I replaced both front rotors, bearings and calipers 300 miles or so ago. I now have a fairly violent shake around 45mph (almost a bounce). I first assumed the bearings didn't seat well and the spindle nut was now loose. So I rechecked everything. Everything looks good on the front end; ball joints are tight, new shocks, springs intact, tie rods tight, spindle nuts okay etc. I checked the manual before taking it to a tire store for wheel balancing. It said a rear wheel axle could cause this. How can I check this without removing everything? Basically I don't want to spend $50 on balancing if it's another problem (yup I'm cheap and the tires are fairly new less than 10k on them). Any ideas what else I should check as well?

1991 2WD F150 5.0 XLT Lariat.

 

My 2 thoughts here are as follows:
A) Your tires are way out of balance.
B) Your driveshaft is out of balance.

 

You could rotate the tires and see if the vibration moves to the rear. While you have it jacked up spin the tires and look for an out of round tire.

 

Sounds like a tire may beginning to separate. Look for any bulges in the tread area. Just because they are new it doesn't mean there couldn't be a defect.

 

There's damn near a million things that can cause this. Not sure which, based on the info you provided. The first thing to do is note the frequency of the vibration- Is it closest to engine, driveshaft, or tire rotation speed? Is it somewhat erratic? Also note the effects of pushing in or letting out the gas. Does it only do it under acceleration, deceleration, etc.? Does it make any kind of noise when it happens?

If it's close to driveshaft speed, or engine speed in OD, it's probably an imbalanced driveshaft, U-Joint, or driveline bearing (tailshaft, pinion bearings). Which trans do you have? The 2wd M5OD does this quite frequently. Put in in neutral and shake stuff to see if anything moves.

If it's erratic, it's a suspension issue. On an 89 it's well withing the realm of possibility that you have a bad spring bushing or stretched hanger (although this may not cause shaking in most situations). Sounds like you gave the front end a pretty good check, BTW!

Given your circumstances, my $$ is on a D-shaped or imbalanced tire. After checking the suspension, you definitely should inspect and rotate the tires like the other posters suggested.

Oh yeah, CHECK FOR LOOSE LUG NUTZ! Tire shops put 'em on wrong ALL THE TIME! (or not at all O_O)

 

If its narrowed down to a certain speed then it's most likely a balance issue somewhere. If its more general say any where from 40 to 50mph then I would guess its suspension related. I will describe what I have found on my vehicles in the past let me know if it sounds similar. 89 f350 my front end felt like it was jumping up and down violently. Like you everything was good and tight in the front so I mounted a gopro camera to the bumper facing the suspension and found that the tires were actually going side to side a couple inches after hitting some potholes. Didn't happen every time but the bump would start the side to side motion and the suspension would keep going side to side around an inch untill you slowered or held the steering strait for a few seconds. This was caused by my steering box wearing out due to large tires and a leaking power steering pump. If you have a little play in your wheel you might want to check for any problems in the steering box, from inside the truck it feels like a violent up and down motion. Another problem could be a loose trak bar. It might look good and feel good when you try to Pull on it but could still be moving. Look up death wobble on you tube there are good videos of what happens and what to look for. I have had both these problems on different fords and two repair shops couldn't diagnose what the cause was. It wasn't untill I got it on film that we were able to sort it out. If you can barrow a camera from someone and mount it somewhere solid you can save yourself a lot of headache searching through every part. If not find an empty road and stick your head out the window watch the front then back wheels and narrow down where the shake is coming from.

 

Problem solved! I had replaced the rotors about 300 hundred miles ago. Those miles were all highway speeds so apparently I accelerated/decelerated through the rough spot. One of the new rotors were cast wrong. Images below. Now that I see it I can't believe I didn't notice. I've never had a rotor this far off. By the way the parts store (Advanced) refused to give me another seal which I had to buy when I returned the rotor. I was shocked. All over a few bucks. Sheesh!


The rotor IS offset. It's not a photo illusion



Compare this ridge with the one below... 180 degrees on the other side of the rotor...



Nearly 3/8" higher!



Apparently some genius decided to attempt to balance a bad casting. Notice the grinding near the rotors face...




COmpare the space between the caliper with the one below...


Just a tad off lol

 

Huh.... Sub standard parts ! You test drove already and no more shake ?

 

Yup, smooth as silk now. I suppose the moral of the story is never assume a newly installed part can't be the cause. I've said that before but apparently can't take my own advise lol.