Front end shimmy

[Craig]

I have a 42 G506 dump that has front end shimmy at speeds over 30 mph. Any suggestions? See pics on the for sale page, thanks.

[armydriver]

This can be caused by several things. Front end alighnment, one tire in a more worn condition than the other tire and worn tie rod ends and sloppy sterring gear. My truck used to do the same and I aligned the front end in accordance with the tech manual and put two new tires on the front. This took care of most of the problem. My steering gear was also worn enough that there was not enough constant pressure put on the steering unless I kept the steering wheel to the left. I replaced the steering gear and problems solved.

[dr deuce]

If the tierod ends are not loose, the box is not loose, then it is probably the steering knuckles. The upper bearing, because of the plate under it tends to rust and the bearing gets loose.

The TM has the procedure for adjusting the # of shims using a torque wrench (the old fashon ones). I also drill a small hole (1/8") in the plate under the upper bearing to prevent water from being trapped in there and doing the bearing in. I have seen this quite a few times now.

[joel gopan]

My take on it is to strip the knuckles completely down replace all steering knuckle bearings and races and the outer axle seals and install new steering knuckle seal kits. It helps to have fresh shims and have a micrometer handy to do the math and get the preload just right. I never use a spring scale to get this, there is a feel for the proper preload. Your races may be worn after 60+ years without proper service. When everything gets set up just right the cause of the shimmy will greatly be reduced. Then allignment, new bushings for the pins for the tie rod ends and setting toe in will eliminate any cause for wear. You may also have a repair patch or boot in one of your front tires that is causing shimmy in straight ahead travel. Believe it or not, the army never balanced the tires on these old trucks, and problems relating to balance were rare.
Joel

[joel gopan]

You can also check for a bent front drive shaft.
Joel

[dr deuce]

The TM says to use a spring gauge or torque wrench

[joel gopan]

After a few hundred, in 50 years, one develops a feel, and the guages and wrenches are effective only when new bearings and races are new. 50 year old bearings and races, and well used bearings and races develop a wear pattern in the straight ahead position and the preload will not be even throughout the range of motion of the knuckle. It is a very precision job.
Joel

[dr deuce]

Done more than a few myself and always used new bearings and races along with seals etc. and followed the TM

[joel gopan]

I have Military service school and Civilian training on Spicer Drive train, We specialized on the Spicer Axles of all makes, I moonlighted on these for years in order to make ends meet, it is sort of fun on Jeeps, and it is possible to get the caps adjusted on the third try. The key is to have all parts squeaky clean. I have listened to all the back yard and gas station cures about "ya just gotta take a shim out" and have found that the only sure fire way is to completely disassemble and build them back up using factory techniques. If that is not done, there is no way to check the condition of races and bearings, what is usually present is brinelling of the races from the constant pounding of loose bearings. NOTE, the M- Series GMC Wiper kits are the same as Banjo Chev and CCKW except for drive flange gaskets. I have one of the last stashes of WWII Banjo Outer Axle seals and send them to dealers around the country. That seal is obsolete and no longer has a direct National or CR replacement.
Joel

[dr deuce]

The outer banjo axle seals are still available. I have used them in my rebuilds. The seals are 1/2 the thickness of the old ones so I install two of them so they ride on a different place on the axle which helps if the axle is worn from the previous seal.

[joel gopan]

Part Number please. I may have to start using them.

[dr deuce]

National 6084 or CR 16650

Use 2 instead of one Banjo only axles

[Craig]

I put a heavy duty steering stablizer on the old girl and the shimmy has dissapeared.

[armydriver]

I am glad that took care of the problem. Also thanks for the tip so others can follow your suggestion.

[Fernando Mendes]

1)Put two news pins,bushings and washers in tie rod end,
2)Put two new NDT Firestone 7,50x20" tires and balanced them.
I think they will cause good result.