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Discussion Starter · #1 ·
Hi everyone.

My first post here, but I've been stalking for many a months. I've had my speed 4 now for just over a year, and am pretty happy with it. I have to be happy with it, the missus won't let me get a new speed triple....

Anyway, we all know about the spongy front brake issue that develops in these bikes. And trawling the forum brings no once and forever fix. I know I can push the pistons back into the calipers, replace seals in the caliper, rebleed the system, cable tie the lever to the handle over night. All of these do not seem to yield permanent results.

I know people have experimented with various different Master Cylinders, and claim it has helped reduce the amount of travel to the bar, and creates a harder pull. I'm not here to talk about different M/C sizes and fluid dynamics, there is already a thread which covers that.

My question is this. After 14 years of the Speed 4 being around, we must know the cause of this spongy brake issue, don't we? So how do we cure it for good?

If I wasn't to ask you guys, I would end up replacing the M/C for an R1 M/C, and running dual lines down to the serviced calipers , (as I can't seem to find a replacement caliper, with exception of the very expensive Beringer setup).
 

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I would expect you could find a rebuild kit for the front calipers. After 14 years, the brake fluid is 100% shot, if it hasn't been changed. Start there. Then rebuild the calipers. I haven't looked for a rebuild kit, but I have a hard time believing those calipers are particularly exotic. Replacing the lines is a good idea after 14 years as well. When rebuilding brakes, keeping everything absolutely clean is critical, as is making sure you have gotten everything dry and have removed all traces of soap or whatever all else you used to clean the caliper parts. I used Simple Green, but I'm sure there's other stuff out there that would work just fine, too. Lubricate the new rubber parts with fresh brake fluid before assembly as well. I typically put in speed bleeders to help with getting air out of the brake fluid, and I like putting a speed bleeder on the master cylinder banjo bolt as well. That makes getting all of the air out easier.

Brake fluid absorbs water over time, and on a bike, that's going to cause the brakes to turn to mush eventually. If you don't feel like you can absolutely nail the rebuild, then best to have a pro do it, because no brakes causes more excitement than you really want. The brakes on a Triumph supersport bike are plenty good enough for just about any purpose if they are working right. I did an accidental stoppie when test riding a TT600 almost 15 years ago. That, along with the high cornering clearance, convinced me I had to have it. The brakes work just fine when they are up to scratch.
 
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Discussion Starter · #3 ·
Thanks for your reply Will. I perhaps should of mentioned that my bike is reasonably well maintained, and in my ownership it has had new pads and brake fluid. The problem of the soft brakes are known on the S4, as I'm sure you are aware. The quick and temporary fixes I have done, but I would like to do a proper fix, so I no longer need to take the calipers off every couple of months, clean and push the pistons back. Hence why I would be tempted to replace most of the components, if a clear answer isn't found.

Changing the lines is first on my list of things to do, as I know that after this amount of time, even braided lines could do with a refresh. My reason for wanting to change to a dual line setup is that there is speculation that air can hide in the bridge between calipers on the current setup, making bleeding them a pain in the bum. Changing to dual lines would get rid of this speculation, Wether it would solve the squishy brake problem or not is to be seen.
 

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I just got my S4, and coming from the harley world, the brakes on this thing are insanely good. I'm new, so I hadn't heard about the development of a spongy brake. Are you seriously cleaning and pushing the pistons back every couple months? What exactly are you doing when you clean and push back the pistons?
 

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Discussion Starter · #5 ·
Are you seriously cleaning and pushing the pistons back every couple months? What exactly are you doing when you clean and push back the pistons?
Hi Munkeyphyst. I have had my bike for just over a year, and in that time I have cleaned the pistons once and pushed the pistons back twice. So every couple of months may be slightly exaggerated, but it's still more regular than it should be.

To clean them, remove one caliper at a time, remove pads, insert something into the gap (thin bit if wood), squeeze brake lever until the pistons are exposed enough (taking care not to pop them out of the caliper, and ensuring the resivoir doesn't run dry!), clean with brake cleaner and rag (some people have been known to use fine grit wet and dry), push the pistons back in, smear some copper grease on the back of the pads, insert, reinstate on bike.

Just found on page 48, a thread call "S4 spongy brakes", seems as if that guy has tried everything I am comtemplating doing, but still had issues. The only thing he has done different to what I would do is the R1 M/C. He puts his problem down to the calipers, but then the thread goes dead, so we don't know if a caliper seal set solves the problem.
 

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The caliper seal will help, but not fix it completely (or didn't in my case). In the end I went down the R1 master cylinder route and fry-your-rotors EBC sintered pads.

The bike will now do a forward somersault. Don't ask me how I know this.
 

