Brake flush

[r65lsk75c]

OK, so I'm ready to consider the possibility that the squealing disk brakes on my '87 K75C are due to the fact that I switched to Dot 5 fluid about 10 years ago. No amount of pad cleaning or anti-squeal goo has lessened the problem. Just pushing the bike around in the garage produces a hair-raising shriek. So, my question is: I know that alcohol is often recommended for flushing glycol-based brake systems. What should I flush my system with to remove the last traces of silicon fluid before I refill with glycol-based (Dot 4) fluid?

All suggestions will be appreciated!

Rick T

[deilenberger]

Originally posted by corvair65
OK, so I'm ready to consider the possibility that the squealing disk brakes on my '87 K75C are due to the fact that I switched to Dot 5 fluid about 10 years ago. No amount of pad cleaning or anti-squeal goo has lessened the problem. Just pushing the bike around in the garage produces a hair-raising shriek. So, my question is: I know that alcohol is often recommended for flushing glycol-based brake systems. What should I flush my system with to remove the last traces of silicon fluid before I refill with glycol-based (Dot 4) fluid?

All suggestions will be appreciated!

Rick T

Wow - tough one. Basically - nothing disolves silicone oil (which is what the DOT5 is..)

What I'd do - is flush/flush/flush the brake systems using DOT4 fluid. For the first bit - a few quarts of inexpensive DOT4 (check the big chain auto-parts stores) could be used, then switch to a better brand (like BMW's for the final flush.)

The upside of the DOT5 is - it has coated all the rubber bits in the brake system and they are very resistant to corrosion. Even after flushing I'd expect some of the silicone oil to remain on the rubber parts. The downside - getting it out of the system so no pockets remain is going to be difficult.

Your symptoms make me think the caliper pistons aren't retracting correctly. The dust cover and the shape of the seal in calipers is normally designed to help the piston retract just a bit when pressure is off them... but since DOT5 silicone fluid is more viscous than DOT4, the pistons may not move as easily.

Also - any water that gets into DOT5 goes to the lowest point in the system, in this case - your front calipers, so there may be corrosion in the calipers.

This might be the time to remove, disassemble the calipers and replace the seals in them.

I highly recommend doing a pressure-bleed on the system when you're done (or if you're just going to flush it.)

Information on building a $25 home made pressure brake bleeder can be found at: http://www.apexcone.com/JimPowellHomepage/Bleeder/bleeder.html

I built one, and made caps for the front and rear brake systems on the K100RT that I added ABS to, and since then wouldn't even think of bleeding or flushing brakes any other way.

To get the caps - see your dealer and ask them if they could save a dead front master-cylinder for you - you want the cap. The rear cap can probably be matched up to some domestic car cap (I seem to remember on my K100 with the reservoir on the sideplates that it matched the GM cap used in the article.)

Best,

[r65lsk75c]

Don,

Thanks for the suggestions. I was thinking along the same lines -probably a good idea to tear down and thoroughly clean the calipers. I am pretty much a rank amateur mechanic and wonder how difficult a task this is. Are special tools or skills needed to disassemble the front brake calipers and replace seals?

Thanks again for your recommendations.

Rick T

[deilenberger]

Originally posted by corvair65
Don,

Thanks for the suggestions. I was thinking along the same lines -probably a good idea to tear down and thoroughly clean the calipers. I am pretty much a rank amateur mechanic and wonder how difficult a task this is. Are special tools or skills needed to disassemble the front brake calipers and replace seals?

Thanks again for your recommendations.

Rick T

Rick,

I haven't done Brembo calipers, I have done various auto ones. I believe some of the K manuals cover rebuilding the calipers.

Basically - from what I read on the Brembos - you have to split the calipers, remove the piston, clean all the bits up, install a new seal on the piston, and a dust cover on it, and new seals where the caliper halves bolt together.

I'd say the most special tool you'll want to use is a torque wrench. A source of compressed air may be useful.

