Heavy vibration at highway speed under load

[77Dmax]

Bad motor mounts will create an odd driveline angle that can cause a vibration. I would start there.

The rotational slop in the driveshaft is probably worn spider gears and cross shaft, especially if you have been doing burnouts all over town.

 

[BRetty]

Bad motor mounts will create an odd driveline angle that can cause a vibration. I would start there.

The rotational slop in the driveshaft is probably worn spider gears and cross shaft, especially if you have been doing burnouts all over town.

DAmn! You caught me! B "Street Takeover" Retty. I will tackle the motor mounts ... which I am not doing today, taking a friend out for his birthday, for drinks at my nice local bar with the pretty young women who are, sadly, it seems, I have concluded after five years, all lesbians.

(I love this song)

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[BRetty]

I've had my wheels/tires balanced and rotated, and also had the transmission shop check the flexplate/TC connection and transmission mounts. The differential place was clear: differentials don't cause vibration. (but they will make NOISE, which is just a higher-frequency kind of vibration ... wasn't worth questioning....) They suggested my U-joints, or take her to the only driveshaft guy left, up in Valencia.

I think it's my engine. I definitely have a vibration at idle. Here's what it fels like;

-- on a cold start, the engine chugs in 4/4 or even double-time: BOOM-buh-buh-buh HOOM-buh-buh-buh. Cold/damp morning I can see steam out the exhaust pipes pulsing. Oddly, though this might be subjective, I feel like right after starting, the exhaust out the driver's side is warm/hot, while the pass. side exhaust is distinctly cooler.
-- Was at mechanic's a couple weeks ago, he said the idle sounded good but smelled rich. (It was not chugging so much that time.)
-- WHen I start it at idle, there's definite vibration from the engine I can feel in the steering wheel. The vibration is a constant frequency, but pulses and ebbs in amplitude, with a period of about 5 seconds. Clerely two different periodic vibrations making harmonics. Maybe one is related to ignition and the other is the mass of the block moving/shaking w/r/t frame?

(My steering column is loose -- something I'm going to fix and Loctite today -- so it's very obvious when the wheel visibly shakes then calms down, about 5 seconds between peaks. I cannot get video of this, I realized because ******* Apple iPhone image stabilization is probably working hard to cancel out what I want to see. Maybe if I stand outside the truck or use a tripod I could capture it.)

So, today/tomorrow I' going to
-- Replace motor mounts if I can by myself
-- put her up on stands and run the drivetrain, try to rev it up and maybe get video of it.
-- take the stethescope to all the front accessories to see if any are screaming
-- check harmonic balancer for play or wobble
-- remove fan and fan clutch then run engine to see if vibration changes
-- Hopefully replace my water pump (currently orig with '73 engiine, I think a short) with a year-old AC Delco long pump from my old engine.

Gotta get up, get out, get there, get under, get busy.

BRetty

Edited - i have a spare LONG water pump, not a LUNG pump.

 

[3 Ton]

If I have not pissed folks off, this may.

I ran Ford 4x4 for decades. The front U-joint is the same size as the rear on a 1/2 GM truck.
We found out in the 80s that GM driveline have balance problem after off roading.

I gave up many a spare U-Joint to my GM buds, it seems they go out of balance.
Ive had this GM for 10 years, replaced the u-joints when I got it, and about 5 years ago when I rebuilt the rearend.

Tire are easy to check, just spin them on a balancer.

 

[BRetty]

If I have not pissed folks off, this may.

I ran Ford 4x4 for decades. The front U-joint is the same size as the rear on a 1/2 GM truck.
We found out in the 80s that GM driveline have balance problem after off roading.

I gave up many a spare U-Joint to my GM buds, it seems they go out of balance.
Ive had this GM for 10 years, replaced the u-joints when I got it, and about 5 years ago when I rebuilt the rearend.

Tire are easy to check, just spin them on a balancer.

Interesting. I just had a buddy shoot video while I ran the drivetrain up on jack stands. Now trying to interpret what I see.

Besides the big CLUNK going into gear, which I see the driveshaft turn 10-15 degrees, which says differential wear, felt the heavy vibration ramp up with RPM, but so far not seeing anything obvious.

 

[Ricko1966]

Interesting. I just had a buddy shoot video while I ran the drivetrain up on jack stands. Now trying to interpret what I see.

Besides the big CLUNK going into gear, which I see the driveshaft turn 10-15 degrees, which says differential wear, felt the heavy vibration ramp up with RPM, but so far not seeing anything obvious.

The rear diff slop is probably NBD if you fix it now or soon. It will be a big deal when it starts making noise. Pinion brgs,differential bearings,inspect the spiders,the cross shaft and diff for wallered out holes.

 

[BRetty]

The rear diff slop is probably NBD if you fix it now or soon. It will be a big deal when it starts making noise. Pinion brgs,differential bearings,inspect the spiders,the cross shaft and diff for wallered out holes.

I keep trying, but Hooper's Rear Ends, the good diff shop, keeps bankers' hours and going there on a Friday afternoon when I get off work won't cut it. I know she needs service, work is a little slow now so I need to just plan 2hrs off, drop her off Tuesday at 7am and get a bus to work, go back Wed or Thurs after 4pm and get the results of the 12-bolt biopsy.

 

[Grit dog]

I think you need a mechanic shop that does more than one thing. Honestly.

 

[DoubleDingo]

I think you need a mechanic shop that does more than one thing. Honestly.

Being in Los Angeles he's done his homework and lucky to find what he has.

 

[Grit dog]

Being in Los Angeles he's done his homework and lucky to find what he has.

Then I might suggest getting a reliable vehicle. The string of this shop to that shop to another shop to the other shop back to the 2nd shop is just crazy.
It don’t pay to drive an old bomber that needs work all the time if you can’t work on it yourself.
JMO