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Discussion Starter · #7 ·
The caliper seal will help, but not fix it completely (or didn't in my case). In the end I went down the R1 master cylinder route and fry-your-rotors EBC sintered pads.

The bike will now do a forward somersault. Don't ask me how I know this.
Haha! How long have you been riding problem free with the R1 M/C on for? Do you think it was the M/C or the thicker EBC pads which helped? Makes me wonder if the seal kit is worth doing at all, what's your opinion on it? And how easy was it to change the seals, and what was the rough cost?

Also, out of interest, what year R1 M/C did you go for?
 

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The M/C made the most difference...the EBC pads were overkill at anything less than triple-digit track speeds, and even then they chewed up rotors like a very chewy thing...but they were for TD's and racing, etc. The seal kit was cheap but fiddly to install...they were only a few dollars, if I recall. The R1 lever and Brembo M/C were from an '07...I'm pretty certain.
TBH, I just took them off a friend's Daytona 600 and didn't pay it any mind...they worked, and that was it.
 

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I had my D600 (same stuff as the S4) for the last 2 years never had an issue with brakes.
I too have removed them cleaned & changed pads and fluids. Still they stop on a dime. A bigger m/c is not alway the answer as these will also have "other" issues to solve.

1st. Check the pads what type/brand are they? Buy a new set from a different brand and test. It is possible that they are not thick enough to tightly squeeze the disc to stop. (Very possible if cheap china pads are installed).

2nd.. Get all the air out... I always do a reverse bleed. This ensures all ar is removed from calipers, Lines & M/C.

3rd.. Replace the line theses loosen and expand over time with age..

Good luck..
 

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It sounds backwards, but a bigger master cylinder piston will actually decrease stopping power because you are spreading the hand lever force across a larger surface (piston).

If you are applying 100 lbs of force at the lever, and the piston is 1 square inch, you are applying 100lbs per square inch to the system. if you increase the piston size to 2 square inches, you are now applying the same 100 lbs of force across 2 inches, or 50 lbs per square inch, less force.

That force is exerted throughout the fluid system. If we imagine the 1 inch master cylinder piston and 100 lbs of force from the lever, and you have one single cylinder caliper that also has a 1 inch piston, you are obviously exerting 100 lbs of force from that caliper piston to squeeze the rotor. If you have a single 2 inch piston at the caliper, you are exerting 200 lbs of force from that caliper. If you have a two piston caliper with 2 inch pistons, you are exerting 400 lbs of force when squeezing the rotor.

TLDR: The most force is applied with a smaller master cylinder and larger total area of caliper piston size.

edit:
I search the forum for specs on the master cylinder swap, and according to this post: http://www.triumphrat.net/triumph-supersports/13033-parts-swap-listing-4.html#post687818
You can "swap your 14mm front master cylinder for that from a 2nd generation SV650S which is a 5/8" bore"
In this swap, the 14mm stock mater cylinder bore is being replaced by the 5/8" (which equals 15.875 millimeters) SVS unit. As this is a larger cylinder in the master cylinder, you are actually reducing the braking force of the system.
 

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Discussion Starter · #11 ·
It sounds backwards, but a bigger master cylinder piston will actually decrease stopping power because you are spreading the hand lever force across a larger surface (piston).

If you are applying 100 lbs of force at the lever, and the piston is 1 square inch, you are applying 100lbs per square inch to the system. if you increase the piston size to 2 square inches, you are now applying the same 100 lbs of force across 2 inches, or 50 lbs per square inch, less force.

That force is exerted throughout the fluid system. If we imagine the 1 inch master cylinder piston and 100 lbs of force from the lever, and you have one single cylinder caliper that also has a 1 inch piston, you are obviously exerting 100 lbs of force from that caliper piston to squeeze the rotor. If you have a single 2 inch piston at the caliper, you are exerting 200 lbs of force from that caliper. If you have a two piston caliper with 2 inch pistons, you are exerting 400 lbs of force when squeezing the rotor.

TLDR: The most force is applied with a smaller master cylinder and larger total area of caliper piston size.

edit:
I search the forum for specs on the master cylinder swap, and according to this post: http://www.triumphrat.net/triumph-supersports/13033-parts-swap-listing-4.html#post687818
You can "swap your 14mm front master cylinder for that from a 2nd generation SV650S which is a 5/8" bore"
In this swap, the 14mm stock mater cylinder bore is being replaced by the 5/8" (which equals 15.875 millimeters) SVS unit. As this is a larger cylinder in the master cylinder, you are actually reducing the braking force of the system.
This has been debated before, but people report good things from swapping to a R1 M/C, here is a link to a thread which talks about the different pressures and possible outcomes of fitting a larger bore M/C.

http://www.triumphrat.net/triumph-supersports/161909-s4-brake-upgrade.html

In the end, they agree to disagree. I've yet to hear people who have done this modification complain about it.
 

