Drum wear - Magnet - Bearing Questions

[Soyboy]

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,

[dznf0g]

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.

[Al and Missy]

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.

[Action]

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.

[Soyboy]

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.

[Soyboy]

BTW, I agree Action that I wish the trailer industry would move into the 21st century when it comes to bearings etc....

[J. Morgan]

Imho the drums and magnets are fine...


1/2 Ton 4WD Truck, 72 Sovereign Hensley Arrow

[J. Morgan]

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.


1/2 Ton 4WD Truck, 72 Sovereign Hensley Arrow

[dznf0g]

Originally Posted by J. Morgan

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.


1/2 Ton 4WD Truck, 72 Sovereign Hensley Arrow

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.

[Action]

Originally Posted by Soyboy

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

[J. Morgan]

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.


1/2 Ton 4WD Truck, 72 Sovereign Hensley Arrow

[dznf0g]

Originally Posted by J. Morgan

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.


1/2 Ton 4WD Truck, 72 Sovereign Hensley Arrow

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.

[Boxite]

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.)

[dznf0g]

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.

[cwf]

Right on about cleanliness!!!!
I think that is the key to "pre-lubed" sealed "units". I respect the professionals here who have seen such an improvement in this issue.

With our AS, we have to face the reality of the high side loads and this is where the "preload" is so important to keep the bearing loads stable as possible. Again this is where the "preloaded" Units can establish strong unit integrity.

In my experience , A specific thing few have ever done is to actually "shim" for proper preload. I do not have the experience of thousands of repacks, probably less than 200 on boat trailers, cars, motorcycles and such. But, every single one I inspected was "loose". I learned to check after the first few short life repacks... I learned to "preload" from a professional... And how to shim.

This fellow wore starched work shirts and really stuck out among the other mechanics. He would get just as dirty as the other guys when necessary, but his work area and tools were really well kept. It stuck to me as well.

One other thing he did was to assemble the hub with gear oil to set the "shim preload" then remove and "hand pack". He only used fresh grease and immaculate clean hands. Can't argue with success....

[idroba]

Dexter Axle service manual, Free PDF
While doing some cleaning in my Argosy, I re found the Dexter service manual for the axle I had installed a few years ago.

I looked at again and found it to be a very very good source of information on everything axle related, from brake magnets, to wiring diagrams, to grease types and qualities, bearing numbers for all Dexter axles , how to lube the bearings and on and on.

I have a paper copy, which is great, but I looked on line and found that they have a PDF version that you can download for free. I didn't search to see if they will send you a paper copy, they may.

This is good, complete information on axles from 600 to 8000 pound capacity.

http://www.dexteraxle.com/i/u/614960...ice_Manual.pdf

[Craig Schrader]

Here are some pics of mine after four years and 20 thousand miles. Leading edges were shattered. I replaced all running gear after finding this. Drums, brakes, bearings, etc...

[Hummer]

Looks like they are getting down there towards the end.

You also need to check for axle set which leaves the arms in the "up" position.

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The above pic shows the old axle (left obviously) in the UP position. New axle on right.

Note on the left the axle center is even with bottom of frame with no load on it. They come with 22° down angle and they "rotate" for lack of a better term up to "0°" at the max load the axle is designed for.

I checked the arm angle at full load and best I could tell they were in the same position loaded as seen in pic as no load.

When a torsion axle rotates another 11° you are getting into a very rough ride condition as the axle moves very little on bumps etc and hits the third position where it will only rotate 5° and at that point it is like you have no cushion at all. Once you get into the 11° range things start breaking. I was having this happen and I really did not realize what was happening till I talked to a torsion bar axle designer.

He told me the ideal load range for axles is 50 - 66% of the axle capacity which is within the first 22°. Thusly if you have a pair of 3500lb axles you have 7000 capacity and the load should not exceed 4620 lbs. According to my data plate my rig gross weight was rated at 3200 lbs per axle or 91% of axle design capacity.

He recommended a pair of 5200 lb (10,400 Cap) and thusly a 6400 lb weight max was 62% and he said the roughest road loads should never get me out of the 22° range and have soft dampening throughout the first range.

He also told me shocks were not required.

I concurred with that because I have a utility trailer with a 8000 single axle and 10 ply tires.

Empty I have seen it wanting to bounce a bit but anything over about 500 lbs on it completely stops that tendancy. On hitting a dip etc it will go down on a a bit first then recover and make a very min 2nd down movement and then nothing. I have had 7000 lbs on it but most I normally carry is my 2200 lb tractor and it is nice and smooth.

I just went to Ft. Bragg and picked up a 800 lb generator and it was nice and smooth all the way home total 600 mile trip. Below is a pic of the gen.



Thusly if a 8000 lb axle does not need a shock absorber with a 800 lb load and rides nice and smooth, seems to concur with what the torsion bar design engineer says.

[Wingeezer]

In the picture that you show of the face of the magnet, you will see three small holes in the face.

I believe that you should see four.

My understanding is that these are witness marks to show the condemning limit of wear - when the holes are no longer visible, then it is time for new magnets.

I'm not sure if this means when all holes vanish or any one of them! Obviously the magnet face is not wearing evenly - I don't know if that is typical.

I think if it were my call, seeing this condition, since you have everything apart, I would be replacing the magnets - I don't think they are that expensive.

I would also look to see if I could see any reason for the uneven wear and if I could correct it.

Brian.

[Action]

Shocks or no shocks have always been a conundrum. AS installed shocks on the trailers to add another compoenant to dampen the jarring to the cabin. Basically an AS travel trailer is big box of air. The outside shell is the weakest piece and has to sustain any loads that are not absorbed by the tires, axle, frame and the floor. While those pieces do a very good at doing this job, adding shocks puts another devise in the system to absorb road shock. Are the needed? Most of the time in my opinon is no. However the interstate at interstate speeds can be an unkind enviroment. Having redundant systems to be a barrier between that hard place is a nice insurance policy that has really a low cost.

For the low cost and effort, why wouldn't one install shocks on a replacement axle assembly?

>>>>>>>>>>>>Action