Irresolvable rear brake drag? *SOLVED with pics*

Dear fellow ST owners,

I have a rear break drag that I have been trying to solve for the past 2 years. I have ridden close to 25K miles with my "rear break on". I go through a set of rear pads in 3-4K miles!!!

It has now been at the HONDA dealership here in Brno, Czech Republic for the past 4 weeks. Very skilled mechanic, knows his STs, cant fix it. He takes care of a Police fleet of 100 bikes.

Why I say irresolvable? Please read what the dealer have replaced so far and still drags:

- of course the entire Secondary Master Cylinder assembly
- completely rebuild proportioning control valve
- completely new delay valve (front wheel, right side)
- they even borrowed the entire rear break caliper assembly from a different bike and it still was dragging
- rear master cylinder inspected

We are running out of options and ideas. Can, for example, the front master cylinder affect rear break? I dont know. It is getting expensive replacing stuff.

I dont think it is the hose system becasue it bleeds nicely without problems. It is the two outer cylinders in the rear caliper that are hard to press back after the break is applied.

Any ideas welcome. I dont know what to do.

Thank you,
MS

Re: Irresolvable rear break drag?

rossilvr said:

Can, for example, the front master cylinder affect rear break? I dont know.

Click to expand...

Absolutely, though indirectly as Mr. jfheath indicated, the front left caliper/secondary master cylinder combination does affect the application of the rear brake caliper.

Here's a link to a sketch I made to assist my comprehension of the linked brake system used on the ST1300, perhaps you will find it helpful.

Re: Irresolvable rear break drag?

Is the rotor warped? No mention of checking that. If it has been that long it could have over heated.

Re: Irresolvable rear break drag?

Have you checked the rear brake master cylinder. It seems as some one here noted a clog in the return orfice of that cylinder making it hard for the rear caliper to return.

Also no one has mentioned this before but I had this happen on my truck. I was getting front brake drag and could not solve it untill a knowlegble mechanic noted that some flexible brake hose lines started to swell and collapse leaving enough to bleed but not to return quickly. He verified this with a brake pad pressure sensor.

Re: Irresolvable rear brake drag?

Thank you all for your replies. There are some things I will try nad let you know.

MS

Re: Irresolvable rear brake drag?

Roderiderg 's suggestion is something that happened to me with a truck a few years back.

The hose swells , in effect making it act as a check valve . Applying the brakes forces fluid through the hose easily due to the high hydraulic pressure , but the swelling prevents the fluid return.

Try releasing the pressure by loosening the bleed screw, let a bit of fluid out, then retighten. The wheel should turn freely now .

Next, apply the rear brake .

If the rear brake refuses to loosen the pressure now , it may be a hose or a cocked piston.

Re: Irresolvable rear break drag?

jfheath said:

Two thoughts

1) Has the system been properly bled - including bleeding everything in the correct order, and tilting the SMC to release trapped air and the bleed valve at the proportional control valve ?

2) Have you checked that the problem is not with the front brakes - perhaps activating the SMC and then not returning properly. Perhaps the front left caliper bracket isn't pivoting properly in its bearings - maybe enough to activate the SMC, but not enough to return once applied. Has the needle bearing seized up ? Are the bolts pinching the left caliper mounting bracket, rather than letting it pivot freely ? Are the psitons in the front caliper clean and free to move back once applied ?

Last time I had a dragging rear brake, it was because the front pads were dragging - they were new and too thick (with the anti-chatter plate and the heat shield layer). The front disc was warm as a result, but not nearly as hot as the rear disc.

Click to expand...

Dang John, you were reading my mind!
And from the sounds of it, some of my prior posts.
Thanks for throwing this out there into the mix.
I find this a problem often.
And to the owner....just because the dealership services the police bikes, does not mean they know everything about the ST1300's. I've seen several LE bikes that had issues that the service people didn't know how to fix, so the officers were just riding them.

Re: Irresolvable rear break drag?

Another thought...have you had the front wheel off to change the tires? I've seen the tech's flop the tires over on the cement and bend the front rotors.
Check to make sure both your rotors are straight and true.
Just trying to think outside the box for ya.
Good luck

Re: Irresolvable rear brake drag?

Hello all,

in adition to my original post we have now rebuild the rear master cylinder and guess what? It still drags. I have checked all of your suggestions (proper bleeding, riding style, warped rotor, etc.) You name it - it has been done. Now I am really out of options.

