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Discussion Starter · #1 ·
Does anyone have an original (not repop) torque tube support bushing that they can measure for me? I'm interested in knowing the height of it. That would be this piece. TIA.
 

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Über Genius
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Good luck finding one that's in the original, non shrunk, length. They are 45 years old.
 

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I've got some NOS ones but they're 100 miles away from me right now.
 

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Discussion Starter · #4 ·
Good luck finding one that's in the original, non shrunk, length. They are 45 years old.
Perhaps. Solid rubber though, so I doubt they've shrunk that much. More likely that they just get hard and non-compliant, sort of like the grouchy old man I'm becoming. :yup:
 

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Discussion Starter · #5 ·
I've got some NOS ones but they're 100 miles away from me right now.
Bob, have you ever noticed whether they're any shorter or taller than the repops?
 

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Perhaps. Solid rubber though, so I doubt they've shrunk that much. More likely that they just get hard and non-compliant, sort of like the grouchy old man I'm becoming. :yup:
Once installed they get crushed down a lot.
 
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Bob, have you ever noticed whether they're any shorter or taller than the repops?
Going off memory, they were a tad shorter (shorter than the non HD as well), and more hourglass shaped.
 

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Discussion Starter · #8 ·
Going off memory, they were a tad shorter (shorter than the non HD as well), and more hourglass shaped.
That's what I suspected. It changes the u-joint operating angles and I wonder if this might be the cause of the vibrations some experience when they change to the HD torque tube donut. In fact it may not be the donut at all, as most replace the support bushings at the same time. Taller support bushings would raise the torque tube at the front, perhaps offsetting the thick (5 mm I think) spacer washers that the factory puts under the torque tube mounting points (which effectively lower the front of the torque tube).

This is just conjecture on my part, but after installing a T5, and having to figure out the correct U-joint operating angles again, I became aware of how a small change at the front of the torque tube quickly affects the driveshaft angle. That made me wonder if this had something to do with why I fought vibration issues when I changed my torque tube donut five years ago. I knew little about driveline angles then, and improved things considerably by adding weight to the driveshaft, but I suspect that was just a band-aid. While the heavier rubber of both the donut and the bushings might contribute to some harshness, I suspect repop bushings that vary in height from the originals might have been the real problem.

By playing around with engine/transmission and torque tube angles I've found that if I get my front and rear U-joint operating angles right (less than 3 degrees each, and within 1 degree of each other) I won't have any vibration issues.
 

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That's what I suspected. It changes the u-joint operating angles and I wonder if this might be the cause of the vibrations some experience when they change to the HD torque tube donut. In fact it may not be the donut at all, as most replace the support bushings at the same time. Taller support bushings would raise the torque tube at the front, perhaps offsetting the thick (5 mm I think) spacer washers that the factory puts under the torque tube mounting points (which effectively lower the front of the torque tube).

This is just conjecture on my part, but after installing a T5, and having to figure out the correct U-joint operating angles again, I became aware of how a small change at the front of the torque tube quickly affects the driveshaft angle. That made me wonder if this had something to do with why I fought vibration issues when I changed my torque tube donut five years ago. I knew little about driveline angles then, and improved things considerably by adding weight to the driveshaft, but I suspect that was just a band-aid. While the heavier rubber of both the donut and the bushings might contribute to some harshness, I suspect repop bushings that vary in height from the originals might have been the real problem.

By playing around with engine/transmission and torque tube angles I've found that if I get my front and rear U-joint operating angles right (less than 3 degrees each, and within 1 degree of each other) I won't have any vibration issues.
!


Does anyone have a diagram about all of this for those of us who have to see things rather than just talk about them? You have raised my interest!

Doug
 

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That's what I suspected. It changes the u-joint operating angles and I wonder if this might be the cause of the vibrations some experience when they change to the HD torque tube donut. In fact it may not be the donut at all, as most replace the support bushings at the same time. Taller support bushings would raise the torque tube at the front, perhaps offsetting the thick (5 mm I think) spacer washers that the factory puts under the torque tube mounting points (which effectively lower the front of the torque tube).
I've modified a lot of Manta TT crossmembers over the years to be adjustable. Functionally they are the same as the GT.

