I had the same issue when I did a 8 3/4 swap a few years ago.
I noticed the u joint when in really easy.
Then as articulated it I saw the cap stay still while the slip joint turned.
Turns out the old joint was dry and must have seized. And hollered out the slip yoke.
I looked for a NOS slip yoke and found a hand full in the 100 to 150 range.
New will be less expensive.
I thought about new but wanted to keep the OEM shape as the new ones are subtilty different.
Good catch on your part. I'm sure there are more guys running around with this same condition and don't know it. Under most driving conditions it is only rotating a few degrees and back. And if there is oil leakage in the area it's probably lubed enough for thousands of miles.
BTW I found there are 2 OEM 904 slip yoke lengths. IIRC the long one was replaced by the shorter one by chrysler due to the longer causing vibrations. (Or that is a wives tail about the vibration)
Both slip yoke can be fully inserted into my 67 904 without interference
New video by Dana Nance
Far right is original installed in 67
Next it NOS
then used long
Then aftermarket
View attachment 1716344962
Ling vs short oem
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