The front wheel works properly - meaning it releases fine and spins freely. Everything is lubed and moving nicely. It doesnt seem to be the hose system because bleeds fine.

Again, I am open to suggestions. I am thinking of finding a total and taking the entire break system off of it and replacing it.

MS

Re: Irresolvable rear brake drag?

This is really, if you will pardon the pun, dragging on....
The dragging rear brake can only really come from 3 sources.
The rear master cylinder circuit.....
The SMC
Your foot on the brake.
You have replaced or repaired the rear master cylinder.
There has been work on the SMC and front left caliper......
Hopefully you have not had your foot on the rear brake.....
I would not be beyond clamping the brake line to the rear brake then cracking open the bleed valve to ease any residual presssure. Ride the bike.
Any change?
If there is, then we know it’s the SMC OR left front caliper.....
If not, leave rear brake line from SMC clamped.... open other bleed nipple and drain rear brake system OR preferably, also clamp that line if possible, of not possible, drain brake fluid. There is a line form the rear brake to the front calipers via some other bits and pieces so it need s to be clamped as near to the rear brake output line as possible...
You now have a non pressurised rear brake system... do NOT touch the rear brake pedal.....
Ride the bike.... still dragging?
Then you have a rear wheel or caliper assmebly issue, wrong brake pads, or something is damaged.

Just because a dealer services you machine it does not mean they actually know what they are doing.
In this instance it seems their diagnostic skills are more than a little limited, but their bank account is filling up.....

Re: Irresolvable rear brake drag?

are the pads seated correctly?It is easy to do incorrectly. also a very slight amount of high temp. grease on the three metal to metal location points for the outer pad seems to insure it releases or floats away from the rotor more easily.

Re: Irresolvable rear brake drag?

Firstpeke said:

This is really, if you will pardon the pun, dragging on....
The dragging rear brake can only really come from 3 sources.
The rear master cylinder circuit.....
The SMC
Your foot on the brake.
You have replaced or repaired the rear master cylinder.
There has been work on the SMC and front left caliper......
Hopefully you have not had your foot on the rear brake.....
I would not be beyond clamping the brake line to the rear brake then cracking open the bleed valve to ease any residual presssure. Ride the bike.
Any change?
If there is, then we know it?s the SMC OR left front caliper.....
If not, leave rear brake line from SMC clamped.... open other bleed nipple and drain rear brake system OR preferably, also clamp that line if possible, of not possible, drain brake fluid. There is a line form the rear brake to the front calipers via some other bits and pieces so it need s to be clamped as near to the rear brake output line as possible...
You now have a non pressurised rear brake system... do NOT touch the rear brake pedal.....
Ride the bike.... still dragging?
Then you have a rear wheel or caliper assmebly issue, wrong brake pads, or something is damaged.

Just because a dealer services you machine it does not mean they actually know what they are doing.
In this instance it seems their diagnostic skills are more than a little limited, but their bank account is filling up.....

Click to expand...

Ok. The problem is definitely on the circuit that goes from the rear master cylinder to the front.

The proportional valve and the delay valve have both been replaced! They even by-passed the delay valve with a break hose (i saw it with my own eyes) and it still drags. There is nothing else in the way except for the break calipers and plumbing.

The front break and SMC function great (the SMC is new).

The ONLY time the break will not drag is when you push the rear caliper cylinders in, you clamp the upper hose going from the rear master cylinder (toward the delay valve) which means you dysfunction the outer two cylinders and you stop the fluid from going to the front calipers - only then the break doesnt drag. Now. When the entire system is pressurized and you open ANY bleed nipple (front or rear) the rear break will NOT release.

Which means it could be something really strange inside a hose letting fluid one way and not the other or something between bleed niples and cylinders inside the front calipers...

OR?

The dealer is not charging me anything for work (40+hours till today). They just dont know. The first ever bike they didnt fix...

Re: Irresolvable rear brake drag?

rossilvr said:

Ok. The problem is definitely on the circuit that goes from the rear master cylinder to the front.

The proportional valve and the delay valve have both been replaced! They even by-passed the delay valve with a break hose (i saw it with my own eyes) and it still drags. There is nothing else in the way except for the break calipers and plumbing.

The front break and SMC function great (the SMC is new).

