Exploded Diagram of the Demon Brake Drum. Source: GCP Site.
Brake Drum Removal, Inspection, Reassembly Notes 2/09/R. Kwas
General
Preferred
and Approved Puller Designs
Preparing for
Normal Drum Removal
Removing a Difficult
One
Inspecting Drum
Wear Lip
Reinstallation of
Brake Drum
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General: Drums do not rust or seize onto axle shafts as a rule(!), the hub is aligned by the taper and actually stretched onto axle as the securing nut is torqued, and this arrangement gives a huge multiplying advantage to the force applied by the nut, to secure the drum...as well it should!...it is the driven link between axle and the road which needs to transfer drive power. But, since no tightening torque spec is given for the castellated nut (as far as I've seen), a wide range of torques and resulting stretch and retention forces can result, because the final position of the nut needs to be tightened until it aligns with the cotter pin holes, so final torque is dependent on the judgement and additude of the guy operating the wrench!. Drum separation from tapered axle against this substantial unifying force, and while removal can be one of the most distressing and difficult procedures which must be periodically performed in normal servicing, it doesn't need to be!
Exploded Diagram of the Demon Brake Drum. Source: GCP Site.
Preferred and Approved Puller Designs: Drums are often difficult to remove and high, to sometimes, extreme levels of force are necessary to successfully separate the drum and axle. With these levels of force required, it stands to reason that it be correctly applied only! Misapplied extreme force will damage or break things, instead of separating the components! Vintage Volvo Brake Job Rule No 1: Use a drum puller of the approved designs ONLY! Not using an approved puller will result in failure to remove drum AND/OR damage to drum and/or lug-studs to the extent that the drum is rendered into scrap and will need to be replaced...and all this before drum has even been removed!!!
Pic of the preferred and approved puller design.
Dogbone striking wrench takes the abuse,
instead of your most favorite (and expensive) 1/2" drive breaker bar.
Pic of a puller design which will not work, is not approved
and which will likely damage drum or itself. Do not use or allow other
parties working on vehicle, to use this type of puller!
Horror stories of cracked drums edges (wrong, edge type puller used), bent lug-studs (wrong puller or correct puller, but misaligned!), wasted axle end or threads (nut not put back on to reinforce axle shaft when extreme force was necessary) and having to cut the drum off with cut-off grinders or oxy-acetylene torches, when everything failed, abound! Just for fun, I asked for stories on the Brickboard Link: http://www.brickboard.com/RWD/volvo/1330565/120-130/demon_brake_drum_removalseek_stories_removal.html ...responses ranged from pretty funny to informative.
Significant force is always necessary (even when Anti-Seize (AS) was been applied to tapered axle shaft during last time drum as assembled), high force is sometimes necessary (no AS was applied to shaft at last reassembly), or extreme force and time under high tension load (no AS was applied AND nut was overtorqued by a primate mechanic...maybe even with an air-wrench!).
Pic of a homemade puller also of an approved design
(nice job!) puller. It uses the same principle of attaching to the lugs, and is
even nicer in that it is just about impossible to misalign. Picture used with
permission, thanks and credit
to Martin "Mcoldie".
Impact is your friend (aka: Shock and Awe at Work in the Garage!): Many pullers also make use of the advantage which impact brings with it. After mounting the puller and making it a solid, concentrically aligned part of the drum, a threaded center shaft pushes against (also straight and concentrically!) the axle. This center shaft has a striking wrench intended to receive blows from a hammer and transfer these as huge pulses of torque onto the nut, which translate into mega pulling pulses on drum. Usually this brings the desired separation pop. Alternately, an air-wrench can be used on this to supply an irresistible force necessary, plus impact!.
Time under tension: Sometimes, in extreme cases, or in cases when air-tools are not available, or when after a session of whacking the striking-wrench, it just feels like the striking wrench is totally solid when it is struck such that nothing seems to move, a rest is called for...a rest for the mechanic, and a rest for the joint. Often if left over night, under the continuous substantial tension of the puller, temperature variations are enough to explosively separate the drum with an impressive sounding report, not to be confused with “shots fired”!! The quick release of all of that pent up force has also been known to be able to send the puller/drum assembly across the garage, if nut has not been turned around after loosening, and loosely applied back onto the axle shaft. To avoid damage to other garage inhabitants, human or otherwise, a heavy rag draped of the preloaded assembly when one leaves it for the night is a real good idea anyway!
Preparing for Normal Drum Removal: While corner is still on the ground, and tire contact with ground keeps wheels from spinning, remove hubcap for access. Break the initial hold of lug nuts, so that they can more easily be fully removed once corner is in the air.. Remove cotter-pin and loosen nut (1 1/4”) only. Lift and support corner of vehicle securely, remove wheels and drum securing nut rest of the way, replace nut back on axle, turned around, with castellation first, to reinforce axle shaft end. With gearbox in neutral, Emergency Brake not engaged, and manual adjustor backed of if possible**),. install a puller of the approved designs, and apply irresistible pulling force correctly with it, until it separates from axle.
