U-Joint angle question
Thread Starter
Joined: Sep 2004
Posts: 3,148
Likes: 12
From: Downers Grove, IL
U-Joint angle question Ever since I put my car together I have had a vibration at high speed (above 85 I knew it was there, about 75 and below it could not be felt at all). I figured it was probably something with the driveshaft, but have not had time to check it out. I swapped to snow tires and it made no difference, and rear drums no difference. Last week I jacked the car up and ran it without tires and it was still there. Still feels like a driveshaft vibe. Today I checked my U-joint angles and the rear has 0 degrees of angle, the front is 2 degrees up (trans sits on a 2 deg angle down towards the back of the car). I know the angles are supposed to be equal and opposite but is being 2 deg off going to give me a BAD vibration over 90, at that speed you can just about hear the vibration through the car. It is a 3.73 gear so at 85mph the driveshaft is spinning at 4100 RPM. Also when I had the shaft balanced and I asked about balancing speed and they didn`t want to say what speed they balanced at. I told them I had a 4.88 gear and that I needed the shaft to be balanced to at least 5500RPM and they said it was within 1 gram and that it would be just fine. What do you think the problem could be, better chance that my u joint angles are wrong or should I look into the driveshaft.
pinion angle doesnt sound like your problem. your pinion is supposed to be a couple degrees down, I forgot exact number. but the degrees you have difference would make no vibations.
Thread Starter
Joined: Sep 2004
Posts: 3,148
Likes: 12
From: Downers Grove, IL
That was kinda what I was thinking, checked the angles and went "WTF these should be close enough" guess I am going to put some hose clamps on and see if I can improve the vibration, and if I can...........then go beat them with their crappy unbalanced driveshaft 
How long is your drive shaft and what diameter tubing? I have been doing some reading on Drive shaft critical speed, and half critical speed. It has to do with the speed at which a drive shaft will start to bend because of RPM. It is a particular problem with over drive transmissions because the drive shaft is spinning faster than the crankshaft. Rather than me try to explain it with my limited knowledge, go to Google and do a search on Drive Shaft critical speed and get the explanation from the experts. Not saying this is your problem, but it is at least something to look at.
Good luck with it and let us know what you figure out.
Pat
Good luck with it and let us know what you figure out.
Pat
Stu Cool got it.
I am guessing you are using your old drive shaft. It was never designed to rotate at the speeds it is seeing behind your overdrive trans. Follow the link below
http://www.nastyz28.com/forum/showthread.php?t=45552
I am guessing you are using your old drive shaft. It was never designed to rotate at the speeds it is seeing behind your overdrive trans. Follow the link below
http://www.nastyz28.com/forum/showthread.php?t=45552
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Thread Starter
Joined: Sep 2004
Posts: 3,148
Likes: 12
From: Downers Grove, IL
That could be it, it is the factory driveshaft, just shortened and rebalanced but it is still 57" long. Not sure what diameter it is. It had a similar vibration in it when I had the old motor, TH350 trans and 4.11 gear in it at about 75mph. I just thought the shaft was out of balance but I guess mabey it had reached the half-critical speed.
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with factory rubber bushings pinion angle should be down 3 deg. or more and with poly bushings 2 to3 deg. and with solid down 1deg. and max 3. The trans side should be slightly down after the joint. But it does sound just like the problem I had with my camaro and it was the driveshaft!
Thread Starter
Joined: Sep 2004
Posts: 3,148
Likes: 12
From: Downers Grove, IL
How about when they changed my u joints and balanced it they reassembeled it with the shaft swapped front to back. I looked at it today and realized that the balance weight that used to be in the front is now in the back. 
Could that also make a difference, do drivshafts take on a twist after a 150 thousand miles and then have problems if you try to spin them the other way?
Could that also make a difference, do drivshafts take on a twist after a 150 thousand miles and then have problems if you try to spin them the other way? If its balanced it should be ok either direction. Also check the tail shaft in your tranny, there is a bearing in there (like cam bearing) Just a flat race kind of one, the driveshaft yoke rides on it. I had one worn and at speeds the actual tranny shaft would wobble a little. I could never figure it out untill if got so bad that tranny fluid was seeping out the back and I grabbed the drive shaft and yanked it back and forth and seen it move a little.
Thread Starter
Joined: Sep 2004
Posts: 3,148
Likes: 12
From: Downers Grove, IL
I checked the tailshaft bearing and it is worn a bit, I can see it has some slop in it if I try to move the driveshaft. When yours was bad could you feel it vibrating while you were driving? Anyone know if there is a difference in the outer diameter of a drivshaft yoke from a th350/th200 yoke to a 4L60E yoke? I think it should be the same but I would hate to pull it apart, replace the bearing and find out all I needed was a different yoke.
i think they are the same. Its been a couple years since i had the prob, But I know it did it while driving yes, I forget the exact symptoms. There should be no side to side movement. Also make sure your yoke isnt out too far. That will cause it to wobble also.
Thread Starter
Joined: Sep 2004
Posts: 3,148
Likes: 12
From: Downers Grove, IL
Found it, well 2 problems actually. I replaced the bearing in the tailhousing of the trans but that wasn`t it. I even tried making a bracket to hold a marker 1/16" from the center of the driveshaft and spinning it up to 7000RPM to see if it was bending like a jump rope, but it wasn`t. I noticed that I could feel a vibration in the tailhousing of the trans, front of the pig and right axle tube if I held a screwdriver up to them while the car was running. I found that the passenger side axle flange wasn`t straight, probably bent in the middle of the axle. But I figured that wouldn`t be causing a vibration in the back of the trans so I pulled the drivshaft and took it back in. The guy said he would check it but he didn`t think it was the driveshaft. He is spinning it and telling me that I should check the rear axle that the problem is there, the driveshaft is fine. AS he is telling me this he grabs 2 weights and welds one on at the front and one at the back 
Oh yeah the drivshaft was fine so your adding Balance weights 
hmm mabey it wasn`t so balanced afterall. I brought it home and put it back in, Quick test drive = DRASTIC reduction in vibration, got rid of the highfrequency drivshaft feeling vibration, good to over 100MPH. Now I can feel another lower frequency vibration, probably the bent axle, but it is not too bad, it was there but tolerable from 80-100mph. Anybody got a set of axles for a Grand National 8.5" 10 bolt? 
Oh yeah the drivshaft was fine so your adding Balance weights hmm mabey it wasn`t so balanced afterall. I brought it home and put it back in, Quick test drive = DRASTIC reduction in vibration, got rid of the highfrequency drivshaft feeling vibration, good to over 100MPH. Now I can feel another lower frequency vibration, probably the bent axle, but it is not too bad, it was there but tolerable from 80-100mph. Anybody got a set of axles for a Grand National 8.5" 10 bolt? 