Death wobble, have I tried everything?

1952 - 1968, M38A1, M170, questions, discussions, regarding anything related to the M38a1 series.
JMZ421
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Re: Death wobble, have I tried everything?

Post by JMZ421 » Sun May 02, 2021 10:32 am

As long as the steering box was centered prior to the pittman arm re-install with the ball directly below that shaft AND the bellcrank was at 90 degrees to the front axle, you should be OK. Any final adjustment for the front wheel has to be done with toe -adjustment and the process ends with toe-adjustment. That's what I learned on this site. Hope all works out, John


JeepdaddyRC
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Re: Death wobble, have I tried everything?

Post by JeepdaddyRC » Mon May 03, 2021 6:45 am

Update and conclusion:
The following steps had been taken to find the M38A1 wobble:
- Rebuilt steering box with new worm shaft and sector
- Steering box bolts tight to frame
- New drag link, adjusted to spec
- Rebuilt bell crank with new bearings, set to 90 degrees to axle
- New tie rod ends
- New shocks
- Tires balanced and inflated to 25 lbs
- New wheel bearings and races
- New king pin bearings and races
- Steering knuckle bearing preload set to specs
- Toe in set to specs
The wobble was still there.
After much trouble shooting, I discovered the PO had not set up the Ross steering box correctly. The point I felt the slight drag on the steering wheel should have been at the midpoint, because the parts are new and the grooves in the Ross box are cut narrower and shallower in the straight ahead position. Unfortunately, the tires were NOT pointed straight ahead when at the midpoint. They were about 10 degrees to the left.
Set the steering box to the midpoint, removed the pitman arm and re-clocked it on the splines. This changed the ball position and moved the drag link to center the wheels per the Ross Maintenance Manual.
This reduced the backlash and play at the wheels. Nice improvement and it returns to center when coming out of a turn!
42 GPW #91366, recovered blue drab registration 20200841, unit markings 104-415-I HQ-21 (Timberwolves)
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Joe Gopan
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Re: Death wobble, have I tried everything?

Post by Joe Gopan » Mon May 03, 2021 9:10 am

Best get the Ord Maint TM for the M-38A1 Body, Frame and powertrain, to check that the assembly procedure has been followed.
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chesty
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Re: Death wobble, have I tried everything?

Post by chesty » Wed May 05, 2021 7:16 pm

Jeepdaddy, I still think your death wobble is related to a tire issue. Have you tried rotating tires ? Check wheel balance again? Tires the same age, wear etc? Good luck Tony
SGT USMC 1967
1952 M38A1
1967 M416

JeepdaddyRC
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Re: Death wobble, have I tried everything?

Post by JeepdaddyRC » Thu May 06, 2021 6:30 am

DOT stamp indicate NDCC tires are 2004.
Tire man spin balanced and found non of the early M38A1 original rims are perfectly true. He stated no dry rot and tires look like new. Put the "truest" up front.
When raising the front end and turning the tires by hand - I still had a full inch of slop/movement before the steering wheel turned.
Adjusted shims to remove backlash at worm gear in Ross steering box.
Up and down movement at steering shaft eliminated and shaft turns freely.
Now tires and steering wheel turn as one.
When I started this adventure, there was 4 inches of rotational play at the steering wheel with Jeep on the ground.
Good news! There is now 1/2 inch of rotational play at steering wheel.
This saga taught me that not all PO repairs/rebuilds are complete/correct.
42 GPW #91366, recovered blue drab registration 20200841, unit markings 104-415-I HQ-21 (Timberwolves)
CJs (x 4)


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