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Old 03-30-2015, 02:58 PM   #1
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Drum wear - Magnet - Bearing Questions

I pull off both of the rear hubs today to re-lube/inspect. I'm never sure how much wear/scoring is acceptable where the magnet rides on the drum. Both sides show some scoring the RR the most (see pics). The magnets still seem to have wear left, but the RR does have a "groove" in it (and of course the drum as mentioned). Again, how much of this is acceptable?

Also the bearing on the RR doesn't appear to be scored etc. but there is black staining on it. Is this normal? Is it from heat? The axle itself looks ok.

BTW the shoes still have over 1/8" of material which as I understand it, is acceptable.

Thanks,
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Old 03-30-2015, 03:05 PM   #2
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It's a bit hard to tell from the pics, but I'd use it like is until it's time for shoes. If magnets are badly worn then, I'd get backing plate assemblies. A good brake lathe operator can use half of the disc setup (on some lathes) and turn the drum magnet face, depending how deep the grooves are. I had it done on my SOB and it came out well. It is hard to keep the harmonics down and get a baby butt smooth surface, but it wore well with the second magnet.
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Old 03-30-2015, 04:29 PM   #3
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From my 2001 Safari Manual:
BRAKE DRUM INSPECTION
There are two areas of the brake drum that are subject to wear and require periodic inspection. These two areas are
the drum surface where the brake shoes make contact during stopping and the armature surface where the magnet
contacts.
The drum surface should be inspected for excessive wear or heavy scoring. If worn more than .020" oversized, or
the drum has worn out of round by more than .015, then the drum surface should be turned. If scoring or other wear
is greater than .090", the drum must be replaced. When turning the drum surface the maximum re-bore diameter is
as follows:
10" Brake Drum- 10.090"
12" Brake Drum- 12.090
The machined inner surface of the brake drum that contacts the brake magnet is called the armature surface. If the
armature surface is scored or worn unevenly it should be refaced to a 120 micro-inch finish by removing not more
than .030" of material. To insure proper contact between the armature face and the magnet face, the magnets should
be replaced whenever the armature surface is refaced and the armature surface should be refaced whenever the
magnets are replaced.

Mine was scored. It looked like yours, but it is hard to say without measuring the depth of the scoring and I don't recall how bad mine was, maybe .010 or .015, because the machine shop said they only took off about that much material and it looked good when they were done. BTW it was REALLY hard to find someone that could machine that surface.

As someone has suggested, if your brakes seem to be performing OK, wait to do anything about the scoring until you replace shoes and then buy new backing plate assemblies (not much more than shoes and magnets) and drums (not much more than machining both surfaces).


and

Your electric brakes are equipped with high quality electromagnets that are designed to provide the proper input
force and friction characteristics. Your magnets should be inspected and replaced if worn unevenly or abnormally.
As indicated below a straightedge should be used to check wear.
Even if wear is normal as indicated by your
straightedge the magnets should be replaced if
any part of the magnet coil has become visible
through the friction material facing of the magnet.
It is also recommended that the drum armature
surface be re-faced when replacing magnets. (See
Brake Drum Section) Magnets should also be
replaced in pairs (both sides of an axle). Use only genuine Dexter replacement parts when replacing your magnets.

The picture in the manual didn't reproduce, but it ways to lay a straightedge across the face of the magnet. As long as the entire surface of the magnet is worn evenly and coils are not visible it is OK. But if one edge is worn at an angle indicating the magnet has been tilted, it should be replaced.
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Old 03-31-2015, 01:18 PM   #4
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The bearing looks like it may have gotten hot. Again like the above posts the pic isn't the best to make that judgement.

Areas to look at that are critical. The axle shaft that the inner bearing sits on from your photo. Those roller bearings (Inner and outer) are not supposed to move on the axle shaft. The movement occurs inside the bearing and against the bearing in the race of the drum. So the very inside of the bearing that sits on the axle shaft should be in a conditions that shows no wear and the same for the axles shaft in the areas that both the bearings sit on. The pic of the bearing appears that there was movement of the bearing on the axle shaft. Usually this is due to improper bearing adjustment upon reassembly. (Too loose)

Next area regarding the bearing is the race inside the drum. There is an inner race and outer race. Both can and should be replaced with new roller bearings. The race should be smooth and shiney. Dull, pits or foreign material imbedded into the race is a issue that would require bearing and race replacement.

