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Front End Shimmy on out T-bucket.

12K views 24 replies 10 participants last post by  BIG Jim 
#1 · (Edited)
Front End Shimmy on our T-bucket.

Hi guys -- new member here. I'm having problems with shimmy on our Tbucket, it happend going over uneven bumps or if the wheels come off the ground due to hard aceleration. if i lock up the brakes for a second and start is fine for a little bit until the front starts shimyin again. we have tryed to adjust the toe-in, but are not sure if we did it rite. could it also be things like camber and caster? will a steering damper like this one help any?http://www.hotrodworks.com/steerstablizer.htm



Thanks in advance.

here is some pictures so you know what type of set-up it is.



 
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#3 ·
we have checked all of the components in the steeing/ suspention system for slop/play and thiere is none in nouthing. i mde sure the kingpins were tight. im thinking that it needs a front end allignmnt but do not know where to ake it because bell tire will not do it i guss u have to find a rod shop or something. the tire inflation on the front is the same as well as the rear, 12PSI in the front and 9 PSI in the rear (bias-ply tiers).
 
#4 ·
Check the toe...

Get a helper and a tape measure. Have the helper hold the end of the tape measure at the center of the tread , and you record the measurement to the center of the opposite tire tread. First measurement should be across the rearmost side of the front tires, the second should be along the forwardmost edge (like at 3 and 9 o-clock).

Your fromt measurement should be around 1/16"-3/16" LESS than the rear measurement. If not, adjust the tie rod that connects the 2 front wheels.

Don't worry about the drag link going to the gearbox, that one is adjusted to center the steering wheel.

If running up to 3/16" of toe-in (front closer than back) does not correct your shimmy problem, I have found on some solid axle frontends that adjusting up to 1/4" TOE OUT many times will get rid of a shimmy.

Any idea what the caster is set at? That's the angle the front kingpins are set at. They should be around 3-5 degrees positive (top farther back than bottom). You can get this angle measurement with a Sears angle finder, works sorta like a weighted pointer deal. You have a tube front axle, so set it on your kingpin sleeve at each end of the axle, check both sides, they should be the same setting. Adjust by tweaking your 4-bars in the front. Shortening the top bar increases caster.

You can easily go as much as 7 degrees and that should help with a shimmy caused by too little caster/not enough weight on front tires.

Camber you don't have to worry about, with those bias front tires, the tread is so rounded across that even if the camber was off, it'd just wear the tire a little more on one side. And that could be minimized by flipping the tires on the front wheels, to wear the other side and even out the wear pattern... you'd need chains, jacks, and a frame table to adjust, by bending the front axle tubing...

Doc
 
#5 · (Edited)
I do see a potential problem with your setup. By reversing the front spindles to place the tie rod in front of the axle, you have changed the geometry. Do a search for "Ackerman Principle". It will explain how to set up the spindles when mounted the way you have them.

I have a link to the site on my computer at home, but I am at work at the moment. I will post the link later today.

Found the site! :D

Here is the link. http://www.nationaltbucketalliance.com/tech_info/chassis/ackerman/Ackerman.asp

Here is another link pertaining to shimmy. http://www.nationaltbucketalliance.com/tech_info/chassis/shimmy/shimmy_help.asp
 
#7 ·
ok, me and my dad tryed all of the above. it shimmying has stoped for the most part, however, at higher speeds 60 MPH+ you can see the passanger side wheel movin around trying to start th ocilation. im thinking about getting one of them steering dampiners (looks like a shock).
 
#8 ·
You may want to have the tires checked for roundness, some are about as round as an egg, also if you decide to have the front aligned at a shop go to a place that aligns heavy trucks, one of the reasons that the average car shop won't do it is that the axle has to be bent sometimes to get the correct alignment. Truck shops are set up to do this. I have run the front tie rod setup before and the only real problem is tire scrub on cornering and non straight line close manuvering.
 
#9 ·
today we noticed the car is fine if drivin like a normal car, but when u get into the powerband and the secondarys open the car get real squarly, we added some preload on the rear shoks and that helped somewhat, but, to me thats seems like it fixing a symptom, not the problem. would a steering daminer help? or wou i just be mending the REAL problem?
 
#10 ·
Looking at the first picture, it looks like you have a spacer off the bat wing, then the locator bars mounted off that in single shear. If that is correct, I would think you may be getting some flexing there that might cause a shimmy. And a steering damper would not help that.
 
#15 ·
What I have seen from steering dampers is that they isolate you from the movements/vibrations. On a set-up like that , you want to know when they are there. Vibrations are a sign that there is something wrong. They also lead to part failure, from broken welds or just the parts themselves.
 
#18 ·
this happens to my truck at about 30 mph.....but on mine my rim and tire combe weighs 140 lbs:D its a 42" tsl on a 10" beadlock...

anyways mine is from bigg *** unbalanced tires.....

on yours i would start by checking all the tre....i noticed on mine the dustboot was keeping mine from seating all the way...
try taking all yout dust covers off the tre's.

next check and double check your panhard bar the bar that holds your axle from side to side....make sure its hela tight...

then check you caster...it should be leaning back anywhere from 4-9 deg...the more you go the tighter the feel in the steering wheel...it wants to return to center more...

hope any of this helps:thumbup:
 
#20 ·
yup........get out the tape measure too and measure your toe in....

you will know if its close or way off even with a tape measure....if your really good you can set it with the tape measure....

toe in should be no more than 1/4"

with a short tire like that i would set it at abut 1/8" to 3/16 "
 
#21 ·
355Chevy said:
if im reading this rite, we have to buy new spindels, correct?
No. The steering arms may have to be bent outward from the present location. I placed a link for you in my previous post. Here it is again.

http://www.nationaltbucketalliance....an/Ackerman.asp

As another poster mentioned earlier; the mounting location of your 4-bar is incorrect and dangerous. They should be connected directly to the "Batwings". That short connecting link that is presently being used needs to be done away with.
 
#23 ·
you could use the same arms........its hard to see in the pics but why is ther a spacer from the axle bracket to the arms????

just take the spacer out and pull the arm to the bracket....it should just go over an inch or so.. the bushing should take up the misalignment
 
#24 ·
355Chevy said:
do you think i couls re-use the present 4 bars? or do i have to have them fabed?
Yeah you can. I don't think I would just pull them over and tighten them without the spacers. That will just put the bushings in a bind, and cause them to wear faster. You will probably need to cut the ends loose and reweld them at a greater angle. Another option is to cut the mount off the axle and weld it in closer to the frame.
 
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