Can anybody tell me what this noise is?

[Max Mini]

It sounds like something thwacking against the bottom of my bus. 1991 Ford E350 7.3 IDI short bus. I am also getting a front end wobble. It's not a wheel bearing or stuck caliper. This is not constant, happens sporadically.

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[Reggie f250]

Possibly a cracked rotor? Could come and go according to brake temperature. The brakes might not stop smoothly either.

 

[Max Mini]

Possibly a cracked rotor? Could come and go according to brake temperature. The brakes might not stop smoothly either.

Interesting! Thanks for the suggestion. It sounded like it was coming from the driver's side, and it's not the rotor on that side, but I wonder if I was hearing it wrong. Maybe it's on the other side?

I would have expected more of a grinding than a thunking from that but I will check it out.

 

[Cubey]

Interesting! Thanks for the suggestion. It sounded like it was coming from the driver's side, and it's not the rotor on that side, but I wonder if I was hearing it wrong. Maybe it's on the other side?

I would have expected more of a grinding than a thunking from that but I will check it out.

A very bad king pin bushing maybe? If it's like my 85 E350 RV, it has that instead of ball joints. I'm guessing they kept that until the next gen in 92.

 

[Max Mini]

A very bad king pin bushing maybe? If it's like my 85 E350 RV, it has that instead of ball joints. I'm guessing they kept that until the next gen in 92.

Yeah I definitely have king pins, thanks, I will check that out!

 

[Cubey]

Oh and check your driveshaft carrier bearing too. Crawl under and see if it does this. If so, it's very much bad.

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[Booyah45828]

It sounds like it corroborates more with wheel speed and tire rotation, over driveline/engine.

I'd double and triple check your brakes, wheels, and tires for anything broken or rubbing.

 

[cozinsky]

Lug nuts all tight? I've heard a similar thumping noise from loose lug nuts.

 

[Max Mini]

It sounds like it corroborates more with wheel speed and tire rotation, over driveline/engine.

I'd double and triple check your brakes, wheels, and tires for anything broken or rubbing.

It does seem to go more with RPM than MPH. I would think a sound this pervasive and big would be coming from something very obvious, but maybe not. I will double and triple check.

 

[david85]

When did you first notice this?

Any recent work done?

Has this vehicle been sitting for a long time?

Can you feel any vibration or thump in the steering wheel while this happens?

Does pressing the brakes have any effect?

Any pulsing in the brake pedal while applying brakes?

I agree with others that it sounds like something at axle speed, not driveshaft speed.

 

[Max Mini]

When did you first notice this?

Any recent work done?

Has this vehicle been sitting for a long time?

Can you feel any vibration or thump in the steering wheel while this happens?

Does pressing the brakes have any effect?

Any pulsing in the brake pedal while applying brakes?

I agree with others that it sounds like something at axle speed, not driveshaft speed.

- No recent work, but a ton of brake work in early 2020. Pretty much the entire brake system, front and back, was replaced.

- Has not been sitting for a long time, though it's been driven a lot less in 2020 than in previous years. Still, it has not gone more than 4 days without being driven somewhere except for a couple of weeks in March 2020.
- I've been driving very differently, though. Three weeks ago I started commuting to a workshop I've been loaned for my interior rebuild; I don't have a garage and it's cold here, so I needed interior space. That has led to driving approximately 3 hours a day round trip for the past couple of weeks. This is very different than the past, where I'm typically driving maybe 20 miles in a day, or else driving hundreds of miles a day, on a longer trip. I have never "commuted" in the bus before. I also have never driven it completely empty, and it is very bouncy empty (everything is out for an interior rebuild). I have been on some extremely bad, torn up roads, at highway speeds in a big empty box (welcome to winter in New England). In one of the videos where the noise is happening you can see a lot of bounce (this one had the best sound but you can't see the front of the bus in the shot).

