Vibration on Acceleration (1 Viewer)

[Options20002001]

Hey guys,

I've got 193k on the truck. Recently it has started vibrating on acceleration. It almost feels like the tires are dragging something. It also feels like it's coming from the rear. It only happens when it first starts accelerating and goes away at about 15-20 mph. Also, it never happens in reverse. It doesn't happen very often; only about 4 times in the past month and I drive it everyday. Usually, I can make it go away when it does happen by throwing it in reverse and backing it up for a little bit and then throwing it back in drive and driving forward a little bit. After 1 or 2 cycles, it's usually gone. My first guess was a driveshaft issue, probably the u-joints, but I'm not sure and don't know how to check. I also recently greased the shafts but it still happened. If it helps, it has a 2.5" OME lift. Lastly, the brakes recently have been noisy as well if that helps too.

Thanks for any help guys.

 

[Options20002001]

Also, in case it is brake related, I've replaced calibers and upgraded to slotted rotors in the recent past.

 

[97CruiserJoe]

Also, in case it is brake related, I've replaced calibers and upgraded to slotted rotors in the recent past.

You might want to check your engine and transmission mounts. They could be bad. I had similar symptom on another vehicle and it was a bad engine mount.

 

[baldilocks]

How old are the drive shaft U-joints? Does it ever vibrate immediately after releasing the accelerator pedal? U joints are a cheap place to start unless you find some obviously loose hardware somewhere in the drive train.

 

[Options20002001]

The u-joints have never been replaced. I've heard they should last at least 200k miles but I'm pretty close to that so I may change them. I gave everything a good shake and couldn't find anything loose. As far as mounts go, I'll look into that. I'm just wondering why it never happens in reverse and only happens (rarely) if I'm giving it gas at really low speeds. I just want to stop it before it becomes an issue or have something break while I'm wheeling.

 

[Options20002001]

I had the diffs regeared to 4.88's about a year ago. Does this sound like an issue with the rear diff?

 

[beachcomberspi]

U joints. My .02

 

[DARKNESS]

Sounds like your parking brake isn't releasing. I'd follow the FSM procedure to set up the parking brake properly.

 

[Options20002001]

Sounds like your parking brake isn't releasing. I'd follow the FSM procedure to set up the parking brake properly.

I'll look into the hand brake as well. Usually the hand brake doesn't do much. It can barely stop the truck from idling forward and is completely useless in low gear. Could it really be causing the vibrations?

 

[BILT4ME]

The u-joints have never been replaced. I've heard they should last at least 200k miles but I'm pretty close to that so I may change them. I gave everything a good shake and couldn't find anything loose. As far as mounts go, I'll look into that. I'm just wondering why it never happens in reverse and only happens (rarely) if I'm giving it gas at really low speeds. I just want to stop it before it becomes an issue or have something break while I'm wheeling.

I'm guessing Universal joint on the drive shaft. Very frequently they can be heard when first put under load or at lower RPM. Then when they get faster the frequency goes up so we can't hear it anymore. Check your U-Joints and slip-yoke. As always, do it with the drive line UNLOADED. Blocked, Chocked, and in neutral.

Block and chock the wheels, put the transmission in neutral and get under the truck.
Try to rotate the DS back and forth. You will feel movement in the ring and pinion as well as the transfer case. This is normal to be a few degrees of movement. Watch for movement between the DS and the cross of the U-joint.
You may also feel movement in each of the u-joints. If you then move EACH end of EACH DS, move it up and down, and side to side, perpendicular to the cross in the U-Joint. You should have NO visible movement here. If you do, it is a bad u-joint. Remove and replace.

Grease your slip-yoke and U-joints when UNLOADED. After you are done on the slip-yoke, depress the ball on the zerk to relieve excess grease pressure. Also make sure the center hole in the end of the yoke is clear to allow grease to push out or air to get in during flexing and driving.

When you grease the U-joints, only put in 3-4 pumps. Do not get carried away and pump grease until it splooges all out. Doing that allows other contaminants to get in because the seal gets blown out.

 

[DARKNESS]

You said it felt like the tires were dragging and that the problem was in the rear. The parking brake affects the rear wheels only, so that would make sense. When I've had the parking brake lock up in other vehicles, especially when cold, rocking back and forth sometimes
frees it. That's consistent with what you describe. Also, if you lock your rear wheels (or just force them to turn slower) and drive you're probably forcing your viscous coupler in your center differential to turn. I don't think that would cause vibration, but I suppose it's possible, especially if it's starting to go bad.

I'm not saying it isn't u-joints, it very well could be. However, u-joint noises shouldn't go away by driving forward and backward a few times. Also, I don't see why a sloppy u-joint would give the sensation that you're dragging your tires.

 

[Options20002001]

Thanks for the advice on checking the u-joints and explaining why it might be the parking brake or viscous coupler in the center diff guys. I'll see if there is anything wrong with them tomorrow.