Black staining in other areas may be from burning grease. As long as the black staining is not on the rollers or the bearing races you could reuse and count your blessings.

Likely the wheel bearings have been loose, caused excessive heat build up and burnt some grease. Proper bearing seating and adjustment is requires on reassembly in a clean area. Most modern cars that used to have serviceable wheel bearings have gone to sealed bearings. This is because servicing bearings in some cases indroduced dirt into the bearing area or improper seal installation or wheel bearing adjustment was a service issue. Modern grease and a design change of sealed hubs with removeable brake parts (Drums or rotors) allow fro non-servceable wheel bearings. I wish the travel trailer industry would step up to this design as well.

>>>>>>>>>>>>>Action.
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Old 03-31-2015, 02:41 PM   #5
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Thanks for the info. Action, the bearing rollers and cages all looked to be in good shape with no discoloration. just the part that "rides" on the spindle was discolored. The axle wasn't discolored either, only the bearing. It's funny because the axle I did myself was ok, the one done by a large RV place locally was the discolored one. Nice.

Tomorrow I hope to pull the front two wheels/hubs an check them out. I am leaning towards just replacing the whole kit and kaboodle with new self adjuster backing plate assemblies and new drums. I think I have an ALKO axle with currently "Reliable" brand drums Part # HD 1206. That is both an ALKO and a Reliable number. I am working on crossing them over to Dexter #s and parts. But I need to wait until I pull the front assembles so I can double check the mounting plates by using the bolt circle measurements. I can also check the drum part # by getting the numbers off of the existing bearings.

I thought about waiting a bit to do this switchover, but in the end, I would rather do it now while it is cool than in the heat of the summer. Plus, even though I think I would be OK as-is for the time being, it's not worth the worry when I'm rolling down the highway.

BTW, I left a message with Dexter support yesterday with questions, they have not called be back (24 hours later). Maybe they should be replaced with a guy over in India so I can get better service LOL. I have a call into Airstream also, we'll see if they get back to me. They guy at etrailer unfortunately wasn't much help, but I was able to gleem info from the Q&A on their website. I think he might have been a rookie and not one of the regular guys. But, as usual, I am slowly piecing it together myself, as I all quite often find ourselves doing these days. It's like I used to say at work (I retired last week... YES!), I spend a lot of time playing Inspector Clouseau just trying to get anything done LOL.

Thanks all for the tips/info. Other input is also welcome.
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Old 03-31-2015, 02:42 PM   #6
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BTW, I agree Action that I wish the trailer industry would move into the 21st century when it comes to bearings etc....
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Old 03-31-2015, 02:56 PM   #7
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Imho the drums and magnets are fine...


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Old 03-31-2015, 03:01 PM   #8
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Most always a bearing that has been hot was assembled too tight, not too loose.

As far as the "new" integrated sealed hubs go.... Well, I hate them.

When they do wear out figure on 10X the cost in parts to repair them.

Give me an old style set of bearings please.


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Old 03-31-2015, 03:08 PM   #9
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Quote:
Originally Posted by J. Morgan View Post
Most always a bearing that has been hot was assembled too tight, not too loose.

As far as the "new" integrated sealed hubs go.... Well, I hate them.

When they do wear out figure on 10X the cost in parts to repair them.

Give me an old style set of bearings please.


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Actually the overall cost is just about the same, whether auto or AS. The sealed bearings last, on average, 75000 - 100,000 miles. (automotive observation on my job). But, you have no periodic labor cost to repack (or time and effort if you do your own). Most auto requirements are a repack every 15k, so there are 4 - 6 repacks required by 75,000 - 100,000 miles. It's about a wash in my analysis. And I like not having to worry about a repack on the AS.

I carry an extra with me, just in case, IIRC it was about $75 from Dexter.
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Old 03-31-2015, 04:20 PM   #10
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Quote:
Originally Posted by Soyboy View Post
Thanks for the info. Action, the bearing rollers and cages all looked to be in good shape with no discoloration. just the part that "rides" on the spindle was discolored. The axle wasn't discolored either, only the bearing. It's funny because the axle I did myself was ok, the one done by a large RV place locally was the discolored one. Nice.

Thanks all for the tips/info. Other input is also welcome.

