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Old 11-03-2014, 09:29 PM
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Rear end bounces @ 40-45 MPH

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Old 11-12-2010, 07:52 PM
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Rear end bounces @ 40-45 MPH

Ever since I picked up my truck (350 6.7, c/c, srw, lb) I get a "bounce" in the back of the truck right at 40 mph and it stops right at 45 mph. My first thought was that I have a bad tire. I have 18" Continental A/S tires on it. The bounce gets progressively worse if I stay between 40-45 mph but clears right up if I slow down or speed up out of that speed range.
This week I took the truck in because of the change oil light came on with only ~1200 miles since oil change. I finally remembered to tell the service department about the bounce. They had my truck for 3 full days and all they have managed to do is confirm my complaint, not fix it. They road pressure balanced the tires 3 times and they still had the bounce. They called the Ford hotline and were told to take the tires off of a brand new lot truck and see how they were. The bounce is still there with the brand new tires.
The bounce is unaffected by rate of excelleration or gear the tranny is in... it just happens at 40-45 mph no matter if I drive like my granny or a jack rabbit. I have heard comments like "its the nature of the beast" but I don't think so.
I took my truck back for the weekend but the tech is waiting on another reply from the hotline as to what to do next.
Since the new tires didn't help my next guess is the drive shaft or rear end since it is definately speed related.
I just realized that I don't think I notice it when I am hauling my 5'er but I am not 100% sure about that.

Anyone have any thoughts?
Thanks,
Thom

2011 F350 6.7L PSD C/C SRW long bed w/ 5'er package.

Last edited by Thom12; 11-12-2010 at 08:28 PM. Reason: added comment about towing 5'er.
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Old 11-13-2010, 12:04 AM
Champ198 Champ198 is offline
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You're not alone. My 350 does that at 50mph. I can feel it coming on at about 45, then gets terrible at 50. It then tapers off. It hops pretty bad if I hold it at 50 over an extended time. Since the tires have been rebalanced, the balancing is messed up over 70mph. I have the Michelin 20s. Local dealer told me the same thing they told you. (characteristic of the truck) I'm taking it to someone else. I haven't had a chance to take it to the other dealer yet.

I've had my tires balanced twice and I get the same hop. It makes me sad and doubt the truck.

Keep us posted.
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Old 11-13-2010, 10:42 PM
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This isn't good....this issue has been a problem for quite a few years with the SD trucks. I really had hopes that they had fixed this by now.
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Old 11-14-2010, 10:15 PM
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i've had no issues with the 11 f-350 dually truck i'm driving. Must just be a SRW problem with the bounce. I wish i could help with this one. COuld it be the suspension on the rear causing it? unloaded does it but does it do it pulling a trailer is then next question?
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Old 11-14-2010, 11:52 PM
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mine has a bounce in the rear but only on the concrete roads and not all of them. on the oiled or asphalt roads it is not an issue.
I fiugre the suspension is stiff, high psi in the tires, and cupped concrete road surface is just causing the rear to bounce on mine.
it sucks but not sure what I can do to prevent it......
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Old 11-15-2010, 08:05 AM
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Sorry I don't have a fix, but was wondering............

Can you experiment by putting some bags of mulch, concrete, sand or something in the bed and see if that helps?

Guess my thinking is that I have a tonneau cover (F-250) and have not noticed anything like that, was wondering if the down pressure caused by the cover helps eliminate this???? Maybe this will stop after the springs/suspension has been exercised more? I am also wondering what Ford is going to do if they determine that this is a characteristic of the truck. Surely they can not view this as acceptable.
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Old 11-15-2010, 04:27 PM
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Quote:
Originally Posted by Adobe 11SD View Post
Sorry I don't have a fix, but was wondering............

Can you experiment by putting some bags of mulch, concrete, sand or something in the bed and see if that helps?

Guess my thinking is that I have a tonneau cover (F-250) and have not noticed anything like that, was wondering if the down pressure caused by the cover helps eliminate this????....
I have a Lear topper on mine and also haven't noticed any bounce or hop, other than what can happen on certain roads to all vehicles (such as on I-43 to/from Milwaukee before they commenced to fix it, and on I-5 SB before the Grapevine, to name a couple).

In fact, after reading some of the posts in this thread, yesterday I did a 50-mile road test out of curiosity, with the following results and conclusions:

Test vehicle: 2011 F350 6.7 SC SWB SRW FX4 3.55 LT275/70R18E Continental Contitracs w/Lear 100XR topper. Unladen weight (including topper and bedliner) 7480 lbs.

Test conditons: dry roads of all condition from very good to moderately poor asphalt, mid-'70s F temp., 3/4 tank of fuel, 200 lb driver, approximately 400 lb cargo ahead of rear axle. Estimated gross vehicle weight 8250 lbs.

