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Discussion Starter #1
I spent some time getting 40+ years of sludge off my newly acquired '73 CB500. I pulled the fender and dust cover for better access... and carved off about a pound of grease, brake dust, dirt, etc. from inside the fender, between the fender and fork...

Looking at the dust shield, I really can't see a "significant" function. Well, beyond the whole dust shield thing. So, I did a search - couldn't find any info. Then, I looked at lots of pics of modified/restomod bikes... and it seems most are leaving these off. But really, I know next to NOTHING about these old bikes. So, before I start pulling things off - to later find out they're kind of important - I figured I'd ask the gurus.

Thanks!

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that is oem meant to AVERT WATER FLING AT SPEED
Is there a specific issue with that bikes brakes that would necessitate It? Or is it more like a period option?
 

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we have had a discussion about these before but I can't seem to find the old thread.

Are the necessary? no, you aren't going to crash with it missing because it is not there. But that doesn't mean they don't serve a function. most cars also have something similar on them from the factory, called disc brake dust shields. So what do they do? 2 things: 1) they divert brake dust down toward the ground instead of allowing it to spray back and cover your forks and wheel; and 2) they divert water spray from the leading edge of the disc from spraying you in the face during a rain storm.

Brake dust is corrosive to certain types of finishes like clear coat, aluminum, chrome, etc...so the less you get it on those things (like your fork, spokes and rim) the better off you are. You don't see them on a lot of new bikes because most new bikes have the calipers mounted behind the fork legs and the dust is already blowing away from the exposed slider. Also most modern front fenders have coverage over the disc to help control water spray. I don't know if you noticed, but the SOHC4 rotor is stainless steel and pretty thick, thicker than almost all other motorcycle brake rotors, and as such it tosses a fair amount of water in the rain or on wet roads. Ironically, guys who run drilled discs on these bikes usually delete them because they are concerned about road debris like a small pebble getting caught between the disc hole and the shield and causing drag and also having a disc full of holes kinda makes the brake dust go everywhere anyway.

If you want my opinion - some honda engineer got paid a decent wage to design that part and have it function, so if you are keeping the stock brakes, put it back on, a stock SOHC4 front end looks kinda naked without it. If you are upgrading and want to ditch it because it has stopped being useful...well that's a different story.
 

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I thought it looked pretty cool in the 1970's was hard to keep clean of what was possibly asbestos :|

Leaving stuff like that off is a cost saving measure,
on recent model 4 pot disc brakes they are starting to leave off the little plastic cover that goes over the pads and pins


:| which sucks because now the brakes ice up real easy in mud and freezing rain conditions,
helps if you urinate on it, but you can only have so much pee and then you run out of brakes :|


:| You know why trials bikes have a full guard on the wave rotor front brake?
... so it doesn't cut the catchers fingers off!
 

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gto i respectfully disagree
it isn't anything at all diust related and it isn't shielding the rotor from anything
it is strictly anti water fling
think about how ,much material a pad would need to sheid in order for it to be a ;roblem
getting new pads in timre would be the issue
brake dust takes time and many braking cycles to accunulate
the shields on car rotors are mostly there to protrect the rotor from the rare bigger foreign object and gritty muddy road water that wil accelerate wear
 

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gto i respectfully disagree
it isn't anything at all diust related and it isn't shielding the rotor from anything
it is strictly anti water fling
think about how ,much material a pad would need to sheid in order for it to be a ;roblem
getting new pads in timre would be the issue
brake dust takes time and many braking cycles to accunulate
the shields on car rotors are mostly there to protrect the rotor from the rare bigger foreign object and gritty muddy road water that wil accelerate wear
I don't clean my bikes usually, maybe once a season at best and just a wash and wax the painted surfaces. I'm not one of those guys that sits there with a tire on a roller and a toothbrush polishing spokes. I can tell you that the CB's I had without that guard always had a little build up of brake dust on the inside of the fork slider after about two seasons, but then again my riding environment at the time was NYC. I am sure some of that was road grime as well, but the bikes with it didn't have that buildup anywhere but in the shield. Then again this was also when cb's were just cheap 20+ year old motorcycles nobody wanted and my version of maintenance was to wait till something failed and then either replace it or buy another $100 honda that ran and transfer over the good parts so I could easily have been riding on crumbly 20+ year old brake pads. YMMV.

I def agree about the spray part - after I had my wreck on my 75, I ran it without a front fender and without that guard, and I could see the rooster tails that came off the whole unfaired front (under 10mph, faster and it got harder to see through the spray) and let me tell you it made a mess of everything, esp if you run though one of those NYC puddles that is part water, part oil, part antifreeze, and part just gutter scum.
 

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you missed dog poo and road kill or is that gutter scum?

... bet my dirt bikes are on average way cleaner then Geeto's street bikes ;)
competition bikes have to be clean just to be competitive.
Races have been won by staying cleaner then the other guy.
 

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gotta have it on a nice correct restoration...unfortunately, I don't have any of those, so I have a pretty big box of spares. The cb750f even had one on the rear disc so as to make sure you are not flinging water on anyone behind you lol. To be honest, I have been in the rain plenty on cb750's and never noticed if water from the disc/s was actually hitting me or not. The stock front fender certainly seems to work well.

One thing I have noticed with well worn oem pads and undrilled discs...heavy rain, grab the handle, and wait for what seems like ages, while the bike feels as if it is accelerating!, until the rotor gets hot enough to keep the wet off the rotor
 

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Discussion Starter #14
Thanks the help on this guys. I cringed when I hit "post" on that question. As a total newbie to old (okay, any) motorcycles, I really don't know whether my questions are in the "hey, do I really need front brakes" category of stupid, or not.

It sounds like - since this CB500 is not a pristine survivor headed for a museum restoration, and will likely not see any (intentional) wet weather - I can keep the "disc fender" in the bin of O.E. parts that have come off and will not go back on... but will be saved. By the way, the car/truck guy in me won't let me just chuck the old parts in a bin. As you may have noticed from that pic - everything that comes off, gets thoroughly cleaned, threads lightly greased, bagged and labeled with hardware.

Next up: Chain guards
(kidding)
 

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Got to agree with XB. The brakes were absolutely F****** terrible when wet. It was meant to keep water off rotor but didn't really do much, water ran down fork leg from mudguard mount then got between fork leg and cover making things worse rather than better (although it did keep your left foot extra wet plus mess up alternator cover by directing a little water away from disc :rolleyes:) mine came off as soon as waranty was up (I did dual disc conversion at same time, 550 needed it, 750 was scary with single disc) I just realised I've had this conversation before with Geeto, probably 2009? ;)
 
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