Article [13] ST1300 - Brake Maintenance - Getting all the air out of the brake system

Ditto. There will be air in the system. It sneaks in in the same way that water sneaks in, and of course, water contains dissolved air. The plunger end of the SMC creates an air trap. Bubbles will float up to it and accumulate if the SMC isn't tilted.

But exercising the SMC is also really important. The fluid enters through the inlet port and is expelled through the outlet, but that leaves a small pocket of brackish fluid between the (normally) upper end of the SMC bore and the inlet port. It stands a chance of never getting changed if you just pump fresh fluid through. The same idea applies to the pocket behind the forward rear piston, and behind the lowest piston on the front calipers. See-saw the outer pistons to sluice out the grotty old stuff.

Disclaimer. I don't know this for a fact. But I do know people who have changed their fluid and still had problems that are normally associated with old fluid. I always do the above every fluid change - usually yearly - and I've never had such issues.
So I put two and two together. Up to you to decide whether I have come up with the right answer.
 
Last edited:
jfheath said:
Ditto. There will be air in the system. It sneaks in in the same way that water sneaks in, and water contains dissolved air. The plunger end of the SMC creates an air trap, bubbles will float up to it and accumulate there if the SMC isn't tilted.

But exercising the SMC is also really important. The fluid enters through the inlet port and is expelled through the outlet, but that leaves a small pocket of brackish fluid between the (normally) upper end of the SMC bore and the inlet port. It stands a chance of never getting changed. The same applies to the pocket behind the forward rear piston, and behind the lowest piston on the front calipers. See-saw the outer pistons to sluice out the grotty old stuff.

Disclaimer. I don't know this for a fact. But I do know people who have changed their fluid and still had problems that are normally associated with old fluid. I always do the above every fluid change - usually yearly - and I've never had such issues.
So I put two and two together. Up to you to decide whether I have come up with the right answer.
Click to expand...
I'm one of those that never had issues with old fluid. Exercise the SMC if it makes you feel good but odds if the service is done correctly and on time one won't have problems. Problem is we assume people know what they are doing. ;)
 
I made a pressure bleeder attachment from an old clutch m/c cap and rear m/c cap (it's a weird size). This is luxury - set it up, apply compressed air, and just go around opening bleeders (in the right order). It's not really necessary at all for the clutch and front (both simple systems) but makes bleeding the rear/smc/etc system much easier, as it gives you an extra free hand, and much increased (and constant) flow to expel bubbles. Great on cars too.

I still use a check valve on the bleeders and still disconnect, angle and massage the SMC each time. The flushed fluid goes into a tub to be used for cleaning 'stuff'.

The main downside is that the reservoirs are very full once you're finished. Drips of brake fluid are almost unavoidable so plenty of protection in place and water at the ready.

For the clutch, it's probably still better to pump the lever and bleed the old-fashioned way - this will extend the piston slightly meaning a small amount of oil fluid has a chance to be bled out. I do wonder if it would be possible to pump a small but significant amount into the system, extending the CSC piston as far as mechanically possible, to flush out as much fluid as possible...
 
I don't recall seeing one. There is some useful information, pics and diagrams in this article about the SMC on pages 8 and 9, but it isn't specifically about replacing it.

edit: So prompted by that, 6 weeks later I put one together.

Article [13] - ST1300 - Brake Maintenance - Replacing the Secondary Master Cylinder (SMC) | ST1300 Articles

The usual format from me - Description, some useful photos and a few tips and tricks to help you to avoid the normal 'Doh!' moments - Like emptying all of the fluid out before realising that you wanted tomove the pistons out as far as possible; Like reftting everything before realising that you...
www.st-owners.com www.st-owners.com

But replacing the SMC unit as a whole is not difficult. The SMC is an integral part of the front left hand caliper bracket. In order to replace the entire bracket you need to detach a few brake hoses, which means that you will need some replacement crush washers for the hydraulic banjo bolts, and the manual calls for brand new caliper bracket bolts. Copper crush washers can be ordered in bulk from parts dealers. Make sure you check the inside and outside diameters. I tend to buy 100 at a time which means that I never have to worry about not having any if I want to remove a caliper or two.

