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Old 08-17-2013, 04:29 AM
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Rear End Hop

I have a 2006 F350 6.0 CC LB with 120k on it that I bought it a few months ago from original owner. It has a very consistent rear end hop between 40-45mph (at lower rpm). I can accelerate through it, and it practically disappears under hard acceleration.

Previous owner had a Diablo tuner, but that came off immediately after I purchased the truck, and I have been running OEM since (want to go with SCT customer tune but waiting to solve the Hopping issue before spending more $). I replaced all fluids and filters, including differentials, (Amsoil and K&N) and a new FICM, and 2.5" level spacers. Motor is strong and smooth.

First thought was tire balance, so that has been done along with rotation in case one tire had bad belts, et. Problem not solved....thought perhaps oem shocks the problem, so I replaced all four with appropriate size to accommodate front end level kit. Problem not solved.

Not sure where to look next, anyone else experience this in the past? Not looking to spend a fortune chasing ghosts...any help would be greatly appreciated.

Thanks.
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Old 12-13-2013, 12:23 PM
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You ever figure this out? My truck has the same hop at 35-40, I spent money on a new driveshaft, new tires, new shocks, and some other stuff. Still no solution.
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Old 12-13-2013, 01:58 PM
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yep, mine does it too from about 40-45......found out it's pretty common for us CCLB guys, something with how much rotating mass there is, although to be honest with you guys, it feels more like it's coming from the front to me.
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Old 12-16-2013, 07:59 PM
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It's very possible your feeling frame bobble. At least thTs what I call it lol. I would get it going over a speed hump or at times regular speed bumps. Frame flex kinda like a gallop, I added some additional crossmembers and it took care of it on my truck. Posted a pic on suspension discussion on a post called looking for ideas or suggestions or something like that by AutoTech.
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Old 12-18-2013, 03:44 PM
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Rear End Hop

Still not fixed, thanks for feedback....
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Old 12-23-2013, 06:58 PM
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Going to list possibilities:

U-Bolts loosened up
Carrier Bearing: loose,rubber isolator degraded and worn loose, bearing worn causing vibration.
U/J's worn or misaligned.
If it's lifted has it been shimmed at the carrier bearing.

Your problem is there in one of those places
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Old 12-24-2013, 05:04 AM
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I've replaced so many things and haven't figured this out either. It will about shake you to death at 43mph! There is a huge thread on ford-trucks that I read when I was searching this problem. I don't think anyone has a firm solution to this. A couple people had custom drive shafts made IIRC. Here is the link.

Rear end bounces @ 40-45 MPH - Ford Truck Enthusiasts Forums

Mine is an ECLB by the way.
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Old 12-24-2013, 07:49 AM
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I think I know what your talking about to a degree. My truck is the same SCLB which is the typical frame same as the CCSB. The vibration I was getting I figured was frame flexing or oscillation that I called frame bobble.

My remedy for it was to add crossmembers to my chassis.
I installed 2 additional cross-members directly above and below the transfer case output shaft. (3/8X6" flat w/1" solid square stock down length for upper)(3"channel lower)


Added another between the radius arm hangers. (3"channel iron)
Added a stiffener to the transmission crossmember which is also 3" channel because it fits inside track of the oem. Drilled three 3/4" holes down length to bolt them together. Also the two transmission mount bolts are used. I used 1" solid steel square stock from the transmission stiffener to radius arm crossmember and diagonally back 18" left and right frame rails.
This 100% stopped my frame bobble or bouncing. Truck drives and behaves much differently now. No longer leans into turns like it did and the biggest change is no more flexing like before. It feels like a shorter chassis to me for whatever reason but no more flexing bobble hop or whatever you want to call it.

One last thing you may try that's easy is: get a oil can and hit the leaf springs between leafs down the length. Make sure you hit all the Teflon slide points on the ends of the leafs too. This is no miracle cure but does help the leafs move back and forth on each other and is actually noticeable.
Good luck on it
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Old 12-24-2013, 07:57 AM
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A picture of front crossmember.
Attached Thumbnails
Rear End Hop-image.jpg  
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  #10  
Old 12-24-2013, 09:43 AM
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Quote:
Originally Posted by mhatlen View Post
I think I know what your talking about to a degree. My truck is the same SCLB which is the typical frame same as the CCSB. The vibration I was getting I figured was frame flexing or oscillation that I called frame bobble.

My remedy for it was to add crossmembers to my chassis.
I installed 2 additional cross-members directly above and below the transfer case output shaft. (3/8X6" flat w/1" solid square stock down length for upper)(3"channel lower)


Added another between the radius arm hangers. (3"channel iron)
Added a stiffener to the transmission crossmember which is also 3" channel because it fits inside track of the oem. Drilled three 3/4" holes down length to bolt them together. Also the two transmission mount bolts are used. I used 1" solid steel square stock from the transmission stiffener to radius arm crossmember and diagonally back 18" left and right frame rails.
This 100% stopped my frame bobble or bouncing. Truck drives and behaves much differently now. No longer leans into turns like it did and the biggest change is no more flexing like before. It feels like a shorter chassis to me for whatever reason but no more flexing bobble hop or whatever you want to call it.

One last thing you may try that's easy is: get a oil can and hit the leaf springs between leafs down the length. Make sure you hit all the Teflon slide points on the ends of the leafs too. This is no miracle cure but does help the leafs move back and forth on each other and is actually noticeable.
Good luck on it
That's kinda how my theory is on this too. Funny enough, I had it on my '87 F150 SCSB too and reading through the thread that sixOH posted, it spreads across many years (one guy had a '78 that did it). I've been working on a fix that is somewhat like yours and I'm glad to hear it worked. I just got all my materials and will be building a new x-member to bolt in.

My theory on this is with just how much material we have working/bouncing down the road and not necessarily the lack of strength our trucks have to hold it, but it doesn't support itself very well. Crawl under your truck and look, especially with us CCLB guys, there's a lot of blank real estate in between the trans crossmember and the back of the frame. There's a couple stamped crossmembers along the top of the frame, but they're more for body mounts, and IMO aren't doing a good enough job tying the frame together. So my running theory is that it's not a drivetrain vibration we're feeling, but a frame vibration. Both rails of the frame are moving at different rates (being pushed around by the springs/axle) because there's not enough crossmembers holding them together.

Now to answer the question "why doesn't it happen on every truck?" well maybe the trucks that it has happened to have done something in their "lives" , like going onto a ramp at a funny angle and getting a little frame twist, to work some things loose and that amplifies it bad enough for us to feel it. Also reading a lot into this I've found that some trucks haven't done it until 50k-100k into their runs. That makes sense, since now bushings are starting to wear and aren't holding the vibrations at bay as well as they once did.

We're not alone, google the "superduty hop" and you'll find tons of threads, articles, etc. I should have my new crossmember done in the next month or so, I'll keep you guys posted on the results
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