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Proper run out or play on front brake rotors
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jeremypbeasley
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PostPosted: Sun Aug 28, 2022 10:41 pm    Post subject: Proper run out or play on front brake rotors Reply with quote

Howdy there internet people.

I just rebuilt my whole front end on my 1985 GL. Still figuring out what height I want to sit at but the more immediate issue is play on the rotors. The ride was obviously noisier and I could feel the wheels rock back and forth when I pulled and pushed on them.

When I replaced the rotors and bearings, I followed the Bentley and other online tutorials for getting the lock nut right. But this much play doesn’t seem right to me. That said, I don’t see a spec to know how loose is actually too loose. Or even how much tighter I need it to be.

To give you something more quantitative, I pulled the wheel, attached my trusty harbor freight machinist dial and rocked it back and forth. Video link below.

Pulling away from the van, the run out is .03” and pushing it’s about .01”, a total range of .04”.

Any tips to get my back to the right amount of play would be very much appreciated!

https://youtu.be/JFHdCzetaDE


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MarkWard
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PostPosted: Mon Aug 29, 2022 5:23 am    Post subject: Re: Proper run out or play on front brake rotors Reply with quote

Did you mean .004”? .04” is a lot. Anyhow it’s a feel thing, but short of that, on new bearings I like to “feel” ever so slight play. You should always recheck after some road miles. The sliding the thrust washer with a screwdriver is a little subjective for owners doing this for the first time.

For your setup, I’d say .001” to .002” would be safe. You don’t want them too tight. That is worse for them than too loose. The Mercedes nuts found in other threads give you the ability to easily readjust vs the vanagon ones.

This will bump your thread.
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jeremypbeasley
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PostPosted: Mon Aug 29, 2022 8:53 am    Post subject: Re: Proper run out or play on front brake rotors Reply with quote

Thanks Mark!

Maybe I'm reading the dial incorrectly. Check out my video link above to see?

For what it's worth, I'm measuring all of this about ~200 miles after the rebuild, so it's had some time on the road to wear in.

If they are, in fact, too loose, do I just pop the lock nut off, replace it with the adjustable Mercedes one and good to go? Guess I assumed that if they were very loose, I'd damaged the bearings or rotor possibly.
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MarkWard
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PostPosted: Mon Aug 29, 2022 9:24 am    Post subject: Re: Proper run out or play on front brake rotors Reply with quote

Well, as best I can tell you are measuring .040 of an inch and I would have to say that is way too much play. I've never measured with a dial indicator so my "feel" may not translate into an actual measurement.

I'd probably pull the nut off and examine the outer bearing and race. repack the bearing if the race and bearing look good and reinstall with the mercedes nut and adjust up till you have no play and back the nut off slightly so you can just feel the slightest movement.

Otherwise you could just replace the nut and tighten up the freeplay to there is a small amount. It's up to you. How is the other side? Since you've run these, they have worn in and maybe you didn't get the original preload exactly right. That's why its best to recheck after some miles on new bearings. Sorry I can't be of more help.
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PostPosted: Mon Aug 29, 2022 9:46 am    Post subject: Re: Proper run out or play on front brake rotors Reply with quote

I have another old car that has a procedure to seat the front bearings: torque to 12 lbs while turning the wheel, back off 1/2 turn, torque to 7 lbs, back off 1/4 turn.

Not sure if there was a similar procedure from VW for this, but it worked well for me on my other antique. The first tightening moved the hub more than I was expecting, but I guess it seated properly and squeezed the grease into all the right places.
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ALIKA T3
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PostPosted: Mon Aug 29, 2022 10:21 am    Post subject: Re: Proper run out or play on front brake rotors Reply with quote

You could have a damaded spindle snout too.