Removing a Difficult One: In the worst cases, preload puller to the maximum pulling force you dare, and leave over night (after first spraying some penetrating solvent like Croil, Liquid Wrench, PB Blaster WD-40(listed alphabetically) onto the drum-hub and axle joint) ...if drum hasn’t separated on its own (often with an explosive report) by the next day, heating the hub with a torch to add some thermal expansion to the mix will likely get the job done. Draping a rag over the assembly will contain the assembly and dampen some of the mechanical violence when it finally does “let go”...so will putting the castellated nut back on (which is highly recommended anyway as it reinforces the end of the axle shaft from the serious forces which will be applied...compressed threads on axle shaft-ends are not unheard-of!), replacing the nut will also prevent the drum/puller assembly from possibly launching itself across the garage and paying a high-speed visit to the wife’s new car!.
** The manual adjustors adjust the rest position separation spacing of the brake shoes. IF these are free and clear to operate (meaning the reader has either new ones - great - or has previously freed and lubed them well with AS per my recommendations), then they should be backed off to the end when they can’t turn anymore counter clockwise, before attempting drum pulling. It should be noted that adjustors DO NOT influence the force required in initially breaking the axle/drum hub bond, because this force is strictly determined by the hub-stretch, but they do make a big difference in removing the drum once the initial hold has been broken, because the shoes don’t have to clear the wear lip. I do also recommend removal of Wear Lip once everything is apart...and why if someone has seen the advantage to rebuilding the adjustors with anti-seize, but hasn’t also heeded the advice to apply it to the axle taper, or grind away a significant Wear Lip, would be beyond me...
Once the Demon Drum has separated from the Axle: [These are some recommended steps which are in addition to any brake inspection or service which the drum needed to be removed for in the first place.]
Inspecting Drum: Once a drum is removed (and your blood pressure has returned back to normal) it can be measured to see how much it has worn, and what its inner diameter (ID) is. If you don’t own a 9 to 10” inside micrometer, I have designed a handy template which can be printed, applied to a cardboard backing, cut out, and used to measure the ID effectively. Accuracy to one thousands of an inch is just not necessary. LINK to 9-10” inside Micrometer. Coming
Drums with excessively worn IDs should be replaced as they are at risk of failing by cracking (not so good for braking!), and they also require the wheel cylinders and shoes to be separated beyond their designed normal working dimension range.
Friction Area Condition: Some circular grooves are always present. So
what! Do not unnecessarily machine drums! The metal you machine off
today will require you to replace that drum that much sooner tomorrow!
Wear Lip: I recommend grinding off the wear-lip which is formed because the shoes don’t make contact right out to the drum edge...this will make disassembly and reassembly easier as shoes don’t need to be compressed for Wear Lip to clear drum edge...then again, adjustor should be backed off when new shoes have been installed so this shouldn’t be an issue on reassembly. But repeating: This lip has ZERO to do with why a puller is required break the drum/axle bond!
Condition of Seal Contact Area: Inspect the contact area and if necessary, use a mild abrasive (Scotchbrite pad or similar) to clean away surface rust which will abrade felt seal rapidly. If key has been installed wrong (taper not first or not towards axle) it WILL cause damage in the form of a split with displacement in this seal contacting area, continuing from keyway in hub. This will hurt the seal felt also.
PLACEHOLDER FOR PIC
Reinstallation of Brake Drum: My normal reassembly practice is apply a very light film of graphite containing AS to the tapered axle shaft*, then place drum on shaft (which has previously been turned such that keyslot is at about a 12 o’clock position), then rotate drum with respect to shaft until its keyslot aligns with that of shaft, install key (insert tapered end first and with taper toward axle) by tapping in until it is just below flush with washer and nut bearing surface, then installing washer and spinning on nut until hand tight. Perform these steps with vehicle in gear to prevent axle rotation, snug nut, but do not bring to final torque. Proceed with shoe and Emergency Brake adjustments, and leave final torqueing of axle nut for when wheel is back on and that corner is back on the ground to prevent turning. Some judgment is called for here...since the nut is castellated and a cotter pin should safety the nut, I generally tighten the nut (after it has been first snugged) to the next clear alignment position with a 1/2” drive and 1 1/4” socket (two holes are available in shaft, one at the key-slot, and one 90 degrees to that...which results in manageable angular increments of 30 deg). In the worst case, if it just “feels” like the nut needs to be tightened too much in order to get to an alignment position the washer can be thinned slightly by grinding on a flat plate with emery cloth...but this is typically not necessary!
* How does AS work specific to axle-to-drum hub joint? Using anti-seize on the tapered axle to drum hub interface will still allow the alignment and stretching which assures proper unification of the parts and safe function, as designed and intended, but the film, containing the stratified graphite particles which easily shear apart, serves as a release agent which never allows the astronomical coefficient of friction which occurs when it is not present. It is this coefficient of friction which the puller must overcome to release drum.
Comments on this article are welcome.
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Legal notices: The term Volvo is used here for reference only. I am not affiliated with Volvo…although I do also Roll…. When did jungles become rainforests? When did Personnel become HR? I have used the procedures presented here in practice many times myself but they are presented strictly as a guide...your results may vary...and you are responsible for your own actions and knuckles! It’s a car, not a phonebooth! If you lived here, you’d be home by now, blah, blah, blah…
The contents of this article are Copyright © 2009 by Ronald Kwas. You are welcome to use this article and its contents for non-commercial purposes. But if you copy and republish it, whole or in part, without giving credit to the author, or linking back to the Sw-Em site as the source, you’re just a lazy, scum sucking plagiarist! Go work for the Washington Post or something!
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