Front Disc Play

Hi All,

Might have some spare time to look at this on the weekend so wanna be quick so i can also go for a ride. The front disc pads and the disc have a lot of clearance between them. So much so that when not in use at certain RPM's they rattle, which if nothing else is very annoying at the lights. I have an updated Master Cylinder from RGM, 13mm, new pads and nothing else. The brake works fine except the travel at the lever and the rattle are getting to me.
If anyone can throw their 2 bob or more at me id be willing to accept...
Cheers

Standard caliper and disc?

Do you feel any pulsing through the brake lever when the break is applied?

It sounds to me like your disc has runout and is knocking the pads back, or you have a problem with the master cylinder, and after the brake is released the cylinder is drawing the pistons back.

Cheers,

cliffa

No problem with run out, was checked before it was put into service and no pulsing at all. Im going with master cylinder pulling the pistons back Cliffa?

Standard caliper and disc

Had similar , take out pads , completely clean the caliper area and the pads, reassemble. I know it makes no sense but there you are.

In addition to Onder's suggestion..

Front wheel bearings ok?

Disc studs / bolts are tight?

If it happens to be an RGM disc purchased last year, there was a bad batch. ( I returned one). They were true but not machined flat on the mounting face or the friction area. Mine was true but fruit bowl shaped. and it was visible using a steel rule.

Cheers,

cliffa.

If you drop the wheel and extend the pistons (put a paint scraper or something thin in between them for ease of getting them back) and then take a brass brush to as much of the side walls as you can, it might help. I have a bike that needs this procedure about twice a year. It's something to do with the piston wanting to stick to the rubber bellows. The bellows then acts like an unwanted return spring. Of course the better procedure would be a proper disassembly and cleaning, but if that's unappealing then this is worth a quick try.

So other thoughts....after having a long battle getting my MC to advance the pistons correctly following a Resleeving kit install. Ultimately determined the MC piston seal was not positioned correctly when brake lever released. The inboard-most seal lip must be to the right of the inboard/left-most hole in the MC reservoir...otherwise no additional fluid can enter the brake hose line down to caliper as the pads wear etc....and when lever is released, the fluid can only return as much as it had advanced then lever pulled...hence you get caliper pistons/pad moving in/out basically exact same amount, even as pad friction material wears down. Can also happen with new pads if caliper pistons cannot advance to a proper rest position.

So I would carefully assess what happens to fluid with a lever pull/rekease. You should see turbulence through the left most tiny hole in resvoir...if not, your seal is not in proper location. Also, if you try to push fluid up from bleeder nipple using a syringe, if none can be pushed up to resvoir with lever relaxed...the seal is not right side of the hole.
This can be remedied by slightly filing material off the lever tongue where it contacts the end of the MC piston.

This might be a little far-fetched, but is it possible that your rotor (disc) is below spec with regard to thickness, leaving the gap you describe?
More likely (to my feeble mind, at least) is that the caliper pistons are not sliding past the seals, but just distorting them. If it was me, I'd pull the pistons out, lube the seals where they contact the pistons, and put them back in, see if it made a difference.

I'd pull the pistons and replace with stainless and new rubber seals for them.

Stainless pistons for sure. The standard items are a real mess after a while, and if left long enough, will rust, pit, and ruin the caliper itself.
But choose your pistons carefully. Various sources not all the same...
http://www.oldbritts.com/14_061896.html

All good points on pistons & rubber seals...but from OP description, it seems this issue only came up after the resleeved MC installed....presumably not behaving this way earlier. So my money is on the MC piston seal position. Does the RGM resleeve include a lever or is the OP installing his own? We know the levers are not consistent over the years in terms of contact point dimensions etc. Thus some fine tuning may be needed.

My money is definitely on the M/C. To be honest as this is an item your life depends on I don’t know why people resleeve anymore as AN now manufacture and sell a 13mm version. (It was different when there was no alternative). The caliper should be checked, but I don’t see any way the seals could draw back the pistons, and If the chrome has flaked it would cause the brake to bind, not this behavior.

Cheers,

cliffa.

Tornado said:

The inboard-most seal lip must be to the right of the inboard/left-most hole in the MC reservoir...

Click to expand...

Yes, but the purpose of the small hole is to allow residual pressure to vent into the reservior.

Tornado said:

otherwise no additional fluid can enter the brake hose line down to caliper as the pads wear etc....