I use this to correct geometry on lowered cars.
 

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Premium Member
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Easiest thing I have done is replace all the rubber parts of the torque tube with polyurethane available at OGTS. I did this years ago, and find they work fine.

Bob
 

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Opeler
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I've modified a lot of Manta TT crossmembers over the years to be adjustable. Functionally they are the same as the GT.

I use this to correct geometry on lowered cars.
Drive shaft geometry can be a nagging problem at lowered car as it can cause vibration. On my 2” lowered GT, I have somewhat lifted front end of torque tube by removing washers under the central support and used heavy duty (longer) rubber bushings.

I like your idea about modification of central support. That should correct the angle between rear axle and central support, however I wonder how much it disturbs the angle between the transmission and central support. It might be beneficial to modify transmission bracket and lift rear end of the transmission. Any thoughts?
 

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Discussion Starter · #13 ·
Easiest thing I have done is replace all the rubber parts of the torque tube with polyurethane available at OGTS. I did this years ago, and find they work fine.

Bob
I just removed all the poly bushings in my rear suspension and put rubber back in. Not enough compliance in the poly for my taste. Fine on smooth roads and race tracks, but hard on the trailing arms and causes weird jerking motions (especially under accceleration) on bumpy roads, which i assume to be from the side to side motions inherent with a panhard rod.

No problems for me with poly in the front suspension.
 

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Discussion Starter · #14 ·
I've modified a lot of Manta TT crossmembers over the years to be adjustable. Functionally they are the same as the GT.

I use this to correct geometry on lowered cars.
Bingo! I should have known that RallyBob had already worked out a solution.

One of the driveline guys told me "It 'aint rocket science. If you get the U-joint operating angles right it will work fine."
 

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Opeler
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!


Does anyone have a diagram about all of this for those of us who have to see things rather than just talk about them? You have raised my interest!

Doug
Here is diagram of various situations. All angles are exaggerated for better understanding.

First diagram shows the driveshaft and torque tube in line, which would be ideal position.

Second diagram shows case of lowered car. Differential goes up, the torque tube is angled as well as rear U-joint (probably exceeding optimal 3 degrees).

Third diagram shows lifted front end of torque tube by removing washers under central support (like I did) or modifying central support. It actually creates "Z" shape of driveshaft where both U-joints are rotating under angle. To me it looks like the worst situation, unless both U-joint are possibly sharing bad driveshaft angle caused by lowering the car, possibly each U-joint not exceeding 3 degrees.

Fourth diagram shows transmission bracket modified, so the transmission is angled. This is causing angle at the front U-joint, so we just moved bad angle from rear U-joint to front U-joint.

Time to take my magnetic angle meter and check real angles…
 

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Dumb luck on my car. I lowered it 1" both front and back although for a while it was only lowered in the front. I have never checked the drive shaft angles. I have had my car up to 115 MPH and never felt a hint of vibration. Hopefully I will remember to check them and report back when I get to Florida next. My lifts are installed dead level so I have the perfect situation to be able to check using a digital level after checking that the tire pressures are all equal. I know that there is more load on the the front tires then on the rears. Maybe I can find a way to measure from the center of the wheel down to the lift and I can adjust the pressure in the rear tires down a little to level the car out. Damn I wish I had my car here :sigh:.
 

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Opeler
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Hot and humid day but I was eager to check the driveshaft angle, so I put some cardboard on the floor, laid down and took few pics under the car.

My car is lowered 2 inches, you can see how the trailing arms are angled (this is entirely another subject but not less interesting).

I already removed washers under the central support and installed longer bushings. This has lifted the torque tube. I measured "0" degrees angle of torque tube. Great!

I also measured the angle of the driveshaft. almost 6 degrees...not so good. As I said in a previous post, let us hope that the angle is shared equally between both U-joints, so it would be less than 3 degrees each.
 

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