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Old 12-03-2012, 09:15 PM   #1
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Ford F53 Front Suspension Death Wobble

A friend described his experience with this phenomena. His MoHo is a 2005 Thor Hurricane 30Q (17k mi, no steering stabilizer, no trac bar). He hit the brakes hard and this caused the steering wheel to shake violently until he slowed way down. The only thing that seemed wrong was low air pressure in both front tires (60psi or so). He corrected to 85psi and has had no recurrences.
My MoHo is similar in size and features, and I have added the TT2403 trac bar and am shopping for a steering stabilizer kit (there are no brackets on mine). I watch my tire pressures. I'd prefer not to experience this event.
I've read in Irv2 all posts that seems to address this issue.

QUESTION to iRV2: Is there a definitive root cause for this event? Is there a sure-fire solution to prevent this from happening?
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Old 12-03-2012, 11:11 PM   #2
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Death wobble is nothing but a harmonic Vibration (Resonance) I have seen this on many Jeeps and other straight axle vehicles. It is usually due to parts being worn.
Every part has a frequency that it will resonate at. Tires included. Air pressure will effect that frequcey. When you hit a pothole of any size you send a frequency insto the front end. Vehicle speed will vay it as well.

Trac bars, and steering stablizers do help to kill the harmonics.
THink of them as a finger resting on the middle of the guitar string.
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Old 12-03-2012, 11:59 PM   #3
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...may not have caused the "death wobble"; but running both front tires 25% below recommended inflation pressure can't be good...
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Old 12-04-2012, 10:20 AM   #4
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Sounds like warped front brake rotors. I would have them checked and turned flat.
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Old 12-04-2012, 05:53 PM   #5
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Alignment

Check your front end alignment, especially caster.
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Old 12-04-2012, 06:01 PM   #6
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I've had Ford chassis from F150 PU's and up get the death shake from incorrect tire pressure.
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Old 12-04-2012, 07:55 PM   #7
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Have never on any car, pickup, M/H or simi, but man you talk about a wobble on an old John Deere M tractor, near bout run off in the ditch. I didnt run over half throttle after that when on the highway.

For a front wheel or both wheels to wobble enough that you feel like you've got to slow down or stop, theres got to be a good amount of play in some parts of the steering.
Could be the king pins are worn bad, tie rod end ball joints worn or nuts loose, ball joint on the steering arm worn or nut loose & then maybe by chance the gear box needs adjusting because the cogs not close enough.
If a wheel bearing was loose & the hub could move in & out, that could cause that wobble. It could only be one wheel thats wobbling & would make the wheel on the other side wobble as well.
Older model Ford pickups, had a steering link that mounted to the tie rod & that ball joint would wear faster than the others & would cause a wobble, but was normally just trucks out on the highways that it would happen.
Ol farmers Ford pickups never got over 45 mph, because of checking crops or looking for deer during hunting season, so they never had a death wobble.
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Old 12-04-2012, 08:05 PM   #8
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It is likely caused from worn bushings in the King Pins and common on ford chassis. Does it also do it over bumps, pot holes, rail road tracks ?
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Old 12-04-2012, 08:13 PM   #9
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Guys listen to the first post 07774 states on hard brake application. Haven't heard caster, tire pressure or worn front parts causing wobble on hard braking. These problems will make the wobble worse tho. I have fixed this many times on cars, trucks, busses and rv's and just turned the rotors. Hope this helps and did not step on toes.
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Old 12-04-2012, 11:31 PM   #10
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You might even be able to solve the issue by re-bedding the pads and rotors and not taking it into a shop. In cars it often works -- and I would expect it to work mechanically in a motorhome. Whether you'd want to do it could be another story.

The procedure is simple. You really need a road that's quite empty at night and will allow you to get to about 50mph. You want to get to that speed, then do a firm brake application (but not a panic) down to about 10mph, then off the brakes, back up to 50mph, another firm brake application, then back up to 50mph, and a brake application, then cruise without using your brakes at any speed 30mph and above (to let the brakes cool).

