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Discussion Starter · #1 ·
Hello I have a 1938 Oldsmobile business coupe with a 6.0 lq4 In It with a 4l60e and a 10 bolt with a triangulated 4 link with Ridetech shockwaves.
My question is at the harmonic balancer I use my digital angle finder and it reads 2.4 deg down towards the rear of the car and I pulled out the drive line and it reads 1.9 to 2.0 deg down and with the drive line in it reads 0 to .1 deg down and my rear end is set to 1.7 deg up I thank you have to bring the frount down to get it zeroed out I have a vibration that starts at 70 sometimes a little less and the faster you go the worse it gets I tryed the bucket trick I will se if I can post the video of it

I’m not sure what reading to go off of the harmonic balancer or the output shaft reading ?
The video say it’s to large
Thank you kelly
 

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To me it seems the balancer should be mounted perpendicular to the crank which will establish the engine/trans angle. Top edge of the valve cover should confirm this. Because you have a triangle rear suspension just go with 2.4 up.

I also have a vibration that starts about 65 MPH and gets worse with more speed. First thing I'm going to do is rotate the driveshaft 90 degrees at the rear end and see if that changes anything. Next would be a radiator hose clamp around the driveshaft.
 

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Discussion Starter · #3 ·
Thank you I’ve had the drive line balanced twice I’ve 90 deg the drive line also still have the vibration.
I baught hub sentric rings and had my tires road forced balanced. We have had lots of snow and ice it’s finally melted but I haven’t taken it out for a ride to check and see if that fixed it.
I figured I had it up in the air but as if it was at ride height on the ground so I could get under and take readings.
At the harmonic balancer I checked it on level ground and read the 2.4 degrees down.

I used a flat edge flush agents the output shaft and it was reading 1.9 to 2.0
I just went out and put the angle finder on the valve cover it’s reading 1.9 to 2.0 just like the output shaft
I also set iT on the fuel rail and it reads the same.
so I’m thanking the harmonic balancer isn’t correct ?
 

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Is your engine or pinion offset from one another in the frame. Like the engine is centered and the pinion is 2" from center?
 

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Discussion Starter · #5 ·
I will have to check that out tomorrow. But if I recall right the pinion is offset to passenger side 1” the motor and transmission is centered in the frame
 

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The angle of the output shaft must be equal to the angle of the pinion. They need to be on parallel planes but not the SAME plane.

If the engine/trans is pointed down 2.4 degrees, the pinion needs to point up 2.4 degrees. From there you need to also make sure that the driveshaft has 1-4 degrees of angle at each u-joint. Some people will say this is so that you end up rotating the caps on the u-joint for lubrication, but that is not the case. You need the angle at the u-joint to help stop vibes. That's why the U-joint yokes are welded on 90 degrees from each other. This actively puts tiny amounts of torque on the driveshaft as it turns and cancels out resonant vibrations that may exist. Kinda like if you have a vibrating guitar string and then touch it, it stops vibrating.

Many people have installed driveshafts with zero degrees at the u-joints and have been fine, but since it's a pain to change it later, engineer in the 1-4 degrees now.
 

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If you can get flat on the damper it's close enough. If you can flat on the rear yoke your also close enough. You want them opposite and equal (-2ish degrees to +2ish degrees) as viewed from the side as well at the top looking down.
Keep in mind in the real world that thing is moving all around so get as as close as you can but don't sweat the small stuff and over think it.
Something to look at while messing around with it is the U-jount cups in the rear end yoke. It's easy to get the caps slightly off the seat registers of the yolk as well as one or two needle bearings in the cups laying down inside the cups and throwing things off center. They still bolt up okay but problems arise you didn't expect.
You can also put a DI on the yolk and the drive shaft and verify the TIR to ensure the caps are all good.
 

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Agreed, Johnsongrass. The balancer should suffice for finding the trans angle.

Just don't use the transmission pan. They are often engineered to be level-ish as installed, so the pan is often at the same angle as the road, not the driveline.
 

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I think the easy button here (if you have the room in the tunnel) is to shim up the transmission mount until your engine/trans is 1.7 degrees, or as close as you can get to that.

As far as the pinion being offset to one side, that isn't a problem, but it makes measuring the actual u-joint angle nearly impossible unless you remembered all of your high school calculus. The overall u-joint deflection angle will be not just the down angle measured from level to the ground. If you measured 0 degrees of driveshaft angle, the pinion offset means that you have a Ujoint angle of something greater than zero.
 

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Discussion Starter · #10 ·
I put the digital angel finder on the drive line by the upper yolk on the drive line and it reads .1 and I put the angle finder on the drive line at the reared the drive line and it reads 0 to .1 deg up angle.
As for the joint cups when I’ve taken in the drive line to get rebalanced they said it’s good.
So they would know if they was bad when they spun it ?
This is a triangulated 4 link so I can set it to where I need.
I was thanking the output shaft is more correct of a reading.
I was thanking the harmonic balancer the rubber might be getting bad and causing the different reading .04
I didn’t use the pan I used the output shaft I pulled the drive line and put a flat piece of metal flat on the out put shaft and the angle finder on that and that’s where I got my reading of 1.9 to 2.0
Yes I figured with the pinion being 1” off set with the drive line at zero and that offset the joint is having movement
 

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Discussion Starter · #11 ·
My car is already built I’m doing the interior right now and trying to fix this vibration problem
Hopefully this year if money is available I’m going to put in a Ford 9” with the 7.625 I’ve snapped the drivers side axel
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Well yes 1" is not going to compound the angle enough to matter but you never know what someone has till you ask.

