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Old 04-24-2008, 08:46 PM
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Rear End vibration driving me insane

I have an 87 caprice that originally had a 7.5" 10bolt rear with 2.73 gears non-posi. I went to the junkyard and scored a police car rear end out of a 1989 caprice so it was a direct bolt in. The new rear was an 8.5" 10 bolt with 30 spline axles.

I had it rebuild with all new parts. I put in a 3.90 yukon gear ring and pinion with an eaton posi and all new bearings, seals, even brand new yukon 30 spline axles. It has the big 12" drums which are all new as well. The problem is when I reach about 65mph on the highway or spin up the tires in a burnout I get such a tremendous vibration it makes my dome light rattle. The loud BZZZZZZZZ is annoying and it makes my rearview mirror useless it shakes so much. I can feel it originating from the rear of the car. It sounds worse than it feels but it still feels bad.

I drove the car for years with the 7.5 rear with no problems. I pulled the car in, swapped out the rear and WHAM from the first test ride with the new rear I get a vibration. Ive tried two different driveshafts including the original one which I had shortened 1" and rebalanced with new ujoints. Ive tried different drums thinking they were out of balance. Ive replaced the axles too! I am at my wits END! Ive even considered the tranny output shaft, but i didnt have the issue hours earlier before the rear swap. I did replace the rear control arm bushings with energy suspension peices while the rear was out. The tranny is a 200-4R overdrive that was rebuilt less than a year ago.

The first night the rear end travel was kinda stiff, like maybe I got the control arm mounting bolts too tight? I could stand on the rear bumper and jump off and the rear of the car would stay down. It has since loosened up a little but it still isnt 100% like it was before.

Any ideas?

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Old 04-26-2008, 09:39 PM
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rear end vibration

You may be causing too much of a driveshaft angle with the new rear end. I have had problems as you have had and once I rule out the driveshaft, drums, and axles I also move to adjust the driveshaft angle. Of course you either need to raise/lower the transmission or most likely your rear end is either pointing to much upward or downward. I don't have the specs but there are many articles posted here with the correct specs.
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Old 04-26-2008, 11:31 PM
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Thanks for the reply, this has really been driving me crazy. I'll look into this.
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Old 09-24-2008, 10:46 PM
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Well after all this time, the problem still exists. If I put my car up on jack stands and start the engine and put it in drive to watch the wheels spin the drivers side looks good. The axle slides in and out like butter when im taking it apart and reassembling. The passenger side has a noticeable circular wobble to it and it is a little harder to slide the axle in and out of the housing when working on it. Almost like the axle is getting in a bind just before its pushed in far enough to get the c-clip out. I thought it was a bent axle even though they are brand new so i swapped it for another new one....same deal.

Could it be something in the differential? outer axle bearing? bent housing?

The diff is a brand new Eaton posi...the bearings are new....everythings new expect the housing I got it at the junkyard. Car wasnt wrecked.

Please someone give me some suggestions. I keep spending hundreds of dollars to get no result.
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Old 09-24-2008, 11:06 PM
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Try swapping tires from side to side and see if the problem switches sides as well. If ity does, then you know the rims tires are the thing to look at..

If not, I'd spend 20 more dollars at a discount tool store on a dial indicator and magnetic base and start checking runout on the axle flange, axle center spud ,(the protruberance that the rim centers itself on).


Later, mikey
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Old 09-24-2008, 11:42 PM
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Just for info's sake , do you mind if I ask what the boneyard charged for the Squad rearend? (I have 2 Caprices, 1-86,1-89). I'm not trying to be nosey, it's just that I may need 2nd upgrade in the forseeable future. (I got the 3.08 that's in my '86 from a complete '83 donor car I got for $100, the '89 still stock/open). -Just curious what the boneyards might charge for P.I. rearend. -Jim (If not comfortable with posting that answer on the thread, then just pm me. -If you don't mind giving an answer, that is).