You may want to move the piston as far out as you can with the caliper off the bike by using compressed air while the piston is still assembled.. I'd put a thin piece of wood where the pads go just to protect it.

Oh - might be a good thing also to replace the bleed nipples (they tend to fatigue with a lot of use and sometimes break) and the rubber covers for the nipples (the sun beats these up..

Once the piston is out - inspect it and the bore in the caliper for corrosion and pitting (a sign of water getting to the metal). If the pitting is really noticeable, I'd be looking for a new used caliper.

Best,

[j-budimlya]

I suspect that all the rubber stuff, seals, gaskets, etc. have absorbed some of the silicone matereial and swelled from the absorbtion....this alone could cause them to bind up...

You will need to replace everything rubber, o-rings, gaskets, etc....

It can't hurt any metal, so whatever is not corrorded is ok to reuse...

JIm Bud

[deilenberger]

Originally posted by j-budimlya
I suspect that all the rubber stuff, seals, gaskets, etc. have absorbed some of the silicone matereial and swelled from the absorbtion....this alone could cause them to bind up...

You will need to replace everything rubber, o-rings, gaskets, etc....

It can't hurt any metal, so whatever is not corrorded is ok to reuse...

JIm Bud

Not to belabor the point - but silicone is specified for protecting rubber materials. It isn't absorbed more than a few molecules deep. It probably isn't a bad idea to do any critical seals at this point since they've been in the bike for a long time, but I wouldn't worry about things binding due to the presence of silicone fluid. It is rated as compatible for brake component rubber.

Best,

[n5xwb]

Hey Group;

I HIGHLY recommmend replacing the factory rear disc. I can not say enough about the value in coasting, pushing, gas mileage and also braking improvement that came from a Spiegler semi-floating disc. It uses your old hub and come assm from them.

I have also replace the fluid with DOT5 after a complete rebuild of master and slave cylinders.

I hear thunder! So, say goodbye.

donn aka N5XWB
Life BMWMOA 4146

[deilenberger]

Originally posted by n5xwb
Hey Group;

I HIGHLY recommmend replacing the factory rear disc. I can not say enough about the value in coasting, pushing, gas mileage and also braking improvement that came from a Spiegler semi-floating disc. It uses your old hub and come assm from them.

I have also replace the fluid with DOT5 after a complete rebuild of master and slave cylinders.

I hear thunder! So, say goodbye.

donn aka N5XWB
Life BMWMOA 4146

Hey Donn..

What was the reason for replacing the factory rear disk? If the braking system was performing as designed, there shouldn't have been any difference in coasting, pushing or gas mileage between a floater or a fixed disk. The only way I can imagine there would be a difference is if your brake system was causing the rear brake to drag.

I - as a general rule - wouldn't recommend DOT5 in a BMW motorcycle. It is not what the manufacturer specifies, and in the case of ABS equipped bikes - is not recommended to be used by the DOT5 manufacturers.

I know this is gonna generate a bunch of email from people who've been using DOT5 in something for at least 100 years and never had to change it, and never had a problem.. but *I* wouldn't do it. Brakes are important.

Best,

[n5xwb]

Hey Group;

The reason for changing to DOT5 is because it will not eat your paint nor is it hydroscopic. It will not hold moisture (down side is if water gets into the system it settles in your slave cyclinders and can be flushed by bleeding) . Yes I did rebuild all of the slaves and master cylinder because the bike is a 1987 model. So, why not? I also cleaned all hoses and bleed the system. Improved breaking and a better feel.

I also replaced that sorry super soft metal BMW factory disc that caused drag and very poor breaking.
That disc may have even been the cause (or partly to blame) of an accident I had on 610 near 59 in Houston.
It had ruts and was warpped. The new disc was less expensive and works correctly. I have about 20K on the rebuilt system and no problems.

[1flyer]

My rear disk was replaced for radial play. As I understand, movement across the back of the bike (left to right as you stand behind to rear wheel) is OK and part of the "floating" between the caliber. Mine had abnormal free play front to rear (or in and out) as you look from the rear. Grasp the disk, push it forward and then pull back. Evidently, free play in one direction is OK but not in the other. Or maybe a little is OK in both axis but “in and out” was more than the limits.

