MY77Z Posted March 15, 2007 Share Posted March 15, 2007 hi guys, well i have a 1977 280z with stock rear end and a 302 ford drivetrain.....my drive shaft is the ford drive shaft shortned and welded the rear part of the Z drive shaft on it, driving the car at low speed is ok and no problem, flooring it 1st,2nd gears are ok too, but as soon as i hit high speed, the car shakes alot, so i pulled the drive shaft, cheked the Z side and it was in a bad shape (shaky joints) so cut it and changed the Z part with a newer one, the car shakes less but still the annoying vibration is there every time i back off the throttle on 3rd and 4th gear.....I CHECKED THE STREETRODDER SITE and didnt really understand the problem of Driveshaft Angles..... as you know guys, i'm not a native speaker, could somebody explain it to me with simple english i'm not sure if its the problem, if any of you guys have a clue, please help me out here and tell me what i should do...... thanks Quote Link to comment Share on other sites More sharing options...
buZy Posted March 15, 2007 Share Posted March 15, 2007 http://home.comcast.net/~pparaska/drivelinemods.htm These are Petes pages very handy and will help better understand why your DS might be causing vibrations . Basically your angles are not paralell and the related DS angle maybe to great. For example, I'm running about 1.2 total DS angle with paralell pinion and output trans tail shafts. Hard to explain but easy once you understand it. Quote Link to comment Share on other sites More sharing options...
MY77Z Posted March 15, 2007 Author Share Posted March 15, 2007 sorry Buzy, but i didnt understand anything Quote Link to comment Share on other sites More sharing options...
DavyZ Posted March 17, 2007 Share Posted March 17, 2007 Just think about your rear differential and your transmission not being exactly in line with one another--one is higher or lower than the other. This creates an angle for the driveshaft. Too big of an angle means vibrations. You have to reduce the amount of angle to reduce the vibrations. Also, your driveshaft should be balanced, especially if you changed something. High speed balancing is the best. Does that help? Davy Quote Link to comment Share on other sites More sharing options...
MY77Z Posted March 17, 2007 Author Share Posted March 17, 2007 davy, yes that helps alot thank you. at least i understand better the idea of DS angles. How to solve this problem? I dont think its possible to high speed balance a DS here in Kuwait. We dont have shops specelized only in DS. whe have normal machinary shops and they dont do high speed balancing. do you have any ideas how to solve the problem? Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted March 17, 2007 Share Posted March 17, 2007 The drive shaft alignment geometry is really pretty simple. Just draw a straight line out of the transmission shaft and one out of the differential shaft. If those two lines are exactly the same distance apart, up and down, side to side, all along the line, then the drive line angles are perfect. Here is one way to check your angles http://forums.hybridz.org/showthread.php?t=109413 The problem is U joints turning through an angle don't turn at a constant, smooth rate. As the U joint goes through it's motion, it kind of speeds up and slows down, speeds up and slows down. Try turning a socket universal joint by hand an you will see what I mean. The bigger the angle, the bigger the change in speed. If you have a second U joint that is at the opposite angle, then the speed change is exactly canceled out. As one joint speeds up, the other slows down. If the angles of the two joints aren't the same, than the rear wheels will speed up and slow down just like the shaft. This causes the vibration. The other thing to look at is make sure the rear U joint was welded onto the shaft with the correct alginment compared to the front U joint. Here is a picture to show what I mean Aluminum drive shafts are suppose to be less likely to cause vibration since they weight less. If you can't find a good shop, here is a link where you can get a custom made shaft done relatively cheap. Don't know what shipping would be like overseas http://www.pstds.com/ One other thing. How good is your front diff mount? If the diff mount is worn out, then under heavy load the nose of the diff can go up or down affecting the driveline angles. Make sure your diff, tranny and engine mounts are solid. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted March 17, 2007 Share Posted March 17, 2007 I had everything correctly aligned and phased when I had my driveshaft shortened and installed, and I still had the type of vibration you describe. Obviously not everybody has this issue or it would come up more frequently. I think one reason I had this issue was the whole solid mounting thing on the transmission and differential. Eventually, I had a way to fix it which is not a method many folks will take on, and that was to move the differential 1" toward the driver's side. I had the vertical plane and angles correct, but the horizontal plane had the propeller shaft offset 1" toward the passenger side (which is normal in the Z and is somewhat an issue with a short driveshaft because it creates larger than desired U-joint angles). Since I was fabricating my own CV jointed half-shafts, I had the opportunity to shorten the driver's side, lengthen the passenger side, and move the whole differential 1" toward the driver. This cured the vibration issue completely. I still have a slight offset vertically, but wanted this to keep the U-joints moving a small amount. Quote Link to comment Share on other sites More sharing options...