Click to expand...

The piston "cup" operates as a one-way valve. When the brake is applied, the lip of the primary cup is forced tightly against the bore by the pressure within the cylinder.
When the brake is released, the return spring forces the piston back, the resulting depression collapses the cup seal causing fluid to be drawn into the cylinder from behind the cup seal (note the larger of the two holes is the feed port), so the cylinder is constantly being replenished as necessary by fluid from the outer piston chamber.

http://www.classicbike.biz/Triumph/.../Lockheed_Hydraulic_Brakes_Triumph_Norton.pdf

"....On releasing the brakes the return spring moves the piston back faster than the fluid can return and this causes the lip of the main rubber cup to relax and fluid passes over the cup from behind, through the holes drilled in the piston head for this purpose."

Tornado said:

and when lever is released, the fluid can only return as much as it had advanced then lever pulled...hence you get caliper pistons/pad moving in/out basically exact same amount, even as pad friction material wears down.

Click to expand...

Can't happen, for the reason previously mentioned because any shortfall in the fluid returning to the master cylinder would immediately be replaced by fluid from the outer piston chamber.

Connie73 said:

No problem with run out, was checked before it was put into service and no pulsing at all. Im going with master cylinder pulling the pistons back

Click to expand...

The master cylinder can't exactly "pull" the caliper pistons back.
Any depression in the cylinder from releasing the brake would immediately cause fluid to be drawn in from the outer chamber. If the master cylinder was "pulling" the pads back then it should do so even if the wheel isn't rotating. With the bike standing, I suggest you operate the brake, wait a short while, then check if the pads are loose or there is excessive lever slack. If not then it seems doubtful the master cylinder is to blame.


http://what-when-how.com/automobile/hydraulic-braking-system-automobile/

"Operation.

When the foot-pedal is applied, the push-rod pushes the master-cylinder piston along its bore. Immediately the bypass or compensation port is sealed ‘off, and fluid ahead of the piston is trapped. The pressure developed in the master-cylinder pushes the lips of the check-valve cup away from the metal body so that fluid is displaced into the pipelines. This forces the caliper or shoe wheel-cylinder pistons, causing the discs or drums to be braked. (Fig. 28.37B).

Fig. 28.37. Lockheed master-cylinder.
When the foot-pedal is released the master-cylinder return-spring moves the piston back against its stop washer and circlip faster than the return of fluid from the disc or drum wheel-cylinders. It therefore causes a depression in the master cylinder. As a consequence the primary seal is drawn away from the piston head distorting it, thereby uncovering the recuperation holes. Fluid from the annular space around the piston then flows through the recuperation holes and removes the temporary pressure difference between the two sides of the piston head (Fig. 28.37C).
At the same time fluid returning from the brakes, being under load from the disc-brake piston seals or drum-brake retraction springs, pushes the whole check-valve body away from its rubber seat and so flows back into the master cylinder. The fully returned piston then uncovers the bypass on[or] compensation port (0.7 mm diameter) so that any excess fluid created by the expansion of the heated fluid is released to the reservoir from the pressure chamber. Fluid always fills the annular space formed between the piston and cylinder by way of the large feed port (Fig. 28.37A)."



The caliper seals pull the pistons away from the disc as they distort when the brake is applied (2) and return to normal shape (1) when the brake is released so they normally move with the piston although the piston advances slowly through the seal as the brake pads wear.

This problem is not caused by the master cyl., if, as the OP states, braking action is good, as expected.
This brake design rigid mounts caliper & disc, relying on pistons in caliper positioning themselves to be in proper proximity to the disc.
Disassemble the caliper, clean, inspect & replace the seals.
I expect you'll find one piston seized in the caliper.

“Hopefully the brakes stay fixed this time?” or “I hope they hold up” “I’m not sure what is wrong with my brakes”?

Think texting teenagers behind the wheel of 3 tons of metal and plastic hurtling down the road at 50 mph.

The only thing more important than acceleration is stopping even faster so you can do it again tomorrow.

What is the downside to dumping 45 year old antiquated Lockheed braking technology and the encompassing repair speculation that that goes with it?

Upgrading to modern braking system/components/technology should be a realistic consideration.

Not trying to lecture here but I have been in an older car with restored original brake technology that did fail and my son was in the car as well.
I wouldn’t wish that experience on anyone.