Master brake cylinder gone bad? - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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post #1 of 11 Old 06-17-2019, 05:47 PM Thread Starter
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Master brake cylinder gone bad?

I've tried all suggested methods to firm up my (ABS) front bakes and recently rebuilt my master cylinder and replace both front calipers but the brakes are still softer than they should be and I often pump them to stop properly. I tired the zip tie method on the brake lever and leaving it that way over night. It didn't work but what I did realize is that if I hold steady pressure on the lever it eventually bottoms out onto my handgrip. So I don't think there's air in the line as I've pumped/bled over 2 quarts through the system, but perhaps my (rebuilt) master cylinder it still may need replacing. Any thoughts?

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post #2 of 11 Old 06-17-2019, 06:33 PM
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If you don't have the adaptor to drive the ABS servos when you bleed the brakes you will never get the air out of them no matter how much fluid you pump through it.
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post #3 of 11 Old 06-17-2019, 07:00 PM
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Dark Angel, A friend and I did the brake flush on our F800ST's with the aid of a 911 and his laptop. Cycling the ABS servo didn't seem to make much of a difference. When opening and closing the valves at the calipers often allows a bit of air to sneak in. i got Speed Bleeders and did my brakes in about 20 minutes with very satisfactory results. Nice firm feel with no give in the lever.
http://kirbysbrakebleeders.ecrater.com/ For about 25 bucks you get 3 and it's a done deal; and just a small can of fluid was needed.
I had a Mighty Vac and that thing never worked well.
Others like to get a big syringe and back feed the fluid from the caliper. That way you are forcing the fluid and air up to the master.
It takes very little air in the system to get the results the OP is experiencing.

Last edited by notacop; 06-17-2019 at 07:26 PM.
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post #4 of 11 Old 06-17-2019, 11:28 PM Thread Starter
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Quote:
Originally Posted by Dark Angel View Post
If you don't have the adaptor to drive the ABS servos when you bleed the brakes you will never get the air out of them no matter how much fluid you pump through it.
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https://www.healtech-electronics.com/products/obd/
This is the first I've heard of this, hence know nothing about it. Thanks I'll look into it. BTW I tried speedbleeders and collapsing both calipers to push the fluid back up with the same results.

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post #5 of 11 Old 06-18-2019, 08:17 AM
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Originally Posted by 96sled View Post
I did realize is that if I hold steady pressure on the lever it eventually bottoms out onto my handgrip.
Cheers
Marty
That should not happen even with air in the system.

With air in the system the leaver will be a little spongy but you should still be able to apply good pressure and have it hold that pressure.

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post #6 of 11 Old 06-18-2019, 08:41 AM
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Rebuilt master cylinder?
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post #7 of 11 Old 06-18-2019, 09:43 AM Thread Starter
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That should not happen even with air in the system.

With air in the system the leaver will be a little spongy but you should still be able to apply good pressure and have it hold that pressure.
Yea. That's the kicker. My other two bikes (crf and cbr), even with a bit of air in the system don't 'leak down' like this. So I don't know if the loss of pressure is happening in the master, the calipers or somewhere I haven't considered.

Rick - I bought a rebuild kit with new springs and seals so yea, rebuilt the master cylinder. But to be honest I don't know if the 'leak down' phenomena occurred before the rebuild since I didn't try the zip tie method before the rebuild. If you have a place in mind that sells master cylinders I'm all ears.

I've never had so much trouble with a braking system in my life. Regret getting the ABS since I've never missed it before I had it. If I put the brake dial on 5 the brakes essentially don't work, if I put the lever on 1 or 2 it's manageable but not safe.

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Last edited by 96sled; 06-18-2019 at 10:23 AM.
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post #8 of 11 Old 06-18-2019, 11:03 AM
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Is the brake fluid level dropping at all?

I recently flushed the braking system on my ABS model. While the brakes still feel somewhat 'mushy', especially compared to my Street Triple, they are reasonably firm. I suspect that's as good as they'll get.
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post #9 of 11 Old 06-18-2019, 03:05 PM
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Quote:
Originally Posted by 96sled View Post
Yea. That's the kicker. My other two bikes (crf and cbr), even with a bit of air in the system don't 'leak down' like this. So I don't know if the loss of pressure is happening in the master, the calipers or somewhere I haven't considered.
It can only be at the MC.

To loose pressure anywhere else would be to loose fluid and that would mean a fluid leak would be evident.

Some of the 19 rides in my shed
2014 V2, Snoopy
2009 Wee, Pumbaa the pig
WR450F, The Blue Postie Bike
YZ250N smoker with rego, Stinky.
Yamaha MT09 (FZ09), The Scud missile.
Club Lead not Club Med.
He with the most toys wins.
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Live life on the edge you will see more that way.
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post #10 of 11 Old 06-18-2019, 03:17 PM
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While running pump the brake lever until it is firm. If it holds in the same place it is air in the lines, if it slowly descends to the handlebar or never pump up firm it is the master cylinder.

It is possible for grit to ruin a master cylinders smooth walls. I've just never heard of it on a V-Strom. Doesn't mean it doesn't happen. Being a frugal guy i would check Ebay. Someone probably crashed a perfectly good bike with a perfectly good master cylinder and it is being parted out.

Last edited by richlandrick; 06-18-2019 at 03:22 PM.
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