Now, obviously, you need the right place to do that in a motorhome that's bigger than you'd need, say, for a Toyota Yaris

What you are doing is getting pad buildup off the rotors (this happens especially if you've had to do a very hard stop and then had to hold the brakes on, so the superhot pads are still pressed against the rotors). 90% of the time that's all turning the rotors is doing.

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Old 08-01-2013, 11:10 AM   #11
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I ran into this issue coming down HWY 281 from Lake Toxaway, NC. Acts like warped rotor, flat ground no issue, even on smaller hill no problem. I'll have the brakes checked, just very odd.
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Old 08-01-2013, 08:49 PM   #12
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Quote:
Originally Posted by stink View Post
Sounds like warped front brake rotors. I would have them checked and turned flat.
Warped brake rotors are a myth.

-Warped- Brake Disc and Other Myths

Ive pushed rotors to well over 1800*F with nary a warped rotor, and you mean to tell me that you can do that with half the temperature? Yeah, I think not. Ill let the peanut gallery figure out what color a brake rotor at 1800*F glows (because the cherry red starts at 1300*F).

The #1 cause of braking vibration is transfer layer deposits, pure and simple. Its not rotor warp or whatever snake oil the mechanic wants to sell you, and a proper bedding of the pads will cure the issue. Its especially prevalent with newer automatic vehicles that require more pedal pressure to prevent movement, resulting in more pad deposits on rotors.
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Old 08-03-2013, 04:30 PM   #13
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Quote:
Originally Posted by Mekanic View Post
Death wobble is nothing but a harmonic Vibration (Resonance) I have seen this on many Jeeps and other straight axle vehicles. It is usually due to parts being worn.
Every part has a frequency that it will resonate at. Tires included. Air pressure will effect that frequency. When you hit a pothole of any size you send a frequency into the front end. Vehicle speed will vary it as well.

Trac bars, and steering stablizers do help to kill the harmonics.
THink of them as a finger resting on the middle of the guitar string.
The above explanation was worth repeating:

14 years ago a Ford Factory Rep told me to install a Davis TruTrac on my 1995 F53 36foot Bounder to correct this front end problem. It took Ford another 5 years to put it on as standard equipment.
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Old 08-03-2013, 06:24 PM   #14
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This, "Death Wobble" that the op is referring to is both front wheels and that includes the rotor, waffling back and forth along with the steering wheel. It is almost an out of control situation and the usual way to stop it is to slow down. It has very little to do with warped rotors. Vibration from warped rotors is usually felt at the brake pedal and the steering wheel. Yes some brake pedal vibration could be associated with the OP's problem but it went out of control because of worn front end parts and resonate vibrations.

Now on to warped rotors. Lets see, 35 years of experience with brake pedal vibration or pulsation upon moderate, (I said MODERATE) brake application. Remove the rotors, mount on brake lathe, use a dial indicator to measure the amount of surface variation (run-out) from side to side movement. It's usually .008 to .015 movement at right angles to the axis of rotation. Machine the required amount of cast iron from both rotor surfaces to restore the rotor surfaces to be at right angles to the axis of rotation, reinstall on vehicle and test drive. Guess what???? The brake pedal pulsation, vibration always, always goes away.

I had a truck that had the rotors machined 4 times before the rotors finally stopped warping. It's last 30,000 miles it didn't warp. Unless dial indicators lie, and all the text books that I read over the last 40 years lied rotors can and do warp, and the surfaces can be trued to again spin at right angles to the axis of rotation

Now on to brake pad/shoe BURNISHING (bedding). Google" Brake burnishing". This is a very important step in properly doing any brake job. Yes brake material is transferred from the material to the surface of the rotors. That's part of the burnish process. What is not part of the burnish process is any hard stopping from high speeds. Excessive heat at the early stage of burnishing will GLAZE the brake material and render them useless. According to the industry standards brakes are not properly burnished until they have been properly applied and cooled 200 times. At that point you will achieve the best braking.

This is not SNAKE OIL SCIENCE but just simple Industry information and standards that have been followed for years and years. Yes as technology has changed so has the brake industry. That's why I studied and read every year that I taught school. If you don't keep up with the changes you are behind. Do a search and you can find this information at any reputable brake industry web sight.
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