Source of loud "WHACK!" after being lifted?

[cognus]

Gang I had a weird week last week so already posted about tire agony/ecstasy, but this one is really really strange.

Discount tire nearby does all our tire stuff and has been heroic for a long time now so this has nothing to do with their work AFAIK. When they mounted/rotated/balanced with a pair of new Kumho Crugen tires, I happened to be about to walk back in the showroom, same time as they were backing my '07 2WD SR5 out of the bay. one tech was watching, another driving. About the time he put it in Drive, there was a loud sorta metallic WHACK! that I heard and both of them heard - and they were really buzzed out. My first impression was that he had run over some biggish metal object, toward the rear. both techs were looking around for any obvious cause and none of us could see a thing. I crawled up under, looked at everything, and went on with my day. no clue

a full day later I was back because of a shaky/vibe at highway speed. They redid the balancing 4 wheels, and handed off. I drove about 300 yards up the entrance road at very low speed and just as I started to brake to the STOP sign WHACK!/! - same thing, with me driving. It felt very metallic in the seat, and I thought I could feel it well in the Steering and imagined it was on the front left. Had a little bit of a ring to it which I thought would be normal given the rigid frame and the bashplate etc metal. I got out and snooped around all the wheels etc. Nothing. could not see a thing.

What is the cause of this?
- Binding U-Joint in the drive shaft?
- Freeze of Control Arm Bushing?
- Sunspots?

Discount lifts by the rails, as you know, on trucks.

???????

 

[Inv4drZm]

I would try jacking the front end up again until the tires are off the ground, lower it back down, then slowly driving until you hear it again, with someone outside the vehicle trying to trace where it's coming from.

 

[blackoutt]

they never torque my front lower control arm bolts to spec 135nm (100ft/lbs) and can cause a clunk when coming to a hard stop/compression, then again at hard accel, droop. I was able to recreate it in the garage by jacking up from frame to get droop, then set it back down and jack it up by the suspension/wheel to compress. Repeated to find the rear bolts of both from LCA's loose. Torqued and clunk was gone.

 

[RonJR]

they never torque my front lower control arm bolts to spec 135nm (100ft/lbs) and can cause a clunk when coming to a hard stop/compression, then again at hard accel, droop. I was able to recreate it in the garage by jacking up from frame to get droop, then set it back down and jack it up by the suspension/wheel to compress. Repeated to find the rear bolts of both from LCA's loose. Torqued and clunk was gone.

That was my first thought as well. For several years I had an occasional loud CLUNK from my '94 front end when reversing directions and turning, that I could never find. Finally, for other reasons, I needed to adjust the LCA's, and one of the adjusting bolts was only moderately tight. I torqued it to spec and the clunk hasn't been back since.

 

[SeanWN86]

Park brake?

I don't know why, but any time I remove the rear wheels, I have to reset my park brake.

 

[cognus]

Wow. I thought about Control arms, and spoke with one of the more experienced tire guys about that but would not have guessed bolts under-force. I appreciate that tip. One of the rears, maybe both, were off the vehicle a year or so ago when I had a rear wheel bearing go bad. Could be its been off since then.
thank you much for the input - I have a great alignment shop nearby and they'll check it out. If anyone can show me the shop manual page about the torque spec I would appreciate it. I assume the spec is different for front/rear. mine is 2wd.

 

[Morphyne]

Is that all the work that was done was tire balance mount and rotate? Was any other suspension part touched lately?

 

[cognus]

Is that all the work that was done was tire balance mount and rotate? Was any other suspension part touched lately?

Nearly 2 years ago passenger side rear bearing replaced. Dealer did work
axle removed, differential serviced. Dont know what the process called for on the driveshaft. Thought I'd give them a call today and ask that question. At 177K, I don't think that driveshaft has ever been lubed or serviced at all.

But not to point finger back that far: the truck has rolled very smoothly from then to now, once I made sure to keep the michelins confined to the rear, keep the Alenza Plus's on the front, and not monkey with them. Some months ago I started noticing at highway speed a little vibe in the steering wheel and I had it in my brain that the michelins were so worn they were causing the issue. It was very slight, very narrow speed-wise just over 70, fading away at faster speed. I could do 90's on the toll road and it was great. Now I wouldn't dare go past 82.