Hello. 2002 F350 7.3, MANUAL transmission ZF6.

Bought this truck used for hauling an excavator, and after fixing damn-near everything engine/turbo/and-cooling-system-related ---- it's finally seeing some use.

Just recently started hauling 12,000lb payloads.

When I accelerate hard in Low gear, and then shift into 1st and accelerate hard again, I feel the whole truck shuddering.

It's like a shimmy-shaking vibration all through the vehicle.

It doesn't happen in higher gears, only when the following conditions are met...
1) Starting from a dead stop
2) 12,000lb payload (heavy)
3) Accelerating hard (Low, First gear)

I would also like to add that I experienced this shuddering vibration very intensely when I put the transfer case in 4wd LOW (front manual hubs left unlocked) and towed 14,000lb up a steep hill in 1st, 2nd, and then 3rd transmission gears.

^^^ By leaving front hubs unlocked and transfer case in 4wd LOW, I was effectively lowering my final drive ratio even more for extra pulling power in 2wd hill-climbing. I don't do this often, only when absolutely necessary. ^^^

I must also add that I do have slightly taller rims/tires than OEM ford WITH the original ford gearing (3.73) so I'm more like 3.51 final drive ratio.

Thanks!

02 F350 7.3l ZF6

 

Have you considered checking the condition of the transfer case fluid? That is some serious weight to be hauling with a transfer case that may not really be designed to handle such heavy loads. I don't know anything about the load limits of the transfer case, but it is worth investigating.

 

I changed the transfer case fluid and trans fluid just a few months ago.

Someone on another forum mentioned a similar issue and said it turned out to be cracks in the transmission bellhousing, and the shuddering only happened under really heavy towing. Now I'm freakin mortified. I don't have the money for such an undertaking it that really is the case. Or broken case. I guess I'm gonna go crawl under my truck again.

I'm thinking it's leaf spring wrap to some degree. It's as if the vibration/shuddering is me actually feeling each combustion of the engine, and there's so much strain through the driveline that it's as if the springs are wrapping and vibrating as a result of each combustion event.

 

Did you use Mercon V for the fluid? It was recommended at one time, then warned against later.

 

New carrier bearing and u-joints fixed that problem with mine.

 

Severe axle wrap causing the driveshaft u-joints to bind.

 

Im thinking this also, thats what it sounds like. Certainly better than a cracked tranny

 

Not sure if you have seen this thread, but it sure sounds similar to what you might be experiencing: https://www.ford-trucks.com/forums/1...installed.html

 

Since my post was just referenced above, I will give my .02 worth. Please read the entire post I made and if you still have questions shoot me a PM.

In addition I will add an update. My wife and I just finished a 7K mile trip from GA to WA and back. Just got home late last night. We had our 10K lb travel trailer in tow for about 6 K miles of the trip. The axle wrap/shudder is much better when towing heavy, but still there a bit when starting on a fairly steep incline. I plan to swap out the 3 u-joints on my single piece drive shaft, replace the pinion seal and see if that eliminates the shudder. If not, I am going to get OUO bolt on small gusset traction bars.

My truck is stock except for a few minor things, but I think the manual transmission and the extra weight of the tow load puts too much stress on the rear suspension.

I look forward to hearing about your thoughts and experiences with "the shudder".

 

I did use Mercon V.

I have replaced the carrier bearing in the past 10k miles.

I'm thinking this is the case.

It happens relative to hard I'm pulling something. Low gear it's definitely noticeable, and in low-range 1/2/3 gears it's very noticeable as well.

Happens when I'm getting a heavy heavy load moving.

I'm thinking traction bars or air bags. And a rear sway bar to help with stability when blazing down the highway at 50mph in strong crosswinds.

 

Transfer cases have been known to pop like a zit with Mercon V in there. You may want to do a little homework on what belongs in there.

I had to go traction bars to stop the carnage in the rear. A nice benefit is the much-smoother shifts.

 

Perhaps you could advise me what does belong in my transfer case?

 

Plain old Dexron III, or Motorcraft transfer case fluid, or certain synthetics.

 

Yeah Ford sells Tranfer case fluid now. It's a thinner red oil, hmmm seems familiar. But that's what they recommend. Motorcraft Mercon V says "Not for use in transfer cases" on the back of the bottle.

 

Such a thorough treatment to solve a weird problem. The guys on this site are amazing. I hope that the problem gets solved with their help. God bless all of you!
Larry