Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: Martin6 on March 20, 2023, 09:58:44 AM
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As you may have seen, I'm recommissioning my new to me, CB750K6. The ignition and carbs are now sorted, just some fine tuning of the carbs. On a 25mile test the bike did well and ticks over evenly (once warm).
Apart from a pilot light bulb and a very slight front fork weep, neither of which are urgent, the final thing on my current list is sorting out the rear brake. When I apply the brake I get a pronounced pulsing from the pedal. The brake is unusable. The shoes were replaced a few years ago and then the bike wasn't ridden. So they're effectively brand new.
I'm going to have a look at them this afternoon. I think there's a bit of a technique to installing the shoes, plus some force. Is it possible to distort the shoes when installing them? Is there a way to check? Any ideas on what else might cause the pulsing?
Thanks, Martin
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I know that Trigger has had problems with DSS aftermarket shoe's, and check that the brake liner is not cracked .
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As above noted, likey the drum is at least distorted such that a tight spot (closer to the centre) is being felt as it passes the brake cam point which has the most movement in terms of how far the lining material is moved toward the drum.
Generally checking for corrosion on interior drum surface, moutN wheel without brake plate and then spin it with a screwdriver or something similar held very close to the friction surface will soon show if it's out of round.
As Julie mentioned, they do crack the lining surface ring sometimes. May just show in spoke tension too, so check them as well.
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Hopefully this picture posts. A fair bit of rust and wear ridges. What do you think, beyond salvage?
The hub looks ok, the rim and spokes are recent and in good condition. Is it possible to get the drum re-lined? If so, any recommendations on where to go?
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The offending article :)
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Yup, cracked hub. Repairable though.
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Yup, cracked hub. Repairable though.
Not sure on the terminology. Is that the drum liner is cracked? The outside part, the hub, that the wheel spokes thread through and holds the bearings / axle, I think that looks ok.
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Yup, cracked hub. Repairable though.
Not sure on the terminology. Is that the drum liner is cracked? The outside part, the hub, that the wheel spokes thread through and holds the bearings / axle, I think that looks ok.
Terminology fine, it's the liner that's cracked and needs replacement. Unsure who is doing this currently as there were some offering to repair, usually by using a car drum brake as source material suitable to machine to correct specification.
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The problem you will have is that after you find a brake drum you can use you will probably have to remove the rim and spokes as the lathe to spin the 18 inch diameter wheel is kin big
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Deffo a strip down job. I know Trigger has repaired them with a new liner shrunk in, pegged and machined. He may not do them now, but I’m sure he will know someone…..
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Didn't someone put up a link to a fella in South Wales who was doing these hubs?
Reasonable cost as well.
I sent the link to Roo but can't find it now.
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Gap bed lathe to get them in if someone is doing many ( bit of the bed under chuck removable to get big dia in ) would avoid stripping wheel.
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Terry Ives?
http://www.sohc.co.uk/index.php/topic,23605.msg263653.html#msg263653
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Or Dave baker…
http://www.sohc.co.uk/index.php/topic,27149.msg250841.html#msg250841
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Dave Baker Phil, cheers.
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I rang around a few engineering firms, who wouldn't touch it.
However, one local to me, asked me to drop it in, to have a look. They were worried about choosing the correct lining material and safely securing the new lining to the hub, without damaging the hub. They recommended a decent used one. On ebay I spotted this one.
I checked it is compatible with a K6 and condition. Hopefully, fingers crossed, this will be right. The vendor is local and happy to guarantee fit. Should be here at the end of the week.
I'd have to break the current wheel down to have it machined anyway, then build it back up, so no difference. Is there an offset I need to build into the rear wheel? I have done a Norton front wheel last year, so i know I'm in for some fun :-\. I'll be aiming to reuse my nearly new spokes and rim.
Again, thanks for the advice, I'm hoping this route might be more simple.
EDIT: meant to add, from the link posted above, Stotfold Engineering told me they no longer do re-lining after the guy they used retired.
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Bet that wasn't cheap.
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Not awful, but still £100 + postage. I think I'd pay more than that to have a re-lining done, if I could find somewhere. But, £100 I could have done without spending. All in, probably a lucky find.
I'm hoping I can do the wheel myself, to keep a lid on cost, so I can enjoy the bike this year, before the next round of improvements.
Anyone got info on run-out for a K6 rear wheel?
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That’s a good price if it’s a good un.
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That’s a good price if it’s a good un.
Yes, that's the risk. OTOH, looks better than what I currently have (in photos!). More pics attached. I'll post what I think, once it arrives. Just realised I'll have to wrestle with the old cush rubbers...
Could do with anything anyone has on wheel run out. So, I have a spec to aim at.
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No offset on any Honda CB SOHC/4 wheels
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That's good news. Thanks.
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Whilst on the subject of rear hub relining, Trigger (Graham) has also recently stopped doing them as well. He had quite a big batch sent in to do a few months ago and some for forum members and they have all been sent back out.
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Was the hub new? if so that's a really good price.
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Was the hub new? if so that's a really good price.
No, used. Only have the photos and the vendors ebay feedback rating. I'm hoping, will find out later this week. Not touching my wheel until it arrives and I've measured it.
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The replacement hub has gone on. It was as good as the photos and a first ride showed smooth progressive rear braking, with new shoes.
Spoking and truing the wheel was straightforward. Used the rear axle in the soft jaws of my vice and a bent coat hanger, as a guide. Just patience, take it in small increments. But removing the old tyre and fitting a new one (Avon RoadRider) was a real bear of a job. I still need to do the front tyre...
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Good news on hub and wheel build.
Fitting tyres, rub some silicone grease around tyre bead, both the seat area and the backside (inside the tyre wall) before you start. This is literally the minimum amount spread sparsely over the whole circumference such that its almost invisible. They pop on easily then, and seat properly with no hang up/alignment struggling.
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I was using diluted car wash in a spray bottle. Not good enough. I've bought some proper tyre soap to use on the front wheel from a local motor factors. They only had a 5kg tub. I hope I find other uses for it, or it lasts 20 years (and me with it!). :)
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I had my money's worth from a local bike shop who advertised 'free removal and fitting on loose wheels' . The tyres on my CB900 resisted them for nearly an hour...they finally gave up and used a hacksaw to cut them off. Like dust inside. I'm glad I didn't ride on them!
I think the new ones went on more easily than the old came off.
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I had to cut my 40 year old tyres off my Lester wheels, Jesus they'd gone rock hard.
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Just done the same on the cb350k0's tyres