1994 F-150 drivetrain vibration

JSW227

MEMBER
1994 FORD F-150
V8
2WD
AUTOMATIC
199,000 MILES

I have a 94' F150 xlt 2wd with the 302cuin, A/T. I had to cut my parking break cable because it froze up on me, I then had to replace the rear breakes, passenger front ball joints and spring hanger, and shocks. The next day, I started feeling a vibration (other then the suspected torque converter shudder that occurs between 3rd-4th and/or into overdrive)that seemed to travel from the seat to the steering wheel and eventually started to vibrate the entire truck. I checked the u-joints, they seemed tight with no sign of rust and the tail shaft seemed a bit sloppy to me. I havn't measured the backlash in the rear end or anything like that. The vibration gets worse every day and happens under load. If I "get on it" it smooths out a lot, if I shift into neutral it goes away. It is worst at normal cruising rpm's from 20mph - 55mph (i won't chance speeds any higher). Leaving work this morning it was really bad. I turned a corner and started accelerate when I heard a single knock/clank/bang, or something of the sort. I tried to think it through and all I could come up with was the spline on the tail shaft possibly skipping a tooth. The sound seemed right and the location of the sound, but I'm not sure if that is even possible. I don't know much about transmissions, in my mind I have narrowed it down to something between the fly wheel and the rear end. What do you think it could be? Something deffinately seems to be wearing out.

Any input is appericiated and I thank you in advance.
JSW

3 Replies

HMAC300

MECHANIC
48,601 POSTS

Best thing to do here, especially if you have already checked th u'joints and norust seen or play in them. Take the rear end cover off if it has one an dlook at the rear end gears for broken teeth, etc. Before you do that however drive the truck in a left circle and see if you hear any noise. If you do check your right wheel bearing. Then drive in a right circle and if you hear noise then check your leftwheel bearing or axle shaft. You might try lubing the driveshaft at the front if there is a grease fitting there, because alot of times the driveshaft can't move forward/back and causes vibrations. That would pretty much eliminate everything but the trans. One other thing, if you have a timing light, make a mark on harmonic balancer mark it accross the rubber part with chalk. Start truck and give a quick rev. Then see if the chalk mark is the same or if onepart of it has moved one way or the other. If it has your rubber broke on the balancer and is giving your vibration. Also check your torque converter bolts for being loose as these will do it as well.