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MC rebuild - what is wrong?

Big T

Big T

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It was about 2 weeks between when I took it part and when I rebuilt it. Silly me, no pictures of "old"

I can't get this MC to pump up more than half way with minimal braking. It's a Salty Monk disc/caliper upgrade and I used to be able to lock the front wheel at 35 mph.

Did I put the parts in wrong?

mc001.jpg


mc003-1.jpg


I reverse fill the system (from the bottom up) so it shouldn't be air.

It's the correct kit for the MC, I checked before, during and after.
 
I believe the parts are in the right order.
Are you sure you didn't put the copper disk first?
That would explain the fact that the pump doesn't work...
The other possibility is that the very small hole that allows to fluid to move out of the cylinder is blocked.
When you prime the brakes, small air bubbles normally come out of there.
 
Bleed the master cylinder without the lever by using a screwdriver. The lever does not push the piston all the way in and there is always a little air trapped behind it.
I don't use the lever to bleed my brakes but a phillip screwdriver.
 
John Kat said:
I believe the parts are in the right order.
Are you sure you didn't put the copper disk first?
That would explain the fact that the pump doesn't work...
The other possibility is that the very small hole that allows to fluid to move out of the cylinder is blocked.
When you prime the brakes, small air bubbles normally come out of there.
Click to expand...

Nope, the picture shows the order in which the parts were inserted and removed

The bleed hole is clear and I got a bunch of small bubble out of there when I put the fluid in from below.

Chef, I'll try the full range pumping of the MC
 
I still can't get any pressure build up.

I reassmbled and reverse bled, once the resevoir was half full i started pumping as Chef recommended.

I got lots of bubbles at first, then none.

I finally took off my resevoir and found that fluid is spurting out of the relief port when I squeeze the brake lever.

What is going on here?
 
TomMLC had something like this... it turned out to be a issue with his fancy new bleed nipple replacements on the calipers leaking (not enough to notice but changing those is what solved his problem).
Just an idea.

:)
 
Dan

I'm thinking there's something wrong with the brake lines.

I put the MC from the 850 on and bled it -still no lever pressure

I'll swap out the brake lines from the Fridge tommorrow and see what happens
 
Not a relief port, it's called the compensating port. The quantity of fluid comng out will depend on how far back the piston cup rests behind the port. It only has to be just behind the port so the hydraulics is not a closed circuit. If too far back the lever travel will be long before the brakes start to engage and a lot of squirt. But it all depends on what the brake engineer's design intent was unless you have an aftermarket piston kit that does not conform to the OE dimensions.

So as far as is there too much fluid squirting out, depends on what it did when originally coming off the assembly line.
 
TooManyToys said:
Not a relief port, it's called the compensating port. The quantity of fluid comng out will depend on how far back the piston cup rests behind the port. It only has to be just behind the port so the hydraulics is not a closed circuit. If too far back the lever travel will be long before the brakes start to engage and a lot of squirt. But it all depends on what the brake engineer's design intent was unless you have an aftermarket piston kit that does not conform to the OE dimensions.

So as far as is there too much fluid squirting out, depends on what it did when originally coming off the assembly line.
Click to expand...

Jack - factory rebuild kit. All of the pumped fluid is coming out of the compensating port-it shot about 4' away to the back of the seat.

So, something is keeping it from going down the lines, I think
 
I'm getting confused between forms or threads. I thought I posed this earlier in this thread.

http://www.thegsresources.com/_forum...1&postcount=36



In your picture that I added the arrow, if you have a stream after this cup passes by the compensating port then the cup is not sealing against the bore. Hydraulic pressure will go to the least resistance which will be the port rather then moving the caliper pistons.

If the squirt stops once the cup passes the port, then it's normal.

The only other reason that fluid would squirt out the compensation port if the cup is good and past the compensation port is if the relief port at the lever end of the bore is clogged.
 
Quick Cal said:
Take a look at the link. Your brass/copper,,what ever it is,,,,check valve may be in backwards. It makes sense about what this guy says about wear marks on the check valve.

Unless of course it just gets smashed flat under pressure. :rolleyes:

http://freetireair.wordpress.com/2011/12/29/rebuild-a-brake-master-cylinder-80s-suzuki-gs650/
Click to expand...

That's an interesting idea - I didn't check for wear marks on the check valve and there's nothing in the FSM that indicates that it should be installed in one direction only. It looked flat to me

I read the link and it mentions putting the curved side against the seal. This is stupid, it's so thin that both sides would have to be curved. Never heard of convex and concave? I'm assuming he means convex.

Any way , off it comes again to check the check valve. Glad I bought extra DOT 3 when I did the tow van's brakes over the weekend
 
Big T said:
That's an interesting idea - I didn't check for wear marks on the check valve and there's nothing in the FSM that indicates that it should be installed in one direction only. It looked flat to me

I read the link and it mentions putting the curved side against the seal. This is stupid, it's so thin that both sides would have to be curved. Never heard of convex and concave? I'm assuming he means convex.

Any way , off it comes again to check the check valve. Glad I bought extra DOT 3 when I did the tow van's brakes over the weekend
Click to expand...

The master in the link is referring to a 650. I don't know if the check valve would be the same for your bike. Maybe one of the Guru's will be along and verify if the check valve is flat or not.
 
Big T said:
That's an interesting idea - I didn't check for wear marks on the check valve and there's nothing in the FSM that indicates that it should be installed in one direction only. It looked flat to me

I read the link and it mentions putting the curved side against the seal. This is stupid, it's so thin that both sides would have to be curved. Never heard of convex and concave? I'm assuming he means convex.

Any way , off it comes again to check the check valve. Glad I bought extra DOT 3 when I did the tow van's brakes over the weekend
Click to expand...


Just a little update.

I just received a OEM rebuild kit and the check valve is flat. So it must be something that happens with use. But I would still put the wear mark like it was when it came apart.
 
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