Vibration diagnostic check list
08-10-2007, 06:40 AM
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Vibration diagnostic check list
As with a lot of people I am fighting a vibration problem at 70mph progressively getting worse as speed increases.
I tried different wheels and tires. Installed an Ls1 driveshaft with new Ujoints. Had it checked for balance and straightness, checked out good.
It still vibrates.
I used a "checklist" that I found on in another thread by RBob and that leads me to believe it is coming from the pinion.
Here is the list with my results in blue.
I isolated the pinion by removing every part of the rear and checking for vibration on stands. Then I pulled the pinion and put in new bearings and races, reinstalled the driveshaft and ran it up to the vibration point with nothing in the housing but the pinion. It still vibrates. Everything "looks" OK.
Pinion yoke problems?
This is a "spare" rear I picked up with broken 4.10's. I installed 4.10's out of an 95 S10 and have no whine, no problems, except this vibration. I can't see any damage to the pinion housing, could that have been a problem?
If there is nothing turning but the motor, tranny, driveshaft, pinion and there is no vibration with the driveshaft removed....it has to be in the pinion or driveshaft, right? I had the driveshaft checked for straightness and balance and they said it is OK. The slip yoke on the LS1 shaft had a little play, so I swapped it for the tighter yoke from my steel shaft. It still vibrates.
I'm not sure where to go from here?
Thanks!! Andy
I tried different wheels and tires. Installed an Ls1 driveshaft with new Ujoints. Had it checked for balance and straightness, checked out good.
It still vibrates.
I used a "checklist" that I found on in another thread by RBob and that leads me to believe it is coming from the pinion.
Here is the list with my results in blue.
Originally Posted by RBob
Fixing vibration problems can be difficult. What I do is to place the
rear on jackstands with the tires a few inches off the ground. Then
raise the front a few inches to match. This is so the vehicle is level.
Note that the rear jackstands are under the rear axle assembly, out by
the trailing arms under the spring seat.
Now start the engine, place the trans in drive (or gear for a stick),
and gently run the MPH up to the point of vibration. Note how it feels,
and remember it. If there isn't any vibration, let the car down and
check the front tires, struts, and such. It isn't in the drive train.
Also check the engine tune, a misfire will cause vibration issues.
Sometimes this can be diagnosed by noting if the vibration occurs only
when the TCC is locked.
If it still vibrates on the jackstands,Still vibrated
remove the wheels/tires and place the lug nuts back onto the axles. Torque lightly.
Start the engine, place the trans in drive (or gear for a stick), and
gently run the MPH up to the point of vibration. Still vibrated
If it doesn't vibrate anymore there is an issue with a/the wheel/tire
assembly.
If it vibrates, remove the brakes drums or rear rotors (which ever it
has).
(AT THIS POINT DO NOT DEPRESS THE BRAKE PEDAL).
Start the engine, place the trans in drive (or gear for a stick), and
gently run the MPH up to the point of vibration. Still vibrated
If it doesn't vibrate anymore there is an issue with a/the brake
drum/rotor assembly.
Before I opened the rear, I put a yoke in the back of the tranny and ran it up to the vibration point. NO VIBRATION!
If it vibrates, pull the axles out. Note that 9-bolt and the 7.5/7.625"
rears are different in how this is done.
Start the engine, place the trans in drive (or gear for a stick), and
gently run the MPH up to the point of vibration. Still vibrated
And so on. . .
The next would be the carrier, Still vibrated then the driveshaft NO VIBRATION(need a yoke in the
trans tailhousing for this). If it smooths out with the driveshaft
removed, the issue can be one or more of three items. The driveshaft,
yoke, or pinion gear. I swapped back to the steel shaft and had the vibration at the same point.... I feel pretty safe to say it isn't the driveshaft.
rear on jackstands with the tires a few inches off the ground. Then
raise the front a few inches to match. This is so the vehicle is level.
Note that the rear jackstands are under the rear axle assembly, out by
the trailing arms under the spring seat.
Now start the engine, place the trans in drive (or gear for a stick),
and gently run the MPH up to the point of vibration. Note how it feels,
and remember it. If there isn't any vibration, let the car down and
check the front tires, struts, and such. It isn't in the drive train.
