Loud vibration around 40mph (1 Viewer)

[cruisergear]

I need help diagnosing a strong vibration at around 40mph in my Land Cruiser.

This vibration has been happening ever since we swapped in a small-block v8 into our FJ60. So it unfortunately manifested itself after introducing many new variables to the equation. (OME lift, new wheels, new tires, new motor, flywheel, 700r4 automatic tranny, adapters, driveshaft, etc)

The vibration is strong and loud and happens in the 30-40 mph range. Like really loud, hard to talk over it loud. The vibration only happens when under load (so it goes away when coasting in gear, or if thrown into neutral in that mph range.) The vibrations happens whether in 2H or 4H. Front hubs locked or unlocked.

It feels as though it is coming from the rear driveshaft, or at least it's coming from something behind the engine.

It doesn't feel like a tire imbalance and the neutral tests suggest it is not from the tires.

I'm fairly convinced it is the drive shaft. Or maybe torque converter? I'm just not familiar enough with what the symptoms would be if it were one of those two things.

Anybody have any ideas? Or tests that would help me narrow it down?

 

[NeverGiveUpYota]

Driveshaft angle? If you added a lift did you check the angle of the driveshafts were accurate from the tcase and back? U joints will cause vibrations too. I watched a bunch of YouTube videos on both those scenarios... lots of info out there on each.

 

[Cruiser Jimmy]

Change the u-joints and put the driveshaft in phase. I just finished up diagnosing a problem with your similar speed range. I changed the u-joints and put it in phase. Now it's gone.

Your torque convertor would give you bigger problems over what you've described thus far.

 

[cruisergear]

i'll check those things out, thanks!

 

[jfnall]

U joints

 

[cruisergear]

My 60 is currently stored at my parents house, but I got a chance to run over there today and take a look at the rear driveshaft. It appears to me that it's in time (that is assuming my understand of driveshaft timing is correct).

Also looked at the driveshaft angle, it seemed pretty mild to me, but again i'm no expert.

Tried to get some photos of the actual U Joints. It doesn't make a lot of sense to me that the U Joints would be bad. Since this entire driveshaft was brand new when the vibration started. It's a custom length one we had made for the 700R4/ Chevy 350 combo.

I'm kinda baffled by this whole vibration thing at the moment to be honest.

 

[cruisergear]

Also couldn't feel any play in the U-Joints in attempting to shake the driveshaft side to side.

 

[NeverGiveUpYota]

Don't quote me but I believe you won't get play on the rear w/o removing the weight off it.
Angle seems really high from mid to rear but again, I'm not expert either.

 

[Code Red]

Two suggestions:

(1) You often can't tell by hand whether the u-joint is bad. The vibrations you describe will often start before you can detect play by hand.

(2) It may be the photos, but it looks like the pinion yoke is pointing towards the output yoke on the transfer case. I believe that this is the proper set up for a double-cardan (a.k.a. "CV") u-joint, but not for standard ones like you have. The yokes should be parallel so that they run at the same angle to the driveshaft. If you have one end pointed up and the other end pointed roughly level, then that could give you vibration with a standard u-joint.

 

[too tall]

Looks like your rear pinion needs to tip down . Looks like it is pointing at the t-case . I'd measure each flange with the shaft off and see what the angles are . They should be close to the same . Maybe try adding a shim to tip it down a bit . If the vibration goes away under deceleration and is there under load then you need to tip the pinion down .

 

[cruisergear]

Was finally able to get underneath the 60 yesterday and really get into things. I took the rear driveshaft off and drove it around in 4wd and it's perfectly smooth and vibration free! I can't wait to fix this so that will be how it always drives! Took some measurements while the shaft was off. Also noted that the rear u-joint needs to be repalced along with the pinion dust shield and pinion bearing. I think all that vibrating from the shaft really did a number on my rear axle. While i have the rear axle apart i figure i might as well throw in a locker. Maybe even regear and do a locker up front too. We'll see.

But here's the measurements:

The angle of the T-Case output flange



The angle of the rear axle pinion flange



Does that mean I need 4 degree caster shims?

