Author Topic: Rear brake noise, Is this bad? (Read 4697 times)

GraveRobber · « **on:** May 03, 2006, 06:54:31 pm »

1974 CB750,
When I step on the rear brake pedal I hear a single pop or clunk sound and feel it in the pedal. This happen 80 percent of the time. If I let off the pedal and immediately press again it doe's NOT make the sound. Pressing the peddle multiple times in a row, it will only make it the first time.
Only seem to happen after I start from a complete stop and ride at least 200-300 feet. Everything seems tight and adjusted right. Is this bad?

HondaMan · « **Reply #1 on:** May 03, 2006, 07:16:03 pm »

Two things to check:

1. How worn are the shoes? You can tell by how far the adjuster is turned in. Very worn shoes will often clunk.
2. If the shoes are good, check the actuator cam. If it's old, it may have lots of slop in it, or it might be "gunky" and need cleaning and a bit of grease. Nobody ever cleans or greases these, and they should be done once a year.

Also look for: the backing plate arm. Make sure the bolts are tight and there's not too much slack in the pivot points.

bowhunter · « **Reply #2 on:** May 03, 2006, 07:18:48 pm »

There may be a crack or split in the brake drum. Remove the wheel, remove the brake assembly, clean the drum and examine the drum, with a magnefier if necesary. If it's cracked, that's your problem! Haven't heard of any fixes for it, other than replacement.

Bowhunter

bowhunter · « **Reply #3 on:** May 03, 2006, 07:22:06 pm »

By the way, post what you find, so others can learn from your experience!

Bowhunter

JOP · « **Reply #4 on:** May 04, 2006, 01:43:55 am »

Quote from: HondaMan on May 03, 2006, 07:16:03 pm

2. If the shoes are good, check the actuator cam. If it's old, it may have lots of slop in it, or it might be "gunky" and need cleaning and a bit of grease. Nobody ever cleans or greases these, and they should be done once a year.

Also look for: the backing plate arm. Make sure the bolts are tight and there's not too much slack in the pivot points.

I get the clunk as well and am very interested in any findings.. What is the "actuator cam"?
Thanks!

mwvachon · « **Reply #5 on:** May 04, 2006, 03:33:57 am »

The actuator cam is the piece that spreads the brake shoes apart. If you look at the brake plate, the shoes have a pivot point (towards the front of the bike). On the other end of the shoe, they rest against a large pin that has two flat sides (actuator cam). You can see that if you rotate the brake arm (outside of the brake back plate) this cam pushes the brake shoes apart as it is rotated.

dusterdude · « **Reply #6 on:** May 04, 2006, 05:24:34 am »

i had an issue with the anchor arm being loose and causing a clunk also.

Mark M · « **Reply #7 on:** May 04, 2006, 05:53:21 am »

Spot on - sounds just like a loose anchor arm - it will take up the slack on first application, then takes some shaking to regain the slack again.

SteveD CB500F · « **Reply #8 on:** May 04, 2006, 06:02:50 am »

Quote from: bowhunter on May 03, 2006, 07:18:48 pm

There may be a crack or split in the brake drum.

The 500/550 suffered from this (both my recent bikes and my old 550 (avatar))

The symptoms are an oscillating brake pedal when you press it and a "wavy line" on the rear brake test machine during MOT (inspection) if your tester bothers. This is caused by the lining of the hub splitting and causing a high spot which will contact the brake shoes before the rest of the drum - and reduced braking effect!

There was no fix until BryanJ recently advised that a mate in Gloucestershire (UK) could reline the hub. Maybe if he's around he could expand on this. Sorry for the hijack.

wheelie · « **Reply #9 on:** May 04, 2006, 07:03:01 am »

Yeah, I get this too. I looked for anything obvious recently since I had the wheel off two seperate times for sprocket and tire change. I greased the cam, checked for lip on drum and checked linkage. It all looked good (really good).

Whenver I think about it now I wonder about the swingarm movement and the effect that may have on the linkage.

I will be watching this thread closely for solutions because it is a very disconcerting sound that is always a distraction.

GraveRobber · « **Reply #10 on:** May 04, 2006, 06:41:24 pm »

Ok, will keep you updated. I am going to replace my tires and will tear it apart then. I'll photograph anything I find and post it.

Jmon99 · « **Reply #11 on:** May 05, 2006, 05:45:42 am »

I could be the brakes sticking on the actuator cam.. ..I bought some recently, and they were a bit tight in the cam. I ended up filing the bit of the brakes that fit inside the actuator cam and they worked a treat.

Another problem with the same symtoms I had was when I'd just fitted the brakes and I'd given them plenty of play so I had to press the pedal down pretty far before the brakes started working. What was happening was, I'd press the brake and the anchor arm would get stuck under the bit of rubber that the centre-stand was held against. This prooved to be a bit dicey as I'd press the brake at speed and they would stick on. Anyway I adjusted the brake and shaped the rubber with a razor blade so if it ever did happen again it would just slide off.

J

Jmon99 · « **Reply #12 on:** May 06, 2006, 09:19:52 pm »

correction to second para:

the anchor arm didn't get stuck.. ...it was the brake operating rod that was getting stuck...

GraveRobber · « **Reply #13 on:** May 24, 2006, 07:43:39 pm »

Finished getting new tires on the bike. Went over the rear brake with much care. Cleaned, measured, lubed contact points etc. Inspected drum for cracks and imperfections, None found.
Two things that I did find. 1 The drive sprocket was loose! 2 the bolt on the rear brake stopper arm on the rear brake panel was some what loose. The hole in the panel has been enlarged a little.

I tightened the sprocket nuts and I replaced the washers on the brake stopper bolt. They were very loose and did not seem to do the job. That tightened the bolt up. Went for a ride and no more rear brake clunk or tap in the pedal.

