I'm hoping someone might have some insight into my issue. I just replaced my motor mounts (Brown Dog Rubber) and transmission mount (Rubber). Before this it ran pretty smooth, no real noticeable vibration, but the mounts were toast.
I took it out for a spin after the install and now once I hit about 25mph the whole Jeep starts to shake. If you let go of the steering wheel you can visibly see it vibrating up and down, the dash is shaking and the shifters as well. It lessens a little if taken out of gear, but does not completely stop.
If I stay on it up to about 45/50mph, it smooths out to the slightest of vibration, almost undetectable.
I am thinking it's possible the driveline changed a good bit and now my angles are off. Normally I would remove the rear drive shaft, put it in 4H and see if the vibration goes away. Problem is I'm locked up front now with manual hubs and solid shafts, so street handling when locked is borderline suicidal on front only.
Attached are a couple pics of my pinion angle in the rear. Any ideas?
Your pictures look, IMO, like the pinion angle at rest is too high. When you get underway, your pinion will actually raise 2° or so. This makes no sense to me because a new trans mount should have raised the trans and tc a bit. Did you buy the 1" lift MM from BrownDog? or are they stock height?
They are stock height mounts. I'm wondering if the pinion angle being a little high, coupled with a now more extreme bend at the cardan joint from the fresh trans mount is the issue.
The old trans mount was getting almost flat, so the new trans mount (as well as motor mounts) did in fact lift everything a bit just from the old stuff being so worn out.
What's strange is that when accelerating from a stop everything is as smooth as can be, until the dreaded vibration around 25.
Gotswap, I agree, that's normally what I would do. Unfortunately I'm locked up front, and trying to drive on that alone gets scary really fast. I have manual hubs though, so the front shaft is not spinning.
I'll probably just lower the pinion angle in the back and see what happens.
What hubs are you running in the front, assuming your profile is updated and you still have the d30. Just lock one side when you run front wheel drive only
I actually tried just locking one side, it didn't seem to like it much. Got about 20yds from the driveway and just backed up. It's the kit that used to be warn, and is now Yukon I believe.
The best thing to do would be to remove your rear shaft and really measure the angle of the rare TC yoke and the rear diff yoke. Then reattach your driveshaft and get the slope of the driveshaft. Take those measurements and find out what angle of the rear yoke nets the two rear most u joints in phase, and then subtract 2 degrees for the torsion load and shim to that. Kinda re do it all.
Your angles have changed so you'll need to rework your math. The vibrations sound really severe for the little bit you are out of phase. So it may not JUST be the driveshaft. But it could be just the driveshaft. Sorry to be so vague.
I went ahead and corrected the pinion angle...still the same issue. It feels like it's definitely coming from the front and I think I hear a slight miss at idle. But why so severe in a certain speed range and not common across a certain RPM range?
When am I gonna learn that my YJ doesn't like to be fixed, it always throws tantrums when I try any kind of preventative maintenance.
The last test drive I took I noticed a distinct clunk, which felt like it was under the trans tunnel. It only does it if I stab the gas pedal, but will do it every time I do.
Climbing under I can't find anything loose, driveshafts are solid, front end is new (ball joints, bearings, every steering component), very few miles since I did the SYE install and the t-case internals looked good. I'm starting to hit the wall where I run out of ideas.
OK so if you installed the trans mount first, and bolted it down, then lifted the engine up, and installed new engine mounts, there's probably some stress on your input shaft.
Get under there and loosen up the trans mount and torque arm bolt and I think you'll see your trans "settle back in" a little bit. Leave the trans bolts loose and get in and start the engine, rev it, then shut it down. retighten the trans mount and torque arm and take her for a drive.
Well, I loosened everything up and revved it a bit, still vibrates.
So I rotated the tires for S&Gs, no change.
Finally, I put the rear up on stands and ran it up to 25/30mph, started vibrating like crazy, meaning I narrowed it down to the rear. I put it in first and just let the tires spin, looked underneath and low and behold it looks as though my rear driveshaft is no longer true. So yes, my ujoints are good, but when spinning the driveshaft by hand I couldn't see the slight bend in it. I'm just not quite sure how it didn't present itself until after the MM and TM replacement, unless I somehow tweaked it in the process!!??
Nice investigative work. Is it possible that your driveshaft slip is not at the same point it was and now it is out of whack??? My front one would do that on me, went through a stock and then another stock one until I threw my hands up and bought an aftermarket DS.
That is very possible. I might mess with it a little bit, but will most likely run it down to the drivetrain shop that made it originally. Hopefully they can confirm my issue and see if there is any way to correct it, before going down the new driveshaft route!
Well, the driveline shop didn't seem to think there was anything wrong with the driveshaft, so I'm at a bit of a loss at this point. Now the jeep always vibrates and seems to just become more of a high pitched vibration at speed (55/60mph) instead of the shake around 25/30mph.
I threw on a hose clamp to see if I could inflict any change, no luck.
Have you checked to see if either your transfer case or rear axle yoke are loose?
I would also recommend checking your rear differential for anything weird. You could start by rotating the rear tires without the driveshaft in place to see if anything feels off but you may need to pull the cover.
After reading this, I was able to tighten the transfer case yoke a little bit, which seems to have improved things, but not quite cured. Thanks for the idea, as my mind is quickly turning to mush, so having others come up with ideas to try has been fantastic!
The rear diff seems good, no strange noises or friction.
At one point I even removed the rear wheels while on stands and still had the vibration around 30mph. I have no doubt a balance in the near future wouldn't hurt though
They are in phase, but thanks for checking, since it is usually the obvious things I can sometimes overlook. I like to over complicate things as a rule!!
Again, it does seem better and at a point I can deal with for a bit. I still don't think the driveshaft is quite right. The guy at the driveline shop was trying to be nice in giving me some ideas to try before throwing more money at it, but ultimately I will probably end up ordering a new one sometime in the future.
I can't thank you all enough for the input you've provided throughout this. I will be sure to update this when I hopefully cure it completely.
I did, probably been a couple of years ago now. I've run it through its paces and it has performed well so far. T-case seems to be running smoothly without the driveshaft attached, no strange noises, leaks or hang ups.
I had it balanced a while ago, but couldn't tell you if it was high speed or not. The driveline shop is the one that welded all the washers/weights to it that you see in the pictures. It just seems to have a little more movement than your average runout would explain.
I mentioned earlier about front drive shafts, that is what kept happening and causing front end vibration. Whether or not that is the only issue is still to be determined
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