MY77Z Posted March 17, 2007 Author Share Posted March 17, 2007 thanks guys for all the explainations, i'll try to check it tomorow and see how it goes. another question is ( since i have two different U joints, front mustang one and rear Z one, does that have to do with the vibration due to the difference in sizes between the 2 joints? if i cannot fix the problem, would it be safe to drive the car like this since the vibration only occurs when i back off the throttle? thanks Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted March 17, 2007 Share Posted March 17, 2007 thanks guys for all the explainations, i'll try to check it tomorow and see how it goes. another question is ( since i have two different U joints, front mustang one and rear Z one, does that have to do with the vibration due to the difference in sizes between the 2 joints? if i cannot fix the problem, would it be safe to drive the car like this since the vibration only occurs when i back off the throttle? thanks Yeah. I could see where that might be an issue. Especially if the joints are different diameters. I don't think safety is and issue. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted March 20, 2007 Share Posted March 20, 2007 Don't want to thread jack but i have a question about driveshaft angles as well. I'm swapping in a 240sx rear end in to my Z. As stated the Z is offset by about an inch... well the 240sx rear end is perfectly centered. So is it ok to square up the rear end with the car and just run the driveshaft slightly angled to the diff? -Ed Quote Link to comment Share on other sites More sharing options...
buZy Posted March 20, 2007 Share Posted March 20, 2007 Yeah. I could see where that might be an issue. Especially if the joints are different diameters. I don't think safety is and issue. Ali, My u joint diameters are the same as yours . Small in back and big in front. The car doesnt vibrate anymore. Though very interesting what Pop n Wood mentioned about it. It may fine tune the driveline better but not needed really. Safety is always an issue. You have great V8 power on that little short driveline. IF your driveline angles are out of specification to a large degree, I feel it can be unsafe. All that energy in that driveshaft shaking the car, driveline, mountings etc. Over time it will break something. When you get the angles set up right it will make a huge difference in the way the car drives. Your car looks so cool it's worth the effort. Sorry about the language barrier as my english too is not perfect. Hope you get all figured out. Brian Quote Link to comment Share on other sites More sharing options...
blueovalz Posted March 20, 2007 Share Posted March 20, 2007 So is it ok to square up the rear end with the car and just run the driveshaft slightly angled to the diff? Should not make any difference as long as the u-joint angles stay small (Pete's site I thinks has the recommended max on this). You probably already have that much in the vertical plane and not even know it. On another note, is there any evidence that different sized u-joints cause vibration? This would surprise me if so. My thoughts are that size makes no differnece as angles will not change regardless of the size of the joint. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted March 20, 2007 Share Posted March 20, 2007 On another note, is there any evidence that different sized u-joints cause vibration? This would surprise me if so. My thoughts are that size makes no differnece as angles will not change regardless of the size of the joint. Just to clarify this was a guess on my part. I have often wanted to work out the math to define exactly how the speed changes through the U joint. I just seems to me that larger diameter joints will exhibit more of a speed variation for a give angle than a smaller one. But like I said I don't know this for sure. Upon further review, the size of the U joint has no effect on the change in angular velocity. Forget what I said about getting more vibration from mismatch U joint sizes. Quote Link to comment Share on other sites More sharing options...
MY77Z Posted March 23, 2007 Author Share Posted March 23, 2007 hi guys, well i haven't touched my Z for the last 6 days (NO TIME), i haven't checked the drive shaft nor the angles and guess what? drove the car yesterday and there is NO VIBRATION at all !! i'm a bit confused because i haven't done anything to the car and the vibration just vanished!! any ideas?? Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted March 23, 2007 Share Posted March 23, 2007 Something might be loose or worn out allowing the suspension-tranny-diff to move. Are you sure it is not a tire vibration or something like that? Quote Link to comment Share on other sites More sharing options...
Paz8 Posted March 23, 2007 Share Posted March 23, 2007 If you think that it is the drive shaft balance look for a local place that performs TRUCK drive line repairs, they can build drive shafts and balance them. Quote Link to comment Share on other sites More sharing options...
MY77Z Posted March 23, 2007 Author Share Posted March 23, 2007 well, i'm pretty sure it's not due to tires. and i'll look more for a shop to balance it just to make sure. suspension??!! maybe, i don't know, i'll have to check it later on, now i have no time at all working almost 100 hours a week (navy officer). thanks guys Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.