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I've been fighting a vibration/noise on my '82 since I completed the LS1/4L60e swap and I think I've narrowed it down to driveshaft angle. I read this excellent thread: https://www.corvetteforum.com/forums...t-angle-2.html, and based on what my measurements are telling me it sounds like I may be best to use the "W" arrangement described by 427 Swede. I measured with my car sitting level and jackstands under the front and rear suspension to simulate sitting on the ground. I got: differential 2 1/2 degree down angle, transmission/engine 2 degree down angle, driveshaft 0 and frame 0. So its almost at a W configuration now, if I took a shim out of the rear transmission mount I'm guessing I'd have a 2 1/2 degree down angle and the trans and diff would be equal. Have any of you had this come up?
I believe that you want the angles opposite. That is one down and one up. I'd add shims to the trans mount and raise it as much as possible. I added 1/4" under the exhaust hanger to center the pipes in the cross member, and another 1/4" under the trans mount.
I'm just feeling this out, and I'm really wondering why my differential has a down angle and a significant one at that. It seems to me that the engine/trans down angle of 2 degrees is just about perfect, and if the differential was at close to zero like most of them seem to be then I don't think I'd be having problems. The W driveshaft arrangement would seem like an easy solution to this, here is a link to the PDF file that describes it: http://www.gwbdriveshaft.com/images/Catalog_english.pdf and here is a screencap from the PDF:
It would be relatively easy to move the differential up 1/2 a degree to match the 2 degree down angle of the engine/transmission, far easier than moving it up the 4 degrees or so to be at a parallel angle of 2 degrees up.
The W arrangement works just fine. I even built a cardboard driveshaft to convince myself and posted a picture in a thread whose existence I've lost. Here's what I did to get the angles right
If you narrowed down where the vibes are coming from, sometimes just un bolting the U joint and turning it 180* then bolt it back in will get rid of a vibration. I would also compare the trans mount to the old one. If it's taller it will throw everything off.
On my 82 it was the pinion bushing. I had to mess with it for hours before i got it right
A single turn on the pinion bush bolt can mean the difference between vibrating or not vibrating. When I finally got it right, I had to double bolt it with a nylon lock bolt. So it would hold it's position. It only had about 10lbs of torque and it would lossen if not double bolted on mine.
If You can feel the vibrations more under acceleration than you have to tighten the pinion bushing some more. Under deceleration the vibes are worse than a few turns lossen the bolt. In some cases you have to trim or shim to get it right. But you'll know after your first test drive if you went the right way.
Hope this helps because the degree level didn't help me at all.
If you narrowed down where the vibes are coming from, sometimes just un bolting the U joint and turning it 180* then bolt it back in will get rid of a vibration. I would also compare the trans mount to the old one. If it's taller it will throw everything off.
On my 82 it was the pinion bushing. I had to mess with it for hours before i got it right
A single turn on the pinion bush bolt can mean the difference between vibrating or not vibrating. When I finally got it right, I had to double bolt it with a nylon lock bolt. So it would hold it's position. It only had about 10lbs of torque and it would lossen if not double bolted on mine.
If You can feel the vibrations more under acceleration than you have to tighten the pinion bushing some more. Under deceleration the vibes are worse than a few turns lossen the bolt. In some cases you have to trim or shim to get it right. But you'll know after your first test drive if you went the right way.
Hope this helps because the degree level didn't help me at all.
I think I'll start with getting the angles right, the W arrangement will make that pretty straightforward. I can add a shim under the transmission mount and see what that does for the vibration. If it's better then I know that I can easily trim the differential isolator to get the 1/2 a degree it needs to match the engine/transmission. The pinion bushing nut should be right, I just had the differential rebuilt by tracdogg2.
The W arrangement works just fine. I even built a cardboard driveshaft to convince myself and posted a picture in a thread whose existence I've lost. Here's what I did to get the angles right
I saw the model you made out of cardboard, I'm surprised that this solution hasn't come up more. It would have saved me some work on other projects with independent rear ends.
"If there is vibration under acceleration, you need to add more downward pinion angle preload. If the opposite occurs, the vibrations tends to decrease or disappear under acceleration, you need to reduce the downward angle preload.
If the vibration steadily increases with driveshaft speed (either accelerating or decelerating) the symptom is primarily the result of a driveshaft imbalance or yoke runout. Sometimes this yoke runout problem can be improved by rotating the U-joint 180-degrees in the rear end differential yoke.
Driveshaft-related vibrations usually occur at roughly engine speed in high gear. Wheel/axle vibrations usually occur at 1/3 rd engine speed or driveshaft speed because of the differential gearing. To determining whether it is the output of the transmission or the pinion in the differential, change gears when the noise occurs and maintain speed. If the vibration/noise changes in frequency, the source is in the transmission or engine. If the frequency remains the same it is a driveline problem."
"If there is vibration under acceleration, you need to add more downward pinion angle preload. If the opposite occurs, the vibrations tends to decrease or disappear under acceleration, you need to reduce the downward angle preload.
If the vibration steadily increases with driveshaft speed (either accelerating or decelerating) the symptom is primarily the result of a driveshaft imbalance or yoke runout. Sometimes this yoke runout problem can be improved by rotating the U-joint 180-degrees in the rear end differential yoke.
