Guys, i know, probably the wrong forum, but i figure sense i cant get an answer on the right one, ill throw it at yall ! while building my 72 camaro i had to save a penny here and there. i wound up going boneyard diggin for a driveshaft for my project. the closest thing i could find to the length i needed was a driveshaft from a 92 astrovan, but its about 1/2" longer than i figured i needed. well i have a vibration ( tight vibration ) that i feel is the driveshaft balance. i did have to use the original yoke from my old driveshaft, so im pretty sure it needs balancing. NOW for the question" with my 2004r trannie, how much room do i need for front to back driveshaft movement on the yoke ? as close as i can measure, i have about .600" of forward movement till it bottoms out on the tailshaft. anyone have a clue on how much or little is safe ?

 

I believe 3/4" is the standard amount to allow for the "slip" some may say different though.

 

.600" clearance is fine. If you replaced the yoke and the u-joints it is recommended that you get the shaft balanced. Also make sure that they check it for run-out at the front, middle, and back. Also, don't for get to check your front and rear u-joint working angles.

Andrew

 

thanks ! front u joint angle is giving me fits. i havent checked with an angle finder, but its not optimal. trannie mount is as high as i can go because the headers are only giving me about 1/2" clearance on the floorpans. With the exhaust and crossmember in the way its hard to get a good eyeball on the u-joint angle but it looks to be at a negative angle !

 

I thought as long as you have 1-5* between the trans yoke and rear yoke you were good? Any clarification?

thanks,
JIm

 

The working angles are the angles that are made between the driveshaft and the pinion gear (rear working angle) and between the driveshaft and the transmission output shaft (front working angle). In order to have smooth operation the front and rear working angles must be equal and as small as possible, but not zero. A slight angle is needed to lubricate the u-joints.

Andrew

 

What you wrote above doesn't really say much. You need to measure the working angles as I described in my post above.

Andrew

 

it is important that the angles be" trans tail high, rear yoke low". correct ?

 

I really don't know what you mean.

What is important the the angle between the output shaft of the transmission and the driveshaft (that is called the front working angle) and the angle between the driveshaft and the pinion gear (that is called the rear working angle).

Andrew

 

some things are better explained with pictures.LOL. after all i am from georgia.. the tail of the trannie should be at an upward angle to the driveshaft centerline and the mating surface for the rear u-joint on the rearend should be lower than the centerline of the driveshaft ? correct?

 

Does this explain it?

 

Yes sir......But ive always believed the angles would be opposite from the drawing. that would bring the driveshaft closer to straight in line with the u-joints on acceleration as the rearend wraps up ( with leafsprings ).

 

As the front of the differential rises on accelleration, the drive shaft angles will get closer to straight but never completly straight. The picture above is what you need to shoot for, even though the angles are exagerated in the pic. If you have a 1.5 degree down angle, on the front of the drive shaft, then you need a 1.5 degree up angle at the back of it. Make sure the rear suspension is at ride height before trying to get these angles. Also make sure the drive shaft clearance, to the tranny, (.600 to .750) is set with the suspension at ride height. The pic above is opposite from what 90% of the cars will be. Most will have the rear of the drive shaft lower than the front. Lowered cars will probably have the angles like the pic above.

 

It doesn't really matter which end is higher, or even side to side, the important thing is that the two angles cancel. And like you say you need to account for the rear end rising up and changing the angle. There is a bit of guestimation involved.

You can put shims in your leaf springs to rotate the front of the diff up or down. Same with the motor.

One question I have for everyone is how do you know if the vibration is due to mismatched U joint angles and not something else like tire balance? Is driveshaft vibration worse under load, cruise? Does it go away when coasting out of gear?

 

Thanks Andrew !

 

Yes, you need to compensate somewhat for the pinion rising due to axle wrap. However, you will need to experiment to see just how much the pinion actually moves. You can always mount a GoPro camera under the car and watch to see how much the pinion moves under acceleration.

Andrew

 

The problem i have is the tail of my trannie is tail low and i dont have the room to raise it because of header fitment. i am having clearance issues with my oilpan and front tierod ends with the musclecar pan, so im changing over to the f-body pan, thats about 3/4 shorter in the front to help with that clearance. point of that statement is , i dont have room to lower the front of the engine, so im really stuck with my trannie position. now, the rearend of a leafspring car rotates up in the front under load. Am i stuck with the set-up in the pic that GatTagO posted up ? with the trannie pointing down and the rear pointing up and just live with the fact that traction with sticky tires could over wrap my rear and possibly damage something!?

 

With a good set of traction bars, you won't have enough wrap to worry about hurting something.

Pop N Wood, drive shaft vibrations usually start as soon as the shaft starts turning, even though you may not notice it. They will get progressively worse as the shaft turns faster. Tire vibration will usually happen at a certain speed, a lot more than other speeds, and will get better by just slowing down a little, where drive shaft vibes won't get much better until you slow down a lot.

 

Its also a very tight vibration. if you set a bucket of water in the floorboard, it would make the water look blurry, instead of a bad tire that would make the water slosh out. did that make sense?

 

Pretty much the standard for OEM installations is the entire engine and trans centerline is 3% low at the rear of the trans. Most OEM manifolds are built around this. A lot of LS retrofits make it very hard to maintain this low of an angle, and it is fairly common to see 4-5 degree downward angles, especially with the newer 6L transmissions. The best I could get was 3.5 degrees on my Chevelle with a 6L80E trans, and I had to cut the hell out of the trans tunnel to get that good. This problem is worse on A and F body cars where people will raise the engine to get better oil pan clearance on the front crossmember.

The angle is not really that much of an issue as long as the rear pinion angle is the opposite of the it. The angle of the shaft can be up or down, as it really does not matter, but the working angles at both ends of the shaft have to be opposite of each other. Anything more than about a 1/2 degree mis-match can cause vibration. On a leaf spring car, tapered shims are about the only option to dial the angle in, but on coil spring cars, you can install adjustable upper control arms to get it perfect. The ride height has a huge amount to do with both the working angle and the matching of the angles, so it is unlikely that any modified car will ever be correct as it sits. My Chevelle sits almost 2" lower than stock, which really aggravated the working angle issue. Since the rear of the driveshaft was at a higher elevation than stock, it made the front working angle increase, and with the greater than optimal engine/trans angle, the best angle I could get was almost 4 degrees. This is more than the ideal 3 degree max, but it is the best I could do without either raising the rear suspension back up, or going to a CV joint on the front of the shaft. I am sure that the higher angle will equate into a lower U joint life, but not dramatically. Ideal working angles are around 1 degree, but you are seldom going to be able to get there, if the car is not a stock ride height.

If you have a real problem that you just can't get the working angles low enough, you can always go to a CV joint on the front of the shaft, and then bring the rear working angle down to 1/2 degree, but this is an expensive option. I was heading in this direction on my Chevelle, but Frank at The Driveshaft Shop talked me into trying a shaft with U joints on both ends and seeing how I liked it. If I find U joint life to be a problem, I can always send it back and have a CV joint put on the front end of the shaft.


Regards, John McGraw