 

[Options20002001]

Just an update. I changed the rear drive shaft (and therefore the u-joints). The vibrations went away for about a week and now they're back. I haven't gotten around to changing the u-joints for the front drive shaft yet. I think a better way of describing these vibrations would be to say that it almost feels like there's something dragging. It feels like something is dragging in the rear. It seems to be torque related. It only happens if I take off very quickly from a complete stop. I think it's torque related because it doesn't happen if I put it in 2nd start no matter how fast I try to take off. This may also be why it doesn't happen in reverse; there is less torque in reverse than in first gear. I don't think it's transmission related because it can happen even in second gear if the t-case is in low. I did get the diffs regeared to 4.88 which adds to the torque but that doesn't kick in until you reach the diffs. I'm beginning to worry that it could be a problem in the diffs themselves. I also don't think it is the hand brake that is dragging because my hand brake is pitiful. It can't even stop the truck from idling forward. Could it be the rear brakes dragging due to the LSPV valve or something? I'm completely stumped guys. Any help is appreciated.

 

[Options20002001]

Going along with what I said earlier, I can completely avoid this dragging/vibrations from happening if I just take off slowly from a stop or drive in 2nd start. I already drive it like it's a tractor so that's why it doesn't happen often. I'm just worried that it's going to get worse until it happens all the time.

 

[Dave 2000]

A couple of things come to mind here. First the drive shafts, vibration can come from various places, out of balance, seized UJ, play in the slider joint, over greasing the slider joint, mounts and so on.

To check the driveshaft it is not sufficient to simply try rotating back and forth the looking for play in the UJ. Lack of lubrication can semi seize the joint disguising play. Sometime greasing the joint loosens it off and the vibrations are worse. Loosing a balance weight would be obvious as you would see a pattern where it previously was fixed.

You need to remove the shaft and rotate the joints by hand, you are looking for a completely smooth action from moving the joint from one side to the other. A slight 'bump' or looseness around the centre (where most wear takes place) of movement is indication the joint is toast, greasing and manipulating can actually make the vibration worse, the worn needle bearings originally rusted/seized in position are now moving around freely.

Over greasing the slider joint is a classic 'I greased the shaft and now have a vibration' claim. Over greasing the slider creates a hydraulic ram effect, this removes the shafts ability to shorten and lengthen according to drivetrain movement, left unattended often results in the bearings in the differentials and transfer boxes being destroyed.

Unfortunately owners are often their own worst enemies and the example of this is:

PM prior to a long journey see's the shaft getting a good greasing, perhaps the slider gets too much and along the journey a vibration sets up. Due to time/location/cost/whatever the vibration is left. Eventually the driveshaft is repaired/replaced and the vibration is still there, the cost of the shaft replacement being declared as money wasted, in reality it was not but, the bearings in the T/box and/or differential have been damaged, you end up chasing your tail.

Another thing I have seen on my own car, I had adjusted the handbrake and everything seemed fine until I took it on a long run, it was as I applied the brakes after driving about 20 miles, there was a shuddering from what felt like the rear of the car, the handbrake had not released completely on one wheel, this heats the drum/disc combo and had distorted it. I guessed what had happened by the smell of the hot linings, A quick skim on the lathe and a readjustment all was well.

I would put a dial gauge on the rear discs and look for any run out before spending any more money. You could also remove the front or rear shaft and lock the centre diff, you could then
drive around on the one shaft to help narrow down any problems.

regards

Dave

 

[Options20002001]

Thanks for the reply Dave. So you think there may be too much grease? I replaced the rear drive shaft but maybe I did put too much. How much should it put? I will try to drive around with one shaft to see if I can narrow down the problem. Do you think that the hand brake could be the problem even when it is practically non functional? I haven't gotten around to adjusting it mostly because the threads on it seemed a bit confusing to me.

Thanks

 

[Dave 2000]

I have never seen the right amount of grease quoted, in the absence of any hard facts to how much grease should go in and unless someone comes up with the correct amount then I would do the following. Measure and record the amount the slider/yoke is protruding from the main shaft, then disconnect the slider end from the transfer, then mark the slider inner and outer so they can be put back 'in phase' at a later date, then pull the yoke with the slider right out and empty all the grease out. Then with grease just on the splines I would reinsert the yoke assembly remembering to line up the marks you made earlier sliding it all the way home. Now start to pump in the grease, as you do you will see the joint start to move outwards under the pressure. I would stop when the slider is out one inch shorter than your original measurement before disconnecting.

Now when you fit you will have to pull the shaft out a little to get the flanges together but, you are guaranteed it will not be under hydraulic pressure and there is sufficient grease in there to do it's job, do the same for the front shaft.

regards

Dave

 

[Iceaxe]

Hey guys-
Just wanted to document here that I had the exact same symptom show up- vibration that appeared to have a certain harmonic between 35-40 mph, then again between 65-70 mph, best felt while accelerating under power. Even better felt while going uphill. Also felt while on the trail going up a serious incline. Difficult to pin down- thought initially it was a wheel bearing, then thought it was the drive shaft... then turned out to be a U joint gone bad.