Master cylinder question for disk brakes

vwracin2win

i have the cheaper 2 piston disc brakes on the rear of my baja with drum front brakes and a stock type 1 master cyclinder with stock pedal assembly. i bled the brakes and i dont have any pedal it seems like my master cylinder isnt pushing enough fluid to compensate for the dic brakes. just curious if i should be using a larger bore master cylinder or something. could be my master is bad too but i want to make sure i get the right one to replace it.
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69 VW baja 1914
73 F-100 built 302

Multi69s · Posted: Thu Sep 11, 2014 2:08 pm Post subject:

Two man operation. Have someone else push the brake pedal, while you watch the disc brake pads. Do they move at all, or just a little bit. I am leaning towards either a bad MC or in need of further bleeding. Even if the MC was too small, it should have enough volume to press the pads out to the discs.
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69 road Bug 2110
73 Squareback - 2L, T4, Automatic W/ AC
Gone, but many fond memories 69 Baja Bug 2010 - 5 Rib Bus Transaxle
Gone but not forgotten 72 Baja Bug 2010
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Fltblkbaja · Posted: Thu Sep 11, 2014 5:57 pm Post subject:

Agreed, if your lucky it needs a little more bleeding, if not new MC. But the MC is fairly cheep and easy to do, let us know what you find
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vwracin2win · Posted: Thu Sep 11, 2014 6:43 pm Post subject:

They will touch the discs but the pedal is almost to the floor with the adjustment push rod from pedal to the master cylinder adjusted pretty close to all the way out.
_________________
69 VW baja 1914
73 F-100 built 302

vwracin2win · Posted: Thu Sep 11, 2014 6:47 pm Post subject:

They will touch the discs but the pedal is almost to the floor with the adjustment push rod from pedal to the master cylinder adjusted pretty close to all the way out. I had it sitting for a couple weeks or so and now it has no brakes at all. Master is most likely bad. Everything is brand new lines, hoses, wheel cyl, disc brake kit, even the master is new. Wouldn't surprise me if it's bad it's happened to me me before but I have never run disc brakes. It just seemed to me I needed a master that would pump more volume? I once heard the bus master cyl is higher volume is this true? Plus it's a little cheaper.
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69 VW baja 1914
73 F-100 built 302

Fltblkbaja · Posted: Thu Sep 11, 2014 6:48 pm Post subject:

Yeah I'd chuck a new MC in there might be pooched
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Everyone chops and drops,
We chop and lift!!!

Fltblkbaja · Posted: Thu Sep 11, 2014 6:50 pm Post subject:

Not sure about the bus MC, maybe ask the bus guys.
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Everyone chops and drops,
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Multi69s · Posted: Thu Sep 11, 2014 8:30 pm Post subject:

The thing about disc brakes in comparison to drums, is that the discs do not have return springs to suck the wheel cylinders back in. With disc brakes, they are designed to be pushed out to the disc, and the only thing that pulls the pads away from the discs, is the flex in the piston seals. So the pads only return a very short distant from the discs. Therefore, if everything is correct, MC bleed, etc, you should get a firm pedal before it reaches the floor. Now with dual pistons, the pedal may be a little lower then stock, but you should still get a good pedal. Also, just because the MC is new, doesn't mean it is good. Been down that road before.
_________________
69 road Bug 2110
73 Squareback - 2L, T4, Automatic W/ AC
Gone, but many fond memories 69 Baja Bug 2010 - 5 Rib Bus Transaxle
Gone but not forgotten 72 Baja Bug 2010
My builds
T4 into Squareback http://www.thesamba.com/vw/forum/viewtopic.php?t=458944&highlight=
Auto Trans Rebuild http://www.thesamba.com/vw/forum/viewtopic.php?t=516066&highlight=
AC in Squareback https://www.thesamba.com/vw/forum/viewtopic.php?t=...highlight=

vwracin2win · Posted: Thu Oct 16, 2014 12:36 pm Post subject:

Started messing.with the brakes again today. Still can not get enough pedal to even bleed. Went around and checked all fittings again to make sure they are tight. I used a rig job vacuum set up and it broke but I got a little pedal then I had my wife give it a few pumps then held it while I let the fluid out and she pumped it again and the pedal never came back up. Wondering if the only way is to vacuum bleed. But then.I wonder is something is wrong with the master so when we pump it it sucks in air. Or maybe it just has a crap load of air in the system from not bench bleeding and it being a new system.
_________________
69 VW baja 1914
73 F-100 built 302

tripicana · Posted: Thu Oct 16, 2014 5:11 pm Post subject:

You need to bench bleed it. You'd be surprised how long you can bench bleed it till all the air is gone. I don't u sees tans why people don't think it's nessecary and wonder why their brakes don't work.
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vwracin2win · Posted: Thu Oct 16, 2014 6:00 pm Post subject:

I just noticed it looks like some of the paint is eaten away a little right under where the master goes through into the car. Wonder if I should try bench bleeding or just get a new master.
_________________
69 VW baja 1914
73 F-100 built 302

vwracin2win · Posted: Thu Oct 30, 2014 7:12 am Post subject:

Just wanted to update this thread. I put a new bus master in it and bench bled it and everything's perfectly and the brakes work great. Hard to say if it were the new master or the bench bleeding. I'm thinking a little bit of both. Thank you to everyone for their advice and help.
_________________
69 VW baja 1914
73 F-100 built 302


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