Driveshaft phasing

[12V71]

"During climbing: says to me "under load."

While I have limited background in multiple driveshafts, I would look at anything that can allow changes (deflection) when under load.

To me, anything with rubber involved, like maybe the hanger bearings?
If it does it slow speed under load (engine braking downhill) I'd also suspect the same.

ADD Side note: I have a trailer that transfers "hopping" to the truck at around 35-40 mph.
I fixed it by not driving in that speed range

ADD side side note: I'd be super curious to mount cameras pointed at various parts of the driveline to see what goes from smooth motion to erratic (if it's something that can be seen). Would be cool to see something simple like axle hop (rear axle input bouncing up and down from internal binding) or the driveshaft starting to swing wide in the mounts or something.

"Under load" says brinelled journals on on cross or another to me. Maybe. One u-joint is new, the other two are originals that have been removed and re-installed. They may feel smooth with hand pressure but could still be bad under load. I see a lot of that on the big trucks.

[whtbaron]

Hmmm.... it's been apart a couple times by the sound of things... what if just one needle fell out of one of those Ujoint caps?

[CAVEMANN]

A very few machine shops near at all. The few there are seem to specialize in something else. Think of it, I might want to ask Zap about it. He has a smaller facility these days, but might point me the right direction.

To be honest, I doubt balance is the cause. Logic says a balance issue would get worse at higher speed, this comes on at low speed, especially climbing.

And no, I'd be happy to pay someone to solve the problem.

Balance will usually come in at different amplitudes depending on the natural frequency of the part, typically vibration can almost completely disappear between multiples of rotational speed, (this is on fixed speed equipment), but it should act similarly, if you actually had someway to measure amplitude you could get an idea. Vibration can cause a phase shift in the part, you could have 8 mils of vibration amplitude at 3600 rpm's, and that vibration can increase or decrease in even multiples or divisible's of the primary rotational rpms, these are known as a critical pass one at 900 rpm's should be 1/4 amplitude , another at 1800 should be 1/2 amplitude, but NOT ALWAYS, does it work that way, one pass at rotational, another double speed etc., the passes at any multiple or divisible may be equal, 1/4, 1/2 equal to or double, quadruple etc., without specialized equipment you can't see these passes. but it's pretty cool when your equipment can plot/graph each phase/pass. If the equipment doesn't come out of it's pass at rotational speed then the equipment will set up a harmonic condition and will self destruct sooner. I'm sure the same thing happens to some degree in a drive shaft. Since you have established that it occurs at many speeds or continuously means that about the only options will be to change driveline angles or rotational mass, you should probably take the shafts to have them properly balanced. I hope my post made some sense because it's kind of hard to accurately describe vibrations and how they come in and go according to speed and amplitude. Also be aware that I've forgotten a lot of it as it's been about 26 years. It may be a bad/binding U-JOINT TOO.

[MinnesotaDave]

"Under load" says brinelled journals on on cross or another to me. Maybe. One u-joint is new, the other two are originals that have been removed and re-installed. They may feel smooth with hand pressure but could still be bad under load. I see a lot of that on the big trucks.

I was wondering about the re-used U-joints as well.

[danielplace]

The rear section has no evidence it was ever balanced. The front section is new, the builder says he has never balanced one. It turns about 2000 RPM at 50 MPH not like a car that might turn 4000 RPM. This shake begins at a much lower speed, maybe even under 1000 RPM.

The bold may be your problem. Not running true. But I recon if you say it is slow turning and this vibration doesn't seem to match that speed. ??

Jack it up and spin the driveline like your driving it while studying it. Certainly the vibration must be able to be honed in on somehow. Something under there is going to be visibly vibrating if it is that noticeable driving it.

[Willie B]

"Under load" says brinelled journals on on cross or another to me. Maybe. One u-joint is new, the other two are originals that have been removed and re-installed. They may feel smooth with hand pressure but could still be bad under load. I see a lot of that on the big trucks.

Would "brinelled journals" be visible when disassembled? Or should they be replaced as a precaution?

I believe I will block it up securely & run it at speed to see if it shows up.

[whtbaron]

Hopefully that works for you, but if you say it occurs more under tension it may not....

[Willie B]

Yeah, I fear it might be the case. Rain is upon us here, expected for three days. I used it late afternoon, I had a 16 foot piece of 1/2" galvanized pipe to move. Believe it or not, it was the easiest way to move. I'm wracking my brain, what is causing this? I went to the steepest gravel hill I know. People driving this road aren't very sharp. Almost all give it throttle going up. It is always washboard! I went up slow, and got the same thing I sometimes got with the previous truck, the driveshaft becomes a torsion spring. It loads & unloads. The fix for the old truck was shift up a gear, it had ten to choose from. This truck has four with torque converter. I get the nagging thought my driveshaft is winding up like a spring & unloading. Everything goes harmonic.

[ezduzit]

...There are no flat surfaces to measure an accurate transmission angle...

