Acceleration shudder diagnosed by Ford!
09-16-2013, 08:01 PM
#291
Neophyte
Not so fast... (to close this thread dc) :)
I have an EB, HD, LB, Screw, 4x4, 2piece, MaxTow built 7.9.2012. I have the problem.
When I first got the truck, it has the issue when I would tow my 8k lbs trailer - truck
empty - its much better now - without doing anything. (I think I know why).
However, when I fill the cab with people, and load the bed with toys - to the max - and then tow my 8k trailer - its bad. Its *really* bad when I'm on an incline - scary bad.
We have two issues related here - pinion angle and axle wrap. My opinion is that the axle wrap/vibration is caused by improper/excessive pinion angle or difference between the pinion angle and operating angle (input shaft side). The reason my empty truck experience improved was because the truck settled in some and changed the pinion angle. To bolster this - when my truck shakes, its shaking frequency is related to speed - not torque. That is - the shaking increases in frequency as you go faster - I'm guessing pulsing with the u-joint bending.
I think that the reason your leaf spring fixed the issue was more from changing the ride height than preventing axle wrap. If true - the RAS or traction bar approach can actually cause this energy go into the drive line - extra stress on center bearings and u joints.
You could loading up enough weight to drop the back end to where it was before (4" down?), and I bet it gets worse again. Try going up an incline. The extra beef on leaf may dampen - but again - may be masking the issue and creating more driveline strain/damage. Did you ever try airbags?
To close out this thread - I think requires some validation. Chicken or egg? Pinion angle or axle wrap? Maybe need both stiffer leaf (like on my HD) and air bags...
I bought air bags (not installed yet) to try to address the issue. I also have a magnetic angle measurement tool.
In the TSB for pinion angle - they have a chart for unloaded pinion angle adjustment based on average load. Does anyone have that chart? BTW - my dealer said it was an "odd used of the truck" to run either fully loaded or empty. Hugh? - in which case average is a poor approximation. BTW - the TSB explicitly states that adjusting for empty/full can cause problems with the other "extreme".
When I first got the truck, it has the issue when I would tow my 8k lbs trailer - truck
empty - its much better now - without doing anything. (I think I know why).
However, when I fill the cab with people, and load the bed with toys - to the max - and then tow my 8k trailer - its bad. Its *really* bad when I'm on an incline - scary bad.
We have two issues related here - pinion angle and axle wrap. My opinion is that the axle wrap/vibration is caused by improper/excessive pinion angle or difference between the pinion angle and operating angle (input shaft side). The reason my empty truck experience improved was because the truck settled in some and changed the pinion angle. To bolster this - when my truck shakes, its shaking frequency is related to speed - not torque. That is - the shaking increases in frequency as you go faster - I'm guessing pulsing with the u-joint bending.
I think that the reason your leaf spring fixed the issue was more from changing the ride height than preventing axle wrap. If true - the RAS or traction bar approach can actually cause this energy go into the drive line - extra stress on center bearings and u joints.
You could loading up enough weight to drop the back end to where it was before (4" down?), and I bet it gets worse again. Try going up an incline. The extra beef on leaf may dampen - but again - may be masking the issue and creating more driveline strain/damage. Did you ever try airbags?
To close out this thread - I think requires some validation. Chicken or egg? Pinion angle or axle wrap? Maybe need both stiffer leaf (like on my HD) and air bags...
I bought air bags (not installed yet) to try to address the issue. I also have a magnetic angle measurement tool.
In the TSB for pinion angle - they have a chart for unloaded pinion angle adjustment based on average load. Does anyone have that chart? BTW - my dealer said it was an "odd used of the truck" to run either fully loaded or empty. Hugh? - in which case average is a poor approximation. BTW - the TSB explicitly states that adjusting for empty/full can cause problems with the other "extreme".
09-16-2013, 08:47 PM
#292
Senior Member
Thread Starter
Sorry but pinion angle is not the cause.
Incorrect pinion angle does cause the Ujoint shake but that is only after axle wrap has moved pinion angle out of the operating range.
I will list some of the many tests I've done to confirm this.