Bob Wessner · « **Reply #14 on:** May 25, 2006, 02:29:08 am »

GraveRobber,

Glad to hear you got it resolved. Thanks for coming back with an update as to what fixed the problem, doesn't always happen that way and the info could be valuable to the next person.

bryanj · « **Reply #15 on:** May 25, 2006, 10:06:19 am »

Hi Steve Been on Holiday/Honeymoon in Florida so catching up slowly on posts. The man who relines the drums is near Halifax in yorkshire close to junction 23 of the M62. He charges about £35 per hub BUT as he has to search for cast pipe of the right diameter it can take a couple of months. If anybody want a phone number please PM or email me

biketaviousmaximus · « **Reply #16 on:** September 03, 2006, 05:43:18 pm »

My 750 k2 is doing the same thing, I think it's the swing arm sliding from side to side causing the clunking?? Trying to get it sorted???

edbikerii · « **Reply #17 on:** April 09, 2007, 06:58:32 pm »

My 77 CB550 was doing the same thing. Clunk on first application, then fine until next acceleration. After even the slightest acceleration the clunk would come back.

Discovered that some previous owner had done work to the nut that attaches the brake to the torque arm, and replaced the castellated nut with a plain old nut, so there was no way to use the cotter pin.

I tightened it up (it was loose by three or four full turns), and all clunking went away. I don't remember ever having such smooth brakes on this old bike!

I'm going to try and find the proper castellated nut and install a proper cotter pin so this never happens again.

griffin · « **Reply #18 on:** April 19, 2007, 04:37:26 pm »

i just had a new rear tire put on my cb350 and i'm getting the clunk too. i just bought this bike and the clunking has become noticable since the tire was replaced. any tips on what i should look at first? i am a total newbie when it comes to working on motorcycles so please talk to me like i am a 10 year old. thanks

edbikerii · « **Reply #19 on:** April 19, 2007, 05:10:36 pm »

Well, if you have a rear drum like the cb550 I have, then you probably have an arm that attaches at the bottom of the drum. The other end attaches to the frame of the bike. One or both ends of that rod have a loose bolt. At least that was my problem. The arm is called the torque arm, and it prevents the brake from turning when the brake is applied.

griffin · « **Reply #20 on:** April 19, 2007, 05:15:17 pm »

Quote from: edbikerii on April 19, 2007, 05:10:36 pm

Well, if you have a rear drum like the cb550 I have, then you probably have an arm that attaches at the bottom of the drum. The other end attaches to the frame of the bike. One or both ends of that rod have a loose bolt. At least that was my problem. The arm is called the torque arm, and it prevents the brake from turning when the brake is applied.

yeah it's a drum. i'll check that out. thanks

griffin · « **Reply #21 on:** April 20, 2007, 09:52:04 am »

so the bolt where the torque are connects to the frame is loose, in that it jiggles around a bit and the torque are can move but it is proving IMPOSSIBLE to tighten or even loosen. this makes me think that the guys didn't mess with it when they took the wheel off for a new tire..... and shouldn't the torque arm pivot in there when the suspension compresses?

edbikerii · « **Reply #22 on:** April 20, 2007, 10:52:52 am »

Quote from: griffin on April 20, 2007, 09:52:04 am

so the bolt where the torque are connects to the frame is loose, in that it jiggles around a bit and the torque are can move but it is proving IMPOSSIBLE to tighten or even loosen. this makes me think that the guys didn't mess with it when they took the wheel off for a new tire..... and shouldn't the torque arm pivot in there when the suspension compresses?

I just checked on my 77 CB550, and sure enough there is a nut and bolt on the frame end of the torque arm as well. It is very tight on mine. I cannot jiggle it at all. The nut is 'castellated' meaning that it has slots in it for a cotter pin to prevent it from turning. Have you got the same, or a similar, setup? If so, you should remove the cotter pin before tightening up that nut, then replace with new cotter pin. As for pivoting, I guess so, but yet mine is tight enough that there are no 'jiggles'.

griffin · « **Reply #23 on:** April 20, 2007, 12:08:42 pm »

Quote from: edbikerii on April 20, 2007, 10:52:52 am

I just checked on my 77 CB550, and sure enough there is a nut and bolt on the frame end of the torque arm as well. It is very tight on mine. I cannot jiggle it at all. The nut is 'castellated' meaning that it has slots in it for a cotter pin to prevent it from turning. Have you got the same, or a similar, setup? If so, you should remove the cotter pin before tightening up that nut, then replace with new cotter pin. As for pivoting, I guess so, but yet mine is tight enough that there are no 'jiggles'.

yep same set up. with the cotter removed i just couldn't tighten it. the washer seemed fused to the nut. i put everything back together and now the clunk is gone so i guess it had something to do with the way the spring end of the brake puller was reinstalled
oh well
thanks for your help

edbikerii · « **Reply #24 on:** April 20, 2007, 02:40:21 pm »

Well, I'm no expert, but I figured you'd have to tighten nut #22 on to bolt #17. It looks like bolt #17 is a shoulder bolt, so perhaps that is where the pivot is supposed to allow for suspension travel?

Again, I'm no expert, so please don't rely upon my advice with respect to your brakes. I was just trying to share my experience with my own repair, in the hopes that it might help you. Right now I'm nervous that the problem seems to have gone away but you don't really know what fixed it. I'd feel much better knowing exactly what the problem was and how it was fixed.

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Author Topic: Rear brake noise, Is this bad? (Read 4697 times)

GraveRobber

bowhunter

bowhunter

JOP

GraveRobber

Jmon99

Jmon99

GraveRobber

biketaviousmaximus

griffin

griffin

griffin

griffin