Last edited by j.d.brown.042964; 09-25-2008 at 12:20 AM.
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Old 09-25-2008, 01:36 AM
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Loosen up the 4 mounting bolts for the rearend and ck. Than tighten bolts back up at ride height .

Last edited by AJ Motorsports; 09-26-2008 at 06:36 PM.
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Old 09-25-2008, 08:32 AM
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Quote:
Originally Posted by AJ Motorsports
If this where my problem this is how I would ck it out 1st put the rear of car on stands run up till vibration happens than remove wheels bolt on drums reck pull ebrake cable and vise grip on each side so you make each side run alone and ck than remove axles and run up to speed if still there than pull drive shaft and run up to speed to ck trans while shaft is out lay it on floor and see if joint ends are in phase meaning end caps are in alignment than put shaft back in and see if there is about and 1.25 inch's to slide drive shaft in before it hits trans to reinstall drive shaft to ck pinon angle put car on stands level as possible put angle gauge on bottom of rear end housing should be 2 to 4 degree's downward angle look for any shinny spots on drive shaft where it could be binding than loosen up the 4 mounting bolts for the rearend and ck than tighten bolts back up at ride height this order of elimination should find the problem
If you used some capital letters and punctuation it would make your post easier to read and understand.

He'd better put a plug in the back of the trans if he wants to run the motor and trans with no driveshaft...Otherwise he'll be cleaning up a big pool of oil.

Are you saying that the rear end pinion angle needs to be 2-4 degrees down in front,or down at the rear?

The way to properly measure the pinion angle is to put the car up on stands with the suspension loaded, then measure the angle of the motor, then measure the pinion angle...In most cases, the pinion shaft needs to be set up so that under a load, the shafts become parralel. With the type suspension he has, that would make the pinion shaft set on an angle that is 1-2* greater than the angle of the motor. You also need to consider the operating angle of theU-joints, which could be way off if the car has been excessively lowered or lifted.

Check this link out..
http://www.drivetrain.com/driveline_angle_problem.html


Making sure the suspension bolts are tightened up when the car is at ride height and checking the driveshaft can slide into the trans are good ideas.


Later, mikey
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Old 09-25-2008, 10:41 AM
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I dont know how to check for axle run out. Ive never used a dial indicator before. I might be able to figure it out.

Quote:
Originally Posted by powerrodsmike
Try swapping tires from side to side and see if the problem switches sides as well. If ity does, then you know the rims tires are the thing to look at..

If not, I'd spend 20 more dollars at a discount tool store on a dial indicator and magnetic base and start checking runout on the axle flange, axle center spud ,(the protruberance that the rim centers itself on).


Later, mikey
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Old 09-25-2008, 10:43 AM
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I got there on a half off day and scored the complete rear minus drums for $50.00 It had 3.42 gears in it originally. It has the large drum brakes.


Quote:
Originally Posted by j.d.brown.042964
Just for info's sake , do you mind if I ask what the boneyard charged for the Squad rearend? (I have 2 Caprices, 1-86,1-89). I'm not trying to be nosey, it's just that I may need 2nd upgrade in the forseeable future. (I got the 3.08 that's in my '86 from a complete '83 donor car I got for $100, the '89 still stock/open). -Just curious what the boneyards might charge for P.I. rearend. -Jim (If not comfortable with posting that answer on the thread, then just pm me. -If you don't mind giving an answer, that is).
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Old 09-25-2008, 10:49 AM
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Its definetly something to do with the right axle or something. Even with the wheel off it looks wobbly. Its a little tight going into the splines on the differential as well. The other side is great. I know now its not the driveshaft, pinion angle or transmission. I cant run the tranny with the driveshaft out. It will make a big mess not to mention the shaft is floating without the slip yoke of the driveshaft slid in there to ride on the bearing. The output shaft would flop all around and cause damage im sure.

