Small rear end vibration at speed
Thread Starter
Racer
Joined: Jan 2005
Posts: 492
Likes: 0
From: Birmingham AL
Small rear end vibration at speed
Now that I'm getting through the various little tuning details I'm able to feel a few small things now. One of these is a small amount of vibration from the rear end that changes depending on the road speed. The amount of vibration doesn't increase but it's presence is either there or not depending on road speed. It is a bit tough to describe but it feels like a small amount of shake in the seat of the pants.
To fill in some other details, this is a complete frame off resto. The trailing arms were completely rebuilt by Van Steel. The u-joints were all replaced on the original half shafts. The shafts were sand blasted and painted to pretty 'em up. The diff was drained and re-filled with new fluid but not rebuilt. The diff mount was replaced with a new rubber unit. The end play on the yokes was within acceptable limits, I think less than 4 mils. The wheels are all brand new and completely balanced. The 9 leaf spring was rebuilt and I am using KYB shocks on all 4 corners.
Any ideas on where to start looking first to determine where it's coming from?
To fill in some other details, this is a complete frame off resto. The trailing arms were completely rebuilt by Van Steel. The u-joints were all replaced on the original half shafts. The shafts were sand blasted and painted to pretty 'em up. The diff was drained and re-filled with new fluid but not rebuilt. The diff mount was replaced with a new rubber unit. The end play on the yokes was within acceptable limits, I think less than 4 mils. The wheels are all brand new and completely balanced. The 9 leaf spring was rebuilt and I am using KYB shocks on all 4 corners.
Any ideas on where to start looking first to determine where it's coming from?
Cruising
Joined: Jan 2006
Posts: 13
Likes: 0
Looks like you had the rear suspension apart... might want to check your rear wheel camber. Wrong camber angle can some time impact on rear axle geometry and can sometimes cause vibration at the half shafts outer u-joints. I had first hand experience. Had adjusting jam nut on camber adjustment arm worked it way loose causing slow and intensifying vibration... Readjusted to correct camber and solved the problem. Check Camber, just a thought.
Regards
Regards
Former Vendor
Joined: Nov 2005
Posts: 683
Likes: 1
From: Mounds View Minnesota
if you've had the rear end out, and sometimes even if you havent, vettes are notorious for misalignment of the trans to diff. not up and down but side to side.
If the drive shaft angles are not exactly the same front and rear you WILL get vibration.
If the drive shaft angles are not exactly the same front and rear you WILL get vibration.
Thread Starter
Racer
Joined: Jan 2005
Posts: 492
Likes: 0
From: Birmingham AL
Originally Posted by Corvette Engineering
if you've had the rear end out, and sometimes even if you havent, vettes are notorious for misalignment of the trans to diff. not up and down but side to side.
If the drive shaft angles are not exactly the same front and rear you WILL get vibration.
If the drive shaft angles are not exactly the same front and rear you WILL get vibration.
Race Director
Joined: Feb 1999
Posts: 19,659
Likes: 34
From: Lenoir City Tennessee
Ci 6, 8 & 10 Veteran
St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15
Originally Posted by steves_77vette
How can you measure the angles to know if they are aligned or not?
My thoughts exactly. I have always thought that I was pretty close with mine but if there is a definate spec that I can check, lets hear it. I think I can fix it till it is broke.
Drifting
Joined: Oct 2003
Posts: 1,426
Likes: 1
From: VetteMOD
St. Jude Donor '05-'07
I am investigating driveline angles on my car. The recommended method is to put a protractor style level on the diff pinion yoke and the trans output yoke. Angles should be equal and opposite. If your engine/trans is rotated down 3 degrees, your pinion should be up 3 degrees.
That said, I don't know if it is possible to have the diff pinion in a C3 up that far. I am making a guage to check, I think Spicer sells one for about $300. Let me know if you buy one, I need to borrow it!
That said, I don't know if it is possible to have the diff pinion in a C3 up that far. I am making a guage to check, I think Spicer sells one for about $300. Let me know if you buy one, I need to borrow it!
Race Director
Joined: Feb 2005
Posts: 16,100
Likes: 17
Suggest also a new alignment and fresh wheel balance first...I had what you describe and it turned out to be the left rear tire had been "counter" balanced by a lazy tech..the dummie used two weights..one was 5 ounces..!!
Rich
Rich
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Former Vendor
Joined: Nov 2005
Posts: 683
Likes: 1
From: Mounds View Minnesota
Wheel vibration is lower frequency, as it is the wheel flopping around, so it will be a thump thump thump.
Driveshaft vibration is at 2 times the engine rpm in the 1:1 gear ( 3rd in a th400, 4th in a 4 speed, 4th in a 5speed overdrive...) so it is fairly high frequency, more of a buzz.
The aligning the drive shaft angles means making the driveshaft to yoke angles the same at both ends. You don't really care what the angle is as long as the front is the same as the rear.
People put the Diff in and don't align it and that cuses angles to be off side to side. Up and down is hard to change unless you have done a transmission swap.
The best way is one of the pinion angle protractors, but good luck getting one on the driveshaft of a C3 with the body on
I used some heavy wire, bent to the angle of one end and a lot of trial and error!
Adjust, drive...adjust, drive...
Driveshaft vibration is at 2 times the engine rpm in the 1:1 gear ( 3rd in a th400, 4th in a 4 speed, 4th in a 5speed overdrive...) so it is fairly high frequency, more of a buzz.
The aligning the drive shaft angles means making the driveshaft to yoke angles the same at both ends. You don't really care what the angle is as long as the front is the same as the rear.
People put the Diff in and don't align it and that cuses angles to be off side to side. Up and down is hard to change unless you have done a transmission swap.
The best way is one of the pinion angle protractors, but good luck getting one on the driveshaft of a C3 with the body on
I used some heavy wire, bent to the angle of one end and a lot of trial and error!
Adjust, drive...adjust, drive...