what Posted January 11, 2013 Report Share Posted January 11, 2013 Hi. Looking for some advice. Have a 1972 521 that has horrible vibration when mph reaches 55. Now it's not the wheels or tires as I have had about 3-4 different sets on it and it still does the same. Another thing is that it does not matter if the car is in gear or not when the vibration happens. So what i am thinking is that it is either the driveline or I have a slightly bent axle. I will put the truck on some jack stands and put it in gear and see what it is. Any other suggestions? Quote Link to comment
Draker Posted January 11, 2013 Report Share Posted January 11, 2013 Jack up the rear, grab the driveline and shake it. If you have any movement then it's either the carrier or u-joints. Quote Link to comment
datzenmike Posted January 11, 2013 Report Share Posted January 11, 2013 Engine mount broken or loose. Tranny rubber mount could be loose or broken. Drive shaft bent or damaged. U joint bolts loose Incredibly bad U joint. Badly worn slip shaft on rear driveshaft. Damaged/torn rubber isolator around the carrier bearing. (carrier bearings (almost) never go bad it's the rubber surround that rots away, driveshaft is now not supported and flops around) Damaged brake drum. Piece missing out of balance. Quote Link to comment
wayno Posted January 12, 2013 Report Share Posted January 12, 2013 Has the truck been lowered? Quote Link to comment
what Posted January 12, 2013 Author Report Share Posted January 12, 2013 Yes it has been lowered Wayno. And iam glad you mentioned that. I was just thinking that when I bought the truck it was at the stock height. I put 3 inch blocks in the back. Anyway Wayno the truck did not vibrate at all before I lowered it. What do you have in mind? And thank for everybody's responces. Quote Link to comment
wayno Posted January 12, 2013 Report Share Posted January 12, 2013 Yes it has been lowered Wayno. And iam glad you mentioned that. I was just thinking that when I bought the truck it was at the stock height. I put 3 inch blocks in the back. Anyway Wayno the truck did not vibrate at all before I lowered it. What do you have in mind? And thank for everybody's responces. There are others that know more about this subject than I do, I just know that at a certain point you have to shim/raise the carrier also, so let us wait and see what the ones that have knowledge of this subject have to say about this new info. Quote Link to comment
Phixius Posted January 12, 2013 Report Share Posted January 12, 2013 Mine did this when I used 4" blocks. My slip joint on the drive shaft was rusted stuck and didnt slide.. Quote Link to comment
datzenmike Posted January 12, 2013 Report Share Posted January 12, 2013 U joints work in pairs. If you have ever held a driveshaft and turned it in your hands you probably noticed that it does not turn smoothly. Instead it tends to be tight then loose tight loose and turns in a jerking motion when there is a bend in it. This is because the u joint actually travels through an ellipse or oval path and has to accelerate and slow down as it turns. Because it is rigidly connected to both driveshafts this acceleration/deceleration becomes a vibration. To eliminate most of this, the second U joint is positioned (180 degrees out) so that it's decelerating while the other is accelerating and they cancel. Because the sharper the bent the harder the driveshaft must accelerate/decelerate, it's important that both driveshaft U joint angles are the same. Vibrations only cancel if they are equal. So, the front driveshaft to the rear driveshaft U joint angle must equal the rear driveshaft to the differential U joint angle. You can shim the rear end where it U bolts to the leaf spring perch. This is what I did on my 710 goon. A 2" lift had the effect of tilting the differential up at the front, so a 1/8" shim between the leaf spring and the rear of the spring perch tilted it down slightly. Luckily when the U bolts were all tightened down the two angles were identical and I had my ride back. The vibration and groaning sound was gone. On a two piece driveshaft I've heard that a 3/4" shim or spacer under the carrier bearing will lift the driveshafts in the middle and cancel out the vibration. You may be able to add washers to adjust. Quote Link to comment
ggzilla Posted January 12, 2013 Report Share Posted January 12, 2013 A normal lift with straight-cut blocks will not change the pinion angle and should not be "corrected". On the other hand, if you put angle-cut blocks in, you need to adjust the angle of the shaft as per Mike's suggestion. Also if you changed the spring shackle length. Quote Link to comment
datzenmike Posted January 12, 2013 Report Share Posted January 12, 2013 The pinion angle relative to the ground remains the same but when the diff is raised the driveshaft angle does change. Yeah I guess I said 'had the effect of tilting the front of the diff up'... with the body lower (or the diff higher) the driveshaft was tilted upward to meet it. Quote Link to comment
ggzilla Posted January 13, 2013 Report Share Posted January 13, 2013 How do level lowering blocks change the angle? Quote Link to comment
