn't straight, but a shimmy?

vibration

Could you try different clocking of the rear drive shaft to differential flange?

Random ideas......(if not tires)

Any humming sound with the vibration? (carrier bearing)

U-Bolts loose? (snap sound on take off)

Carrier Bearing caps came loose?

Still have the 5th shock installed? (New leafs changed pinion angle)

4point- i thought of doing that. i also called the exhaust shop to ask them if they did have to unbolt the driveshaft when they did the exhaust HOPING they did. but he said they didnt, so that didnt change
greg- major humming sound. almost sounds like a sub woofer playing a bass track. but its a short driveshaft, and has no hanger on it. also it never had the 5th shock on it from factory. as well as it never had a weight hanging from the diff from factory either.
explorersport77's (tara's) boyfriend who makes monster truck diffs as a side job was asking me what the angles are. i am going to get a angle finder and hang it both from the diff, then the trans pan to see what the angles are. buddy also told me to jack up the back, and run it at that speed and see if it does it while its in the air. might be chasing something in the wrong part of the truck to being with.

vroomzoomboom said:

we will have to rule out tires. the summer rims have been on it for a bit now.

Click to expand...

Meaning that the vibration was there with the winter tyres and the summer tyres?

Does it hum when changing speeds or is it a constant and gets louder the faster you go?

Pinion bearing hum is on the accelerator.
Carrier bearing hum is constant, gets louder the faster you go.

Might have to shim the axle at the perches.

I still think it could be in the rear axle. The worn bushing you mention could have been allowing sloppy axle. Now that the bushing it tight, the vibration is making it through the frame. Getting the rear up and running it might just show something.

for all you math geeks here, see if these are good or not.
i took some angles (and it wasnt easy for a fat guy to lay under a lowered truck to get em either!).
transfer (with gauge at output shaft seal) 5-6 degrees
drive shaft (near rear u joint, with gauge running the length of the drive shaft) 0-1 degree
rear diff (with gauge on companion flange also running with the length of drive shaft) 8-9 degrees
i took the rear drive shaft out (i dont have the front in at the moment), and all the u joints turn free, and dont bind. i dont know if put it back in the same spot however. another thing i tried (out of desperation) was i remembered when i put the leafs back in, i didnt preload them. so with the truck on all four tires, i loosened off all the leaf bolts, bounced the truck a few time in the back, then re tightened them.

Before you put that driveshaft back in, check the pinion gear shaft for slop. Crush sleeve might have loosened, and need torque again with the pinion nut.

Which measure direction is the angle at on the diff?

im not saying your wrong greg, so dont think that, but i dont even have 100kms since we put the diff in on tuesday, so it cant be that. also the vibration was there before we changed the diff (preload was good, so was back lash).
for the direction of measurement, think of it as, you looking at the gauge from the side of the truck thew the wheel well if that helps

Alright, sweet. Just an idea to check the pinion nut torque since the shaft was off. The crush sleeve can be a tricky booger sometimes.

The straighter the alignment is for the shaft to the diff the better. 10 degrees difference doesn't seem that bad.

Im just trying to think if things that you might not have is all.

So, another out of the box idea I have is the transfer case. I don't know the specifics of the 4406, but im wondering if it could be the issue. Have you tried to put the Trans in neutral at the speed it is humming at?

did the neutral thing as well. same thing

vibration

Just some thoughts......
It is vehicle speed related, you ruled out engine already.
Is it a fast vibration or slow vibration? knowing the frequency could help determine what area it is in.
Know anyone with an EVA (electronic vibration analyzer)? Saw some on eBay a long time ago.
There was a program called vibrate 5.0 that worked with the EVA to point out possibility's.
The driveshaft, transfer case, and transmission spin faster than the axle shafts and wheels/tires. However the driveline vibration may not just go away like yours does at a certain mph? Unless the transmission is shifting and it is internal to the trans?
The noise was not there before the exhaust was modified again, was the vehicle put on a drive on lift or other type?