Based on your description the bearing is OK. Likely it slipped some on the axle shaft and not enough to cause an isue such as it was needed to be replaced. And likely it was loose because the rolling surface of the bearings did not take a hit, which happens if too tight.

Regarding permanent sealed bearings.
I have a Lincoln Mark VIII with over 200,000 miles, a Toyota Camry with just under 200,000 miles and a newer Focus with over 70,000 miles and the hubs have not been off of the spindles for any of these rides. It would be the front wheel bearings for the Lincoln and rears for the other cars. I am a believer of permanent sealed wheel bearings and I used to want to repack bearings. The technology has proved it's value and is especially adapted to higher end stuff. While an Airstream is high end the travel trailer industry axle manufacturers cater to all types of trailers. Some where a buck extra means no sale.

>>>>>>>>>>>>>>>>Action
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Old 03-31-2015, 05:07 PM   #11
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In my experience the sealed units last about as long as the old style, and I only repacked when I was changing brakes, and sometimes not even then.

The hubs on my o4 Tahoe expired at about 170,ooo miles.

I don't consider that really great, no better, and arguably worse than the spindle and bearing setups of old.


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Old 03-31-2015, 05:16 PM   #12
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Originally Posted by J. Morgan View Post
In my experience the sealed units last about as long as the old style, and I only repacked when I was changing brakes, and sometimes not even then.

The hubs on my o4 Tahoe expired at about 170,ooo miles.

I don't consider that really great, no better, and arguably worse than the spindle and bearing setups of old.


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Unfortunately the repack effectiveness is a direct function of the person doing the repack/adjustment. I hear what you are saying. As a trained tech, I do a particularly thorough repack, utilizing a methodology which will last much longer than 15K. I usually pull mine at 25k and I could go much longer based on what I always see. I have occasionally, over the years, found issues related to bearing quality, not related to lubrication, that were caught only because of a regular inspection. I agree that average longevity is about the same with conventional bearings and sealed units.
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Old 03-31-2015, 05:28 PM   #13
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As a maintenance instructor and former axle specialist (Toyota axle technician paying the way thru college/flight school) I can say that cone bearings should not be "loose", regardless of the improper instructions found at most axle and bearing literature. Cone bearings should be slightly "pre-loaded" rather than loose. Hand tighten the nut as much as possible with your hand only, then advance to the next cotter pin or locking-device increment. (Most literature, even from axle mfr's, advise oppositely, to loosen to the last increment. Unfortunately this will allow the bearing to "chatter" and also forces individual rollers to carry more load while others "loaf". A bearing with pre-load will share the load simultaneously with ALL rollers... just like all the spokes in a properly adjusted bicycle wheel.

The main reason sealed units last longer is because they have better seals (less contamination) they are pre-loaded at assembly, and they are assembled with SYNTHETIC greases, which are longer-lasting than mineral greases.

Lastly, when re-packing bearing do NOT MIX different types of greases. (Greases are hymogenous mixes of oil and metallic soaps, such as lithium, or calcium, or aluminum, etc etc., and mixing them will RUIN your bearings in short-order.)
Clean ALL vestiges of old grease from the bearings using a clean solvent and dry them,.. NEVER spin them with compressed air (dangerous and harmful to the bearings AND your eyes and fingers when the unrestrained roller literally explode out of the cage) and use a high quality wheel bearing grease which meets the recommendation of the bearin mfr'r. (My personal favorites are marine trailer bearing greases because they are waterproof.)
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Old 03-31-2015, 05:41 PM   #14
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Boxite! Now you're giving away my tech secrets. I agree with everything you say, but I do the preload a bit differently. I actually torque the bearing set down pretty tight (not with a torque wrench, but by experienced feel....maybe about 15 lb/ft) then loosen until I like the hub drag....again by feel. The reason is, I want to remove any possibility of cocked bearing, etc. I never allow for any rocking of the hub. The other important parts of your writeup is almost surgical room cleanliness of the bearing set and the hub bore. Clean it, then clean it again....and maybe again.

Quality synthetic grease is a must. Building a dam of grease on the inside of the outer cones to prevent any outflow away from the bearing is a good idea. And FULLY pack the bearing set. Mechanical packers are OK for loading the bulk, but inspect and do the "grease in palm" to remove any air pockets in the roller set.
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