R12RT rear brake caliper piston seal replacement

[PNWrider]

I am replacing the caliper piston seals on my 2011 R12RT.  I have the 34-21-7-674-607 seal kit in hand.  Upon examination with a magnifying glass, I can’t determine if there is any top/bottom orientation to either of the 2 seals in each bore?.?  I have also looked with no luck to see if there is any marking on the individual seals to indicate orientation.  

 

Some caliper piston seals apparently do have an inner circumstance bevel to help with sealing and piston retraction - is this true for the BMW seals as well?  Or do  the BMW seals have no inner circumference taper.  
 

thanks.  

Bill 

[dirtrider]

14 hours ago, PNWrider said:

I am replacing the caliper piston seals on my 2011 R12RT.  I have the 34-21-7-674-607 seal kit in hand.  Upon examination with a magnifying glass, I can’t determine if there is any top/bottom orientation to either of the 2 seals in each bore?.?  I have also looked with no luck to see if there is any marking on the individual seals to indicate orientation.  

 

Some caliper piston seals apparently do have an inner circumstance bevel to help with sealing and piston retraction - is this true for the BMW seals as well?  Or do  the BMW seals have no inner circumference taper.  
 

thanks.  

Bill 

Afternoons Bill

 

If no ID sheet came with the kit, and there are no marks, numbers, or marks that would allow you to tell top from bottom, & you can't identify any angular inner surfaces then even IF there was an install direction how could you tell top from bottom?

 

Lay the seals on a flat surface then see if there is any crown or bow in either direction.  If they are flat with no obvious angular cut on the inner sealing surfaces then they can't be directional. (the angular cut is used for slight piston retraction but not all brake calipers use that).

 

Now, IF there are any marks, ticks, numbers, etc that would allow you to identify direction or identify top/bottom then just match the mark location  (ie top or bottom)   to the removed seals.  

 

 

[PNWrider]

Thank you, DR for the information and advice.  I re-examined the old seals as well as the new ones with a magnifying glass. No marks / ridges / writing was seen. The thicker seals were laid out on a piece of plate glass to see if there was a discernible bevel.. if there is a inner circumference bevel, I can’t see it.  
 

1. The caliper pistons were cleaned as well as the seal grooves and caliper bores.  

2. New dust seal and piston seal were installed in each bore.  

3. Caliper sliding pins were cleaned and lightly lubed.  

4. The 2 spring ships that locate the pads were cleaned and reinstalled.  

5. Gaffer semi metallic pads installed. 
 

so I reassembled the caliper, installed it back on the bike - (the pistons can be compresses with finger pressure); bled the brake lines.  There is about 3-4 mm free play in the brake pedal before it contacts the master brake cylinder.  The fluid level is below the “max” level in the brake fluid reservoir. 

 

And the rear  brake is still slightly dragging.  😕 And creating a fair amount of dust on the rear wheel - much more than the front brakes / front wheel. 

 

so I am at a loss on where next to look - 2011 bike with stock braided line to rear caliper?  

 

 

[dirtrider]

5 hours ago, PNWrider said:

Thank you, DR for the information and advice.  I re-examined the old seals as well as the new ones with a magnifying glass. No marks / ridges / writing was seen. The thicker seals were laid out on a piece of plate glass to see if there was a discernible bevel.. if there is a inner circumference bevel, I can’t see it.  
 

1. The caliper pistons were cleaned as well as the seal grooves and caliper bores.  

2. New dust seal and piston seal were installed in each bore.  

3. Caliper sliding pins were cleaned and lightly lubed.  

4. The 2 spring ships that locate the pads were cleaned and reinstalled.  

5. Gaffer semi metallic pads installed. 
 

so I reassembled the caliper, installed it back on the bike - (the pistons can be compresses with finger pressure); bled the brake lines.  There is about 3-4 mm free play in the brake pedal before it contacts the master brake cylinder.  The fluid level is below the “max” level in the brake fluid reservoir. 

 

And the rear  brake is still slightly dragging.  😕 And creating a fair amount of dust on the rear wheel - much more than the front brakes / front wheel. 

 

so I am at a loss on where next to look - 2011 bike with stock braided line to rear caliper?  

 

 

Morning Bill 

 

This is difficult to advise on as it might be normal or might be indicating a problem. 

 

The rear brake has 2 separate apply sources, one source is definitely the rear brake master cylinder, the other source is from the rear servo pump that comes on with the front brake apply. (which ever one supplies the most pressure closes a valve in it's favor then operates the rear brake).

 

This system is difficult to diagnose as the cross-over valve & servo apply side is inside the ABS module.

 

My guess is that you are operating normal but keep in mind that is just a guess based on very little hands-on information.

 

The first thing I would do is put the motorcycle on the center stand (rear wheel off the ground), then use rear brake pedal to apply the rear brake, then release the brake pedal. Now give the rear wheel a spin & see how much residual brake drag you have. 

