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Rebuilt front brake master - cannot get pressure

14K views 70 replies 13 participants last post by  extractable 
#1 · (Edited)
So as the post indicates I rebuilt my front brake master cylinder, which is a 200* Triumph Speed Triple 955i on a 2007 Triumph Bonneville. I also installed a set of New Bonneville speed bleeders.

I switched to 7/8" bars a while back when I installed my m-Unit and tore out my wiring harness and built a new one front scratch.

Anywho -- the "action" on the brake as soon as I originally installed it during the electrical work was real "woody" and stiff. It braked fine, not much action, it's on or off. However, I was having issues with it being so stiff that I couldn't squeeze it in far enough to actuate the brake switch.

So, I figured, heck, I'll rebuild the cylinder and see how it goes. I followed this (http://www.triumphrat.net/t3-sport-...-master-and-slave-cylinder-rebuild-story.html) rebuild minus all of the stuff that doesn't apply.
I removed the dust cap, removed the circlip using ring clip pliers, removed the old piston/front seal, spring and cap. I installed new spring/cap lubed with brake fluid, installed the new piston/front seal (lubed as well) and reinstalled the circlip and dust boot. I will note that in my master cylinder there is no washer after the circlip. In the image it goes dust boot, circlip, washer, piston/front seal, spring cap.


I put it all back together, filled up the reservoir and poof, nada. No pressure.

The NB speed bleeder is closed.

Any ideas?
 
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#2 ·
Bleeding the stock system is a pain in the a$$, plenty of threads to help if you do a quick search, the tie-wrapping-the-lever-down-overnight is well worth doing. You may end up in the same boat with regards to brake feel. I believe that the 2008 Speed Triple has twin 4 piston calipers whereas the Bonneville has only one 2 piston caliper. When I installed my 4 piston Brembo kit I fitted a Rocket III master cylinder. That was designed to move 6 pistons in 2 triple piston calipers. The result was a good working brake with fairly wooden feel similar to what you noted. I replaced my master cylinder with one from a twin disc Speedmaster with 4 pistons and it works just as well and has nice feel. There are people on this forum that could give you better advice re piston diameter versus master cylinder swept volume etc. but I'm thinking that if you still have the stock caliper then you will still have the original problem.
Good luck with it.
 
#3 ·
Thanks for responding. What I'm concerned about is that I have no pressure what so ever.

Everything is reconnected and the reservoir is filled again and yet when I pull the lever in the piston just backs all the way in like there is no pressure behind it. When I pump the lever nothing comes out. Even when I take the banjo bolt off it's like nothing is coming out of the reservoir.

I did change the rubber hose between the reservoir and the cylinder. I had to shorten the length because it looked like it was getting pinched and bending in the middle. But now it looks clear.

I have the cap on, bleeder closed and I have the handle pulled to overnight.
 
#4 · (Edited)
You should get a master cylinder from a Bonny SE, 7/8" and an 11mm piston, even when you get your system bled it's going to feel like it did before, it's a 14mm piston.
But as far as bleeding, unless you use a vacuum bleeder, is to pinch bleed the line, take the banjo off the caliper, put it in a sandwich bag and pinch it with your thumb and index finger, pump, pinch, release the lever, repeat. When you have line pressure, reattach the banjo then bleed the caliper.
 
#9 ·
Y is to pinch bleed the line, take the banjo off the caliper, put it in a sandwich bag and pinch it with your thumb and index finger, pump, pinch, release the lever, repeat. When you have line pressure, reattach the banjo then bleed the caliper.
So, am I pump/pinch/releasing using the bleeder line or is the "pinch" (after I've pinched the bleeder line) actually pinching around the banjo?
 
#5 · (Edited)
This bit's got me thinking...

The NB speed bleeder is closed.
I might have misunderstood what you've done and I hope I'm not stating the obvious, but...

The speed bleeder is a normal bleed nipple with a one-way valve in it to assist bleeding (especially if you're working by yourself): you still need to bleed the brakes in the same old way.

