Yeah I figured that out after I wrote that post.
They don't have a dunce cap smiley face.

 

Ok, finally had a day off to get some work done so I got underneath the 350 to pay attention to that slip joint. Unbolted the support and pulled it down and back. Holy crap it was tight. Greased the living crap out of it and immediately noticed a difference in how it slid. Put it back together with no clamps on the boot and drove down to the Ford dealer to ask about new clamps.
Senix and Brown Dog you were both absolutely correct. No thump at all.
I didn't think at first that there would be that much spring wrap (suspension movement) on a 350 but the proof is in the pudding. There is!
Talked to one of the mechanics at the dealer. He told me it would need it every 20k! Kinda wonder why it's not mentioned for normal maintenance.
Also talked to him about clamps and the tool to close the stock style clamps. I'll do some more research and report back.
In the meantime I bought some nice little clamps called Speedi-boot! (pic below)
I didn't want to use normal screw clamps as they are a bit bulky for this area and I didn't like them spinning around on the boot. They work pretty well though they are not so speedi. (pic below)
All in all very happy with the fix so far. It's an easy job. Will add it to the list of normal maintenance.
Also included a pic of the exploded view so that you can see part #s.
If you go through Ford the boot and clamps come together and cost $34.16.
I bought the Speedi-boot clamps for $6.

 

For the record you will probably never touch it again. I have 60K on mine and have never greased mine.

 

My eyebrows did raise when he said that.

 

I still hadn't greased mine yet :-(
I'd like to drill & tap for a grease fitting like my old 77-79 (owned 1 of ea model) had.

 

If it wasn't such an easy job I'd consider that.
Two hanger bolts and a pull, just a little longer than using a grease gun.

 

I greased at 90,000 miles now at 133,000 everything is great.

 

Ours are similar then.
Mine's 87k
Still can't believe the difference.
BTW, have my local fastener guy trying to track down the original style clamps.
Will inform.
Another BTW
In the pic below, the cap at the shaft end of the t case housing moves about an 1/8 inch when shaking the drive shaft. I noticed it as I was pulling the slide apart to grease. Also noticed the rust thrown up onto the cab underside. Rust seems to be coming from front side of ring. Anything to worry about? My initial thought is no, but thought I would throw it out there. Just concerns me a bit as it could be a seal or bearing screwed up by the original thump as it was pretty bound up.

 

wipe it clean and watch it. Don't think it is too much to worry about just yet.

 

I took the lazy mans method to grease my slip yoke.

I used a Grease Needle on my grease gun, stuck it

Thru the rubber boot & filled it full of Red Hi Temp

Grease - BINGO

No leaks & Thump is Gone

 

Funny you bring up the needles. I was just messing with two of them the other day.
I bought a couple of u joints for my '74 and they came with needle fittings instead of zirks. Broke one needle trying to insert. Bought another and still can't get it to insert in that damn fitting. I've never seen this type of fitting before and I hope I never see them again. What a pain in the A.
I'm back on zirks.

 

Those fittings are to be greased with a pointed Thick walled
Needle that won't bend, rather than the surgical needle used
to grease a rubber boot.

 

Yeah, I had the one that was called for but I still don't understand that whole idea of the needle. Just foreign to me. Seems like a new fangled idea that sucks.
I do like the idea of shooting it through a rubber boot though.

 

Forgot to post this link.
I found the original style clamps for the boot.
https://www.belmetric.com/hose-clamp...pg747r577geb73

 

Marc I saw those dreadful things when I was getting Ujoints for the ol 64 I went with non greaseable Local shops had them for anywhere from $25-37 per. I got the same ones on Rock Auto for 10.67 each...3 for the price of one... They are the super heavy duty and US made..A friend of mine with a driveline shop suggested them. A few shops were trying to sell me on those needle deals, but my thought was that I am getting to old and fat to keep climbing under my truck and shootin' it up, like some drug addict every few months... The up side is that the non-greaseable are much stronger, as they are not drilled out through the middle of the cross tree so that grease can pass through. hence the reason that none of the manufacturers use the greasable any more...