Hey all,
I got a 91 f150 and its having a pretty bad shake (sometimes) when going around 35ish mph right after it shifts into 3rd gear it feels like.

I thought it might be the tires but sears balanced them (only 1 new weight on a tire btw) so i don't think they were bad. I'm kinda lost, i suppose it could be maybe a drive shaft or u joint but I got under her and twisted the shaft and the joints were nice and tight (they are probly around 20k since i replaced the old) only the slip spindle thing that goes into the tranny moves a little bit.

Really not sure, its been happening for around 8k i think, and Im afraid that when I go home for the summer from ny to boston something will finally break.

 

I removed your other thread for you.

I would get a rebalance done elsewhere. I just had to do that myself. Some guys just miss it. I have mine rotated and balanced avery 4000 or so. It was smooth but time for a rotation and when I left, had a shake from 50 to 60 mph. I just took it elsewhere yesterday and it is smooth as can be once more.

 

Just took her to work and back and decided to try diff gears to see if it made a difference. In 3rd it happens and in 2nd it doesn't really happen, maybe just barely. Drive shaft then?

 

I'd be looking at a possible misfire.

 

Have you checked the bell housing bolts? I have seen and had this problem myself before on an automatic. The shake wouldn't be noticeable until the last gear. It started with having this swishing sound relevent to RPM, but pronounced on the hwy. As I continued driving it, it got worse with every fillup.