High Speed Wobble Diagnosis - Ford Bronco Forum
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post #1 of 16 (permalink) Old 04-15-2019, 02:17 PM Thread Starter
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High Speed Wobble Diagnosis

My '85 wobbles and shakes at speeds above 70mph. I had a loose front wheel bearing (had wobble above 62 prior to tightening the bearing), but got that sorted out, now I'm wondering how to diagnose the shake. It could be my driveshaft since I've had that out multiple times and forgot to mark where it was and put it back in the way it was, but the internet seems to say that a driveshaft should cause vibration, not shake. Is there a way to determine the cause?
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post #2 of 16 (permalink) Old 04-15-2019, 03:36 PM
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Yeah, a driveshaft will cause a vibration, like a tire being out of balance.

A shake/wobble is going to be more along the lines of your suspension.

General culprits would be your tie rod ends (hopefully, as they're the easiest to replace) and ball joints. Also, if your pitman arm or steering box have slop, it can allow your wheels to change direction slightly without the steering wheel moving.

To check the ball joints, jack up the front end and put a crow bar under the tire. Then lift the crowbar and see if you can see the tire clunk up and down at the joints. It should be pretty obvious if so. Although, the bigger your tires are the harder it'll be due to their weight.


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post #3 of 16 (permalink) Old 04-15-2019, 04:09 PM
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It doesnt matter which way you put the driveshaft in, as long as you have the correct end where it's supposed to be.

I've had bad tires that didnt look that bad cause a serious shake in the steering wheel above 55.

I've also had the TTB axle pivot brackets come loose and cause the truck to buck like a bull going around corners. Felt like I had square tires.

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post #4 of 16 (permalink) Old 04-15-2019, 05:42 PM
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Mine shook between 60 and 67. Replaced tires and problem gone
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post #5 of 16 (permalink) Old 04-15-2019, 05:45 PM
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Good point.

TripleHP, do you have steel rims?

On my '81, I had steel rims, and the center hole was damaged. So, no matter how well they balanced the tire, it was always out of balance when I'd bolt it back on since it went onto the balancing machine crooked.
I went through everything on that vehicle, and looked and diagnosed that stupid wobble for 2 years before I figured that out.

I replaced the steel rims with new aluminum rims and it was suddenly smooth as glass.


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post #6 of 16 (permalink) Old 04-15-2019, 07:05 PM Thread Starter
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Could bad sway bar bushings cause the wobble? After checking out the front end, the ball joints and tie rods seem fine and have no play. The sway bar was kinda loose though and I could wiggle the drivers side of it.
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post #7 of 16 (permalink) Old 04-15-2019, 07:07 PM Thread Starter
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I'm gonna tighten it up and take a test drive. If it solves the problem I'll pick up some bushings and get some fresh ones in there.
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post #8 of 16 (permalink) Old 04-15-2019, 07:40 PM Thread Starter
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tightening the sway bar did nothing lol. Maybe an alignment and tire balance would help? Any other probable causes?
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post #9 of 16 (permalink) Old 04-15-2019, 08:03 PM
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Is it in the seat or steering wheel?

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post #10 of 16 (permalink) Old 04-15-2019, 08:05 PM Thread Starter
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It's the entire front end. Radio shakes like hell. But I definitely feel it in the steering wheel more than the seat.
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post #11 of 16 (permalink) Old 04-15-2019, 08:23 PM
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And its only above 70? No shake at all below 70?

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post #12 of 16 (permalink) Old 04-15-2019, 09:35 PM Thread Starter
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Yep. Shake starts around 68-71mph. Went up to 80 and it did not go away. Kinda scared to go faster in this rustbucket
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post #13 of 16 (permalink) Old 04-15-2019, 09:53 PM
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Switch the front and rear wheels.
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post #14 of 16 (permalink) Old 04-15-2019, 09:55 PM Thread Starter
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Good idea. I'll give it a shot
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post #15 of 16 (permalink) Old 04-15-2019, 10:27 PM
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Quote:
Originally Posted by Wrencher61 View Post
Switch the front and rear wheels.
I was just about to suggest that lol, i agree, swap wheels front and rear, if it quits it was in one of the front tires, if it persists it may be a suspension component

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post #16 of 16 (permalink) Old 04-16-2019, 08:50 AM
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yo Triple,
Wobble Diagnosis by Carl J @ https://web.archive.org/web/20060220...athwobbles.php

B]MIESK5 NOTE; I removed most non-FSB info from Carl's article here...[/B].. and some don't apply to just high speeds.
"...Death wobbles are caused by two main factors; loose or incorrect front-end alignment parts and large out of round or imbalanced tires. Assuming your tires are still in balance, not full of dirt clods and you don't have a bent rim, here is what I look for when experiencing "death wobbles" on the following rigs.
*Note: Always have your rig on level ground with motor off prior to doing any vehicle inspection!
One thing to remember - a steering stabilizer or two may get rid of the death wobbles, but will not fix the problem that is causing the wobbles. I have personally run 44" tires on all my rigs for the past 21 years and have been able to run without a steering stabilizer once the root cause was corrected.

