…..so, having completed rear axle seals and bearings, U-joints, and rear shocks - I have a distinct vibration while cruising (above 40-45). Going back under to check integrity of u-joints and drive shaft in general, I have no rotational flexion - but lateral. The slip yoke is tight in the tailpiece, but left to right (hence lateral) there is about a 1/16th on an inch movement of the tailpiece. The rear engine mount appears OK. Scratching my head as to wear the “freedom” might be coming from - any ideas?
The slip yoke is supported by a bushing in the extension housing. Check the yoke for wear first. If it’s in good shape, then the bushing is likely to be worn.
1970 MERCURY COUGAR 5.8L 351cid V8 Extension Housing Bushing | RockAuto
Thanks; it doesn’t appear the yoke is moving laterally in the tailshaft - the whole tailshaft appears to be moving, is this still the suspect?
There should be some movement from the transmission mount.
did you have the vibration before doing the work or is it something new?
Well, I’m not sure. Prior to this I thought I blew an axle seal - and I did, but it was because of a lunched axle bearing (when I pulled the axle free balls fell out and two split races on the shaft). After replacing the bearings and seals (both sides) I went right onto the U-joints. I’m pretty sure I put it back according to my indexing, but it is possible I messed up. Point being the car is so much smoother overall now that I can discern the vibration that I maybe just wasn’t aware of before (both u-joints were damaged on one of their respective spider’s legs. I was thinking about rotating the shaft 180 degrees.
Sounds like you need to have the U joints replaced and the drive shaft rebuilt. Now is the time to have the drive shaft re-balanced too so may as well take the whole drive shaft to the drive shaft shop and let them do it.
Thanks Royce; u-joints are new, but I may have to have the driveshaft balanced. Now it’s just finding the place to do it - there’s got to be a local shop.
Since you have play in one of them I thought you needed a new set still.
I got you. U-joints are excellent, the play is at the tranny tail shaft - and not the slip yoke in the shaft, the whole extension housing appears to move about 1/16” left to right. I’ve been given to understand that might be normal. I have found a couple places reasonably close that do driveshaft balancing and I have new motor mounts on the way. Appreciate the counsel.
Do I read right? the tail housing is loose enough to move? Its bolted to the trans & it does not move, unless the trans mount is broken, loose, or crossmember is loose.(or balance as stated)
The shaft inside will move alot, but once the yolk is inserted no movement, which brings us to what I believe may be the issue.
The tail shaft bushing.
Known to go bad, cause vibrations due to play.
Requires a special tool, or a good trans shop. Less than an hour to pull & replace.
Basically yes; just saying when I grip the drive shaft at the slip yoke and do a left to right “push/pull” there is no slop in the yoke, but the tail end of the extension housing shows movement of about 1/16”. I am suspecting it may be a bad rear mount, because the front engine mounts are both shot. All three inbound and will report later in the week when I put them in. Thanks for the input Bill - and when this is all over I still have that power steering control valve to rebuild!
…and the answer is: transmission mount, replaced today - play is gone. Imagine that. I hear Don Rush buys OEM parts, I wonder how much he’ll give me for this?
He might give you a hard time…
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