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Allow me to preface this by saying this is not my truck, it belongs to my father but I use it almost as often as he does, and only I have noticed this problem. It started a few months ago, at around 55 mph it would shudder gently, every few seconds. At 50 it would stop, and at 60 it would stop. The problem gradually worsened and now it does it at 55, 60, 65, and 70. It also will sometimes do it at 45 and 50, but not nearly as often. The shuddering is also becoming stronger. The longer you maintain the speed, the more intensely and the more frequently it shudders, eventually becoming one constant shake. A deviation in speed or revs of even 2 mph or 200 rpm will make it stop. It generally happens when you have maintained one of the above speeds for over a minute, and only once the RPMs have settled to about 1500-1750. This truck runs and drives like brand new in every other way, including when accelerating and decelerating. All of the above leads me to suspect the overdrive. On the other hand, a trusted friend of mine who rode in the truck and experienced the shaking believes that the torque converter is going out. He said that he had to replace one on his old F-150 because it was having similar symptoms of only shaking when the overdrive engaged. I’d like more opinions though, so I thank you for any and all help you can provide.
Some stuff you should probably know:
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The transmission stuff I added helped a bit, but not as much as I was hoping. I have definitely pinpointed the shuddering as a transmission or transfer case issue though, because when it happens, the 4WD lever oscillates. I unfortunately have nothing else to report.
I’ll get the trans fluid changed when I can, and hopefully it stops then. If not, I’ll have to assume its the transfer case. I guess I could try driving it in 4WD, and see if any new problems make themselves known, which would narrow it down. The 4WD hasn’t been used in a couple years, so I wouldn’t know if there was something wrong with it.
I don’t think you can conclude that it’s a transmission issue just yet, perhaps try a power brake test. Find a safe spot where you won’t hit anything, put your foot firmly on the brake and put the truck in drive, push the accelerator to the floor and hold it for about 5 seconds or so, if it does this smoothly and doesn’t vibrate the engine is most likely OK but if you notice a miss or other performance issue then I would look to the engine for the source of the problem. If the engine is having an issue it can shake and move the entire drivetrain including the transfer case, don’t assume because you see movement there that it’s coming from the transmission or drivetrain because it could just as easily be the engine.
All signs lead to the engine being fine because it only shudders when maintaining certain speeds. You can rev the engine all you want, whether while moving or not, and it doesn’t shake one bit. I nearly redlined it accelerating from 20 up to 70 and it’s as smooth as you could ask for. I haven’t actually floored it from a full stop before though.
That’s good news and we can probably take that off the list of probable causes however I would focus on final drive before the transmission such as the drive shafts, their joints and the rear end as in my experience these things are more likely to be responsible for a vibration than the transmission would. I can’t remember but have we ruled out a tire balance or tire problem yet?
Yes we have, since going that speed isn’t a problem, but maintaining it for a few seconds is. I also had the rear end on jack stands and it was still doing it. I read on a Jeep forum that someone with a close in year Grand Cherokee with the exact same symptoms as me, and their transfer case ended up being the issue. Both being Chrysler products, (and the transfer cases possibly being the same?) I’m a little bit suspicious of that still. Thanks again for all the help.
The transfer case is possible but what you describe is referred to as ‘resonance’ which is something that happens at a given RPM on a rotating part, if it’s out of balance or has some other issue it will manifest gradually as you describe as the resonance will increase the longer you maintain the given RPM that the condition occurs. Honestly I really don’t have a test for a transfer case with this issue and it’s a big expensive job to just do on suspicion, you would need to eliminate the drive shaft and the differential first in my opinion. The only thing inside the transfer case is a couple of gears and a chain and the mechanism to engage them, perhaps if you changed the fluid in the transfer case and then rechecked for the symptom, if it changes or goes away this could point to an issue there, you could also remove the front drive shaft to see if things change (which actually might indicate a problem with the front drive shaft or front differential come to think of it), I don’t think you could remove the rear without loosing all the fluid though.
Interesting point, I hadn’t considered a resonance problem since we eliminated “death wobble” as a cause. As my physics education reminds me, resonance is a particular pain in the neck to fix when it’s causing a problem. Even a nearly immeasurable shift in any of the rotating parts off center could cause this. I’ll inspect the drive shaft and all u-joints along it tomorrow and look for anything out of order.
I also have a new development: You can’t shift the transfer case into 4L. You can move it from 2WD into Neutal and 4H, and back to 2WD, and they all engage. Regardless of the transmission being in P, D, R, N, or low range, trying to shift into 4L just grinds. Conventional wisdom says that this is probably related. This would suggest to me that there is a gear or clutch in there which isn’t disengaged, and should be. And since the truck wouldn’t be going anywhere near 45 to 60 in 4L, it isn’t playing nicely with those speeds, and may resonate with another part when they are maintained. I can go exactly 30 or 35, or anything under that, all day long any day of the week, and it vibrates as much as a car with a quarter of the mileage.
I don’t know if I would go there just yet, in my experience 4L is not a gear that gets used often and as a result the linkage has a tendency to rust up, sometimes so much you can’t move the lever at all, in short it could be the linkage and not the transfer case itself. Once again there really isn’t much in there to go wrong as it’s really just a couple of big gears and a chain. I’m not saying it CAN’T be the problem but rather it’s not high on the list of probable causes in my opinion. Resonance is difficult to track down but checking the rotating assemblies is a good place to start. Keep us posted.
At this point the only assumption I can make is that the shuddering issue is somehow related to my blown plenum gasket discussed in my other thread. I believe its possible that the engine only acts up while under load, and this is why it didn’t shake in neutral or on stands. Also I hauled a relatively heavy wooden picnic table for a friend the other day (it didn’t quite fit into his Prius lol) and the truck didn’t shudder at all the whole time it was carrying the weight.
Quoted From LJ11194:
At this point the only assumption I can make is that the shuddering issue is somehow related to my blown plenum gasket discussed in my other thread. I believe its possible that the engine only acts up while under load, and this is why it didn’t shake in neutral or on stands. Also I hauled a relatively heavy wooden picnic table for a friend the other day (it didn’t quite fit into his Prius lol) and the truck didn’t shudder at all the whole time it was carrying the weight.
now i just found this thread and read almost the hole thing WOW lol anyways now i see you stated it is burning oil very fast and the ping and that slight vibration all leads to a text book case of a blown plenum gasket.
just do as i said in your other thread and check for oil at the bottom of the intake (inside). i would bet you find oil film. if so change the plenum gasket and replace the PVC valve while you are at it. please update us.
Thought I should update this old thread. When it came down to it, the truck still technically belongs to my dad and he didn’t want me tearing the engine apart, so it’s sitting at our local mechanic’s shop right now. It should be done by the end of today and I’ll let you guys know if the misfiring from the plenum gasket was, in fact, making it shake.
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