The ONLY time the break will not drag is when you push the rear caliper cylinders in, you clamp the upper hose going from the rear master cylinder (toward the delay valve) which means you dysfunction the outer two cylinders and you stop the fluid from going to the front calipers - only then the break doesnt drag. Now. When the entire system is pressurized and you open ANY bleed nipple (front or rear) the rear break will NOT release.

Which means it could be something really strange inside a hose letting fluid one way and not the other or something between bleed niples and cylinders inside the front calipers...

OR?

The dealer is not charging me anything for work (40+hours till today). They just dont know. The first ever bike they didnt fix...

Click to expand...

You say the SMC is new? Does this mean they REBUILT (replaced) the piston and rubber grommets, or replaced the entire unit? I've seen a couple fail after rebuilding them due to scoring inside the housing causing the new one's to stick as before. In your first post you said the PCV was "REBUILT" as well.. Rebuilt or replaced?
Did you check the pivot point that rides on the needle bearings? is it dry? is the bushing scored, causing it to bind, and activate the SMC. Its got to be something simple, staring us in the face. Check hose routing? shoe resting on the peddle?
Keep us informed.
IGF

Re: Irresolvable rear brake drag?

Igofar said:

You say the SMC is new? Does this mean they REBUILT (replaced) the piston and rubber grommets, or replaced the entire unit? I've seen a couple fail after rebuilding them due to scoring inside the housing causing the new one's to stick as before. In your first post you said the PCV was "REBUILT" as well.. Rebuilt or replaced?
Did you check the pivot point that rides on the needle bearings? is it dry? is the bushing scored, causing it to bind, and activate the SMC. Its got to be something simple, staring us in the face. Check hose routing? shoe resting on the peddle?
Keep us informed.
IGF

Click to expand...

Thank you for the effort Igofar,

A little perspective: I have never, ever taken my bike to a dealer for service. I do it all myself including valve adjustment, etc. I have done everything I could to fix the rear drag with no result.

In addition: I have, religiously, read most (if not all) of your very helpful posts regarding the SMC, testing the SMC operation, etc.:bow1: And I have definitely read ALL posts regarding the rear break drag on this forum and I am 100% positive that my issue is genuine to all listed here.

My SMC is brand new (entire) releases fine and works great. Everything is lubed and torqued right. That whole circuit from the SMC through the PCV to the rear break works fine.

Even the curcuit from the rear master cylinder to the middle rear caliper piston works fine.

It is the circuit from the rear MC to the front calipers that causes the drag. There is the delay valve in the way which I have also replaced. The delaer installed (just to make sure) another delay valve from a different bike (which was working fine) and it still didnt work. They even took the whole left front caliper + SMC assembly and put that on.

As I said in the previous post it is something strange inside the front calipers? But when I open the front bleeders (any) it doesnt release the rear break. The front wheel spins fine (no drag).

Or it is the plumbing. I have checked the routing and I dont have any squeezes, etc. stopping fluid from flowing freely

Re: Irresolvable rear brake drag?

Without reading everything again, you have checked the brake pedal isn't sticking down a little or that the brake isn't being applied slightly with the pedal in its normal position, requiring the pedal to be adjusted up..... just thinking out loud...... well out text.....

Re: Irresolvable rear brake drag?

rossilvr said:

Thank you for the effort Igofar,

A little perspective: I have never, ever taken my bike to a dealer for service. I do it all myself including valve adjustment, etc. I have done everything I could to fix the rear drag with no result.

In addition: I have, religiously, read most (if not all) of your very helpful posts regarding the SMC, testing the SMC operation, etc.:bow1: And I have definitely read ALL posts regarding the rear break drag on this forum and I am 100% positive that my issue is genuine to all listed here.

My SMC is brand new (entire) releases fine and works great. Everything is lubed and torqued right. That whole circuit from the SMC through the PCV to the rear break works fine.

Even the curcuit from the rear master cylinder to the middle rear caliper piston works fine.

It is the circuit from the rear MC to the front calipers that causes the drag. There is the delay valve in the way which I have also replaced. The delaer installed (just to make sure) another delay valve from a different bike (which was working fine) and it still didnt work. They even took the whole left front caliper + SMC assembly and put that on.

As I said in the previous post it is something strange inside the front calipers? But when I open the front bleeders (any) it doesnt release the rear break. The front wheel spins fine (no drag).

Or it is the plumbing. I have checked the routing and I dont have any squeezes, etc. stopping fluid from flowing freely

Click to expand...