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Monkeyphyst has a point...the larger area of the bore/surface area, etc. spreads the pressure....it's the location of the pivot in the lever itself which makes the difference here if I recall.
I forget every detail involved....I wasn't so much concerned with how it worked as to whether it worked....lap times don't lie.
 

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Discussion Starter · #13 ·
So, I have looked for an R1 2007 M/C, and I didn't want to pay £100+ pounds for one. So instead, after a couple of pints this afternoon and some unrelated searching, I have bought a new Brembo RCS 19 x 18 x 20 radial M/C and lever for £200. http://www.ebay.co.uk/itm/BREMBO-19...DER-110-A263-10-110A26310-18-20-/121810926512 Don't ask why, I couldn't tell you. All I can do is report back my findings. I expect it will be way too harsh, and I'll end up selling for a 16 x "xx", but you don't learn if you don't try I guess. Sometimes I hate my drunk self....
 

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As a general rule:

Bigger master = less braking force but a stiffer feeling lever

Smaller master = more braking force but a softer feeling lever


My front master is off an R1, and works very well, as it's not too big a step up. Stock is 14mm conventional, and R1 is a 16mm radial. Because of the way the radial master works, it does even out a bit of the difference in bore size in regards to feel.

I've also swapped my rear master, as I didn't like the wooden feel of the stock. I put a 1/2" rear master from a Kawasaki KX250, and I get a lot less feel, but it's actually useful now.
 

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When I was looking for alternative controls for my sporty, I found a set of joker machines for a really great price, except instead of 9/16" (about 14mm) MC for a single disk setup, it has 11/16 (about 17.5mm) MC for dual disk.
I installed it with new pads (EBC Sintered), new stainless lines, and a new rotor. I did the same in the rear, except stock MC. Both use the stock calipers. The lever is very hard, not spongy. I can't pull it back to the bar, and it stops the bike, but I absolutely can't lock the front. There just isn't enough force to do it. The brakes on my speed four with the stock MC is super touchy. Especially compared to my experience with Harleys, and going from a 14mm to a 15.8mm probably doesn't reduce the forces as significantly as my swap did. And if the R1 MC is radial, the improve lever force from the relocated pivot point probably more than makes up for it.
Obviously, installed my setup and I still run it, it works. I'm not trying to tell people what to do with their bikes, just trying to explain how things work so people can make informed decisions.
 

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I've checked the part numbers the Speed Four and the Speed Triple (my model at least) and they're the same calipers. Speed Triples with these calipers tend to get similar issues as you're describing so it might be worth having a look over on that bit of the forum to see what else people have tried if you haven't already. I think Sprints used them too.

One thing that I've heard done is replacing the pistons with those from a 675 daytona which has helped, thread here:

http://www.triumphrat.net/speed-triple-forum/596946-955-front-brakes.html

I'm planning to do it on my bike when I have the cash spare.
 

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Discussion Starter · #17 ·

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That was kinda the conclusion I've come to from reading up on it but I'm by no means an expert. If you do go with the daytona pistons let us know what you think and if it's worth it as I'll certainly be interested in knowing :)
 

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Discussion Starter · #19 ·
That was kinda the conclusion I've come to from reading up on it but I'm by no means an expert. If you do go with the daytona pistons let us know what you think and if it's worth it as I'll certainly be interested in knowing :)
I have ordered a pair of daytona 675 calipers second hand off of eBay for £60, which have the Teflon coated pistons in. A new seal set for our calipers cost me another £40. Still less than a single set of new pistons in the UK, so a good deal I think. I still need to order a couple of new Banjos, fluid, and I may get new lines too. I am going to try with the old pads and discs initially, to try to compare the difference.

Today I done the standard, calipers off, pump out pistons, clean, push in, pump out, push in, reinstate on bike. Lever feels hard again now, but I'm not convinced that it is braking quite as hard as it should. We'll see what happens after I rebuild the caliper with the new pistons!
 

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Hi just my 2 cents quickly.
I had exactly the same issue. spongy brakes for years. cable tied down most nights. Replaced brake lines. Replaced calipers. Replaced master cylinder internals. Modified lever. Only think that would work for a few weeks would be flushing lines and pushing back pistons.

Always been unhappy with it. thought i was going to have to s

Finally splashed the cash bought a used brembo master cylinder from a modern Speed Triple. Ended up having to revert to old lines too to make it fit.

Problem solved. New M/C has my vote. Guessing the speed triple m/c is about a 17mm one
 
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