Also check the engine tune, a misfire will cause vibration issues.
Sometimes this can be diagnosed by noting if the vibration occurs only
when the TCC is locked.
If it still vibrates on the jackstands,Still vibrated
remove the wheels/tires and place the lug nuts back onto the axles. Torque lightly.
Start the engine, place the trans in drive (or gear for a stick), and
gently run the MPH up to the point of vibration. Still vibrated
If it doesn't vibrate anymore there is an issue with a/the wheel/tire
assembly.
If it vibrates, remove the brakes drums or rear rotors (which ever it
has).
(AT THIS POINT DO NOT DEPRESS THE BRAKE PEDAL).
Start the engine, place the trans in drive (or gear for a stick), and
gently run the MPH up to the point of vibration. Still vibrated
If it doesn't vibrate anymore there is an issue with a/the brake
drum/rotor assembly.
Before I opened the rear, I put a yoke in the back of the tranny and ran it up to the vibration point. NO VIBRATION!
If it vibrates, pull the axles out. Note that 9-bolt and the 7.5/7.625"
rears are different in how this is done.
Start the engine, place the trans in drive (or gear for a stick), and
gently run the MPH up to the point of vibration. Still vibrated
And so on. . .
The next would be the carrier, Still vibrated then the driveshaft NO VIBRATION(need a yoke in the
trans tailhousing for this). If it smooths out with the driveshaft
removed, the issue can be one or more of three items. The driveshaft,
yoke, or pinion gear. I swapped back to the steel shaft and had the vibration at the same point.... I feel pretty safe to say it isn't the driveshaft.
Pinion yoke problems?
This is a "spare" rear I picked up with broken 4.10's. I installed 4.10's out of an 95 S10 and have no whine, no problems, except this vibration. I can't see any damage to the pinion housing, could that have been a problem?
If there is nothing turning but the motor, tranny, driveshaft, pinion and there is no vibration with the driveshaft removed....it has to be in the pinion or driveshaft, right? I had the driveshaft checked for straightness and balance and they said it is OK. The slip yoke on the LS1 shaft had a little play, so I swapped it for the tighter yoke from my steel shaft. It still vibrates.
I'm not sure where to go from here?
Thanks!! Andy
08-10-2007, 09:45 AM
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Re: Vibration diagnostic check list
It may be the alignment of the yoke on the pinion. Even though the individual pieces may be OK, sometimes they don't line up once torqued down. To check this will need a dial indicator and a method of mounting it to the rear assembly.
Note: this is para-phrased from the '92 FSM.
First check the driveshaft runout near the rear pinion yoke. Maximum runout is 0.040", if it exceeds this, disconnect driveshaft at rear, rotate 180 degrees and re-check runout. If it is still over spec then check the pinion yoke.
This gets tricky as it needs to be checked where the u-joint caps seat, IOW, the inner surfaces. The GM tool for this is a u-joint with a hollow or round center. The max runout is 0.006". If within this spec, and there is a balance weight on the yoke, remove the balance weight.
However, if there is a balance weight on the yoke then the max allowable runout is 0.015". ONLY if the balance weight is near the low point of runout, then it is OK.
If the balance weight is not near the low point of runout, then remove the weight, and R&R the pinion yoke and rotate it on the pinion until the runout is within 0.010" (I would shoot for a tighter tolerance, and do this without the crush sleeve installed. Then mark the location and install with crush sleeve).
From what I can tell of this, GM counter balanced the pinion yokes to make up for runout.
Replacement yokes don't have a balance weight.
What is interesting is that the '92 FSM chapter on the Propeller Shaft (!) is 90% vibration troubleshooting. From checking runout, driveshaft (oops, propeller shaft) inclination and balancing via hose clamps.
RBob.
Note: this is para-phrased from the '92 FSM.
First check the driveshaft runout near the rear pinion yoke. Maximum runout is 0.040", if it exceeds this, disconnect driveshaft at rear, rotate 180 degrees and re-check runout. If it is still over spec then check the pinion yoke.
This gets tricky as it needs to be checked where the u-joint caps seat, IOW, the inner surfaces. The GM tool for this is a u-joint with a hollow or round center. The max runout is 0.006". If within this spec, and there is a balance weight on the yoke, remove the balance weight.
