Vibration at take off

[CO2Ranger]

fyi, my 2021 does this. i just got truck earlier this month. with 1400 miles on it now they say there is a tsb. There is. It supercedes the one covering 2019-2020 models and now covers all 2019-2021 models. Same fix. TSB is 21-2136 dated April 30 2021. I have an appt for next month for that as well as the weird sliding/thumping i have coming to a stop and upon acceleration. SR told me they will do the tsb first to see if that fixes both issues. He also said since it's an fx4, it may be normal. um. no. it's not. Anyhow, I think based on my readings, it won't fix that part. I think that's an unlubed slip yoke spline, but who knows..

Please post if you find the TSB# and also what your outcome is.

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[silverflash]

Please post if you find the TSB# and also what your outcome is.

looks like i did post it?

 

[CO2Ranger]

looks like i did post it?

So you did. It's been a long day...

 

[Mitch65]

I had that vibration when the transmission is under load and the engine is at low rpm, sort of like the transmission is trying to downshift but cant. Usually occurred when starting up a hill at low speeds, like in a neighborhood or something when I am super soft on the throttle. I now know that when I come to a hill at low speed I need to give it a little extra or tap the gas to get the transmission into a lower gear.

I used to have a similar thing happen when accelerating around 90 degree corners such as a right turn at a stop light but that has gone away. Apparently the computer "learns" the driver's habits and adjusts the engine and transmission accordingly. Plus now that I am at about 900 miles things seem to be bedding-in and mellowing out.

The 21 I just bought last week has this exact same issue! It doesn’t bother me too much but just wanted to make sure nothing was wrong with the truck. Did you ever have any issues down the road with yours?

 

[CO2Ranger]

The 21 I just bought last week has this exact same issue! It doesn’t bother me too much but just wanted to make sure nothing was wrong with the truck. Did you ever have any issues down the road with yours?

Throw 140-210lbs of tube sand in the back of the bed. See what that does for you.

 

[Fitzmotor]

Has anybody set up the driveline according to known good practices, no more than 0.5 degree angle on the front shaft to the trans or T case, then equal working angles on the rear shaft.
That is a standard 2 piece driveshaft setup, I am close to that, but after lowering the back of the truck it looks as though the AU center support bearing with the higher mounting position is what I need, now I have the stock one flipped upside down and shimmed to the .5 angle the rear is close to equal angles, I do need to increase the pinon angle some to hit equal rear shaft numbers (it's almost good statically but under load it may get close to zero angle)
What is the joint at the back? is it a ball/cage type or the 3 big rollers with the torrington type needle brgs, like a CV joint, the reason I ask if it was a U joint it should vibrate the way it is but the truck is smooth with the pinon angle too low.

 

[VegasRanger]

My truck has the shutter at take off and vibration at highway speeds. 2021 4x4 3,700 miles.

Only mods: eibach struts set to 3" and 265/70/17 tires.

I am going to try adding the shims today to the center carrier and see what that does.

 

[navsnipe]

Has anybody set up the driveline according to known good practices, no more than 0.5 degree angle on the front shaft to the trans or T case, then equal working angles on the rear shaft.
That is a standard 2 piece driveshaft setup, I am close to that, but after lowering the back of the truck it looks as though the AU center support bearing with the higher mounting position is what I need, now I have the stock one flipped upside down and shimmed to the .5 angle the rear is close to equal angles, I do need to increase the pinon angle some to hit equal rear shaft numbers (it's almost good statically but under load it may get close to zero angle)
What is the joint at the back? is it a ball/cage type or the 3 big rollers with the torrington type needle brgs, like a CV joint, the reason I ask if it was a U joint it should vibrate the way it is but the truck is smooth with the pinon angle too low.

Do you have the take off shudder? Only the Tremor model has the CV joint at the axle pinion position, all others is a U-joint.

 

[kieefer]

I’ve got a new one.
On occasion, coming to a stop, mine will shake as if the brake rotors are warped.
Not every stop but does seem to be more common on downhill grades.

 

[JTDay]

I'm thinking this is another common symptom of whatever the problem is. Mine does the same thing.

 

[Fitzmotor]

I dont have any shudder or vibration, I spoke with a couple of driveshaft shops, they said to treat the CVJ joint as they called it just like a U joint as far as working angles.

Got a good lesson on the three different ways to set up 2 piece drive shafts, gee that's not confusing, and I also got the "if it doesn't vibrate leave it alone" no matter what the angles, but I am unable to do that, I will probably go with the 3 equal angles method vs the 1 joint straight method.

 

[navsnipe]

I dont have any shudder or vibration, I spoke with a couple of driveshaft shops, they said to treat the CVJ joint as they called it just like a U joint as far as working angles.