Hanging a bracket off a bolt, using V-blocks or magnetic bases, etc, there is always a way to do it.

Check runouts using a dial indicator. Also you might try using a strobe light while running in gear.

[CAVEMANN]

If you can find a way to trigger a strobe from the drive shaft & return to the same speed each time you could balance it by the method we used. Base run will establish a phase angle, hang a trial weight & it would induce a change in angle, it would be trial & error without an accurate way to measure the amplitude, but could be done.

[12V71]

Would "brinelled journals" be visible when disassembled? Or should they be replaced as a precaution?

I believe I will block it up securely & run it at speed to see if it shows up.

Yes, they will show wear lines on the cross journals from the needles in the caps, if you take them apart grease them well first to keep the needles in place.

One other thought, you took what, two feet out of the wheel base? You might try shimming the carrier down about one inch, sounds goofy but it could help. I really doubt with the Allison and convertor that you are getting a harmonic twist, convertors are just to smooth and "soft". I could see that with a stick, had a similar GMC with a 5 speed and the 8.2 engine that would audibly "twang" the driveline in lugging situations.

[Willie B]

Yes, they will show wear lines on the cross journals from the needles in the caps, if you take them apart grease them well first to keep the needles in place.

One other thought, you took what, two feet out of the wheel base? You might try shimming the carrier down about one inch, sounds goofy but it could help. I really doubt with the Allison and convertor that you are getting a harmonic twist, convertors are just to smooth and "soft". I could see that with a stick, had a similar GMC with a 5 speed and the 8.2 engine that would audibly "twang" the driveline in lugging situations.

I took a foot out of the wheelbase. The carrier was & is mounted to the same crossmember, it got moved forward also. The big fire pump did sort of serve as a divorced transfer case. A short shaft powered it, a two piece shaft was behind the pump. The new 4' section of shaft replaced two sections of shaft & fire pump. The carrier bearing happens to give no angle to the shafts. I know this makes for short U joint life, but I'd live with that if it otherwise worked OK.

[MinnesotaDave]

This thread reminded me there are videos of this stuff

[whtbaron]

I was looking at those and didn't see one for a 3 U joint system. I suspect the culprit is one of 3.... 1) poor or improperly installed U joints , 2) as he shortened the wheelbase a foot, the angle between the hanger bearing and the rear joint has increased, and the hanger will need to be lowered to get the front to rear angles closer to being the same, 3) the new shaft is either welded slightly crooked or off balance.

[danielplace]

I was looking at those and didn't see one for a 3 U joint system. I suspect the culprit is one of 3.... 1) poor or improperly installed U joints , 2) as he shortened the wheelbase a foot, the angle between the hanger bearing and the rear joint has increased, and the hanger will need to be lowered to get the front to rear angles closer to being the same, 3) the new shaft is either welded slightly crooked or off balance.

He only made one driveshaft I believe and it wasn't the rear one.

I think he took the length out of the driveline where he replaced the two driveshafts going in and out of the pump with one shorter one than the length of what the two and the pump added up to.

Not positive but if that was the case it wouldn't have changed the rear drive angle.

That will only cause light oscillations. If you look at most any of the lifted trucks the angle of the rear end never matches the drop/angle of the transmission and it is barely noticeable in big 4 wheel drive truck with big wheel/tires. All the lift kits are designed that way.

Yes we know both ends needs to go into rear and transmission at similar angles to work properly but it is not set in gold by any means. It isn't always even possible to keep them at same angles and if you did it would have tragic outcome even worse. There is definitely a point when you have to angle the rear up at the transmission to get the driveline to work at all.

Just saying it doesn't seem like a forward/aft driveline oscillation issue to me. Something different completely. That would be more of a high speed vibration usually I believe.

[Willie B]

He only made one driveshaft I believe and it wasn't the rear one.

I think he took the length out of the driveline where he replaced the two driveshafts going in and out of the pump with one shorter one than the length of what the two and the pump added up to.

Not positive but if that was the case it wouldn't have changed the rear drive angle.

That will only cause light oscillations. If you look at most any of the lifted trucks the angle of the rear end never matches the drop/angle of the transmission and it is barely noticeable in big 4 wheel drive truck with big wheel/tires. All the lift kits are designed that way.

Yes we know both ends needs to go into rear and transmission at similar angles to work properly but it is not set in gold by any means. It isn't always even possible to keep them at same angles and if you did it would have tragic outcome even worse. There is definitely a point when you have to angle the rear up at the transmission to get the driveline to work at all.

Just saying it doesn't seem like a forward/aft driveline oscillation issue to me. Something different completely. That would be more of a high speed vibration usually I believe.

You are correct, I don't know for sure this is driveshaft produced. I've explored many other possible causes. I've even wondered if it might be like many anecdotal stories of GM big block gas engines where some are self balanced, others require weighted vibration dampeners, or flywheels.

