Newbie w/ 1994 F-SUPERDUTY (450) Violent/Deadly shake! Help!

[dRock96f450]

Hello, my name is Derek and i am an active member on a few Ford panther platform forums, specifically www.CrownVic.net.

I made the following post on an off-topic forum there, but another member reffered me to this site and to one of your members, AGNEM.

Here is a copy/paste of the problem, I hope this is the correct forum for this as I am seeing mainly engine-specific threads.


Ok, I am not quite sure how to describe this;

Ever since my father purchased this truck new (a 1994 f-450 cab/chassis, Steel dumping bed, 7.3l IDI Diesel) it seems to have an intermittent violent shake when the front end suddenly hits a depression or bump in road. It first started developing at around 1000 miles. THe entire truck shakes incredibly violently, it is very hard to describe but if you were to experience it, you would think you are about to die in the damn thing. It feels like a wheel is falling off or like the tie-rods have just fallen out. The force of the shaking transmits into a violent shake throughout the whole truck. The shaking is exhibited through the steering wheel, and any steering input is useless. Both hands need to be firmmmmmly grasped on the wheel or the truck will try and loose control. You can see it occuring when following or driving in fornt of the truck, looks like it will loose control any second. It won't stop doing it until the truck's speed is brought below 10mph, it appears to be self-perpetuating. It will occur more often/more violently with the more weight added to the truck. It will happen at any speed above ~10mph, including highway speeds. The faster the truck is moving the more severe as well, when it occurs on a rough highway you'd think the frame is about to snap thats how rough it is. You can feel it right before it will start to do it in the steering wheel, which we have learned since to promptly slow the truck down as fast as possible. It has gone into multiple dealers and private mechaincs numerous times to tryand remedy but no-one can figure it out. THe service manager at one of the dealers was a woman, and after she test drove it she returned looking very disturbed. She descibed it as the scariest thing that has every happened to her, and that she thought she was about to die She had everyhting they thought could possibly cause it, without loosing her job.

At first it was deemed a brake system issue, all the calipers, rotors, brake lines, pads, master cylinder, hydro-booster, and power steering pump and hoses were replaced. Many of which multiple times, with no avail. THe rear end was checked as a possible cause (5.13 geared Dana 80) and was replaced to eliminate possibility. Over the years, both front and rear leaf springs, swaybars/endlinks/bushings, shocks and various suspension bushings, and ALL steering components were changed as well, nothing seems to solve this

THe truck has been inspected countless times, no-one spots anything unusual.

We have made several inquires about this, we have found a few reports of similar occurances, only in trucks with the 7.3l diesel. 2 mentioned sway bar replacement solved it, however we have already had them both replaced. It is obviously weight related to the heavy 7.3, I think it is suspension related as the steering is very tight under normal operation ...But i can't isolate any better than anyone else who has tried. I would like to upgrade the swaybars to the largest ones I can find, as fars as OEM goes these are the biggest, anyone know if there is an aftermarket set available? Also, anyone know if ENS makes poly bushings and endlinks for this thing?

The truck has less than 75000 miles, and was not used for much work during this time due to concerns. THis truck may just be cursed, as it is on IIRC its 4th transmission now, 2nd rear end, 3rd or 4th set of calipers with double that in rotor sets, an overall PITA headache. The only thing that has been absolutely trouble free is the engine and cooling systems, though at its mileage a diesel is hardly even broken in. I take that back, it did need new valve cover gaskets ;P THe eterior and interior are mint condition, as it wasn't even really used much and maintained exceptionally well. You think it would show us a little more respect ;P

This problem does not occur on any of our other f-450s, including my 96 f-450 which, suspension-wise, is virtually indentical. His truck and mine are the two lowest-mileage trucks in our fleet (mine has only ~22k, his ~73k)

I appreciate any help or suggestions you guys may have, and am hapy to be a new member on OilBurners.net

 

[krawlr]

Sounds like death wobble from lack of caster or even too much toe. Has it been on an alighment rack? Did they print out the readings?

 

[dRock96f450]

Yes, numerous times.

I would assume the readings were printed out, however I have no idea where they would be now :shrug:

I found a similar topic, coincidentally also on a 94 f450 in the Medium-Duty truck forum, I posted in this one as the person who reffered me said I should.

 

[dRock96f450]

'96 Grand Marquis pimp ride, Auburn posi, cop shocks, and big swaybars.

BTW, I own a lightly modded 96 Grand Marquis as well. What swaybars you running?
You can read all about my mods here http://www.crownvic.net/drock96marquis/MERCmods.htm

 

[troupp]

I've had a dodge truck in the shop that would do this, and it turned out the track bar was loose on the one end, a problem that would have never been noticed, either sitting on the ground or lifted up on the lift, I just happened to put the air gun on it trying to find this mystery death shake it had, and got almost a full turn out of it. Directly fixing the problem. Check both ends, I'm sure that truck also has one. also, lack of caster will usually only cause a wander, chasing the vehicle back and forth across the road as it changes, and toe would more likely cause tire wear inside or out, and most commonly if it was that far out, give you squealing on turns. Just some input though

 

[82fordtruck]

One of my trucks does this, but it doesn't sound as bad as yours. Mine's in the wheels. If I rotate them, it goes away, and I rotate again and it's back.

