Shaky Deal


1967 D100, 318. I swapped my granny gear 4-speed to a
518 OD trans and now there’s a vibration
around 50 MPH. It was smooth with
4-speed. I had the propshaft fabricated and
took it back and they said it was OK but
still vibrated. Took it to another shop and
they said same thing. I can put in neutral at
speed and still vibrates. I read in another
tech question there should be about 3/ 8˝ of
yoke showing, mine has about 1½˝ showing
and I can pull and push on and the
yoke moves up and down noticeably. I’m
pretty sure this is the problem but another
yoke I have shows about the same. Does
the 518 have same output size as 727?
Also Phoenix in Weatherford, Texas built the
trans and converter, I wanted a high stall
because of Mother Thumper cam and they
said it was hard to get a high stall with this
combo but said they should get around 2800 but it’s only about 1500. They said if I bring the truck back they will see what they can do. Do you think they should be able to get more stall out of it? Truck has 4.10 Dana, Indy 2.02” heads, Ed’s RPM intake, Holley 650, Revenator module. Revenator instructions says vacuum advance is not needed, I know, I know, but with timing light as soon as I touch the throttle the timing jumps up perfectly. The truck hauls ass but I need to correct vibration problem and really let it eat.

The yoke should be quite snug, and, at normal ride height, almost touching the boot, roughly ½˝ max clearance. Your ’shaft is simply too short (mine too.) The output bushing is, in all likelihood, now chewed up from the too-short ’shaft.
727 and 518 slip yokes are identical.
I suggest measuring the U-joint angles also.

A hotter cam reduces low end torque, this reduces stall RPM. I assume you tested this
at WOT? Any other test is meaningless. Converters can’t actually be rated at stall RPM, the spec is a K factor. The same converter – identical – may stall at 1200 RPM behind a 273, and 4000 behind some stroker big block. Really!

A street driven vehicle must have vacuum advance. MUST. Unless you wanna give up 5 MPG, dilute the oil, and wear out your rings in 5,000 miles. No matter what type of ignition system you use. End of story.

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