I hope that you are not thinking of replacing just the piston/seals

If you are talking about the SMC 'service kit' which includes piston, seals, circlip, boot and push rod assembly then let me try to dissuade you. This involves additional stuff to do. My advice is not to even contemplate doing this. There is a high probability that it will not solve whatever problems you are having with the SMC and the piece of mind and improved braking performance that you will get from a complete new unit far outweighs the additional cost. A brand new SMC comes ready assembled and the additional cost is little more than the amount that it costs to fill your car with fuel. (2022 prices. July 5th. 6:00am).

Your bike is 18 years old. The SMC bore is likely to be worn out, corroded or slightly distorted after a knock or two. A service kit isn't going to fix that, and the kit doesn't include an important filter for the inlet port which is likely to clogged with crud and gunge. Look at the link I gave above and the dismantled SMC. That had a new service kit 2 years before the photos were taken. It didn't solve the issue, which was more to do with a damaged or worn out cylinder bore.

A brand new SMC caliper bracket gets round all such problems.
 
Last edited:
thanks jfheath for the info. Last week I used the white courtsey phone and spoke with Igofar, he easily diagnosed the bad SMC. He gave same advise. I have a complete new SMC and a bunch of other bits that he suggested I order, including crush washers, pins etc.
I have obtained a Honda service manual. Glad to hear that replacing the SMC is not that hard. I will review the article you cited. I fear the bleading process, maybe b/c I am a RN!!!!! see what I did there.... bleeding process!!!! I am a funny guy!
 
Happy Rob said:
thanks jfheath for the info. Last week I used the white courtsey phone and spoke with Igofar, he easily diagnosed the bad SMC. He gave same advise. I have a complete new SMC and a bunch of other bits that he suggested I order, including crush washers, pins etc.
I have obtained a Honda service manual. Glad to hear that replacing the SMC is not that hard. I will review the article you cited. I fear the bleading process, maybe b/c I am a RN!!!!! see what I did there.... bleeding process!!!! I am a funny guy!
Click to expand...
Yesterday I completed the exact service you're setting out to do, Rob.

I had Larry on the WCP, storms in Arizona and Verizon connection quality not withstanding.

Here are a couple of tips fresh off the presses.

Break loose as many bolts as you can while the parts are still place. This especially applies to the banjo bolts on the SMC. I got to the forward one by going through from the other side of the front wheel and used the closed end of a 12mm combination wrench with an offset angle to get to the rear one. I couldn't easily use my torque wrench on that one during reassembly, but my calibrated elbow let me match the two after torqueing the one I could get to. Others you'll want to do are the brake pad retaining pins and the bleeder screws.

Have Q-tips and an old length of shoelace handy to wipe down the exposed portions of the pistons before pressing them back into their bores. The shoelace worked best on the rear caliper - wrap it around the piston and rub like you're shining a shoe, or as someone else said, drying your back with a towel - but the front calipers had to come off the fork to retract the pistons and once off I found the Q-tips were easier than the shoelace.

I've used a syringe to extract the old fluid from the reservoir in the past, but I couldn't find it in my Empire of Dirt™ and Larry recommended a squeeze bulb style which worked great. Much easier to control than the typical syringe. Find it in the infant or ear care section of your nearby pharmacy.

1657042007161.png

Before starting, source that piece of wood equal to or slightly thinner than 5mm to place between the left front caliper's brake pads when bleeding the SMC while it's tilted. I poured over John's excellent guide several times leading up to doing this service and I overlooked that when it actually came time. I found the center piston fully extended (YIKES!) but it pressed back into its bore without too much difficulty using a large C-clamp.

Have a brass bristle brush, pipe cleaners and small drill bits handy. The banjo bolt on the rear fitting of the SMC showed the evidence of why the SMC was inoperable. I scoured the corrosion from the exterior of the bolt with the wire brush and then cleaned its bore with the largest twist drill that could be inserted. I used the drill's flutes to scrape the gunk from the wall of the bore. I have real pipe cleaners, but all I could find at the time were pieces of chenille (sometimes called "pipe cleaners" in crafting circles). My chenille didn't cut it.

1657044278161.png

After all your hard work is done, Larry advised leaving it overnight with a ziptie holding the front brake lever on and a weight to press the rear pedal. I started with a half cinderblock which was too heavy and ungainly. I settled on a full 5qt plastic oil bottle rested on the pedal and the foot peg and held in position with my small air compressor which was heavy enough to stay in place overnight.

If you're replacing the pads too, do the SMC replacement first, followed by the pads and the flush and bleed - the SMC replacement will spill some fluid, no sense getting that on your new pads.