However, if there is a balance weight on the yoke then the max allowable runout is 0.015". ONLY if the balance weight is near the low point of runout, then it is OK.
If the balance weight is not near the low point of runout, then remove the weight, and R&R the pinion yoke and rotate it on the pinion until the runout is within 0.010" (I would shoot for a tighter tolerance, and do this without the crush sleeve installed. Then mark the location and install with crush sleeve).
From what I can tell of this, GM counter balanced the pinion yokes to make up for runout.
Replacement yokes don't have a balance weight.
What is interesting is that the '92 FSM chapter on the Propeller Shaft (!) is 90% vibration troubleshooting. From checking runout, driveshaft (oops, propeller shaft) inclination and balancing via hose clamps.
RBob.
08-10-2007, 10:19 AM
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Re: Vibration diagnostic check list
I'm still not quite following how to check the run out in the yoke seats.... I need to read that again. I also want to check the runout on both ends of the shaft as installed. (Just to see)
Interestingly enough, the yoke I'm using has no balance weight and no obvious signs of it breaking off. My original rear has a balance weight.
When I install the pinion I use an impact wrench. Is it possible I'm screwing something up when I'm reinstalling the pinion? The pinion is set at 20"lbs rotating.
This rear also came with LCA relocation brackets. My car is stock height, stock contol arms. I am running the middle hole. Relocation brackets shouldn't change the pinion angle, just the torque arm, right?
There has to be a way to diagnose what is wrong with this thing before I spend more money!
08-10-2007, 12:20 PM
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Car: 89 Formula
Engine: LB9
Transmission: T5
Axle/Gears: 9 bolt / 3:45
Re: Vibration diagnostic check list
ahusted
I am dealing with a very similar issue with my car, vibs at 70+mph and also have also isolated the issue down to the driveshaft or the yoke. My problem is worse when coasting in neutral or “floating” with the throttle.
I do have an additional troubleshooting idea that may help you.
Put the car on jackstands with the rear wheels removed.
Get a stick about 3-4 feet long, like a broom stick, and attach a magic marker to the stick at about a 45 degree angle with electrical tape or similar.
Have someone run the car up to vibration speed. While it is vibrating, carefully reach under the car with the magic marker stick and just barely touch the driveshaft with the tip of the marker. Keep all your body parts away from the rotating parts!! This procedure will make a mark on the driveshaft where it is “high” when vibrating. In my case, it was obvious that the driveshaft was vibrating the most at the tail end of the transmission, so that is where I placed the marker.
Make a note of where on the driveshaft the mark was made on the circumference, and draw a line in another color, etc, then clean off the original “”high spot” mark.
Disconnect the driveshaft at the rear yoke and rotate (index) 180 degrees. Tighten everything back up.
Repeat the marking procedure with the driveshaft in the new indexed position.
If the mark now moves to the opposite side of the shaft (180 degrees) , then you can make the assumption that the problem is with the pinion or the rear yoke (runout), since it is not following the driveshaft, but following the rear yoke position.
If the mark stays in the same spot on the driveshaft, the results are less conclusive- the problem may be an improperly balanced driveshaft, or a some resonance from a bent yoke, maybe some other installation issue.
This procedure may help you eliminate the driveshaft as the culprit, so it is worth a try. I have noticed that many of the cars with difficult to solve vibration issues have high gear ratios. I have 3:45, which are middle of the road. Still, that puts my driveshaft is over 4000 rpm at 85mph. Your 4.10’s will cause the driveshaft RPM’s to be even higher. I wonder if typical driveshaft balancing is “good enough” for the higher shaft rpms, although I think more people would have vibration problems if that were the case.
I just did the marking procedure on my car. Even with a twice professionally balanced LS1 driveshaft, with new u-joints, the mark stays in the same spot on the driveshaft after indexing. I can make the mark move by putting a hose clamp on the driveshaft to act as a weight, but can not get the vib to go away by field balancing with the clamps.
I am dealing with a very similar issue with my car, vibs at 70+mph and also have also isolated the issue down to the driveshaft or the yoke. My problem is worse when coasting in neutral or “floating” with the throttle.
I do have an additional troubleshooting idea that may help you.
Put the car on jackstands with the rear wheels removed.