- Different elements of it were noticed at different times. I have noticed an occasional sort of a "bang" or "pop" that seems like it's coming from under the driver's side, but very sporadically, for a few months. I first had a significant issue after I went to a truck scale a few weeks ago, and could not seem to pull off of it. I just couldn't move forward. Granted, I was on a slab of ice, but I drive on ice all the time. I eventually just gave it A LOT more gas than I should have had to, and got moving. It didn't feel like a transmission issue, but something was off. It wasn't just the ice. Later that day I started experiencing a pretty big shimmy in the front end, which I chalked up to needing an alignment until the crazy noise started. If you look the bus from the front, the wheels do not look aligned.
- I first heard the noise when I was slowing to a stop, with brakes. I assumed it was a brake issue right off the bat, like a stuck caliper, but in my experience that smells really strongly of burning brakes, and it doesn't quite behave like a stuck caliper. For example, it's very random when it's going to happen. Plus, the caliper looked great.

- Yes, big vibration in the steering wheel, however, NOT with the noise. Separately.

- As far as pressing the brakes goes... I don't think the brakes themselves have any effect on the noise but it generally begins when I and deccelerating so it's hard to say for sure.

- No pulsing in the pedal, though the firmness of the brakes does not always feel the same.

Thank you for digging in on this!

 

[david85]

Hmm, Well I looked at your longer video and it's a little tricky to figure out where the noise is most prominent. But it seems to never happen at 0 MPH, right? I'm just trying to eliminate the engine or transmission as a possible cause.

Vibration in the steering wheel can be a few things:

1. Tire out of balance. This is most noticeable as you get to medium speeds and higher. Say...35 MPH and up.

2. Tire has a broken belt. A broken belt will be noticeable as a regular thump or hop all the way down to parking lot speeds. It can be found by raising the suspect wheel on a jack, and spinning the tire by hand to look for any bulges. Replace the tire immediately, if you see anything like this.

I'm assuming your mechanic already checked for this, since he did have the front corner torn down to the spindle to inspect the bearing.

3. Warped rotors. Typically, this would only be present while under braking and should vanish when you lift off the pedal (assuming no other problems...see below).

4. Death wobble. This is rare on Twin I-Beam setups like yours, but it can happen. This also ties into what your mechanic said about the steering being loose. Now, these E-series and F-series trucks are famous for loose steering boxes and that won't be a problem here. However, if the slack is somewhere in the suspension system and not the steering shaft/steering box, it could be your problem.

This also fits with your alignment theory. Death wobble can be most prominent at specific speeds, and can be "set off" by a sudden bump in the road. If you have warped rotors, applying the brakes may also induce vibration. This vibration can be self sustaining, too.

Here's the catch. Most mechanics hate Twin I-Beam suspension systems and many shops don't know how to work on them. My advice would be to try and find an older mechanic that has lot's of experience with older light ford trucks. Ask specifically if he knows how to troubleshoot Twin I-Beam setups. In addition to the usual ball joints, tie rods and King-Pins, the places I would check are:

A. Axle Pivot bushings. These are common wear items.

B. Axle pivot bracket rivets. These brackets attach to the engine cross member (one bracket on each side). They generally don't come loose but that doesn't mean they can't. Also check for cracks in the brackets and the frame in this area.

C. Radius arm bushings. Another common wear item.

D. Radius arm bracket rivets. Again, these don't usually fail, but check them anyway.

F. Radius arm to I-Beam attaching bolts. These are the big bolts that attach the bottom of the coil spring to the axle. Make sure they haven't come loose.

A competent shop will inspect all of these points as part of an alignment. In spite of what many say about TIB suspensions, the 2wds actually work VERY well in stock form.

 

[david85]

As a followup, here is an example of what the axle pivot bushings can look like when they fail. This is on an older F250, but the system is the same on your E-Series.

Notice how the loss of rubber allows for metal to metal contact in extreme cases, which might explain the knocking sound you're getting. Also, if this were to happen on the PASSENGER side I-beam pivot bushing, the noise would appear on the driver's side, and vice-versa for the Driver's side I-beam pivot, since each beam reaches to the opposite side of the vehicle. This might explain why your mechanic found nothing on the driver's side.

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[Max Mini]

Hmm, Well I looked at your longer video and it's a little tricky to figure out where the noise is most prominent. But it seems to never happen at 0 MPH, right? I'm just trying to eliminate the engine or transmission as a possible cause.