Quote:
Originally Posted by AJ Motorsports
If this where my problem this is how I would ck it out 1st put the rear of car on stands run up till vibration happens than remove wheels bolt on drums reck pull ebrake cable and vise grip on each side so you make each side run alone and ck than remove axles and run up to speed if still there than pull drive shaft and run up to speed to ck trans while shaft is out lay it on floor and see if joint ends are in phase meaning end caps are in alignment than put shaft back in and see if there is about and 1.25 inch's to slide drive shaft in before it hits trans to reinstall drive shaft to ck pinon angle put car on stands level as possible put angle gauge on bottom of rear end housing should be 2 to 4 degree's downward angle look for any shinny spots on drive shaft where it could be binding than loosen up the 4 mounting bolts for the rearend and ck than tighten bolts back up at ride height this order of elimination should find the problem
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Old 09-25-2008, 10:50 AM
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I think i'll shoot some video of the axle and let you all see what I mean. Keep the suggestions rolling in though maybe I can get it nailed. I appreciate all the response!


Quote:
Originally Posted by powerrodsmike
If you used some capital letters and punctuation it would make your post easier to read and understand.

He'd better put a plug in the back of the trans if he wants to run the motor and trans with no driveshaft...Otherwise he'll be cleaning up a big pool of oil.

Are you saying that the rear end pinion angle needs to be 2-4 degrees down in front,or down at the rear?

The way to properly measure the pinion angle is to put the car up on stands with the suspension loaded, then measure the angle of the motor, then measure the pinion angle...In most cases, the pinion shaft needs to be set up so that under a load, the shafts become parralel. With the type suspension he has, that would make the pinion shaft set on an angle that is 1-2* greater than the angle of the motor. You also need to consider the operating angle of theU-joints, which could be way off if the car has been excessively lowered or lifted.

Check this link out..
http://www.drivetrain.com/driveline_angle_problem.html


Making sure the suspension bolts are tightened up when the car is at ride height and checking the driveshaft can slide into the trans are good ideas.


Later, mikey
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Old 09-25-2008, 10:51 AM
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Quote:
Originally Posted by 973kgt
I dont know how to check for axle run out. Ive never used a dial indicator before. I might be able to figure it out.
It's easy, check google image search for "checking axle runout" or "axle flange runout" for a bunch of different pictures of setups, indicator types, etc..I see pics of guys who are checking tire runout as well with a dial indicator.

The flexible arm type base is easier to work with, but more expensive.




here is the results I got..
http://images.google.com/images?hl=e...h+Images&gbv=2

Later, mikey
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Old 09-25-2008, 11:02 AM
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Normally,If it's a angle causing the shake, it will do it under acceleration or decel. Double check the u-joint at the rear,That year of car should have a joint with Spicer#5-3147X, To double check this,Your pinion yoke should have NO Tab's on the outside of the yoke to center the joint.That joint uses inside snap rings on the cap to center the joint in the pinion yoke. I've seen many instances where people forget to put the snap ring's on the cap's and it will vibrate. Just something to double check.
Cap Dia of the joint is: 1.125
Snap ring dimension "inside" : 2.562
O/A width "outside to outside cap" : 3.370
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Old 09-25-2008, 12:01 PM
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Thanks for answering my nosey question about the cost. I would have figured more $ than that for a factory posi unit from boneyard. I did notice a mention in your earlier portion of the post that may warrant closer attention. Specifically :The passenger side has a noticeable circular wobble to it and it is a little harder to slide the axle in and out of the housing when working on it. Almost like the axle is getting in a bind just before its pushed in far enough to get the c-clip out. I thought it was a bent axle even though they are brand new so i swapped it for another new one....same deal.
Could it be something in the differential? outer axle bearing? bent housing?.
I wonder if POSSIBLY the axletube could have been tweaked or bent if the squad jumped a curb during a chase? Because the tubes are only press-fit into the centerhousing and not normally welded, (unless modified by a hotrodder) I would really be curious if this could potentially be your problem? -Hope you find the cause soon, and can return to actually enjoying your ride. -Jim
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