'72 Combat rear assembly Sovled mystery

I've had some weird issues assembling Trixie rear drum in past, the brake cover lips dragged in the drum groove so put a Combat cam brass thrust washer + thinner steel washer between the brake plate and the drum for noiseless spin for a couple years and still silent - BUT- discovered the DS snout of the drum was rubbing on the brake plate, so snout has scrubbed off swirl finish and some witness marks on brake plate center rim. The drum must spin w/o rubbing on brake plate but I can't figure out how that spacing is provided for to attain it.

Above graphic shows #21-washer which Trixie has, but what does it do? It passes through the drum hole so does not space dumb axle in drum nor is it clamped between drum and plate - just loose w/o a function I can tell. There is nothing shown or present at home to space drum off brake plate but for the length of the dumb axle beyond its seating in drum snout. If dumb axle section before its stop rim was ~1/4" shorter then drum would be pulled closer to brake plate and wheel side assembly would not be affected.

Biggest mystery is when #44 dumb axle lip is seated on drum snout rim, as would be when nipped up, so its end a butts on brake plate, the brake shoes & plate is held 1/4" off the drum groove. This would allow drum to shift 1/4" loose on dumb axle slack only centered by drive chain. in other words when axles clamped together the dumb axle is not pulled up tight inside drum but allows ~1/4" shift of drum on dumb axle. Does not compute. I know there are like different dumb axles but this is the one Trixie came with.

My dumb logic says if I could put 1/4" spacer between dumb axle lip and drum hole rim then drum would be held close to brake plate yet not rub it. Essentially this/these spacers would go where useless #21 shown but bigger OD/ID to land on the dumb axle rim. So I'm stumped, as all items shown in manual are present and in correct order yet don't work out as advertised. Its worked fine for like 9000+ miles riding but don't know how it did. Need advice on what to do next.

Re: '72 Combat rear assembly bumble mystery

Discard ALL supurflous components .

Re: '72 Combat rear assembly bumble mystery

ya mean i can disrequard a floating drive drum?
Nipping up the axles ends bares through the inner races and spacers but don't loacate the drum form siding on dumb axle and cushion slots.

Re: '72 Combat rear assembly bumble mystery

#21 washer is 'AR' - as required. It is specifically to space the backing plate properly in relation to the drum.

Re: '72 Combat rear assembly bumble mystery

Isn't it the shoulder of the dummy axle that abuts the inside of the brake plate?

Re: '72 Combat rear assembly bumble mystery

grandpaul said:

Isn't it the shoulder of the dummy axle that abuts the inside of the brake plate?

Click to expand...

The #21 washer fits on that shoulder. Parts book calls it a washer, but it should be called a shim

Re: '72 Combat rear assembly bumble Solved

In my Combats when the long axle is run into the dumb axle - it holds the drum/dual row bearing tight to wheel side, which also pulls the drum snout away from the dumb axle rim seating. Nipping up the dumb axle nut should then pull stub axle tight and centered in drum snout rim-lip and about same time cause stub axle end to seat on brake plate, but it don't in Trixie's case, the only thing holding drum from sliding to DS is the dual row bearing circlip, which I've found undone twice now on tire changes plus the tire casing custom cushions chewed up or laid down under paddle gap created by the ~1/4" slack-space when bearing is freed and drum slides away from wheel hub. I assemble rear by nipping up dumb axle first with rear brake applied hard then long axle ok. If I put enough washer/spacers in place of #21 it would space drum away from DS, with shoes/plate held away from drum ~1/4", exposing shoes to view, ugh. Only placing spacers on the dumb axle lip inside the drum snout would hold drum toward brake plate - so plate lip almost rubs in the drum groove. Special spacers there would require special machining of narrow rim washer. My conclusion is somehow wrong size stub axle installed. None of this is apparent if assembling in normal sequence ie: dumb axle first then long axle. This sliding of drum on dual row bearing likely helped fission Trixie's axle in parking lot peg scratch fling. This un-traped drive drum apparently put enough tip torque on the dual bearing to heat it to loose its grease then cook the seal-balls composite spacer to crumble out state so now need new dual bearing though its still turning smooth enough to get away with a while. The hive collective mind has helped me visualize and reason out the wierdness so thanks for looking in.

Re: '72 Combat rear assembly bumble mystery

I call Fred at Old Brits to get set straight on what's going on. Standard Norton old dual row bearings are deeper than new age sealed double row replacements as Trixie has now worn out. Solution for Trixie is just put spacer enough on deep end of bearing so dumb axle is a bit loose until nipped up. Fine tuning by shims till drum just misses brake plate. Same stub axle used for '71-'73's 750's but changed after that. This space behind bearing is usually taken up by felt seal stack, not needed with sealed bearing. Will be back in business when new bearing arrives and spacer+shims made.