I think I have bent wheels, and when they're in the back it's not a big deal, but in front it is. Mine sill bounce the truck up and down about 6" in the cab, but I never felt like I was going to die. Mine comes and goes, but starts about 57 mph. Don't know what I need to go faster than that for anyway.

Try rotating the tires and see if it goes away. Many times people don't rotate duallies, so the same wheel could have stayed on the front forever.

 

[krawlr]

If I were to guess without knowing specs I would try some 2deg shims on the spring packs to get more caster.

Things I've seen do this:
-not enough caster
-too much toe (would cause excessive tire wear)
-trac or panhard with loose bushings or mounts
-ball joints worn or not preloaded right

I personally had my bronco axle do the last thing mentioned. The preload nut was cracked. Felt like it was ok and seemed to torque fine but it really wasn't preloading the balljoint. 36" TSL Swampers on beadlocks makes deathwobble an extra challenge.

 

[dRock96f450]

krawlr: We will get it aligned again as a precaution, and will also ahve the balljoints looked at again. IIRC this set only has about 15k miles on them now, the factory balljoints did this as well but we will have them checked again. I will make sure to take a look at the track/panhard bar setup.

troupp, thank you very much for the suggestion. I am searching around the net some for the largest swaybars I can get for this truck as well, would anyone happen to have a link for some?

82fordtruck: THe wheels have been rotated about every other oil change, typically balanced at the same time. None of the rims have any physical, or for that matter cosmetic damage. It has only needed 1 new round of tires, wear pattern was perfectly even as well.

The shaking can occur at any speed above ~10mph, and it just comes out of the blue after hitting a bump, or dip in the road. Normally if just one side hits it. The severity of the shaking is further amplified by faster speeds/more weight in the truck. And it will continue doing so until the truck is brought to a near stop. Because of this we don't think it is wheel or tire related, the driveline feels perfectly smooth as well. It feels like something to do with the front suspension, and I am sure the OEM rubber bushings getting mushier by the day aren't helping one bit.

 

[towcat]

welcome!
if you don't have the steering dampener installed already, drop by the stealership parts counter and ask for the "anti deathwobble kit". trust me, if the counterman knows his beans, he will know what you are talking about. I have three f450's draining my wallet, so I do know the ins and outs of these brutes.

 

[Mr_Roboto]

Try reading this very long thread: http://forums.thedieselstop.com/ubb...s=Death+wobble&topic=&Search=true#Post1522583

I would also suggest having the tires and wheels "road force" balanced. It's expensive, but it allows the wheels and tires to be accurately measured for runout, and the tires and wheels are matchmated. This would allow you to POSITIVELY eliminate the tires and wheels, which is something that a conventional balance job just can't do. A wheel can be bent in all different directions, but still balance out fine on a spin balancer.

 

[dRock96f450]

Thanks for the welcome towcat.

The truck is one its IIRC 2nd replacement Motorcraft steering dampener. Is there a heavier-duty aftermarket unit available?

Any part numbers or links would be much appreciated, I can't seem to access the full-line catalog on Motocraft.com anymore

Mr_Roboto, how much would a road force balance typically run on one of these? Thanks for getting the styx song in my head again btw

 

[towcat]

once you have the kit, improving the dampener is easy. just take off your factory unit and hunt down the local 4 wheel parts store. I have one of those fancy Rancho units painted black to blend in with the rest of the under carriage.

 

[93turbo_animal]

Good looking truck by the way my 96 F-350 does this although not as bad as what yours does by the sounds of it but I beleive whats happening is your track bar is loose either bushings or bolts and your spring bushings are getting some slack in it too however your steering is tight so when you hit a bump your axle actually shifts side ways thus turning your tires and it whips the front end the other way causing your wheels to turn back the other way whipping the front end back the other way causing a never ending cycly until you slow down enough the front end doesn't have the momentum to travel sideways so far basically I beleive it is more suspension related then alignment

 

[Mr_Roboto]

Mr_Roboto, how much would a road force balance typically run on one of these? Thanks for getting the styx song in my head again btw

The last time I had it done it was about $120 for 4 tires, however this was in 2002. I can say for what is done, it is well worth the money. Match mating the tires to the wheels gives a better ride and will make the tires last longer. And you get a printed readout of the before and after so you can see if there were problems to begin with.

Here's a locator for finding a road force balancer: http://www.gsp9700.com/pub/search/findgsp9700.cfm

 

[h2odrx]

Welcome to the brotherhood!!!!

would worn shocks or springs have any effect here??