Author Topic: 7" front brake plate issue. SORTED, sort of.  (Read 232 times)

Online Minto

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7" front brake plate issue. SORTED, sort of.
« on: 20.07. 2021 19:51 »
Hey all, Ive had a look at my front brake this morning and noticed something that seems wrong to me. I'm going to attach some pics as they will say more than I can explain.
But my brake plate does not sit evenly on the drum, I've dismantled it again this morning and I'm wondering whether there's something missing.
The cam side of the plate sits 3 1/4 mm further off the drum than the fulcrum side.
I can't find any info on this brake, or its component parts but it really feels like there may be a part missing as it just wobbles on the drum until you tighten the two large nuts either end of the hollow spindle, then anything more than finger tight siezes the brake up on the hub, and it also does not sit flat or evenly.
Everything there is is in the second picture (apart from the nut and washer for the hollow spindle).
Any help would be gratefully received.
Since taking it apart and scrubbing it up a bit last week it has improved markedly and the shoes are now making way more contact than before, but I'm sure it could be improved further.
52 A10 plunger
Aprilia RSVR

Online muskrat

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Re: 7" front brake plate issue.
« Reply #1 on: 20.07. 2021 21:32 »
G'day Minto.
The plate looks bent to me. The cam and shoe will not be square with the drum. Did you notice the shoe is worn at a slight angle?
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Muskys Plunger A7

Online Minto

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Re: 7" front brake plate issue.
« Reply #2 on: 21.07. 2021 00:12 »
Hey Musky,
The shoes are worn at an angle, when I had it apart last week, they were only worn at about an inch on the leading edge, diagonally to about two inches. Since tightening it all up the wear pattern covers about 2/3 of the shoe, but still diagonally. Not sure it shows that clearly on this pic.
I didn't notice the plate was bent, I'll have a closer look when I get a bit of time.
Bugga, I need to clean my garage again.
52 A10 plunger
Aprilia RSVR

Offline Swarfcut

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Re: 7" front brake plate issue.
« Reply #3 on: 21.07. 2021 07:28 »
Jase. Can't tell from the pix if you have spacer collar 65 5890 which fits between backplate and bearing. If you have, it is possibly worn or damaged and now a bit too thin so the plate touches the drum. Without it the plate simply meets the edge of the drum. The plate is not well supported in this design and relies to an extent on the anchor arrangement to keep it aligned across the face of the drum. I would expect uneven wear on the shoes with this poor set up even when assembled correctly.
 Here's a 7" backplate with a witness mark around the central boss which may help sort it out.

https://www.ebay.co.uk/itm/154535771745?hash=item23fb0cbe61:g:WuwAAOSwhfZg7YWD

 Swarfy.

Online Rex

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Re: 7" front brake plate issue.
« Reply #4 on: 21.07. 2021 09:25 »
Not a great design for a bike of this capacity, that's for sure, and probably my biggest concern when riding the A7.
Unhappily, the (unridden, as yet) Sunbeam S8 has the same brake though it's a heavier bike, so it may be an even bigger concern on that one.. *eek*

Online Minto

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Re: 7" front brake plate issue.
« Reply #5 on: 21.07. 2021 11:33 »
Hi Swarfy
Thanks for the part number, from that I was able to find the exploded diagram on the DF site. According to that, everything is present though as you say may well be worn, or even assembled incorrectly.
The plate you referenced on eBay is one of them that I'd looked at, that collar in the centre isn't on mine, but neither is it shown in the DF diagram. It does show a "spindle sleeve" 65 5891 but that appears to go between the bearing locking ring and the INSIDE of the brake plate, and that is how it seems to be assembled on my brake. (Is this correct or should it pass through the back plate from the outside then through the bearing locking ring??)
Thanks again mate, massive help as always.
Jase
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Offline Swarfcut

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Re: 7" front brake plate issue.
« Reply #6 on: 21.07. 2021 15:31 »
 Jase  65 5891 would be the part that separates the backplate from the bearing inner. Internet search brings up lots of images, and other folks with the same problem. Stewart Engineering are listed as a manufacturer of this part for the aftermarket by some suppliers. Can't tell  whether it goes from the outside of the plate. If it does, something on the inside needs to support the backplate away from the drum. Some images show a plain backplate, others with a central boss that looks pretty well fixed in place.

  This may help, with thanks expressed to those contributing to this following useful thread. No infringement of copyright intended.

 https://www.bsaownersclub.co.uk/bsaoc_forum/index.php?topic=5579.0

 Still can't tell if this is the answer.