Get a stick about 3-4 feet long, like a broom stick, and attach a magic marker to the stick at about a 45 degree angle with electrical tape or similar.
Have someone run the car up to vibration speed. While it is vibrating, carefully reach under the car with the magic marker stick and just barely touch the driveshaft with the tip of the marker. Keep all your body parts away from the rotating parts!! This procedure will make a mark on the driveshaft where it is “high” when vibrating. In my case, it was obvious that the driveshaft was vibrating the most at the tail end of the transmission, so that is where I placed the marker.
Make a note of where on the driveshaft the mark was made on the circumference, and draw a line in another color, etc, then clean off the original “”high spot” mark.
Disconnect the driveshaft at the rear yoke and rotate (index) 180 degrees. Tighten everything back up.
Repeat the marking procedure with the driveshaft in the new indexed position.
If the mark now moves to the opposite side of the shaft (180 degrees) , then you can make the assumption that the problem is with the pinion or the rear yoke (runout), since it is not following the driveshaft, but following the rear yoke position.
If the mark stays in the same spot on the driveshaft, the results are less conclusive- the problem may be an improperly balanced driveshaft, or a some resonance from a bent yoke, maybe some other installation issue.
This procedure may help you eliminate the driveshaft as the culprit, so it is worth a try. I have noticed that many of the cars with difficult to solve vibration issues have high gear ratios. I have 3:45, which are middle of the road. Still, that puts my driveshaft is over 4000 rpm at 85mph. Your 4.10’s will cause the driveshaft RPM’s to be even higher. I wonder if typical driveshaft balancing is “good enough” for the higher shaft rpms, although I think more people would have vibration problems if that were the case.
I just did the marking procedure on my car. Even with a twice professionally balanced LS1 driveshaft, with new u-joints, the mark stays in the same spot on the driveshaft after indexing. I can make the mark move by putting a hose clamp on the driveshaft to act as a weight, but can not get the vib to go away by field balancing with the clamps.
08-10-2007, 01:25 PM
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Re: Vibration diagnostic check list
I'm still not quite following how to check the run out in the yoke seats.... I need to read that again. I also want to check the runout on both ends of the shaft as installed. (Just to see)
Interestingly enough, the yoke I'm using has no balance weight and no obvious signs of it breaking off. My original rear has a balance weight.
Interestingly enough, the yoke I'm using has no balance weight and no obvious signs of it breaking off. My original rear has a balance weight.
Note where the snap rings are in the pinion yoke once the driveshaft is installed. Those inner yoke surfaces locate the u-joint in the yoke. Use a dial indicator and zero it on one of the inner surfaces, then rotate the yoke 180 degrees and read the dial indicator. The deviation from 0 is the runout.
This is tricky to do as you need to use the same location on the yoke relative to each ear. The areas where the snap ring seats is flat. So need to pick spots that is truely 180 degrees from the other. The area at the base of the bearing cup is best. This spot is also closest to the center line of the pinion shaft.
The run-out gauge GM shows is nifty. Hold a u-joint up in front of you so that it looks like a big plus sign ('+'). Then bore a hole right through the center. It will look sorta' like this (the opening is larger relative to the end caps):
Code:
| --O-- |
RBob.
08-10-2007, 01:53 PM
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Re: Vibration diagnostic check list
Thanks guys!!
I was so excited when I really started to isolate my vibration problem. I had no idea it would be this hard to figure out once I got there.....
Looks like i need to do some more work. I guess I'll start with the runout and then move to marking.
This yoke has no weight welded to it, is it possible it just didn't need it? Or should I use a yoke with a weight on it?
I should get a little time to mess with it this weekend.
I was so excited when I really started to isolate my vibration problem. I had no idea it would be this hard to figure out once I got there.....
Looks like i need to do some more work. I guess I'll start with the runout and then move to marking.
This yoke has no weight welded to it, is it possible it just didn't need it? Or should I use a yoke with a weight on it?
I should get a little time to mess with it this weekend.
08-10-2007, 04:23 PM
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Re: Vibration diagnostic check list
I got a run out on the driveshaft tube on both ends. .012 on both ends in roughly the same spot..... (Under the spec of .040)
Guess I need to find a way to check the pinion runout.
Guess I need to find a way to check the pinion runout.
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