Test results: very minor vibration at 45 MPH and at 59 MPH. So minor that it wouldn't be noticeable if you weren't consciously trying to find it. In fact, it presented as a minor noise as much as it did as a vibration. Tested on several different road surfaces to rule out a road-only cause. In addition, manual mode was used to lock transmission in 4/5/6 gears to identify a possible drive-train cause. No obvious difference noted.

Conclusions: IMO, the minor vibration/noise I found was probably a result of the truck chassis and body (and topper) assembly achieving a particular resonant frequency, as opposed to any out-of-balance cause, or a condition caused by the suspension and load alone. Payload or load distribution is very likely a consideration (see thread in this forum from about a week ago regarding 2011 F350 ride issues), and a topper or tonneau cover may also have an effect in stiffening the cargo box to a certain extent.

Disclaimer: Non-scientific test by a 60 YO driver who is more than a little hard of hearing, among other minor maladies. Said semi-decrepit driver only drove the truck unladen for about 300 miles and didn't notice anything except what appears to be a relatively stiff ride for a modern 350. The other 8300 miles have been with various loads in the truck, and/or the topper installed. No warranty is expressed or implied; in fact, no usefulness of any kind is implied, except that I was sincerely trying to help.

Joe
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Old 11-15-2010, 04:31 PM
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"semi-decrepit"

LOL
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Old 11-15-2010, 07:19 PM
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Joe,
Thank you for performing such an indepth test attempting to duplicate my issue! My Ford dealership has been able to duplicate it very regularly even with differant tires. So atleast they appear to be concerned. I will let them play with it some more when the parts they have on order for my front seat come in.

I only wish that your Non-scientific test by a 60 YO driver who is more than a little hard of hearing, among other minor maladies, would have been a documented scientific test, I would have been able to reimburse you for the fuel and 55 cents a mile, but thanks again.

Thom
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Old 11-15-2010, 07:48 PM
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No bounce, but 80 psi in the rear tires makes it pretty rough. I brought it down to 70 and made a world of difference. 65 in the front and 70 in rear seems to be the ticket for my particular truck, others might be different.
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Old 11-16-2010, 11:40 AM
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I wonder... has either of you had the balance checked on your driveshafts? I have a buddy with a 2000 250 SRW 7.3 who had his done. He told me that it made a world of difference in all sorts of characteristics on the truck. Wheel hop was one of them. HTH
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Old 11-16-2010, 05:39 PM
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No, I have not had the drive shaft balanced yet. My truck goes back to the dealership in the morning for thier next road of troubleshooting. I agree with the shaft as a possibility especially with the two part shaft & carrier bearing on the long bed of mine.

Thom
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Old 11-16-2010, 06:09 PM
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I have not gotten that far yet. The new dealer is going to want to road force balance the tires and start fresh. I have to go through all that just to get to the discussion about the drive shaft. I hope to get it to the shop tomorrow.

I have a cousin who was an engineer at Coats manufacturing (they made tire balancing machines and he's got lots of balancing experience) who believes it is not the Michelin tires but possibly the drive shaft. I have to let the Ford guys come to that conclusion. I believe that it may take several trips and several weeks to work through this but we will get it solved.
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Old 11-22-2010, 07:23 PM
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Just an update for those with the same problem...
My truck has been in the shop since Wednesday and I got a call Saturday saying it was ready for pickup. I got there Saturday afternooon and my regular service advisor was gone for the day but he left all the paperwork with someone else. I read the paperwork and it said the bounce must be normal because even though they can duplicate it, they can't find anything wrong. Boy was I hot! I actually felt sorry for the poor guy that had my keys and paperwork because he took the abuse of the messenger getting shot with both barrels and he kept a very cool head and he actually agreed with me that he didn't think it was normal.
I left the truck sitting right there that day. This morning (Monday) I called the Service Manager on his cell even before he got into work and told him I did not agree that it was normal and my truck is sitting at his shop waiting for him to test drive and let me know if he thought it was normal.
30 minutes latter he called me and asked if I meant the bounce at 40 mph and I said exactly. He said he will get to the bottom of it.
He called at 3 this afternoon and said they have been in constant contact with the Ford engineers all day and are going through everything the engineers can think of but still haven't found the cause....
They still have the truck but atleast I feel now I have them actually working it.

I will keep ya'll posted as the saga continues.
Thom
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Old 11-22-2010, 08:42 PM
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You have to keep pushing.

Years ago I had a car that just would not stop straight. We changed everything from the brakes to the front suspension components (Chrysler product) Spent over 40 hours on it. This was a little different in that we (the techs) knew there was something wrong, just couldn't solve it.

In the end we had 3 "white coated" engineers fly out from Detroit. They drove the car, pulled a bushing out of their briefcase and had us install it. Problem solved.

Point is, as unique as your problem may be, the factory may already know about it and working on a solution. You just need to get the right people involved.
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