Truck is smooth empty and unloaded.
Truck shakes when trailer put on with no equalizer and allowing full sag.
Truck shakes when equalizer put on and load lifted back to empty ride height.
Ford changed my pinion angle to make shudder go away when loaded. No change.
RAS put on and towing shudder reduced. This was because it helps prevent axle wrap but not cure it. Ride height stays up and again can be perfectly matched with empty ride heights. Rear ride heights have zero effect on the shudder in any towing setup.
The new leaf installed in the correct location cured the shudder. Period.
With no other suspension mods (totally stock) I made and installed Caltrac style traction bars and they totally cured the shudder whether rear end sagged or not.
The only time there is shudder is when there is enough resistance and torque in the drive train to flex (wrap) the springs.
The transmission and steady bearing mounts can also move and affect pinion angle but to a smaller amount.
So to summarize : regardless of the angle of the drive train (pinion angle) there is shudder unless an anti axle wrap device is installed.
I've done 3 types, all indicating an axle wrap problem.
Incorrect pinion angle does cause the Ujoint shake but that is only after axle wrap has moved pinion angle out of the operating range.
I will list some of the many tests I've done to confirm this.
Truck is smooth empty and unloaded.
Truck shakes when trailer put on with no equalizer and allowing full sag.
Truck shakes when equalizer put on and load lifted back to empty ride height.
Ford changed my pinion angle to make shudder go away when loaded. No change.
RAS put on and towing shudder reduced. This was because it helps prevent axle wrap but not cure it. Ride height stays up and again can be perfectly matched with empty ride heights. Rear ride heights have zero effect on the shudder in any towing setup.
The new leaf installed in the correct location cured the shudder. Period.
With no other suspension mods (totally stock) I made and installed Caltrac style traction bars and they totally cured the shudder whether rear end sagged or not.
The only time there is shudder is when there is enough resistance and torque in the drive train to flex (wrap) the springs.
The transmission and steady bearing mounts can also move and affect pinion angle but to a smaller amount.
So to summarize : regardless of the angle of the drive train (pinion angle) there is shudder unless an anti axle wrap device is installed.
I've done 3 types, all indicating an axle wrap problem.
The following users liked this post:
ute (09-20-2013)
09-20-2013, 09:20 PM
#293
As DC stated it is 100% wrap ..which induce's pinion angle change
Ford's fix is just a non starter because it moves the problem around adjust for unload truck its at the loaded end if adjust for loaded truck its at the unloaded end.
The RAS helped but is still there. I just got back from towing my 5er this week under load hard acceleration going up a steep long hill the vibe is still there ...reduced but there
So for me I will follow DC's fix and have a new leaf installed
Ford's fix is just a non starter because it moves the problem around adjust for unload truck its at the loaded end if adjust for loaded truck its at the unloaded end.
The RAS helped but is still there. I just got back from towing my 5er this week under load hard acceleration going up a steep long hill the vibe is still there ...reduced but there
So for me I will follow DC's fix and have a new leaf installed
09-20-2013, 10:08 PM
#294
Senior Member
As DC stated it is 100% wrap ..which induce's pinion angle change
Ford's fix is just a non starter because it moves the problem around adjust for unload truck its at the loaded end if adjust for loaded truck its at the unloaded end.
The RAS helped but is still there. I just got back from towing my 5er this week under load hard acceleration going up a steep long hill the vibe is still there ...reduced but there
So for me I will follow DC's fix and have a new leaf installed
Ford's fix is just a non starter because it moves the problem around adjust for unload truck its at the loaded end if adjust for loaded truck its at the unloaded end.
The RAS helped but is still there. I just got back from towing my 5er this week under load hard acceleration going up a steep long hill the vibe is still there ...reduced but there
So for me I will follow DC's fix and have a new leaf installed
09-21-2013, 09:22 AM
#295
Junior Member
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As DC stated it is 100% wrap ..which induce's pinion angle change
Ford's fix is just a non starter because it moves the problem around adjust for unload truck its at the loaded end if adjust for loaded truck its at the unloaded end.