 

[Output Shaft]

As @Code Red mentioned, the transfer and pinion should be parallel. Also the driveshaft should be dynamically balanced at a driveshaft shop if the u-joints are replaced.

 

[cruisergear]

so in theory 4 degree caster shims would get them back to parallel status?

 

[too tall]

From what I can see you have 1.4 + 5.6 so 7 degrees to get it back to parallel . I'd try a 4 degree shim and see how it goes . I like to pick a spot where there is a bit of grade downhill so you can coast at speed then it is easier to see the effect of acceleration/deceleration on the vibration .

 

[Tin basher]

You actually want the pinion angle a few degrees lower than parallel
the pinion tips up under power
I'm thinking where you caused the problem is the engine is mounted lower than original
This lessens the transfer case out put angle
It should be 3 to 5 degrees down
So if you could space the engine mounts up
Or lower the transmission mount and get it to 3 to 5 degrees down
What you have now is \ / between transfer case and pinion and need \ \
The carb flange on a small block chev is machined on a 4 deg angle I always level the chassis and then level the carb flange and the angles are right on

 

[cruisergear]

From what I can see you have 1.4 + 5.6 so 7 degrees to get it back to parallel . I'd try a 4 degree shim and see how it goes . I like to pick a spot where there is a bit of grade downhill so you can coast at speed then it is easier to see the effect of acceleration/deceleration on the vibration .

Oh i think you're right. because it would be
1.4 -(-5.6) = 7

Good catch! That's why I left engineering school for art school LMAO.

You actually want the pinion angle a few degrees lower than parallel
the pinion tips up under power
I'm thinking where you caused the problem is the engine is mounted lower than original
This lessens the transfer case out put angle
It should be 3 to 5 degrees down
So if you could space the engine mounts up
Or lower the transmission mount and get it to 3 to 5 degrees down
What you have now is \ / between transfer case and pinion and need \ \
The carb flange on a small block chev is machined on a 4 deg angle I always level the chassis and then level the carb flange and the angles are right on

You may be right with the whole engine-mounted-too-low thing. Right now the rear output of the T-case is pretty much parallel to the ground. So if it's supposed to be pointing downwards towards the pinion that's probably where our problem originated.

If the engine is mounted too low, then caster shims are really just a bandaid solution over a different problem. But considering you're talking to a guy who doesn't have access to the tools it would take to raise the motor, would caster shims be an acceptable long-term solution?

And if a 7* shim would get them parallel again, should i go with something bigger like you said? maybe 9*? 10*?

Thanks for the advice!

 

[too tall]

I don't think you need to be exactly spot on for it to run acceptably . Not are you are going to find a 7degree shim let alone a 9 or 10 degree one ? I personally wouldn't run shims in the rear . I would use shims to find the correct/best angle , then I would cut the perches off and re-weld them on in the proper position . I know a lot of guys don't have issues with shims I just don't like them in the rear . All of that said , I would put a 4 degree shim in and see how it is .

 

[Tin basher]

I'm with to tall on not running shims in the rear
I have spit them out
And right now your t case flange is 1.5 facing away from ground like the bottom picture in that driveshaft diag someone posted so shims might mask the problem but I think it will still tear up ujoints.
Depending on how the engine is mounted
It might be as easy as adding spacers under mounts to lift motor up
Or spacing trans mount xmember down
Maybe if you can take some pictures of the motor mounts and trans x member

 

[doug720]

But as an test, call George (Orange45) and order a set of 6% shims. Cost is maybe $30, an hour of work, and you will know if you are on the right track. Make sure the u-joints are good also.

If it works, or makes it better, work on a permanent solution.

 

[cruisergear]

Just exploring all my options here. The vibration over the last 14k miles has worn out my pinion bearing so i'm going to be tearing into the rear end soon.

As Code Red said, what about the alternate solution of having a double cardon (CV) rear driveshaft? I have a double cardon on the front with no issues. I ran the rig in mini-van mode (4wd with the rear driveshaft removed) and everything is SUPER smooth and quiet.

Would you be concerned with the current t-case/pinion angles prematurely wearing out u-joints in a CV setup?