I have never replaced U Joints, so Im unsure which ones I need. For my truck, the parts store has three types offered - 1330, 1350, and 1310-WJ. Do these numbers refer to size? How do I find out which ones I need? Do I take the old ones out and measure outer diameter?

 

Application is all based on options like; engine, 2 or 4 wheel drive, GVW, and wheelbase.

Are you certain you need new universals?

Yes those numbers reflect how big the cups are and how wide the cross is.
Whether the cups are retained from the inside or the outside, and where the grease fitting (if any) is located.

Sometimes Ford used "b a s t a r d" U-joints. (for whatever reason that word hits the forum "naughty" filter)
These are ones with different cups on either yoke.

Maybe it's best to bring the old one into the store to match it up.

This page may help if you have a caliper to measure them.
U-Joint series identification

 

As I posted recently in another thread, I finally got time to work on the truck. So, I started by replacing the timing chain. That didnt help the vibration at all. Next, I got a decent set of used tires LT285/75R16 and all 4 wheels balanced - didnt help a bit, except I like the new tire size much better than the original 235/85. Next on my list is U joints. I found good deal on ebay and ordered u joints. most parts catalogs I looked at for my truck (86 f250 4x4, standard cab, single rear driveshaft) offered same part number just under different manufacturer names, and I chose MOOG 354 (rear driveshaft at transfer case), MOOG 434 (rear driveshaft at rear axle)

While my driveshaft is out, Im thinking I may as well get it balanced as that may by one or part of the issue.

Just a recap: In Park, the truck starts up and idles fine and revs fine and runs at WOT with no problems. when cruising down road at light throttle, when speed gets to about 35mph or over, the truck vibrates at light throttle. let off the throttle, and mostly the vibration goes away. The mentioned vibration starts around 35 and gets the worst around 55+ mph. Giving it medium to WOT during any speed the vibration occurs, and the vibration reduces some, until the throttle is let off and goes back to partial throttle. Also, and I think most importantly, when crusing at 35+ mph, if I put the tranny in Neutral and take my foot off the gas, the vibration comes on after a couple seconds very strong and wont go awy until the truck is put back in gear. Vibration usually always goes away during engine braking.

 

I will also be sure to check for slop in the driveshaft, and inspect my slip yoke.

I think the locknut mentioned in a post on this thread is in good shape, if the part Im looking at is indeed the locknut. But, i will take step by step pictures along the way. I want to make sure I inspect every part of the drive shaft, tranny and rear axle that I can inspect with the driveshaft out, and eliminate any possible causes for the this vibration... its really pissing me off

 

I'll bet it is the slip yoke. Your symptoms are very familiar, although not exactly the same, and my slip yoke was gone. BAD! Paid the slop wasn't easily spotted on the truck - apparently because the forces on the rear axle when driving cause the axle to move and lengthen the shaft. So when stopped the splines are more meshed than when driving. So pull the shaft apart and inspect the splines.

 

If the splines in the slip yoke are bad, will the splines they mate up with rear axle be bad too?

 

I think we are talking about two different things. My drive shafts are two-piece units with a short section that has the front u-joint and that goes onto the output shaft of the transfer case. That shaft has splines that match up with the splines on the rear section of the drive shaft. And it is those splines that were badly worn on mine. So badly that it cost $300 to have the driveshaft rebuilt.

Your drive shaft may be different as there were several versions, but all of them had some means of collapsing/extending because the rear suspension lets the rear axle move fore and aft as the weight varies. It is in the slip joint that the wear occurs.

 

OK I see what you are saying now. All I know for sure about my driveshaft is that there is no carrier bearing. Ill take pics

 

I don't have a carrier bearing either. My trucks are both 4x4 standard cab, long-bed F150's.

 

And, I can take pics tomorrow if you want, and can point to the slip joint.

 

Here is a pic of my drive shaft, then the slip-joint slid in all the way, and then out all the way. If there is the slightest wobble in that slip joint at any point in its slide in/out it can cause a vibration like you described. The wobble I got was by having it mounted in the truck and pushing it side to side. However, mine was worn so badly that it was easy to find. One less worn would still vibe but might not be easy to find.

 

Mine looks similar to yours, except it has an accordion style dust boot and I cant see under it until I take it off

 

So, Im going to put my truck in neutral, chock the wheels, and try to move the driveline side to side, up and down, and back and forth. When I remove it, do I disconnect at the axle companion flange then pull the driveshaft out of the transmission extension (slip yoke?)

 

The easiest place to check for movement is on the vehicle as both ends are held securely. But, it is very possible to have slop in one spot on the splines but not in another. So, it might not move side-to-side sitting still, but since the rear axle moves when driving and that changes the length of the shaft, it might still have movement then.

 

If I understand your pictures correctly it bolts into both the tranny and differential. So, to remove it you will have to unbolt it from both ends.