I wanted to ask you guys if you had any insight on this.... I had a lot of trouble with vibrations in my driveline so I checked it out....

First I put a new center with a new pinion yoke in the truck. The truck ran well at most normal speeds but had a bad vibration at highway speeds.....

So I looked it over and found the shaft was too short by 1.25" the tailshaft bushing was also bad and I had a lot of play at the slip yoke... so I got a new yoke and tailhousing bushing.

I had a longer driveshaft made, that I was told had to be aluminum because it was 73.75" center to center that also has a new slip yoke.... I had a new tailshaft bushing pressed in and put the tailhousing back on the trans.

Now I have a vibration when in all the gears, especially third, at low speeds! This is when I start out... at highway speed its smooth.

I checked the angles.... the tailshaft is at a downward 4.5 degree angle, the rear is pointing up 2 degrees

Where do I go from here? Anybody have any suggestions?

 

Sounds like your new shaft is not balanced. Your problem got worse when you put the new shaft in. How in the world did you determine the shaft was 1 1/4" short? What piece is missing? Is this a lifted 4x4? Is this truck all stock? You have about 1/2"-3/4" adjustment in the midship bearing. Seems to me if that was all the way the wrong way you would have been just fine.

Alum shaft? Isn't the original steel? Next on the list would be slip yoke. Has the trans been swapped out. You do not need a slip yoke on the front shaft where it goes into the trans. Try this. Take the back half of the driveshaft out. Start the truck up and run through the gears. Vibration yes it's in the front shaft or trans but I would bet the shaft. If no I would bet it in te rear half BUT remember it got worse after adding the "new" alum shaft.

 

I knew a guy that was chasing down a similar problem once and it turned out to be a bad bearing inside the trans.

Not sure if there is a good way to check for a trans problem, but something to think about.

 

All the pieces of the are new in the drivehsaft I also think the new shaft is balanced because of the fact it runs smooth at speeds.... I have a 4 by 2.... I think it's stock but it could have little lift spring in the back.... After I measured the angles in the drive line I am wondering if I need a shim to kick the read up... It'd only two degrees up.... Maybe when it loads with the driveshaft it noses down a bit and then causes the vibration.... Or like meborder days it could be a bad bearing in the trans or a bent yoke at the rear.... Or bent output shaft....

 

Just because the parts are new doesn't make them good.

 

I had a bad vibration at highway speed on my 2004 F250. I took it to the driveline shop and replaced the carrier bearing. Better but still had an anoying vibration above 50. Went back to driveline shop when they weren't busy and had them balance the drive shaft. The technician told me take it for a ride and let him know if it helped. At highway speed the vibration seems to be gone. Between 40 and 50 mph I have a high speed vibration...definately the drive shaft. I am currently living with the high speed vibration because I hated the bouncing at highway speed.

 

I don't think the new shaft is the problem.... I wish I had it made as a CV style shaft and think the shop should have suggested that, but I can see where they were thinking why upsell the CV and loose the sale as too expensive, or have me say turn my old steel shaft into a cv shaft and loose the money on a aluminum one... I could always have that changed too... just a matter of money.... I did some digging that I probably should have done in the first place... and found Spicer says no more that 2 degrees for u joints... well the rear is up 2 degrees and the tail shaft is down 4.5 degrees.... looks like its a case of raise the tail shaft.... I am going to start by installing a new transmission mount... mine is god knows how old... maybe original... and then re-measure the angle... then take it to 2 degrees from there.... and let you all know what happens...

 

How are you measuring "down" 4 1/2 degrees? You should take a reading from the shaft going to the third member and again measure the angle of the shaft it is connected to. Subtracting the angle of shaft 1 from shaft 2 will give you the "down" angle. The up of the third member again only has reference when related to the driveshaft. So if you again use the same formula as above you then will obtain the angle the U Joint is operating in. If you took your 4.5 measurement off of the rear shaft then your final operating angle at the third member is 2.5. If you took it off of the front shaft you have not taken the second shaft angle so you have no valid number to reference from. I guess you could in theory subtract the 2 from the 4.5 again arriving at 2.5 that you would divide by 2 (you have 2 ends) giving you a final number of 1.25 at each end. Not a valid way to do it but it is another way.

I personally think you are shooting yourself in the foot to automatically eliminate any piece in the equation but that is your decision. From what you describe the problem got worse when you replaced the front shaft new or not. Why build a CV shaft? The truck didn't come with one when it was new and didn't have this problem. You would only be further complicating finding the solution. I also do not believe your angles have anything to do with it. Again the truck has had these angles since new and no problem with them.

I assume you are talking about a vibration that feels like the entire ruck is about to come apart and not something like wheel balance.

 

I adjusted the back of the trans up so that protractor showed the same angle on the pinion u joint and the tailshaft u joint.... And the vibration disappeared on a test drive.... Then I hit a hole on the road and had a slightly different problem.... I have a spring broken at the eye!

 

Let you know how things turn out when I replace springs...

 

Sometimes when the converter is going south they will vibrate at odd times as well but its usually rpm related not mph.

 

Maybe the spring was cracked and had something to to with the vibration also. Hitting the hole was the final force needed to finish the break.

 

I am wondering about that oldstyle.... The other shaft was 1.5" too short and the tail bushing was gone.... So I think getting a new drivehsatf was in order.... But it when your spring cracks at the eye you have to wonder how that factors in

 

Got the new springs on.... angle on the tailshaft U-joing = angle of the pinion U-joint..... vibration is gone! Finally.... onto the next problem

 

Good to hear you got it figured out.