Vibration in the steering wheel can be a few things:

1. Tire out of balance. This is most noticeable as you get to medium speeds and higher. Say...35 MPH and up.

2. Tire has a broken belt. A broken belt will be noticeable as a regular thump or hop all the way down to parking lot speeds. It can be found by raising the suspect wheel on a jack, and spinning the tire by hand to look for any bulges. Replace the tire immediately, if you see anything like this.

I'm assuming your mechanic already checked for this, since he did have the front corner torn down to the spindle to inspect the bearing.

3. Warped rotors. Typically, this would only be present while under braking and should vanish when you lift off the pedal (assuming no other problems...see below).

4. Death wobble. This is rare on Twin I-Beam setups like yours, but it can happen. This also ties into what your mechanic said about the steering being loose. Now, these E-series and F-series trucks are famous for loose steering boxes and that won't be a problem here. However, if the slack is somewhere in the suspension system and not the steering shaft/steering box, it could be your problem.

This also fits with your alignment theory. Death wobble can be most prominent at specific speeds, and can be "set off" by a sudden bump in the road. If you have warped rotors, applying the brakes may also induce vibration. This vibration can be self sustaining, too.

Here's the catch. Most mechanics hate Twin I-Beam suspension systems and many shops don't know how to work on them. My advice would be to try and find an older mechanic that has lot's of experience with older light ford trucks. Ask specifically if he knows how to troubleshoot Twin I-Beam setups. In addition to the usual ball joints, tie rods and King-Pins, the places I would check are:

A. Axle Pivot bushings. These are common wear items.

B. Axle pivot bracket rivets. These brackets attach to the engine cross member (one bracket on each side). They generally don't come loose but that doesn't mean they can't. Also check for cracks in the brackets and the frame in this area.

C. Radius arm bushings. Another common wear item.

D. Radius arm bracket rivets. Again, these don't usually fail, but check them anyway.

F. Radius arm to I-Beam attaching bolts. These are the big bolts that attach the bottom of the coil spring to the axle. Make sure they haven't come loose.

A competent shop will inspect all of these points as part of an alignment. In spite of what many say about TIB suspensions, the 2wds actually work VERY well in stock form.

OK, this makes a lot of sense. You're right that it never happens at 0 mph.

I’m trying to figure out how to present all this to the mechanic without seeming like I’m trying to tell him how to do his job. He mainly works on much bigger trucks so I don’t know what his level of experience with this particular set up is. I’m going to crawl under there and see if I can see anything that matches anything that’s been described so far, but realistically I don’t have a clue what I’m doing as I’m sure you can tell. I thought the mechanic would be able to see me today but it looks like it’s going to be tomorrow instead. Finding someone to work on this beast has been daunting to say the least and a lot of shops go into ripoff mode when they see a woman with a bus. This guy seems like a totally straight shooter. He just doesn't have a ton of time to mess with this because he has a small, super busy shop.

I had hoped to just find a video with a sound that is so similar it's a no brainer, but I really haven't found anything that sounds like this.

Thanks again for weighing in!

I’m confused by the death wobble thing, though, isn’t that a symptom rather than a specific thing? I can’t tell you whether what I’m feeling is death wobble or not. I just thought of it as a shimmy but it’s a significant shimmy.

 

[david85]

Yes, death wobble is symptom, not a component. I can see how it would be described as a shimmy, if the symptoms are mild enough. It's usually caused by loose suspension components. Here is an extreme example (4wd, but the geometry is similar to your Twin I-Beam):

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Pay attention to the pivot bushing on the right hand side once the wobble starts. You can just barely see the pivot below the bottom "skyjacker" steering damper shock (right under the letter "K"). See how it moves sideways, along with the entire axle beam on the right hand side?

Also notice how the wobble keeps going once started. In his case, the bracket itself was cracked and about to break away from the engine cross member (Pivot bracket is hidden behind the dual steering damper shocks). The axles should be able to swing up and down at the tire end, but NEVER side to side. The pivot bracket shouldn't move at all in any direction. Also notice how one of the axles is wobbling the most (right hand side), while the other is still fairly solid.

In the previous video I posted, it was the pivot bushing that failed and not the bracket itself, so his symptoms were no where near as dramatic as this. If this is your problem, I would be looking for torn rubber at the axle pivot bushings.