Driveshaft-related vibrations usually occur at roughly engine speed in high gear. Wheel/axle vibrations usually occur at 1/3 rd engine speed or driveshaft speed because of the differential gearing. To determining whether it is the output of the transmission or the pinion in the differential, change gears when the noise occurs and maintain speed. If the vibration/noise changes in frequency, the source is in the transmission or engine. If the frequency remains the same it is a driveline problem."
That is a great article! I've had the driveshaft balanced to the yoke, so I can cross that off of the list. And the vibration remains unchanged regardless of what gear it's in or even if it's in gear. It does have a greater occurrence when decelerating, I'm guessing that this is because of the larger downward angle at the pinion. Today I'm going to cut the isolator cushion to bring the pinion up and see how that affects things. If I get the angles equal the vibration/noise should disappear.
I've been experimenting with it, and it appears to work in either "W" or "Z" configuration. Tomorrow I'm going to see if I can get it to solve my problem, my head is spinning from trying to figure this out.
If you narrowed down where the vibes are coming from, sometimes just un bolting the U joint and turning it 180* then bolt it back in will get rid of a vibration. I would also compare the trans mount to the old one. If it's taller it will throw everything off.
On my 82 it was the pinion bushing. I had to mess with it for hours before i got it right
A single turn on the pinion bush bolt can mean the difference between vibrating or not vibrating. When I finally got it right, I had to double bolt it with a nylon lock bolt. So it would hold it's position. It only had about 10lbs of torque and it would lossen if not double bolted on mine.
If You can feel the vibrations more under acceleration than you have to tighten the pinion bushing some more. Under deceleration the vibes are worse than a few turns lossen the bolt. In some cases you have to trim or shim to get it right. But you'll know after your first test drive if you went the right way.
Hope this helps because the degree level didn't help me at all.
So far the degree thing isn't helping a bit. The thing is I just had tracdogg2 rebuild my differential so it shouldn't be having any problems but I'm running out of things to replace and the noise just gets louder.
You seem to know what you are doing, so don't take it wrong for me asking a stupid question. Because it is a swap - Is there any angle in the drive-line from left to right, not just up and down? These angles also have to match to keep the joints speeds similar.
You seem to know what you are doing, so don't take it wrong for me asking a stupid question. Because it is a swap - Is there any angle in the drive-line from left to right, not just up and down? These angles also have to match to keep the joints speeds similar.
The engine/trans are still offset the the passenger side and all of the mounts are in the stock position. After reading everything ever written about C3 corvette differential mounting I now know that the differential is mounted parallel to the frame, that is at a 0 degree angle. Mine is pointing down and that's where my problem originates. Today I'm going to try to figure out why this is. If it was at 0 degrees it would be childs play to get the driveline angles in spec.
The pinion at zero to the frame does not say anything about the joint angle. I have an LS swap as well, and I would check left to right angles if you rule out everything else.
The pinion at zero to the frame does not say anything about the joint angle. I have an LS swap as well, and I would check left to right angles if you rule out everything else.
I'll do that, and I appreciate your advice! First I want to bring the vertical? angles in spec as I'm afraid that I won't get the offset angles right if they aren't.
Just a thought I had and not something I've tried, but ... if you removed (say) the transmission bolts, or alternatively the snubber and loosened the differential some, and then turned over the driveline by hand, it would seem that a dial indicator somewhere could determine that the universals were forcing the major components to move, and in what direction.
I realize that is just a diagnostic but you might find out whether things were moving up and down or left or right.
Congratulations on finding an app. I used a digital angle gauge. Maybe uses the same chips but readout was fractions of a degree and it was convenient since it magnetically adhered to things.
On the other hand as my boss would say to me ... don't turn this into a science project!
Watching with some interest as I've been here too.
I worked on it today and got the differential up to at least zero by cutting the isolator cushion down to about 1/8. After painstakingly measuring and shimming I was able to get these final driveline angles: Transmission yoke angle 1.1 Differential angle .8 and driveline operating angle .3. These figures are all in the green using the Tremec app, and a test drive revealed that while there is still some noise, it drives very smooth and vibration free. I called tracdogg2, and after a lengthy conversation with him I'm pretty confident that it's not the pinion or anything else in the differential. He thinks it could be something in the transmission, and maybe it is because it came out of this:
As far as the offset angles go, I really wouldn't know how to measure them, but the transmission is centered in it's mount and the engine is also centered in it's mounts. So I'm going to live with it for a while and see if it gets worse or something fails. The car really is a pleasure to drive other than this, and the only time I hear the noise is when the stereo isn't turned up.
You seem to know what you are doing, so don't take it wrong for me asking a stupid question. Because it is a swap - Is there any angle in the drive-line from left to right, not just up and down? These angles also have to match to keep the joints speeds similar.
Now that I've got the up/down thing right I've been thinking about the right/left thing. Let me ask you this, is your driveshaft centered in the tunnel? Because mine is closer to the passenger side than the driver side. My transmission mount isn't really adjustable for side to side movement although it could be modified easily enough. At that point I'd have to re-weld my exhaust system, but if it got rid of the last of the noise it'd be worth it.
The engine/trans is offset to the passenger side as stock. I had to re-work the trans cross-member to fit the TR6060 and built motor mount plates to lower the combination a little. So - there was a lot of old school string and measuring, plus angle finding on the up/down plane. If you are hearing noise, and think it might be internal to the trans, maybe remove the drive shaft, (fun) and run a little to see if it is still there. If something is grinding inside the auto, you should start seeing evidence in the bottom of the pan.
08-28-2014, 07:11 PM
Driveshaft angle and vibrations.