 Swarfy.

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Re: 7" front brake plate issue.
« Reply #7 on: 21.07. 2021 15:57 »
Dunno if it's a trick of the camera, but the pic of that backplate against the wheel tells me the backplate is bent. Best strip it and mount in a lathe (or pillar drill on very slow speed) to check its OK. Can be done on a flat surface, but bit more of a fiddle.
As for 7" brakes generally, they make reasonable doorstops. About the only thing they'll stop, unfortunately. Made in an era when slowing down was the only emergency one was likely to come across.
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

Online Minto

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Re: 7" front brake plate issue.
« Reply #8 on: 21.07. 2021 16:09 »
Swarfy,
Thanks so much for hunting that thread down for me, I've never been into or particularly proficient with interweb searching and stuff, takes me a week to do what others seem to achieve in moments with one hand and eyes closed. (Fnar!)
I think that could be at least a starting point, my assembly also starts to lock up if done up any more than firm finger tight.
Im away on it next week so I'll have to make some time to check all this.
Thanks again

52 A10 plunger
Aprilia RSVR

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Re: 7" front brake plate issue.
« Reply #9 on: 21.07. 2021 16:12 »
RD
Cheers for the input, Musky also suggested it looks deformed. I hadn't noticed and can't say that it looks bent to me in the pictures, but I'll do as you suggest and get it in the  bench drill to have a proper look, if it'll fit.
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Re: 7" front brake plate issue.
« Reply #10 on: 21.07. 2021 16:17 »
Rex
Cheers, I've always fancied one of those Sunbeams, great looking bike, good luck getting it all finished.
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Re: 7" front brake plate issue.
« Reply #11 on: 21.07. 2021 17:54 »
Thanks for that Minto. The bike should've been done a month or so back but I took the engine and 'box out to cure a leaking main bearing oil seal and a very dodgy clutch action, sorted all that but a sudden reoccurrence of a medical issue means I'm not allowed to lift the (heavy!) power unit back in for a couple of weeks. The head's also off to cure a leaking head gasket (a common issue with these bikes) plus the rear wheel is out awaiting it's new tyre to be fitted.

Regarding the brake plate and checking how true it is, I mount the wheel spindle vertically in the vice and spin the wheel slowly to see if or where it rubs. Usually the addition of a washer will space the plate away from the hub if it's too close.

Online chaterlea25

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Re: 7" front brake plate issue.
« Reply #12 on: 22.07. 2021 01:29 »
Hi All
I have one of those 7in. hubs (21in rim) on my Ariel HT5 raather than the full width alloy it should have,.
Its just the way things happened when buying at an auto jumble back in 1983 a complete forks and wheel  for £25 if  remember correctly
It had green Ferodo linings and these provided decent stopping until they were worn out
At the time "Supreme Motorcycles" were doing classic brakes, the  first  linings they fitted were woven fibre but they did not work anymore once they got wet so I sent  them back and had non woven soft linings fitted
I had previously skimmed the drum and turned the new linings to size
This Ariel is a lot lighter than an A7 or B31/33 but I have to say the front brake just takes a two finger effort to stop the bike, grab some more and the front wheel will lock  *eek* so much so I have to warn anyone who takes it out about how good the brakes are *ex* *smile*

John
1961 Super Rocket
1963 RGS (ongoing)

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Re: 7" front brake plate issue.
« Reply #13 on: 22.07. 2021 10:15 »
Hey John
That's encouraging knowing they can be improved then.
Forks and wheel complete for 25 quid?? Those were the days!
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Re: 7" front brake plate issue.
« Reply #14 on: Today at 19:17 »
Well got it apart again this morning to check further, I'm not sure how Musky and RDfella spotted it but they're both right, the plate is bent. Not across the face, that's straight enough checked with a straight edge in a multitude of different planes, but the central boss section is out, and not by much either, but the .25 mm (or whatever) in the centre is multiplied at the outer edge, and doubled again from one side to the other ( raise one side, the other lowers by an equal amount so a big discrepancy.
Anyway, what I've done is, file a tiny bit off the high side of the centre of the back plate then bias filed a washer, and placed the washer filed side to the plate between the central bearing collar and the brake plate, all of this remains static and just gets clamped together when the brake plate centre securing nut is done up.
It took a bit of trial and file on/off faffing but the brake plate now sits pretty much evenly on the drum and no longer locks up when the nuts are tightened properly.
The third pic is the washer in place on the hub.
The last two pics are for comparison, after and before.
So again, thank you all for the help, advice and eagle-eyed detective work.
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