CB750 Caliper rattle

[Lobo]

New back to biking after 30yrs - and can't find any tolerances / specs on this.  Basically my 1971 K2's caliper moves up & down by upto 1/8" due slop in the carrier. This pin (I guess) is OK as a snug fit into the upper / lower caliper holder mounts (& shows no waisting) - so the play is within the holder itself. This translates into a fairly mechanical 'clunk-clunk' noise when transversing bumps etc  at low speed. It, of course, goes away if any drag on the brake.
I pointed this out at the recent MOT - no concerns at all. So, is it normal, and if not any suggestions eg bushings - or am I up for a new holder? I read in the various maintenance manuals about calipers seizing on with lack of use - can't ever imagine mine seizing with this amount of free play!
Cheers.

[Waggles]

As you so rightly say, they are more prone to seizing than excess play so I'd say no, its not normal, mine certainly doesn't do that. It may have got through the MOT but I wouldn't be happy with it, the slopping around could cause damage.

Dunno the cost of new but I would replace arm and possibly spindle too ( it may look OK and the arm will wear first but it might be damaged ) a good second hand set shouldn't be too hard to find if cost is an issue

[florence]

That does not sound right to me.  I would take it apart and inspect.

[Bryanj]

There is a Honda bulletin on this, bug me early in the new year when I ain't dragging booze round the country for god knows how many hours a shift and i will find it and scan it!!

[Lobo]

Thanks guys, thanks Bryanj,

Yup, had the thing apart (twice) and have to say, nothing particularly alarming. There is minimal slop in the pin, but, I guess when magnified 6" away at the caliper head it does become quite apparent.
I'm a little 'reluctant' to simply buy a second hand carrier off ebay etc, as in all likelihood I'll simply end up a similarly worn part.  Hence my question on bushings...

Will now wait to see if Bryanj can shed light.... thanks again so far
Lobo

[steff750]

  there are two sizes of shim in the parts list 0.1mm-0.2mm,that can be fitted between the lower part of the caliper and the caliper holder ,use either one or the other or even both as the parts list shows you can have any number of shims . i have seen this so many times that i would say that it was a common fault,and as the shims are not shown in the first parts list but they are in the fourth parts list . i would say that honda tried to correct the problem (bryan said there is a parts bulletin for it), and i have seen so many calipers without shims anyway. and yes i would say you would probably buy a secondhand one just has bad as yours. my advice would be get the shims and go from there,may aswell get the two orings while you are at it and grease the pin

[Lobo]

Steff - I think you've just fixed it! Thanks.

Whilst I do indeed have those O rings, there are no 0.1  / 0.2 mm washers. And whilst the slop appears  minimal at the carrier head it is not so at the caliper, ie seems I just now have to find those spacer washers......

Many thanks again,
Lobo

[K2-K6]

Because they only rotate a very small amount it's unusual to get a significant wear on either component, but this is why they end up siezed when not greased.

If you are saying that the caliper support is moving by sliding up and down the pin, then shiming should be a reasonable way to cure that.

If the caliper support is moving in an arc i.e. the hole is too big for the pin, then the problem would seem more serious. Any plan to use a bush would be difficult as the material around this location is maybe not generous enough to make an adaption.

[Lobo]

Hi K2-K6,

Agreed, and yes, it does move in an arc - suggesting hole wear? I figured if a spacer were slotted in between all mating faces then this would arrest any 'nodding' of the carrier. The fact that Honda show optional washers in the parts diagram, and Bryanj mentions a Bulletin, all attest to the fact that it may be a known problem. Surely Honda wouldn't bother supplying a washer to stop a 0.1mm slide up & down the pin - but I could see it as a preventative measure to minimise exagerated nodding at the caliper.

Have got to add, it is not as alarming as it all sounds... which is why I guess the MOT man wasn't concerned. I've had it all stripped down, there's no obvious wear, or signs of abuse etc. My main gripe is the odd clunk over bumps etc.

The bike was semi-restored when I bought it, and perhaps the carrier had been seized at some point and subsequent corrosion removal has taken material away too. In which case I'm up for a new carrier...
But will try a spacer first...
Cheers, Lobo.

[Bryanj]

OK just finished another booze run and found the bulletin so here you are

[Lobo]

Thanks Bryan for taking the trouble.
Not certain (after all) it describes my problem and thinking I'm in for a DSS £100 new carrier.
Ah well, tis Christmas after all....
As a general note to all out there we should perhaps bear this in mind if considering a second hand carrier off ebay!
Cheers,
Lobo.

[K2-K6]

It does seem that the bulletin deals with a "float" along the shaft that results in a clunk as the caliper mass is moved, and seems to be the right way to control this.

The load path of the pivot axis is arranged so that when the caliper force is applied (braking) then the full length of the pivot is used (this is because it sits partly outside the disc swept area and differs from the fork angle). This is a good situation and should not result in undue stress or integrity during braking as it will natuarally align due to the braking forces. I don't think at this level it's any compromise to safety at all as it essentially has a design to cope with this.

Think you are right to try shims in order to control the movement and clunking when the brake is not in use which is just annoying rather than a particular fault. I have heard it on others over the years so it's by no means isolated.

If it was mine, I'd go with the shims as I've never seen a failure of this part.

One other consideration is the bolts used to fix the brake to the fork leg, these have to be of the correct type and would ordinarily have a dowel type shank that locates the braket in it's correct position and gives positive location, if these have been swapped for bolts with threads right up to the bolt-head then that function is lost and can contribute to spacing issues.

[Lobo]

Thanks K2-K6,

DSS had 01 OEM Carrier in stock, a couple of pins,  one 0.1mm spacer & nil 0.2mm. I won't be near the bike until NY day, and so simply thought 'sod it' & ordered the last carrier, pin & shim. My problem is I can only get hands-on with the bikes a couple of days PCM, and to order / play with shims, find not cured & thence DSS nil more carriers was too much to bear!

And ta for the heads up on the shank bolts - will take a look.

The issue, I am 99% sure, is the 'nodding' of the caliper - it was getting silly in that to stop the annoying clunk I was involuntarily applying slight front brake over bumps. Furthermore the Honda bulletin descibes a different problem (seemingly) to what I was experiencing - ie clunk with brake.
Again, thanks for your help.
Cheers, Lobo.

[Bryanj]

OK the pin should be a tight fit with no play in the static bracket and a sliding fit with minimal play in the swinging bracket, it is unusual to get excess play in the swinging piece and I have never seen play in the bolted piece, excess play can only be caused by over exuberance of cleaning corrosion after a siezure(which was very common---siezure that is)

[Lobo]

Anyone able to help with my caliper carrier - which now doesnt seem to be K2 spec. i ordered DSS p/n 45115300030 only to find its visually identical (almost) but about 1/2" longer than my carrier, and with the stopper bolt hole further down towards the caliper. It fits the holder, but is unusable due stopper bolt hole position...and length!
So...don't know what my bike has - are the forks non-CB750K2?

Out of interest (to the preceding thread) both carriers (old & incorrect new) have (approx) 0.3mm slide up & down the pin. The pin is new, and both carriers exhibit slight nod at the caliper - no play detected in the bolted holder. I fitted the one and only washer DSS had (0.1mm) - which isn't enough, but did lessen the 'nod'. I am (almost) convinced a little more spacings (as per the Honda bulletin) may solve my problem. ie it may simply be the 'Joint -Caliper holder' (ie bolt on piece) jaws are minimally too far apart?.
So...still looking for a Honda 0.2 mm spacer....