datzenmike Posted January 13, 2013 Report Share Posted January 13, 2013 The differential doesn't move at all. The body lowers down over it. The driveshaft angle changes. Quote Link to comment
ggzilla Posted January 13, 2013 Report Share Posted January 13, 2013 Oh, so you are only lowering the back of the car. That might do it. Quote Link to comment
Phixius Posted January 13, 2013 Report Share Posted January 13, 2013 Remembering my vibration at speed was from unbalanced wheels. It was under accel and deaccel that I had vibration with the stuck slip joint. Quote Link to comment
Bentaxlebob Posted January 13, 2013 Report Share Posted January 13, 2013 Additionally check the exhaust pipe, from collector to rear tip. I had trouble with that once. Terrible vibration. When I did go to the muffler shop I could never reproduce the vibration sdue to RPMs ( street unable to reproduce rpm+speed) Specially if new or modified exhaust system has been replaced. You could have an out of balance drive shaft. Perhaops you lost some balancing weights from it. Loose or worn out wheel bearings. I know you said your wheels are balanced, but once i had a problem with wheels out of balance. The shop I was going to ( kind of cheap location) kept telling me the wheels were balanced, but there it was, vibration. Went to a better shop ( better machines/technology at hand ) and no more vibration. Quote Link to comment
what Posted January 13, 2013 Author Report Share Posted January 13, 2013 Thanks for all the advice. I will be going under the truck here in the next few days. I will keep you posted on it. Quote Link to comment
banzai510(hainz) Posted January 13, 2013 Report Share Posted January 13, 2013 ck the driveline bolts by the trans, then if 5 speed lowerd maybe make a spacer under carrier bearing. the carrier bearing can let the driveling move about a 1/4 in inside so dont panic. mine does this also. Mine was the bolt getting loose ans onl 2 bolts holding it on. tighten it up and was ok Quote Link to comment
mrbigtanker Posted January 13, 2013 Report Share Posted January 13, 2013 Just raise back up and your problem is solved haha.I got 4" blocks and i got a slight groan at speeds over 80 mph but you have to have something alot more going on under there.Check your blocks first is what should be the first thing and make sure you got the fat pins all ligned up on the blocks to the spring plate and it is all sitting flush,second i would check to make sure you also tightened it up all well to.Some times we get in a hurry and we miss things,so in my opinion if it did not do it before start with what you did first and work your way out from there. 1 Quote Link to comment
datzenmike Posted January 13, 2013 Report Share Posted January 13, 2013 Also if using worn U joints putting more bend on the driveshaft will make everything even worse. Quote Link to comment
gene knight Posted January 15, 2013 Report Share Posted January 15, 2013 so i have a set of 4" angled drop blocks in the rear of my 521 and new ujoints on my 2 piece driveshaft i did have an issue with driveshaft being offset but that was with 3" straight cut blocks but now that i have changed them for the 4" the issue seems better but do i need to use some shims/spacers to make sure my drive shaft/pinon angle with not vibrate and i am using stock 4 speed trannny Quote Link to comment
ggzilla Posted January 15, 2013 Report Share Posted January 15, 2013 Yes, the angle blocks are used to reduce the angle of the U-joints, and do require the transmission to be angled down the same amount. With his 3" lowering blocks, the driveshaft should be OK unless it is marginal (stiff U-joints or binding slip yoke surfaces) -- those problems may be OK with the standard suspension but not when it's lowered. Quote Link to comment
datzenmike Posted January 15, 2013 Report Share Posted January 15, 2013 Best to just look at the two angles. I removed the driveshaft and held a geometry set compass against the differential yoke where the driveshaft bolts up to. Hold a piece of string with a couple of nuts tied on the end for a plumb bob. You may have to get creative but what you are looking for is the angle at both ends of the driveshaft to be the same or as close as you can get them. Do the same and the transmission end or the back of the second driveshaft. By dumb luck my first set of shims that I added tilted the differential up at the front and this was just enough to equal the transmission end. I couldn't see any differences between them... so good enough. The difference was noticable immediately. Quote Link to comment
gene knight Posted January 16, 2013 Report Share Posted January 16, 2013 now do i have to shim center support bearing cuz i noticed that the rubber around csb is lower and is not touching d.s.loop Quote Link to comment
ggzilla Posted January 16, 2013 Report Share Posted January 16, 2013 No, but you might need to replace the cushion rubber or the bearing rubber. Quote Link to comment
what Posted February 13, 2013 Author Report Share Posted February 13, 2013 Shimed up the carrier bearing and what a improvement. Thanks for all of your help. P.s. A freind of mine has a complete 521 (1971) rear end complete with leaf springs for sale. He wants $150.00 for it. Quote Link to comment
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