Got a good lesson on the three different ways to set up 2 piece drive shafts, gee that's not confusing, and I also got the "if it doesn't vibrate leave it alone" no matter what the angles, but I am unable to do that, I will probably go with the 3 equal angles method vs the 1 joint straight method.

If I didn't have any take off shudder I would have never gone down the rabbit hole of learning about drivelines. My suggestion to you is if you have no issues don't screw with it. If you do, keep meticulous notes to get back to where you are now if your course of adjustments goes awry.

 

[Fitzmotor]

Yeah, I can't leave it alone, the pinon angle is too low (meaning it's not pointed down enough) it may cross over center on accell or with a heavy load.
If I keep anymore notes I'm going to have a book, but I have full adjustability, I have flipped over the center support bearing and raised it as a temporary setup to play with the angles, I lowered the rear of the truck 1.5" and now it's just the fine tune of the angles, but I need to source a global center support bearing, the AU ones are different and I think I have my truck close to the global ride height, instead of the NA stink bug look.

 

[Fitzmotor]

I have tried all 3 known methods for driveline angles, to my surprise the 3 equal working angles had a slight vibration.

The zero angle at the front joint (almost, only 0.5) with equal at the 2 rear joints had no vibration.

The zero at the center joint (same minor 0.5, but is supposed to act like a single shaft) with equal angles at front and rear I think had very minor vibration, hard to tell.

I also tried zero at the rear joint and equal at the other 2 had no vibration, but that is the CVJ, a regular U joint should have vibrated.

Here is the final ride height, 37" at all the wheel openings.

 

[Shoran12]

Well. I think I may have found the solution to the vibration issue and confirmed my suspicions in one fell swoop. Keep in mind testing is very limited (less than 30 miles) and I am not suggesting that anyone do this. What I am saying is that I tried it and the initial results are so far, amazing.

Based on the previously mentioned kit I went looking for uniform steel shims that could be used to lower the carrier bearing. After pulling out one of the carrier bearing bolts to see how thick they are I decided on picking up a set of old school alignment shims. These come in thicknesses from 1/64 - 1/8 per shim. The AU kits recommend starting with one shim washer that is 3.9mm and converts to 5/64 and then increasing it until the vibration is gone.

Installation time took about 2 min. total. It honestly took me longer to get my tools out than it did installing the shims.

You will need a similar shim kit, a 15mm socket, 6 inch extension to clear the drive shaft and a ratchet. Wanting to be conservative because the rear suspension is at stock height, I started out with just a pair of 1/8 shims (3.175mm). I backed each carrier bearing bolt out about 4 or 5 turns, lowering the shaft just enough so the shims would slide in-between the mount and bearing. They slid in and fit perfectly around the bolts with a satisfying clink and almost no slop. Tightened the bolts back down and took the truck out for a test drive.

To my amazement the vibration was significantly reduced almost to the point of being very difficult to feel much of any at all. During the test drive I stopped at Home Depot and picked up supplies I needed to build a fence for my chicken run. This added about 500 +/- pounds of weight in the back of the truck lowering it about 1.5" from stock. Driving with the load there was no absolutely no vibration at all when accelerating from a stop. So I took it up on the freeway and nothing. No vibration at 65-75mph either.

I got home unloaded and added an additional a pair of 1/32 shims to the existing 1/8 shims to bring the total adjustment to 5/32 or 3.96mm. Went out for a second test drive and it felt as buttery smooth off the line as it did with the load. There was absolutely no vibration at all. Easy acceleration, hard acceleration, freeway speeds, nothing. It has never been this smooth off the line. It's almost like driving a different truck now. I would put a camera on the underside to film it to confirm the vibration is totally gone if I had one that would work for that.

If anyone should decide to shim their carrier bearing in this manner, I strongly advise caution with going anything more than 5/32. The stock bolts are not that long and would not leave enough threads to properly clear the mount when shimming it any more than 5/32. If you need to add more than 5/32 you will need to look at getting longer bolts. Also the alignment shims also do reduce the contact area between the bearing and the mount. It's probably fine, but I'd feel better getting something better suited for this, like square cut shims with a center drilled hole.

Bottom line is this works for me and as far as I am concerned it pretty much confirms my suspicion that Ford NA added the rear leaf spring shims and possible a taller mount, effectively lifting the rear of the truck by 1.5-2" compared the the AU version altering the geometry of the drive line. They then didn't account for the change in the angle on the drive shafe and as a result introduced a minor vibration during acceleration.

Interesting. I was thinking about switching my leaf springs out for the global leaf springs and I’m wondering if swapping to the global multi leafs might cause vibration? They are a bit taller so I would need to use shorter bump stops so I don’t limit travel.

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