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Tobias A
 
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Need your advise, Rear Bearings "play"

Hi Guys,

I hope I can get some help from you regarding my rear bearings on my 930. Was out driving the other day running higher speeds. I've got some very nasty vibrations from the rear when going above 110 mph. Reaching approx 140 mph got very scary and "shaky". I suspected that my rear bearings are causing these bad vibrations.

I got new bearings installed 2 years ago. Had them replace by a Porsche workshop as we didn't dare to change ourselves. I'm told that they need to me torqued correct and everything has to be just right. As our 930's go very fast you want to make sure everything is correct.

I now suspect that there is too much play at my bearings. Everything was swapped to new parts incl the "crunch sleeve".

I have filmed the "play" on both sides. If you turn up the volume you can hear the knocking sound. It's kind of hard to see the play as the car starts to rock a bit. When going fast and then slowing down you can hear a "huming" sound. This goes away if I steer back and forth or if I slighty press the brake pedal.

Here are the 2 vids:

Left side: https://www.youtube.com/watch?v=K8YJa7X-sqM

Right side: https://www.youtube.com/watch?v=cp4DUMWK2cg


Many thanks in advance!

/ Tobias

Old 05-29-2013, 06:53 AM
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The only way to measure the rear bearing runout {play}, is with a dial indicator located on the far outside of a perfectly flat rear rotor.
As the axle & rotor assembly is rotated, there is a maximum of .004 runout tolerance allowed, as read on the indicator.
This is so small of a measurement that it can NOT be seen with the naked eye, anything seen by the naked eye is very bad.

While your videos are an eye opener to a problem, further disassembly and inspection is required, in order to find out exactly what is wrong with your rear axle assemblies.

Best of luck.

Mark

Last edited by full quack; 05-29-2013 at 08:34 AM..
Old 05-29-2013, 08:29 AM
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i would jack the rear up and put on stands. then i would put a jack under the trailing arm and jack that up to put weight on it. then i would put the dial on the top edge of the rim. then with another jack i would gently jack the bottom outside edge of the tire. its kind of how i check ball joints except i dont use a dial.
it may tell you something and it may not. dont think it would hurt to try.
it should not take much pressure under the tire to tell if anything is lose.

have you had the car that fast and everyting fine? did they remove the trailing arm? what about rear end alignment? have you had the toe checked on the rear.
was it like a wheel out of balance? front end alignment?
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Last edited by T77911S; 05-29-2013 at 09:17 AM..
Old 05-29-2013, 09:15 AM
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Tobias A
 
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Thanks for the answers!

I removed the trailing arms and turned them in for swapping bearings. After that I had a high adjustment and all wheels aligned. Tires balanced as well.

I think this problem has escalated more and more. I remember I had small vibrations in the beginning. But now it's too scary to go fast, so the vibrations are really bad at the moment :-/
Old 05-29-2013, 01:55 PM
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Tobias A
 
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Hi again,

I just checked my "play" on the bearings and it appers to be approx avg 15/100 mm, which is way too much :-/

Check my video here: 930 rear bearing play 15/100mm - YouTube

What do you think?
Old 05-30-2013, 02:36 PM
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It looks like you're not checking axial play the way you move... Try to move only in and out. Limit is 4/100mm as you know, but desired is more until zero, even slight force is allowed, see manual. I would go through the complete procedure according manual

Check my post here:

Adjusting rear wheel bearings 930
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930 Turbo '81 Too many modifications to list

Last edited by proffighter; 05-31-2013 at 04:39 AM..
Old 05-31-2013, 04:32 AM
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Tobias A
 
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Thumbs up Done!

Thanks Roland!

I think I got em right now! Play is almost nothing now. 0 - 0.01mm and the car feels much better at higher speed. I still have some small vibrations in the rear, but I think the rear tires may be a little off balance.

Got to borrow a badass Torque Wrench from a Porsche friend, and got some good input from him. Torque at the rear left ended up at 425nm and 440nm on the right hand side.

Old 06-05-2013, 02:03 AM
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but don't forget to adjust too the 300nm at the end, means do not leave them on the 400+ level, this is only to crush the bushes!
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930 Turbo '81 Too many modifications to list
Old 06-05-2013, 03:47 AM
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Tobias A
 
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Roland, are you sure that I shall "Turn back" the nut to 300nm ? Wouldn't that give me too much play again?
Old 06-05-2013, 04:42 AM
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Quote:
Originally Posted by Toby930 View Post
Roland, are you sure that I shall "Turn back" the nut to 300nm ? Wouldn't that give me too much play again?
No, as play is given by the spacer deformed while increasing to max torque (or until desired play is reached). Check manual below

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930 Turbo '81 Too many modifications to list
Old 06-05-2013, 07:55 AM
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Tobias A
 
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OK! But, can anything get damaged if the nuts are torqued to 425 - 440 nm?
Old 06-05-2013, 12:44 PM
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My factory service manual clearly states that the nut can be over tightened as needed to obtain the correct crush, but then MUST be loosened and re-torqued to the correct torque setting for the bearings.

Mark
Old 06-05-2013, 01:00 PM
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Quote:
Originally Posted by full quack View Post
My factory service manual clearly states that the nut can be over tightened as needed to obtain the correct crush, but then MUST be loosened and re-torqued to the correct torque setting for the bearings.

Mark
Finally, what I wanted to say from beginning... Sorry for my poor english

TSCHULDIGUNG!

BTW the page I added is from a factory manual I guess, got only a PDF, I have an real one, but that's german, so not ideal for posting here...

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930 Turbo '81 Too many modifications to list

Last edited by proffighter; 06-05-2013 at 02:26 PM..
Old 06-05-2013, 02:24 PM
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