Drive shaft vibration?

[Steve Van Gent]

I have 700R4 and drive shaft shop shortened drive shaft, 2 piece with new carrier bearing. All should be new and balenced. WHen I accelrate hard, I have vibration that feels like coming from drive shaft or rear end. ANyone else had this?

[65Custom]

Do some Googling as I have read some things on this subject related to later model engine and trans in earlier model cars, I which one of the forums for LS1 or LT1 engines i found it on but

Try this one out http://www.ls1tech.com/forums/

[fleetsidelarry]

Steve, just to clarify, it only does it under hard acceleration, not during normal part-throttle run-up thru the gears or cruising? And, I assume, no problem before the switch to the 700r4/shorter drive shaft? Truck is lowered or no?

[padresag]

could be the centre brg support( even if it is new), perhaps you dropped a needle brg, motor or trans mount
ron

[Steve Van Gent]

Larry-Yes, yes and yes-5 inch drop...I suspect you think it might be the shaft is no longer in alignment with rear end?

[Keith Seymore]

When you accelerate hard from a stop, or accelerate after you are rolling?

If it is a "couple of kicks" (three, maybe) when accelerating from a stop then it sounds like typical "Launch Shudder". I did some playing around one time and found it can be related to the length of the front shaft vs length of the rear shaft, with the two shafts being closer in length being best case.

If so, then I could imagine shortening the front shaft to create a launch shudder as described.

K

[fleetsidelarry]

just trying to isolate the possible cause.

Since the only change is the longer transmission and subsequent shorter front driveshaft (AND, therefore, relocated front u-joint), the shorter front shaft could be causing what Keith describes. for reference, my front driveshaft is 31", the rear is 35". My engine has clam-shell mounts and sits about 2-2.5" ahead of the original location as near as I can tell. if your engine is in the original location, your front driveshaft is going to be that much shorter, which may be causing the aforementioned problem.

On the otherhand, the relocated (rearward) u-joint would be accentuating the normal u-joint angle. Also, I assume you modified the tranny mount, if so the relocated mount may have effected this angle by raising or lowering the u-joint location.

Just things to consider. Aligning these 2 piece shafts has never been explained well in any of the sources I've read. I'm just surprised more people don't seem to have problems, especially with lowering so popular.

[trevota]

axle wrap??? rear susp. bushing all in good shape??

[TR65]

Check your operating angles. If they are equal the drive shaft forces from each universal cancel each other. If the operating angles are different they do not and give a vibration. The vibration would be worse in proportion to the torque applied. So it might be acceptable for normal acceleration but not for high torque starts.

Here is the definitive source for aligning drive shafts I think.

http://www2.dana.com/pdf/J3311-1-HVTSS.PDF

Good luck,

TR

[padresag]

the length of the frt shaft has nothing to do with it. all 3 ujoints should be in the same plane. all of the crosses should be the same. you will have to drop the d/shaft and move all of the joints by hand to seee if one is binding which would be cause by a dropped needle ( the needle is usually jammed between the end of the cross and the cap. the rear cross may not be fully seated in the rear yoke due to a dropped needle. this happens to a lot of people.
ron

[Keith Seymore]

Originally Posted by padresag

the length of the frt shaft has nothing to do with it.

Not true.

When I was a driveline engineer for GM Fullsize truck, at the GM Desert Proving Ground, we performed a series of experiments on a GMT400 extended cab. These trucks had an inherent propensity for launch shudder, which resulted in a full scale effort to fix the problem. By equalizing the lengths of the front and rear shafts (ie, increasing the length of the front shaft), keeping the u joint working angles the same as before, I was able to minimize or eliminate the launch shudder in these models. I received a patent for this work.

I will agree, however, that for most people, in dealing with production components, what you have said is true. But it is simply not true universally, when throwing off the constraints of having to use the production vehicle architecture.

I normally wouldn't have brought it up, except it seemed relevant here since the original poster had shortened his original front shaft (directionally incorrect, according to my earlier experiments). He may have introduced some fundamental lever force imbalances (not rotational forces) that refinement of u joint working angles may not be able to overcome.

BTW - I always run a one piece shaft whenever I can get away with it (through increased shaft diameter, premium materials or reduced vehicle speed), just to avoid these types of problems.

K

[padresag]

Originally Posted by Keith Seymore

Not true.

When I was a driveline engineer for GM Fullsize truck, at the GM Desert Proving Ground, we performed a series of experiments on a GMT400 extended cab. These trucks had an inherent propensity for launch shudder, which resulted in a full scale effort to fix the problem. By equalizing the lengths of the front and rear shafts (ie, increasing the length of the front shaft), keeping the u joint working angles the same as before, I was able to minimize or eliminate the launch shudder in these models. I received a patent for this work.

I will agree, however, that for most people, in dealing with production components, what you have said is true. But it is simply not true universally, when throwing off the constraints of having to use the production vehicle architecture.

I normally wouldn't have brought it up, except it seemed relevant here since the original poster had shortened his original front shaft (directionally incorrect, according to my earlier experiments).

K

I may not be an engineer and I am not arguing your position' but must ask he question. here we have a shaft that has been shortened a few inches. that is the only part of the equation that has been modified(that we know of). the carrier brg and support are in the same location, so the d/shaft should be running in the same plane. we haven't lengthened it and added dimensional flexibility. what are the causes which make this problem occur.
in your exercise you wer using an extended tube to make up the vairiance for an extended cab. how much of an extension. unless one changes the other dimensional qualities of the tubing for the length of the shaft, you could get flex in the shaft
it if don't ask, you don't know
I used to spec out trucks(IHC & Pacific)in the early -mid 70's from l/duty to off hwy
ron

[fleetsidelarry]

Originally Posted by TR65

Here is the definitive source for aligning drive shafts I think.

http://www2.dana.com/pdf/J3311-1-HVTSS.PDF

Good luck,

TR

Yes, this site DOES explain it, thanks for the link, TR65