I bought this truck, drove it perhaps 50 miles with no evidence of the shake I now have.

I look to what has changed:
The fire body & tank full of water is gone.
The frame has been shortened 15".
The axle & carrier bearing are moved forward 12".
The pump is gone, replaced by a new section of driveshaft.
I drove it when the rear axle was first reinstalled with the newly configured driveshaft. It then had no dump body, very little weight in rear. I was alarmed about the shake, hoped it would improve with weight of the dump body.

Since, I have presented the issue to everyone I hope could fix it. Someone in another state suggested John Rouse. He is well known throughout VT as an expert. He firmly believed front tires were the fix. New front wheels & tires made no change. He then balanced rear tires, no change.

I had once studied driveshaft phasing when 33 years ago, I bought a 1956 Dodge Power Wagon that was unusable. The fix was absolute, learning how wasn't easy.

The symptoms of this truck feel very similar.

[MinnesotaDave]

This will sound dumb...but have you had anyone follow you in a low car (visibility) to try and find the shake, tire hop, wobble, or anything else that looks unusual?

[danielplace]

Doesn't sound dumb at all. Look at all he has done to fix it already. Nothing sounds dumb at this point. Lol.

You can also utilize a go pro camera under the vehicle aimed different directions until you maybe spot something.

[CAVEMANN]

This will sound dumb...but have you had anyone follow you in a low car (visibility) to try and find the shake, tire hop, wobble, or anything else that looks unusual?

That doesn't sound dumb at all, in 1976 I was working for a CHEV, OLDS, & PONTIAC dealer & we had a customer that had bought a new Pontiac, I think it was a Le Mans, & it had a tremendously loud rattle like the entire car was literally falling apart, every peson in the shop had gone over that car with a fine tooth comb & we couldn't find anything. We finally got 2 of us together & took it for a ride or the roughest road in town, One guy got out & walked a couple hundred yards up the road and the othe drove the car slowly toward him, that revealed the problem quickly. The entire front end sheetmetal, core support and everything related to the front body was bouncing around like a basketball. Back at the shop we found a core support that had NO bushings, it was very hard to see where they were supposed to be, we ordered the bushing and installed them and the car was finally fixed.

[bcguide]

I fixed a similar problem on a friend's ford, after he had changed 2 ujoints. A coil had quit working.
If the shake goes away with no load on the drive line it is probably not a drive line problem.

[Willie B]

This will sound dumb...but have you had anyone follow you in a low car (visibility) to try and find the shake, tire hop, wobble, or anything else that looks unusual?

We will try that today.

[Denis G]

You are correct, I don't know for sure this is driveshaft produced. I've explored many other possible causes. I've even wondered if it might be like many anecdotal stories of GM big block gas engines where some are self balanced, others require weighted vibration dampeners, or flywheels.

I bought this truck, drove it perhaps 50 miles with no evidence of the shake I now have.

I look to what has changed:
The fire body & tank full of water is gone.
The frame has been shortened 15".
The axle & carrier bearing are moved forward 12".
The pump is gone, replaced by a new section of driveshaft.
I drove it when the rear axle was first reinstalled with the newly configured driveshaft. It then had no dump body, very little weight in rear. I was alarmed about the shake, hoped it would improve with weight of the dump body.

Since, I have presented the issue to everyone I hope could fix it. Someone in another state suggested John Rouse. He is well known throughout VT as an expert. He firmly believed front tires were the fix. New front wheels & tires made no change. He then balanced rear tires, no change.

I had once studied driveshaft phasing when 33 years ago, I bought a 1956 Dodge Power Wagon that was unusable. The fix was absolute, learning how wasn't easy.

The symptoms of this truck feel very similar.

Why didn't he take out the driveshaft(s) and put them on his machine? Would they not fit his balancing machine?
It doesn't sound like he did due diligence and maybe his reputation is not deserved.

I'd try Gilbert Driveline in Manchester NH next, but then I'm in another state with no chips in the game.

[farmersammm]

Like 12V71, I'm leaning towards a bad U joint. Disassemble the thing, all shafts, and check if the cross thingys turn freely, without binding. Sometimes even a pry bar can't isolate a bad u joint. Check your yokes for loosness too (caps, etc). Check the exposed cross shafts for wear when you have it apart.

Next, take a gander at the output bearing on the tranny, and pinion bearing on the rear. These can cause vibration under load. And sometimes they just cause vibration at certain speeds. I have an output bearing on the Ford that moves almost 1/4"......been that way for about 9 months......vibrates like Hell at anything under 70mph. I need to fix it before it leaves me walking.

The key is "load". Anything that vibrates other than when coasting, is usually in the driveline...........or possibly motor mount, tranny mount, or something else that needs to be solid when loaded.

[farmersammm]

I'm sure someone's already mentioned it, but put the damn thing up in the air, and spin it up while observing the driveline, and listening for looseness at any point along the driveline.

[whtbaron]

So Willie.... any luck sorting this thing out?