I should have asked more questions but it showed up as warranty work when I picked up the bike after it was in for other maintenance. This was third disk I’ve heard of being replaced though not by the same dealer.

[Will]

In my previous life I had the opportunity to fix many different makes of automotive brake systems but never would guess that fluid would cause any type of noise.

Pushing around the garage and getting noise would suggest to me a dragging caliper. Your brakes have some miles so I would expect that something is dragging slightly.

for what it is worth here is how I would address a brake noise on an automotive system, this may be slightly different on a motorcycle but I'm thinking that disc brakes are disc brakes.

1. verify that there is not a run out issue with the brake rotor. this would require measurement with a dial indicator and comparison to the specification. small amout of run out could cause brake pads to move when they are not suppose to be moving.

2. remove pads and look for any spots that look like the pads are in contact with other metal. no rust or bright spot is what you are looking for. when you find the points of contact lube them up, I have most success in using permatex anti-seize as a lube, some guys like to also spray that anti noise goo on the pads as well. I would use the spay goo in addition to the permatex.

3. if the anti-seize does not work it's into the calipers, buy a overhaul kit and replace everything. I would bet that you may find a small amount of rust on the caliper piston just under the outer dust cover that is causing the piston to drag and not return correctly. look at where the seal rides on the caliper piston, any pitting or rust replace the caliper piston. If there is rust or small pitting above where the seal rides it can be remove with a little brake fluid on on some 400 grit sand paper. also be sure to hone the caliper or use the 400 grit paper to clean up the caliper. clean up, reassemble, bleed away and you are ready to go.

4. as with any brake system don't touch them unless you are qualified. (legal disclaimer)

hope this helps.....

[n5xwb]

Hey Bill;

I do agree with you on the noise issue.

On my K100LT the factory made a very poor quality rear disc. It wore more thatn the pads.
The resulting drag was sogreat that pushing the bike was a pain. Besides it made shifts more dificult and less smooth.

I did change it to a Spiegler Semi Floating disc and installed Ferodo FDB108PR pads. I also rebuilt the slave calipers and master cylinder installing new rubber parts. Flushed completely and then install synthetic (spelling Senior Momment!). Cost was around $350.00 total.

Life is builtiful and coasting is fun. I can't say gas mileage improved but safety has.

[dlearl476]

Not to belabor the point - but silicone is specified for protecting rubber materials. It isn't absorbed more than a few molecules deep. It probably isn't a bad idea to do any critical seals at this point since they've been in the bike for a long time, but I wouldn't worry about things binding due to the presence of silicone fluid. It is rated as compatible for brake component rubber.

Best,


DOT-5 brake fluid in Brembo brake systems: TSW Vehicle Concepts - submitted by Mark Kaczmarczyk

IMPORTANT: All brembo braking products use natural-rubber base seals, and therefore are INCOMPATIBLE with DOT-5 SILICONE-based brake fluids.

DOT-5 SILICONE-based fluids react with natural-rubber seals to swell them WHICH CAN CAUSE SEVERE PISTON RETRACTION PROBLEMS. There is no cure for problems caused by DOT- 5 use other than complete seals replacement - USE ONLY DOT-3/4 NON-SILICONE TYPE FLUIDS in your brembo components.

(Yes, we know the cap on the rectangular master cylinders says DOT 3 - 5 Fluids - BUT PLEASE NOTE: Silicone DOT- 5 fluids are NOT generally in use in Europe, but Glycol-based DOT-5.1 fluids ARE. Hence, the DOT-5 cap designation)

For best braking performance, they recommend changing brake fluid twice a year. If the machine is to be stored in a damp environment (over the winter, say), they recommend installing fresh fluid before and after the storage period. At minimum service levels, glycol brake fluids MUST be completely changed at intervals not to exceed a period of 18 months.

One last time, RTFM.