The RAS helped but is still there. I just got back from towing my 5er this week under load hard acceleration going up a steep long hill the vibe is still there ...reduced but there
So for me I will follow DC's fix and have a new leaf installed
Ford's fix is just a non starter because it moves the problem around adjust for unload truck its at the loaded end if adjust for loaded truck its at the unloaded end.
The RAS helped but is still there. I just got back from towing my 5er this week under load hard acceleration going up a steep long hill the vibe is still there ...reduced but there
So for me I will follow DC's fix and have a new leaf installed
09-21-2013, 11:25 AM
#296
Senior Member
Thread Starter
I've had quite a few miles testing out the extra leaf fix both empty and towing.
It does definitely fix the problem.
It is definitely very stiff in the back. Handles a load like a HD truck.
Loaded ride is pretty good, empty ride is much better than a HD but the rear is much stiffer than stock.
You can really feel the stiffness when you are empty but left the max air pressure in the LT off road tires after towing. Can be harsh on bigger bumps.
I would do it again and too bad I didn't do it two years ago. Overall it is an improvement to the truck unless you value it as a luxury car first. Still very comfortable.
I think the RAS system was the best suspension improvement I have made, it made every aspect of the rear suspension better. Only it was not a complete fix for axle-wrap. A pity.
It does definitely fix the problem.
It is definitely very stiff in the back. Handles a load like a HD truck.
Loaded ride is pretty good, empty ride is much better than a HD but the rear is much stiffer than stock.
You can really feel the stiffness when you are empty but left the max air pressure in the LT off road tires after towing. Can be harsh on bigger bumps.
I would do it again and too bad I didn't do it two years ago. Overall it is an improvement to the truck unless you value it as a luxury car first. Still very comfortable.
I think the RAS system was the best suspension improvement I have made, it made every aspect of the rear suspension better. Only it was not a complete fix for axle-wrap. A pity.
09-21-2013, 08:43 PM
#297
I've had quite a few miles testing out the extra leaf fix both empty and towing.
It does definitely fix the problem.
It is definitely very stiff in the back. Handles a load like a HD truck.
Loaded ride is pretty good, empty ride is much better than a HD but the rear is much stiffer than stock.
You can really feel the stiffness when you are empty but left the max air pressure in the LT off road tires after towing. Can be harsh on bigger bumps.
I would do it again and too bad I didn't do it two years ago. Overall it is an improvement to the truck unless you value it as a luxury car first. Still very comfortable.
I think the RAS system was the best suspension improvement I have made, it made every aspect of the rear suspension better. Only it was not a complete fix for axle-wrap. A pity.
It does definitely fix the problem.
It is definitely very stiff in the back. Handles a load like a HD truck.
Loaded ride is pretty good, empty ride is much better than a HD but the rear is much stiffer than stock.
You can really feel the stiffness when you are empty but left the max air pressure in the LT off road tires after towing. Can be harsh on bigger bumps.
I would do it again and too bad I didn't do it two years ago. Overall it is an improvement to the truck unless you value it as a luxury car first. Still very comfortable.
I think the RAS system was the best suspension improvement I have made, it made every aspect of the rear suspension better. Only it was not a complete fix for axle-wrap. A pity.
09-21-2013, 11:32 PM
#298
Senior Member
Thread Starter
Anything that stiffens up the springs in a way that helps the axle resist twisting will help.
BUT, for maximum effectiveness you need a spring or stopper to mount as close as possible to the mounting eyes and shackles that are at the ends of your longest spring.
Google for a picture or diagram of axle-wrap and you can see how the design on our F150s has too much space between leaf one and two.
BUT, for maximum effectiveness you need a spring or stopper to mount as close as possible to the mounting eyes and shackles that are at the ends of your longest spring.
Google for a picture or diagram of axle-wrap and you can see how the design on our F150s has too much space between leaf one and two.
09-22-2013, 01:27 AM
#300
Senior Member
I don't think people actually understand how much u-joints are designed to flex. It would take axle wrap close to this severe before feeling vibration:
Last edited by jonbar87; 09-22-2013 at 01:49 AM.