Bronco's & Ford ˝ tons:
I'm going to assume that the rig by this time has already had someone install the 14 piece urethane bushing kit in the front end trying to remedy some of the death wobbles. If not install a kit and look for the following as you do it.
Check that the steering box mount to the frame is solid. Some Bronco owners have reported frame cracks. See my post #2 @ https://www.fullsizebronco.com/forum...ering-box.html
Check the steering box bolts, are they loose? Look for chipped paint or rust rings around the bolts, better yet just go ahead and retorque them now, you will probably get a full turn out of them. If they do not tighten to a firm stop... FIX by installing new solid sleeves between frame rails.
miesk5 Note, while you're down there, check for Steering Box Frame Crack(s).

3rd Tighten the pitman arm nut; you can usually get ˝ a turn out of it.
MIESK5 NOTE; BE VERY CAREFUL HERE; see Steve's Pre-load Adjustment, All Bronco & Ford, mid-70s to 00..
and his Steering Troubleshooting

Check all the tie rod ends for endplay. With the wheel-rocking trick, start at the pitman arm, there should be no motion between the arm and the drag link, or the drag link to the tie rod, or the tire rod to the steering arms. Replace and align as required.
Place the front end on jack stands, then grasp the tire at top and bottom and alternately pull and push the tires with opposite hands. If the tire moves more than 1/16" either the upper and lower ball joints need to be replaced or the wheel bearings need adjustment, or in a worse case scenario the spindle is cracking or the spindle bolts are lose.

Leaf spring vehicles:
My 1st death wobbles occurred when I was about 16 years old and decided to lift my Scout with 12” long shackles. I bought 2 kits used for raising the back of a Mustang and in a couple of hours I had the tallest Scout in town. My 1st drive was quite interesting; any speed over 30 miles per hour and it was all over the road. After talking with several experts it was decided that my caster had changed. At the time I did not have the $14 bucks for a couple of degree shims and so with 16 year old logic decided that since the rig had leaf springs under the axles all the weight of the vehicle was carried through the U bolts and that a set of wooden shims would not carry any weight but would tilt the front end in the correct direction. After several practice splits with a sharp hatchet and some carving with a knife I had a set that looked about what I needed. I loosened the U-bolts placed in the shims and sure enough it drove fairly good again. Unfortunately about 100 miles from home a week later the wood splintered and came out. I did not have a wrench with me to tighten up the bolts so I had to drive at 15 miles per hour all the way home because anything more produced death wobble. So……
1ST thing to check for is loose U bolts and then have a friend rock the wheel back and forth about 1/3 of turn while you observe the following steering components.
2nd I check for loose spring bushings
3rd look for loose tie rod ends & drag link ends.
4th Check that the steering box mount to the frame is solid.

.
Independent Front Suspensions:
Look for all the loose stuff mentioned above and look for loose bolts holding the A-arms onto the frame and or loose center pivot bushings.
Finding loose parts is best accomplished by having a friend (MOTOR OFF!) Rock the steering wheel back and forth about a 1/3 of a turn at 1 second intervals with the vehicle sitting on the ground, in park or 1st gear with Emergency brake set, while you crawl underneath and check for relative motion on every suspension connection and steering component..."

"While the wheel is being moved, observe the lower spindle arm and the lower part of the axle jaw. A 0.794mm (1/32-inch) or greater movement between the lower portion of the I-beam and the lower spindle arm indicates that the front suspension lower arm ball joint must be replaced.

To check the front suspension upper ball joints, grasp the upper edge of the tire and move the wheel in and out. A 0.794mm (1/32-inch) or greater movement between the upper spindle arm and the upper portion of the I-beam indicates that the front suspension upper ball joint must be replaced." by Ford @
1996 Bronco/F-Series

°
"Section 11-02B: Steering Gear, Power, Ford
1996 F-150, F-250, F-350, F-Super Duty and Bronco Workshop Manual
ADJUSTMENTS
Meshload
During the vehicle breaking-in period, some factory adjustments may change. These changes in adjustment will not necessarily affect operation of the steering gear assembly. If excessive steering lash is encountered, then meshload should be checked and adjustment may be required.
In 1996 Bronco Workshop Manual
°
"Section 11-02B: Steering Gear, Power, Ford
1996 F-150, F-250, F-350, F-Super Duty and Bronco Workshop Manual
ADJUSTMENTS
In-Vehicle Adjustment
SPECIAL SERVICE TOOL(S) REQUIRED
Description Tool Number
Pitman Arm Puller T64P-3590-F
Adjust total on center load to eliminate excessive lash between the sector and rack teeth as follows.
With the engine (6007) off, turn the steering wheel (3600) from full right stop to full left stop at least once.
Refer to Section 11-04 for proper steering wheel hub cover removal procedure.
Disconnect the steering gear sector shaft arm (3590) from the steering gear sector shaft (3575) using Pitman Arm Puller T64P-3590-F.
Attach a newton meter (pound-inch) torque wrench to the steering wheel hub nut and determine the torque required to rotate the power steering gear input shaft and control (3D517) back and forth across the center position (± 90 degrees).
Reset the meshload only if the measured torque for total on-center load is less than 1.5 Nm (13 lb-in). If reset is required, loosen the adjuster lock nut and turn the sector shaft adjuster screw until the measured total on-center load torque is 2.0 Nm (18 lb-in). Hold the sector shaft screw in place and tighten the lock nut to 48-61 Nm (35-45 lb-ft).
Recheck torque readings and replace the steering gear sector shaft arm. Tighten the pitman arm-to-sector shaft nut 230-310 Nm (170-228 lb-ft).
Verify no binding condition in steering throughout full stop-to-stop travel. Verify customer concern is resolved.
Replace steering wheel hub cover."

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