 

Now lightly push the rear  pads back (just a little), then turn the ignition key ON, then while spinning the rear wheel with your foot (or having someone else spinning the rear wheel) apply the front brake lever. The rear brake should instantly lock up (does it?).

 

Then see how much residual rear brake drag you have (is it about the same as the when you used the rear brake pedal).

 

As a final test I usually ride the motorcycle from cold without using the brakes, this can be difficult if you live in a congested area. If you can't do that from home or work then find a place in the country that you can stop for lunch or a (for a while anyhow), then allow the brakes to cool off, then  ride for a few miles without touching the brake lever or pedal.

 

Then cost to a stop (turn engine off & use engine braking to stop the motorcycle), now feel the rear brake to see if it is just lightly warm or is it HOT! If hot you have a problem.

 

Now do the same test but this time as you ride off from cold use the rear brake pedal  just once but only momentarily (just enough to apply the rear brake quickly)  then after riding, coast to a stop, & feel the rear brake again  (is it any hotter than it was with no brake apply?)

 

Now do the same test as above but only use the front brake lever (quickly & only once), see if the rear brake is any hotter after costing to a stop.

 

There are no return springs in your brake calipers. Just seals so you get very little brake piston retraction, so some light brake pad drag is normal.  If you have a little rear crown bearing play that allows the slight rear wheel displacement to kick the brake pads back slightly.       

 

 

[PNWrider]

Good morning, DR,

I have done the rear wheel rotational test already:

  1.  Pads pushed back - 1 full revolution   

  2.  Pads against disk after rear brake pedal engagement - 3/4 revolution 

 

Consistent results; This test has been done many times before and after the seal replacement / caliper cleaning with little apparent change in rotational resistance.  I have tried, as much as possible, to be consistent in the force applied. 
 

Earlier in the year when I first noticed the rear brake pad dragging issue, the GS911 ABS diagnostic test was performed with no faults noted.  About 3,500 miles since the GS911 check.
 

Front brakes are fine - rotate easily (obviously no drive line resistance) and very little brake dusting.  
 

In late 2019 I replaced the clutch pack on this 2011 RT at ~ 59,000 miles and, as required, disconnected the rear brake ABS lines.  A new rear disc and pads were also installed at that time.  I rode little during 2020 due to COVID.  The mileage now is 66,000. 
 

I will do the front brake test today. The on-bike tests you suggested will be a little more difficult here in the traffic congested Puget Sound region. I have pyrometer that will use for temperature readings. 
 

A question;  there must be some valving of some sort at the junction where the ABS line joins the rear brake lines at the rear brake master cylinder?  Is it possible that this valving might be the cause of slight residual rear brake pressure?
 

as always, thanks very much for your thoughts and time.

 

Bill

[dirtrider]

Afternoon Bill 

 

I have done the rear wheel rotational test already:

  1.  Pads pushed back - 1 full revolution   

  2.  Pads against disk after rear brake pedal engagement - 3/4 revolution --  This isn't the type of testing I was suggesting as there will usually be some brake pad drag after an apply. The wheel spinning with vehicle load on (ie riding)  will  usually kick the pads/pistons  back a little more. 

 

Consistent results; This test has been done many times before and after the seal replacement / caliper cleaning with little apparent change in rotational resistance.  I have tried, as much as possible, to be consistent in the force applied. -- Not a real good test without riding the vehicle.
 

Earlier in the year when I first noticed the rear brake pad dragging issue, the GS911 ABS diagnostic test was performed with no faults noted.  About 3,500 miles since the GS911 check.-- I don't doubt that as there isn't any codes for a dragging brake.
 

Front brakes are fine - rotate easily (obviously no drive line resistance) and very little brake dusting. --Fronts usually dust less as they have better air flow to blow the dust away.  My BMW's rear brakes always put way more brake dust on the rear wheel.  Fronts hardly any. 
 

 

I will do the front brake test today. The on-bike tests you suggested will be a little more difficult here in the traffic congested Puget Sound region. I have pyrometer that will use for temperature readings. --If you can do it that it will probably tell you more than any in-place wheel spinning.
 

A question;  there must be some valving of some sort at the junction where the ABS line joins the rear brake lines at the rear brake master cylinder?  Is it possible that this valving might be the cause of slight residual rear brake pressure?-- The rear brake crossover valve is internal to the ABS module. If you can easily push the rear caliper pistons back then probably no residual pressure present. If you have residual rear brake pressure then the- (one brake apply then riding without using brakes should tell the story  through brake rotor heat) 
 

 

 

[PNWrider]

Good morning, DR,

with the R12RT on the center stand, key in the “on” position and while I was rotating the rear wheel,  I applied the front brake - instant rear wheel stop.  I’ll try for the coasting tests and some temperature readings over the next couple of days. 
Bill