The washer on the drop link bushing seems wrong on the picture, the cup should be up, not cupping the bushing, or it'll cut into the bushing.
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PostPosted: Mon Aug 29, 2022 12:02 pm    Post subject: Re: Proper run out or play on front brake rotors Reply with quote

PDXWesty wrote:
I have another old car that has a procedure to seat the front bearings: torque to 12 lbs while turning the wheel, back off 1/2 turn, torque to 7 lbs, back off 1/4 turn.

Not sure if there was a similar procedure from VW for this, but it worked well for me on my other antique. The first tightening moved the hub more than I was expecting, but I guess it seated properly and squeezed the grease into all the right places.


Backing off 1/4 turn would give way too much clearance for my Vanagons.
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PostPosted: Mon Aug 29, 2022 1:04 pm    Post subject: Re: Proper run out or play on front brake rotors Reply with quote

The measuring setup in the youtube video will not result in accurate measurement of the wheel bearing free play. In the setup shown, the measurement is exaggerated due to the fact that the dial indicator is at the end of a long lever arm. If we are going to compare specs (I have not seen any specs in the Bentley manual), then the measurement needs to be reproducible. As depicted, the setup also includes in the measurement whatever play exists in the upper ball joint. At maximum compression or droop, ball joints can have more play than in the mid-point of A-arm travel.

The better approach would be to fix the magnet (or a bolted approach) to the steering knuckle and adjust so that the tip of the dial indicator touches the rotor.

Having said that, I would suggest that it is possible that the new bearing races were not pressed squarely into place, which could cause runout and also prevent effective wheel bearing adjustment.

The "adjustable" wheel bearing nuts are always preferable to the "staked" variety. Hope this helps.
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PostPosted: Mon Aug 29, 2022 1:26 pm    Post subject: Re: Proper run out or play on front brake rotors Reply with quote

An old German mechanic taught me a simple technique for adjusting roller wheel bearings that are for a disc brake about 55 years ago. Tighten the nut as tight as you can with your fingers while spinning the hub. Then using a wrench tighten the nut a little more to put a pre-load on the bearings. Spin the hub to express excess grease from the bearings. Loosen the nut. Tighten the nut as hard as you can with your fingers again. Tighten the nut again with a wrench a small amount, maybe 5 degrees or less. There should now be the smallest pre-load on the bearing. Run-out from bearing play should now be non-existant.

This is tighter than the factory specifies. But having the rotor run perfectly true on a disc brake system is a good thing. This has been my standard procedure for adjusting roller wheel bearings since then even on drum brake systems. I have done this hundreds or thousands of times with no observed ill effects. If there is slop after doing this there is another problem.

Or you could do like Mercedes says. They want to achieve play of one to two thousands of an inch at the edge of the rotor. Some people think the bearing cannot be pre-loaded. But I have seen many roller bearings pre-loaded in factory applications. I have driven hundreds of thousands of miles with slightly pre-loaded roller wheels bearings. And my customers have driven millions of miles with pre-loaded roller bearings. Of course the technology is obsolete now. The modern sealed bearing assemblies are highly pre-loaded roller bearings.
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jeremypbeasley
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PostPosted: Mon Aug 29, 2022 6:42 pm    Post subject: Re: Proper run out or play on front brake rotors Reply with quote

Howesight wrote:
The measuring setup in the youtube video will not result in accurate measurement of the wheel bearing free play. ...


Great point! I've adjusted it to it's just hitting the knuckle.

Going to remove both rotors (begrudgingly), inspect for any damage, and then put them back on once my Mercedes lock nuts arrive.

Thanks to another thread, I found the part numbers: 16W48 and 1163340372.

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dobryan
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PostPosted: Tue Aug 30, 2022 5:44 am    Post subject: Re: Proper run out or play on front brake rotors Reply with quote

Not piling on but that setup still does not measure the play correctly. The dial gauge needs to be positioned at a 90 degree angle from the object being measured and against a surface 90 degrees to the dial probe. The angles present in that setup will not give you the actual amount the disc is moving in and out along the axle.

I would mount the base on the control arm and have the dial gauge probe resting on the vertical surface of the rotor.
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