My gut is telling me to remove both the front calipers, brake pads, then remove all the pistons and their seals.
I'm wondering if you've got dirt or debris behind the pistons causing them to bind or jam.
Have you lubed the pins that the calipers slide on as well as the hanger pins?
Could the anti-rattle spring be installed backwards? It is possible.
Are the pads fitting in the end clips correctly?
Did you lube the ends of the pads and all the mating surfaces with brake lubricant grease?
We'll not give up on ya till we figure this out!
take your hand and gently rotate the wheel (rotors) and feel for any burs on the edges of any of the holes?
Wheel spacers in correct positions
Axle greased?
Proper assembly sequence...left, axle, right, loosen, left, caliper bolts etc.?
Igofar

Re: Irresolvable rear brake drag?

Hello all,

I am probably going to dissapoint you but after replacing almost EVERYTHING throughout the "SMC - MC - Rear break caliper" circuit with no result and dragging rear brake I decided to de-link the linked system. Yes, I would still rather fix the problem but after spending so much money with no result and with the riding season at full swing I had no other option. I want to ride "drag free"

And finally after 20K+ dragging kilometres I had a pleasant ride to work today.

So what did I do?

Drain the SMC circuit as per the manual. There are two hoses running from the rear caliper (middle piston and the outer two pistons) to the rear master cylinder. They are attached on top of each other on the MC by a doublehole bolt (or however it is called).

I used to lower hose (going to the middle piston /rear caliper) and attached only that one to the MC by a singlehole bolt. Done.

So I now have a separate front and rear break on my ST. I would say the stopping power is down by maybe 10% which I am ok with regarding the neverending story with my rear break. The fornt break stopping power feels the same.

The next thing I am going to do is order two steel braided lines for the rear break so I can run one to the middle piston and the second one to the outer two pistons - this will increase the stopping power. Now with the one piston it is not sufficient.

And I am goign to fill up the SMC with break fluid in plug it up so it doesnt move so much when I apply the front break. And actually I can now also get two steel braided lines for the front break and get rid of all the complicated plumbing of the front break.

rossilvr

Re: Irresolvable rear brake drag?

RossiLvr, I had the exact same problem. Rear drug so bad that I warped the rear rotor. Replaced it and all the pads. Changed the brake fluid and bled per manual and the How To on this site.
Still drug. Pulled the rear caliper apart and cleaned the road grim off of the rear pistons. Replaced them and refilled\re-bled the entire system.
Still drug.
I finally solved the problem by bleeding the proportioning valve again, but this time I compressed the left caliper to the fork using a big wood clamp.
Had my wife hold the clamp and continue to squeeze while I cracked the prop valve. Sure enough their was air still trapped in that line. Note: After you crack the valve and your assistant continues to squeeze more fluid comes out.
Repeated a second time and then bled it from the rear brake pedal.
This finally solved the problem!
No more dragging rear brake and no more soft\spongy feel in the rear brake pedal.
Now the brakes are great and feel like they should.
No more straining to move a 650 pound motorcycle with a dragging rear brake either.
Like your self I dealt with this problem for a year before I finally found a working solution.
Hope this helps.

Re: Irresolvable rear brake drag?

Jack_Attack said:

I finally solved the problem by bleeding the proportioning valve again, but this time I compressed the left caliper to the fork using a big wood clamp.

Click to expand...

Interesting. Just for clarification, when you say that you compressed the left caliper to the fork do you actually mean that you were engaging the pushrod on the Secondary Master Cylinder? A picture would be nice...

Re: Irresolvable rear brake drag?

It sounds as though you have modified your brake bleeding sequence similar to my modification (summary below). My reasoning and observations can be found here.

Brake Lever

1. Left Outer (upper) bleed valve.
2. Right Outer (upper) bleed valve.

Brake Pedal

1. Remove and tilt left front caliper 15 degrees (wood shims inserted between the pads will keep the pads from extending while~if pedal is pumped)
2. Proportioning Control bleed valve. While the SMC (front left caliper) is removed and tilted, manually pump the SMC piston one stroke inward and hold, and have a buddy pump the rear brake pedal to continue bleeding from the proportioning control valve bleeder, which simultaneously re-extends the SMC to the fully out position. Repeat the sequence as necessary.
3. Rear Brake Center bleed valve.
4. Right Front Center bleed valve.
5. Left Front Center bleed valve.
6. Rear Outer (forward) bleed valve.