Death wobble, have I tried everything

JeepdaddyRC · Post by **JeepdaddyRC** » Wed Apr 28, 2021 1:14 pm

The following have been taken to find the M38A1 wobble:
- Rebuilt steering box with new shaft and sector
- New drag link, adjusted to spec
- Rebuilt bell crank with new bearings
- New tie rod ends
- New shocks
- Tires inflated to 25 lbs
- New wheel bearings and races
- New king pin bearings and races
- Steering knuckle bearing preload set to 9 lbs of pull based TM9-8014, p 257 (5)
The wobble is still there. What am I missing?

Post by **wesk** » Wed Apr 28, 2021 3:57 pm

With the front wheels off the floor, the steering wheel anchored dead tight/still is there any play/slop in any off the repaired/replaced units. If so exactly how much. Please give play in a measurement not an adjective. Exactly how much travel measured at the top of each front tire and at the front of each front tire?

Finally are both front wheels perfectly true/straight?

Mike_B · Post by **Mike_B** » Wed Apr 28, 2021 8:18 pm

Don't overlook the leaf spring pins and shackles...

Mike B

RonD2 · Post by **RonD2** » Wed Apr 28, 2021 8:56 pm

JeepDaddy usually always posts his questions both here and the G503 forum (M38/M38A1 tech forum) at the same time. He usually gets quite a bit of feedback, answers, and suggestions in both places at the same time, with the expected overlap. Both forums seem to be helpful of what he needs with good stuff, but keeping up with it all is kind of a chore.

I've noticed that one forum or the other usually fades away with no solution ever posted to close it out for the audience. The good news is that usually he titles both threads the same, which simplifies the searching feature.

JeepdaddyRC · Post by **JeepdaddyRC** » Thu Apr 29, 2021 8:45 am

I will report back with results.
It is helpful for future readers to provide a summary/conclusion.
Hopefully I can pinpoint the issue because the wobble begins at a slow speed (25-35 mph), triggered by only minor bumps in the road - but it is pretty violent. The PO's steering stabilizer was a band aid.

JeepdaddyRC · Post by **JeepdaddyRC** » Thu Apr 29, 2021 12:40 pm

As promised here is the video link.
Please note this was filmed with a wide angle GoPro focusing on the driver side knuckle and tie rod end.
The tires are almost new 16x7 Military NDCC.
The first view is regular speed, followed by slow motion. This occurred at 28 mph over minor bumps in the road.

https://www.youtube.com/watch?v=NHu-jmiR5jM

Post by **wesk** » Thu Apr 29, 2021 12:43 pm

What I saw in that video was a very bent wheel or tire carcass defect. Try using a different set of wheels and tires on the front.

JeepdaddyRC · Post by **JeepdaddyRC** » Thu Apr 29, 2021 1:15 pm

Wes, what do your expert eyes (with decades of experience) see in that video that I can't spot that indicates a very bent rim or tire issue?

Mike_B · Post by **Mike_B** » Thu Apr 29, 2021 1:56 pm

What I see is a lot of left to right movement of the springs and shocks...could just be a side effect, but...

Jack the jeep up and set it on a good set of jack stands so it won't fall off. Then see if you have side to side movement of the entire front suspension while pushing/pulling on the tires with your hands at 3 and 9 o'clock. It may take two people, one shacking it hard while one is looking/feeling for movement at the shackles and pins...

Mike B

RonD2 · Post by **RonD2** » Thu Apr 29, 2021 3:32 pm

Not to distract from troubleshooting, but what's that large shiny silver bracket clamped around the axle on the inboard side of the spring pack?

JeepdaddyRC · Post by **JeepdaddyRC** » Thu Apr 29, 2021 4:48 pm

RonD2,
Good observation and question.
That is the one of the brackets from the PO's steering stabilizer. The other bracket is on the passenger side tie rod.
I removed the stabilizer shock absorber, but not the brackets yet.
Apparently the stabilizer was the POs answer to "a little shimmy".

RonD2 · Post by **RonD2** » Thu Apr 29, 2021 5:12 pm

Thanks JeepDaddy.

That kind of leads me to another question.....the TM has a procedure and measurements with tolerances for checking frame straightness, true and square. Plumb-bob, pencil, tape measure, and flat garage floor are all that's needed. Out of curiosity, have you checked it?

You mentioned that you did a front wheel alignment for correct toe-in. I'm guessing unless you did that yourself, any shop you took it to for alignment would probably have discovered a bent frame and told you.

Even without death wobble, I couldn't resist checking mine. It came out within specifications. Kind of amazing after 65+ years.

Just a thought.

It's obviously much easier to swap front wheels with the rear to see if that's the problem, and to re-check torque value on every part involved (both good ideas) than it would be to deal with a bent frame.

I'm only asking because maybe the PO had a problem he couldn't solve without the dampener? Assuming there was no wobble or "shimmy" before you disassembled and rebuilt the steering? Or was there?

Good luck!

JeepdaddyRC · Post by **JeepdaddyRC** » Thu Apr 29, 2021 9:23 pm

These nice original early M38A1 4.5x16 military wheels (with 1/8 pilot hole and safety bead) are headed to the wheel and tire pros for evaluation.
I will also continue the search for "hidden" steering play and report back.
I now believe the PO could not locate the issue, gave up, and added a steering stabilizer.
I am determined to figure out this mystery.
Appreciate the help.

Mike_B · Post by **Mike_B** » Thu Apr 29, 2021 9:57 pm

Have you had the tires balanced?

Mike B

JeepdaddyRC · Post by **JeepdaddyRC** » Fri Apr 30, 2021 10:40 am

We have our first clue in the mystery.
Followed Wes's diagnostic procedure of firmly anchoring the steering wheel, raising the front end on jackstands and moving tires back and forth - with the goal to locate any play/looseness.
Results with steering wheel anchored:
1. No play at tire/wheel when grasped at 12:00 and 6:00 o'clock position (the king pin bearings and wheel bearings were just replaced).
2. One inch of play in each direction at tire/wheel when grasped at 3:00 and 9:00 o'clock positions and moved side to side (without movement of steering wheel)!
3. Tie rod ends moving with tire
4. Drag link moving with tire
I believe the "play" is narrowed down to the steering gear. The PO replaced the sector shaft, worm drive and pitman arm. You can feel slight movement up and down in the steering wheel (towards the driver) without the steering wheel turning with someone moving the tires back and forth at 3:00 and 9:00 o'clock.
Thoughts?