1) Take the cap off the fluid reservoir and run a short length of clear plastic tubing that fits snugly over the speed bleeder to an empty glass jar.
2) Undo the speed bleeder about 1/4 of a turn, pump the front brake keeping the reservoir topped up (about 3/4 full is fine). Do NOT let it get empty or you'll have to start all over again.
3) Before too long you'll start to get a stream of brake fluid (and, initially, bubbles) in the plastic tubing - when it's coming through with no bubbles you can tighten up the speed bleeder.
3a) I was recently doing the same thing on a '73 Honda 350 Four - the brakes refused to build pressure during bleeding. I eventually got some pressure by sucking on a long, clean section of new tube and keeping a very careful eye on the caliper end of the tube...
4) Top up the reservoir to the correct level, pump the lever 4-5 times to build pressure. While maintaining pressure on the lever, SLOWLY slacken the speed bleeder - and nip it up quick BEFORE the lever gets back to the bar.
5) Test the lever for feel/pressure. Repeat stage 4) as necessary.
6) Fill reservoir to correct level. Spray everything down with brake cleaner (unless you like to have your paint bubbling off...)

Tim
 
#6 ·
NickGoodwin's information was helpful. I think the issue is that I don't have line pressure.

Tim's info is equally helpful. Thanks guys!

I'll look at a Bonneville SE piston! I don't have stock controls anymore as I'm using the m-switch, will this matter?

Anyone have a recommendation for a good after market clutch perch?
 
#7 ·
Have you made sure the master cylinder is actually getting any fluid fed to it? If not it will simply be pumping and compressing air.

If the piston is not returning far enough to uncover the hole to the reservoir then no fluid will enter (likewise no air can return hence holding the lever in will never to anything to help bleed your brakes) and you will simply continue to pump air which will probably feel like you are not generating any pressure as it compresses easily particularly if there is a lot in the system as in when you have rebuilt it.

There is no magic (black or any other colour to bleeding brakes) simply attention to detail on the physics particularly the bit about air rising to the top.

Oh, by the way a speed bleeder can have enough 'blow off' pressure that you will not open it before you've compressed all the air in the system, so no movement of air or fluid will occur.
 
#8 ·
What's a front brake caliper upgrade I can use that goes with the 14mm master cylinder?
 
#12 ·
Hey Nick - I've tried and it just wont work. It keeps just pushing out air. I can see the bag moving in and out with the lever pulses but no fluid comes out.

The reservoir is filled and I've tried it both with the cap on and off.
 
#18 ·
Fill a syringe with clean brake fluid.
Attach syringe to caliper bleeder fixture via clear vinyl tubing. (Shorter is better.)

Open M/C res for fluid to come in.

Open bleeder and push new fluid from the caliper, up to the M/C.

You should get a few bubbles as the fluid travels "upstream."

You should then have a decent "lever."
 
#21 ·
I get some sputters of brake fluid into the plastic bag when I try NickGoodwin's method but nothing substantial and then it just stops. I'll re-do the rebuild and see if I get any better results. This is getting annoying :)

Z
 
#23 ·
Then it's definitely not working. I removed the cylinder banjo and confirmed that when I depress the lever that no fluid is leaving the reservoir through the master cylinder. So, either there is a blockage or I screwed up the rebuild!
 
#24 · (Edited)
Good day gents and gent-esses,

I tore the master cylinder apart again and pieced it back together. What I'm seeing is that when I fill up the reservoir and pump the piston I'm getting a slow stream of fluid coming out.

Is that normal and expected or should it be a rush?

One thing I'm struggling with is that the dust cover on the end of the piston keeps sliding up the end of the push rod every time I depress the lever. Imagine the finger of a rubber glove when you pull it off. It slides up over the finger but the "cap" of it stays on the tip (yes, I realize there was a more illustrative example I could have used here but I'm trying to limit the phallic references; ha!).

Does any of this sound normal or am I still screwing it all up?

The Pretech caliper is a little out of my price range.

Can someone tell me a cheaper alternative, such as a Nissin 2-pot I've heard about. What models are compatible with our set up? Do you need to change the brake lines?
 
#25 ·
It's a Nissin 3 piston, I have one off a, if I remember correctly, 09 VFR 800, with a mounting bracket from a DN-01. You must use an 06 and on VFR caliper and you need to drill out a journal and block of a banjo hole. I tried it with a speed trip mc and it's wooden, it works great with an 11mm mc, you can rebuild that mc all you want but it's still going to feel like dog doo. There is one on eBay now with a broken mirror tab for 40 bucks.
 
#26 · (Edited)
Grumble. Nothing is easy. Oh wait, stock controls was easy. Ha!

I still prefer the 7/8" and the Renthal bars.

I'd rather just get the stock caliper working again :( This is really frustrating. Am I getting any closer?

Did you say there is an 11mm on ebay? Link?
 
#28 ·
I think in the short term I want to get my stock caliper back on the road and deal with the woody master cylinder. But yes, I would love the technical information on how to do the 3-pot Nissan conversion.

