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Dominator rear hub...frustration!

Submitted by john_baker2 on Wednesday, 16 October, 2013 - 01:00
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Heavy Twins

Having sat in the corner whilst other work was done, the rebuilt rear wheel has just today been fitted back into the frame.

Spinning up the wheel created a rythmic clunk which naturally causing concern led to immediate removal of wheel for further inspection.

SO...logic indicates that the brake plate should fit snuggly into the groove in the sprocket/brake hub. It doesnt and rocks on the stub axle, hence the noise.

Logic further suggests that the flange on LH nearside stub axle should be a fitagainst the bearing . It isnt and sits proud.

So rear hub stripped right down again, bearing removed all checked for correctness and reassembled.....same problem.

Both bearings are new (and have been measure checked against those removed). Single bearing on RH speedo drive side with the long side of spacer tube.Lock ring, felt and spacer fitted. Thedouble bearing on LH drive side with short end of spacer, washers and felt. Stub axle does not then fit snuggly against this.

Having again dismantled hub all I can see is that the shoulder on the short side of the spacer does not line up with the hub bearing recess....so this gap would appear to equate with the stub axle not fitting and the brake plate failing to recess correctly. BUT the spacer will not drive any further into the hub/RH bearing setup. I cannot find any obstructions in the hub.

To recap..bearings are new and correct, felts are new, sprocket/brake hubis new...everything else is as removed. Build sequence has matched my dismantling notes and Haynes manual and exploded parts list diag.

Help and advise much appreciated.....apologies for the lengthy detail.

regards JMB

Submitted by phil_hannam on Wednesday, 16 October, 2013 - 01:01

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I get the impression that your problem lies in the brake drum/sprocket area and not with the bearings.

The brake plate should pull up hard against the swinging arm when the stub axle and LH spacer are added and the nut tightened. It may be that your LH spacer is the wrong thickness. If you check out pic 8.4 in your Haynes wheel section you will see that the spacer and stub axle shoulder are flush. If not then the brake plate can wobble around.

All this can be checked by leaving the wheel to one side and just fitting the brake plate in place using the stub axle, spacer and wheel nut.

Submitted by john_baker2 on Thursday, 17 October, 2013 - 01:00

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Good idea, Phil.

Checked 8.4 as you said... the spacer sits about 5mm proud of the stub axle shoulder...but when fittedinto position as you suggestthere is no wobble.The spacer is the original but as the brake plate has had a face lift,a problem, maybe distortion, could be there. This does appear to be where some of the'space' has been lost.

So another query for you.....as this could be where the remaining difference is....looking atfig 7.2 assembly..should the large flangeon the stub axlebutt up against the hub centre ? When the brake drum is bolted to the hub the stub axle seems a little loose and only goes firm when the wheel spindle is tightened through.

Also to set my mind at rest....should the shoulder on the short endof the bearing spacer be flush with the recess inside the hub centre, which I had presumed was where the bearing should butt.

Meantime thanks for advice.

Regards JMB

Submitted by phil_hannam on Friday, 18 October, 2013 - 01:00

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'should the large flangeon the stub axlebutt up against the hub centre ?'

I am not so sure about the answer to this as it is 4 years since I last looked at these bits on my bike. From memory (dulled by a large Scotch) the end of the stub axle is pulled up tight against the bearing inner race and rotates inside the dished washer. Thelarge shoulder must just clear the dished washer and the boss of the hub.

'should the shoulder on the short endof the bearing spacer be flush with the recess inside the hub centre, which I had presumed was where the bearing should butt?'

The bearing sits inside the hub boss deep enough for the dished washer to also just sit inside. But not enough to allow any peening to hold it in place. The end of the bearing spacer just reaches through the to the edge of the inner race. It does not protrude. If it is protruding then either the bearings are incorrect or something is wrong with the spacer.

The whole arrangement is a real pigs ear as on assembly it is too easy for all the bits to drop out of place and then get crunched when the axle nuts are tightened. eg. the felt washer can push the dished spacer out of the hub boss. It is best to put it on the stub axle using the felt to hold it in place. But then you have to rely on grease to hold the thin steel washer against the bearing. A sealed double bearing would make life much easier here.

Good fun is it when things go a bit adrift???

Submitted by neil_wyatt on Friday, 18 October, 2013 - 01:02

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Good stuff gents, just one thing and that is to check that the brake plate is not bent. I have a bent one I didn't realise, even had it powder coated and all was fine until I put it into the drum. I still have it if anyone wants it!!!

Anyway, now I always check that the bare plate sits square in the hub. Yes then can be bent.

Submitted by phil_hannam on Friday, 18 October, 2013 - 01:03

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A 03.07 reply.....and I thought that I was burning the midnight oil!!!!

Good point about banana shaped brake plates. A very well known feature of early 60s Dommies due to the off-set lever putting more effort into pulling the end of the plate forward than operating the shoes.

Submitted by john_baker2 on Thursday, 24 October, 2013 - 01:00

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Phil, Neil...thanks for the replies.

Firstly Phil, your 4yr memory is spot on.....the stub passes through outer hub washer and sits against the inner race of bearing. The hub spacer end is flush with the bearing race.

So its back to the brake plate as you first said......and Neil has sort of got the right area.

As a check, sorted out the old drum/sprocket and assembled....same problem as with new drum/sprocket (forgot to mention that item earlier)

Turns out its indirectly (at least I like to think so) my fault. In my zeal to smarten things up I had the brake plate powder coated...full on version. This therefore seemed to be pushing things out of sync!!

So carefull scraping, chipping of p/coat where the stub axle fits the inside of brake plate....ditto exercise where the stub axle spacer fits against the outside of the brake plate. Also (and this might be the major problem)...the pillars on brake plate that the shoes are captive on were p/coated....had already cleaned off for them to turn but now also needed to clean base of each pillar AND the top where the plate and lock washer fits. I think it likely that as the plate/washerswere not seating correctly the shoes must have been rattling in the drum .Re-assembled with old drum and all seems to be OK.

Repeat performance with new drum/sprocket and all now OK...BUT somewhat confused as the NEW drum is not identical to OLD drum. The castings and base of the three mounting bolts are some 3 to 4 mm less....which suggests the drum is being pulled closer to the hub. Heyho, so much for the 'spares to original spec' that I'v been paying for!!

Also a curiosity.....of the three drum mounting bolts....why has one got a deeper collar then the other two ? makes no difference which way its fitted and all the sleeve nuts are the same...odd!. Funnily this is same on both old and new drums.

Many thanks again for advise, suggestions and support.

regards JMB

 

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