Lets get back to basics.
When does the thing vibrate at what speed, gear, rpm?
Does it vibrate to a lesser degree at the same rpm in a diffrent gear?
Is the vibration on acceleration, deceleration, in the turns, or after a bump?
Are there any visual signs of damage to the driveshaft, the yokes, u joints etc. These can be scrapes or scoring, grease thrown, blue caps, loose retainers. Grabing onto the driveshaft and "shaking" it sometimes can reveal a bad pinion input or transmission output bearing as well as other things like some yoke play.

Checking for balancer vibrations can be done in netural by slowly reving the engine off idle to near its peak rpm no faster then 500rpm a second.

Sometimes the body itself can cause a vibration. I have 2 panels in the cab of a s10 that vibrate around 20 mph. A bit of silicone will fix that one of these "warm" days.

Steering toe/camber can also cause a vibration which may change in turns.
 

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Discussion Starter · #13 ·
At 60 mph the rpm is 1800.
At 65 rpm is 1930
At 70 mph the rpm is 2061
It starts at 65 or 70 and gets worse the faster you go
It’s when it’s in drive
I haven’t noticed any change with gear change or acceleration or on deceleration .
I’ve noticed that the speed it starts at changes some times .
I have 9 thousand miles on the rebuilt transmission
Their was a little slop in the yolk in the rear of the transmission the transmission guy guy said he didn’t Change the bushing in the tail shaft so I got one from him and installed it so now their is almost no play.
I haven’t driven the car very far since I changed that bushing and I talked a shift kit.
Weather hasn’t allowed me to drive it the snow is finally melted ..

I will have to get the pinion set to 2.0 up so it matches the output shaft and put the drive line in and get it back on the ground.
And get back with you thank you everyone for the help .
The drive line shop redid the driveline tube the first time I had it made it needed to be extended .

Thank you kelly
 

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I put the digital angel finder on the drive line by the upper yolk on the drive line and it reads .1 and I put the angle finder on the drive line at the reared the drive line and it reads 0 to .1 deg up angle.
As for the joint cups when I’ve taken in the drive line to get rebalanced they said it’s good.
So they would know if they was bad when they spun it ?
This is a triangulated 4 link so I can set it to where I need.
I was thanking the output shaft is more correct of a reading.
I was thanking the harmonic balancer the rubber might be getting bad and causing the different reading .04
I didn’t use the pan I used the output shaft I pulled the drive line and put a flat piece of metal flat on the out put shaft and the angle finder on that and that’s where I got my reading of 1.9 to 2.0
Yes I figured with the pinion being 1” off set with the drive line at zero and that offset the joint is having movement
So, that tells me that the drive shaft is level to the ground, which is not the important part. The important part is that tells me you have an acceptable u joint angle. If the shaft is level and the trans points down 2.4, then you have a U joint angle of 2.4 (plus whatever the 1" side offset adds). Now we just need to get the pinion and trans to match.

Two ways of doing that: Shim up the trans to match the 1.7 of the pinion, or adjust the trailing arms so the pinion matches the 2.4 of the trans. Keep in mind that whatever you do will change the u-joint angle because the shaft will no longer be at 0 degrees, but I think you're OK to pick either one... or both. In your situation, I might suggest shimming the transmission up. The reason being that if you're already at about 2.4 degrees, there is no need to add more ujoint angle, which is what would happen if you raised the pinion. Raising the trans would reduce ujoint angle, but not enough to drop you below the recommended 1 degree.
 

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Discussion Starter · #15 ·
Yea from the reading I get is the yolk and pinion of the rearend are level with each other.
So what your saying is that I should use the 2.4 deg I got off the harmonic balancer?
Not off the end of the output shaft flat reading I got was the 2.0.
I have about 1/2” before the transmission hits the floor
thank you for all your help
 

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Just a suggestion, as I think everyone is doing an awesome job trying to help you-
For a second affirmation on your pinion angle, Tremec (the Transmission manufacturer) offers a free Driveline angle checker app-using your smartphone-I used it on my Car and it is very easy to use (it shows the angles and calculates whether you're within range -just a thought-
 

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Discussion Starter · #18 ·
Yea they are. I have the app I will have to try it later tomorrow.
went to eye doc today and can’t see
 

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That picture is correct, 2.0 or 2.4, a half a degree doesn't mean anything.
Also, twisted splines are bad.
 

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Discussion Starter · #20 ·
Yep I was on the freeway and traffic slowed down and a guy cut me off so I left a car and a half length I frount of me and I stepped on it and let off and that’s when the splines twisted and snapped the Axel on the drivers side
 
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