Odd Vibration

[MythX]

I'm getting an odd vibration. The faster I'm going the more noticeable it is. It's detectable at about 45 mph.

It seems to happen when there's no stress between the transmission and engine, such as when I press the clutch. It also happens when I'm traveling down the highway with just enough gas pedal to maintain coasting speed.

It's a subtle vibration, and since I'm mainly just driving to and from work, I'm rarely on the highway. Am I detecting something that's normal?

Truck is a '94 Sport - 5-Speed - 4x4

 

[Anime]

Vibrations, shudder, and shaking can be anything from wheels/tires that need to be re-balanced, misaligned front wheels, worn ball joints, worn radius arm bushings, worn driveshaft u-jonts, a rusty, crusty driveshaft that's slightly off balance, or even something like worn shocks.

 

[MythX]

Anime,
Thanks for the reply. I don't think it's front-end/wheels related. I'm not feeling it in the steering wheel at all and it sounds/feels drive-line related. Is there a way to troubleshoot this w/out throwing parts at it?

Thanks

 

[natenkiki2004]

Swap your wheels, front to back and back to front. If it changes, then you know. Do you have manual or automatic hubs in it? If they're automatic, maybe they're sticking and actually turning the front driveshaft with frozen u-joints or bearings.

 

[MythX]

I'll get up early and rotate tires. Hubs are manual, I'll check them while they're off and report back.

Thanks for the tips.

 

[Anime]

If you bought your tires at a place that gives free balancing for the life of the tires, you should probably do that before chasing any other possible causes down.

You can also just get under there and look at the rear driveshaft, check the surface and if it's completely covered in flaky rust scales, you should sand/wire brush it and then paint it with some rust preventative paint.

While you're checking out the driveshaft, be sure to check the condition of the circular balance weights - if the weights are missing, you can be sure that's a cause of vibration. You should grab the driveshaft and shake it, checking if there is wobble or play, either from the flange bolts on either end or possibly the bearings at the transmission/transfer case or differential. The slip joint in the drivehshaft will let it flex/wobble some, which is normal. That can be another cause of vibration too, if the slip joint isn't lubed and has gone dry and is binding at the in-between points between being under load and cruising speed.

Also use a flashlight and check out the u-joints visually. Look at the seals and note if the grease seems to be leaking out - if there is a ton of buildup around the seals and it's all black, wet grime, you may want to sseriously consider some nice new u-joints. Dry joints can be bad too though, if they are really rusty and there is rust dust, showing that the rollers probably aren't lubed anymore. Even better case for new u-joints.


You should also check the wheel bearings front and back, just grab the tire with the vehicle off the ground and check for play side to side and top to bottom.

While you're under there, check out the condition of the suspension, even the basic stuff like the shackles, spring hangers, the leaf springs themselves, u-bolts, nuts, and the bushings. it may even be something in the front suspension even though you feel it in the rear.

 

[MythX]

OK, rotated tires this morning.
Checked bearings - No play

Checked Drive Shaft - Clean, though I doubt I could tell if a balance weight was missing or installed improperly. U-Joints looked clean and dry, do they need to be removed to be inspected? I'm seeing no rust around them at all. Drive shaft doesn't shake, and barely moves one way or the other before engaging the wheels.

Checked suspension - All 4 struts are due for replacement, they're aftermarket and I'm guessing not the greatest quality. The rear most shackle on the drivers side has some pretty severe rust (layers are peeling away). It's tight, no sign of movement, so I'm not sure it's a problem yet, but the others look just fine, so it's kinda out of place.

Thanks for the help. I think I'll start with the struts just because they need to be done anyway.

As for the rusted shackle, I'm assuming replacing one means I should replace all. Should that be a priority for this?

Thanks for the advice.

 

[Anime]

If you still have the vibration after rotating tires, get the wheels balanced if it's free, and definitely get new shocks if the ones on there now are old. New shocks and balanced wheels might not only be the fix but make it ride smoother than ever.

You can take a scraper/screwdriver to the shackle and scrape away the peeling paint and rust, wire brush or sand it and see how much is eaten away. If the shackle doesn't look compromised or unsafe, you can just paint with rust preventative paint and it should be good.

You don't have to replace the shackles in pairs, but if one is rusting by the the steel and paint flaking apart, you may want to at least take a screwdriver and stab at the other shackle in a few spots to check its integrity as well.

 

[2stroke]

If all you have is paint flaking off, its plenty safe. I've seen vehicles go for years, not that I recommend it, with a good size hole right through them. Keep an eye on it, and replace it when it finally eats a hole through it.

Is the vibration RPM related, or speed related? One thing not mentioned is bad drum brakes.

 

[MythX]

The shackle is definitely rusted, though it doesn't appear compromised, it's not just paint flaking. Layered thick pieces of rust. I'll work it next weekend and check the others. I'm not seeing any evidence of movement, I doubt it's the source of the vibration.

The vibration is speed related, not rpm. Happens when clutch in, or when trans is in neutral.

I did the rear brakes a couple months ago, had the same vibration prior to that. Had the drums turned, but not replaced. I suppose they could be the cause.

Still, thinking to start with rear shocks. Who knows what I'll find while working on those?

Thanks for all the help. It'll be a while before I'll have time to tackle those shocks, but once I do, I'll post an update.