I dont have ready access to a drill press but I'm sure someone in San Francisco has one I can use for 10 minutes.
 
#31 ·
What does Europe only mean?

So I rebuilt the piston again last night and I did notice when comparing it to one of the Chinese ones I bought that the end of the piston was sticking out maybe 1/8-1/4 of an inch farther on my Nissin rebuilt. So, I re-did the circlip and got it to look exactly like the cheap Chinese one.

Fluid is definitely flowing from the reservoir to the cylinder but I'm not experiencing anything like you guys have said "pressure that would push your finger".

This is frustrating
 
#32 ·
So I tried the old suck on the end of the bleeder line and that definitely got fluid coming out of the reservoir into the line. And, I was even able to pump the lever and keep pushing fluid out. However, after a while of pumping and about 1/2 of the reservoir empty I just lost pressure and nothing else would go.

Frustrated.
 
#39 ·
It seems to me your originally had the problem I mentioned way back of the fluid not getting into the system, now it seems you've solved that but maybe just haven't got the system bled, if you have air in the system then it will just compress and you won't feel much resistance at the lever. If you don't have the parts of the system in a good orientation when you are bleeding you can suck or blow as much fluid as you like and it won't shift it. The aim is not to get as much fluid through the system as possible but to get all the air out.


Make sure your caliper is vertical (in both axes) so that the bleeder is at the top (I'd not bother with a speed bleeder as the spring pressure can complicate things), also make sure your mastercylinder is pointing down hill to the outlet, this means that any air will travel back to the piston and leak out into the reservoir.

Just think air rises to the top and you can't go far wrong.

It may also be worth pushing the pistons back in the caliper, the resulting smaller volume in the cylinders makes it harder for air to hide. And when someone inevitably tells you that tying the lever back to the bar overnight will sort it either don't listen or tell them they're talking garbage (depending on how much you like/dislike upsetting people) as this cannot assist bleeding, in-fact it does the opposite.
 
#33 ·
Europe only means that the unlinked brake caliper was on Hondas that are only available in Europe.
For the sake of your sanity, I would snag that eBay mc or any 7/8 Bonny mc. The clip on Thruxtons also had a 7/8 bar. The reason I say this is, even if you get it rebuilt it's still going to push too much fluid for the caliper and feel like wood.
 
#34 ·
Yeah dude but I don't have Stock controls anymore. I have m-Unit m-switches so it will look all jacked.

I'm fine with the woody feel at this point b/c I can just upgrade the caliper later. I just can't get on the road now.
 
#38 · (Edited)
it's not quite as simple as that extractable if you use a 6 pot caliper later,
the 11mm piston diameter of the bonnie se or thrux master cylinder will not displace enough brake fluid to move the 6 pistons of the 6 pot caliper far enough to apply sufficient pressure on the pads, which means your brake lever will travel further to try to displace enough fluid (probably it will come in to the handlebar) although if you only use a 3 pot caliper you will be ok.
to displace enough fluid to have a "normal" lever action you will need a master cylinder with a 14mm piston.

i have a single 4 pot nissin caliper (i have triumph tt600 forks on my bike so it's no good for you extractable) and use the standard t100 11mm master cylinder, with careful bleeding the lever action is still good enough, but a 14mm would probably be better.
 
#40 ·
Okay - score! I ended up getting an 11mm Bonneville master cylinder for a 7/8" bar so I'll be going back to the old setup. Whew. Hopefully it works and I can get it bled. Stand by for more inane questions I'm sure. And, thanks for all your help and recommendations as always.
 
#41 ·
Well the continued frustration continues...

I installed the "new" 11mm Bonneville SE master cylinder. I was able to get line pressure using NickGoodwin's method (I finally felt the force you were saying that prays the thumb and forefinger apart). Then, I proceeded to start the bleeding process, which seemed to be working fine. I was able to flush about three reservoir's worth of fluid through, buttoned everything back up and then tried to use the brake; nothing. No pressure, no braking action, nada.

Any thoughts?
 
#43 ·
I think I mentioned before, bleeding isn't about how much fluid you can get through but how much air you can get out.

On one of the kit car forums I frequent there was a guy had a bleeding problem all sorts of posts back and too, he'd put about a gallon of fluid trough (and an Imperial one not one of those tiny US ones) and then came the one liner regarding the bleed nipple under the caliper. UNDER! Dozy twonk had fitted the calipers to the wrong sides thinking having the nipple at the bottom would help the fluid escape.

If you don't have the nipple at the highest point you can/will get air rising to that highest point and flushing an ocean of fluid through won't shift it.
 
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