Again, thanks for the tips Larry!
 
Thanks for this advise. I took today off work to do this and other jobs.
Step one... Find out what all the parts and bits igofar had me buy are for !
Step two read ifheaths pitfalls again.
Step three. Find the notes I wrote when I talked with igofar last week.
I sure wish I had a more experienced bike mechanic watching me. I really would not trust any local bike shop to do this correctly.
Wish me luck! Gulp
 
All you have to do is ask. If it is any consolation, the first time that I did these jobs, I didn't know either.
If something doesn't make sense to you, don't make assumptions. Ask the question to make sure. (There's a slight delay reaching to the UK, but there are plenty of others will help).

Happy Rob said:
I sure wish I had a more experienced bike mechanic watching me.
Click to expand...

That'll be you when you have finished ! You have a camera ?
 
What is "rubber brake grease"? Jfheaths brake instructions suggest it on exposed parts of pistons? Will either of these do? I have synthetic brake lubricant, and just bought silicone ceramic brake lube
 

Attachments

  • 16571365688395269206813929643370.jpg
    16571365688395269206813929643370.jpg
    183.8 KB · Views: 19
Over on his side of the pond they have a lot of road corrosion, so he coats the pistons to stop rust.
I would suggest not putting anything on the exposed pistons, as it will collect dirt and cause stuff to jam up and not work correctly.
Clean dot 4 brake fluid on the exposed pistons and a small amount of rubber friendly grease on the seals upon assembly.
 
Thanks so much for your quick reply. Now to cook supper and go back at it! So far so good. Everything is falling in place! Following your advise.
 
Rubber grease is a red, vegetable based lubricant developed for hydraulic seals, and still sold in the uk as 'red rubber grease'.
Info Link

As Larry said - I use it to keep the crud off the exposed part of my pistons. In the Uk the road grime that is washed up from the roads in wet weather, dries and sticks to anything. It then gets damp, holds the water and remains attached to the surface quietly eating away at it. With rubber grease on there, yes it sticks to the grease, but the grease shifts easily. My pistons get a wipe clean (thats all it takes) at least every tyre change which is every 5000 miles, or every year. Nothing has ever jammed up. But go with what works in your Climate.

I have tried not applying rubber grease. It doesn't work out well on the mbike.

I also copper grease the backs of my pads (except I now use Ceratec), which is another peculiarity which works for me in keeping the rust at bay.
 
Happy Rob said:
What is "rubber brake grease"? Jfheaths brake instructions suggest it on exposed parts of pistons? Will either of these do? I have synthetic brake lubricant, and just bought silicone ceramic brake lube
Click to expand...

The squeeze tube of lubricant you have is rubber friendly. I've been using that on my brake caliper slide pins for my vehicles for many years.
 
All is well in the world again. SMC, and me back pads installed. I used 2.5l of brake fluid. Chasing air. I finally have up last night and left both brake levers depressed, with tape on front and cinder block on back.... When I checked this morning, one final flush and no bubbles and full brake lever! Whew. Glad that's over.
Thanks again for help from this fab forum.
 
Happy Rob said:
All is well in the world again. SMC, and me back pads installed. I used 2.5l of brake fluid. Chasing air. I finally have up last night and left both brake levers depressed, with tape on front and cinder block on back.... When I checked this morning, one final flush and no bubbles and full brake lever! Whew. Glad that's over.
Thanks again for help from this fab forum.
Click to expand...

Well done Rob.
I went looking through all of my notes for a how to on the SMC, and was surprised that I hadn't done one. So I set about creating one, hoping that I could knock something up in time to help you.

I failed miserably. I'm just getting over Covid - After 2.5 years of being oh-so-careful, it finally caught up with us, so things happen at a very slow pace at the moment. I get tired very quickly.

Anyway - sorry it is far too late for you, but I've just finished one for the ST1300 Articles.

Thanks for the prompt - it gave me a good project to try to get my brain to focus on something again.
 
The best way of getting air bubbles removed from a tube or brake line is to make sure there are no high/low points in between.
Make sure one end is higher so the bubble will rise.
This process can be speed up if the temperature is higher hence viscosity will be lower.
For instance during winter getting the bubbles of the system could be more challenging

But I do not advise you to heat to up the brake fluid. So I don't take any responsibility
 
You must log in or register to reply here.
Back
Top Bottom