Switching to a shared reservoir brake master cylinder

[Frankenchevy]

truck is a K30 with hydroboost. It currently has the factory master cylinder with a divided brake fluid reservoir. Does anyone know off the top of their head if there is any newer brake master cylinder with a single large reservoir to supply both circuits that is compatible with my hydroboost system?

 

[Blue Ox]

Why would you want something like that?

 

[Frankenchevy]

Why would you want something like that?

Im disc front and rear with a new disc/disc proportioning valve. The small side of the reservoir is really small. I was hoping to get increased brake fluid volume for the system to share.

Is this a silly thought? I also figured newer tech on brake system stuff would be better and thought there may be a good reason that newer 1-ton diesels are shared reservoir. But I’ve had plenty of stupid ideas before, so it wouldn’t be a shocker if this was another one!

 

[Blue Ox]

I see. I'm sure you already know the divided reservoir is to keep the split system separate in case of a failure. The only reason I can think of for a common reservoir would be in an antilock system that has a computer keeping an eye on things. Maybe look for a later model truck that has rear discs and look at the cylinder/piston sizes to find something compatible.

 

[73c20jim]

Why not get a corvette master cylinder? Its a disc/disc MC.

 

[legopnuematic]

I know that an 02 GMC 3500 has a single chamber master with 4 way disc brakes and hydroboost, other than that I have no idea if it would fit and work without an abs system.

 

[Frankenchevy]

Why not get a corvette master cylinder? Its a disc/disc MC.

I was looking for something hydroboost native. It would just make me more comfortable that the master cylinder was designed with a 1-ton truck in mind. Not to mention, I’m not sure the vette MC would bolt up to the hydroboost pump or not...

I know that an 02 GMC 3500 has a single chamber master with 4 way disc brakes and hydroboost, other than that I have no idea if it would fit and work without an abs system.

After @Blue Ox ’s point, I’ll need to research the ABS compatibility issues.

Thanks for the suggestions guys. Clearly I have some homework to do. I tend to over think stuff...

 

[Craig 85]

I had thought about the Corvette MC due to the larger size, but Napa shows the bore is only 1 1/8". K30 is 1 5/16". The only other thing I could think of is the late 90's 3500 HD trucks (see below). They have 4 wheels disc brakes with a hydro boost system. Those bores are 40mm (1 37/64") The brake line threads are the same though. Here's a couple of Napa parts to look at NMC M3305 & NMC M3159. These don't look like shared MC's.

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[smoothandlow84]

Just run smaller diameter brake lines to the rear. Smaller lines = higher pressure, having more fluid capacity wont necessarily help add power to the rear brakes. Fine tune the proportioning valve....install an aftermarket adjustable unit. Having two seperate resevoirs makes more sense in case of failure.

 

[Blue Ox]

Just run smaller diameter brake lines to the rear. Smaller lines = higher pressure, having more fluid capacity wont necessarily help add power to the rear brakes. Fine tune the proportioning valve....install an aftermarket adjustable unit. Having two seperate resevoirs makes more sense in case of failure.

I didn't get the impression that he was looking for more power. Just dealing with the larger volume of the caliper Pistons vs the wheel cylinders.

I'm kind of lost on how smaller lines lead to higher pressures.

 

[legopnuematic]

I didn't get the impression that he was looking for more power. Just dealing with the larger volume of the caliper Pistons vs the wheel cylinders.

I'm kind of lost on how smaller lines lead to higher pressures.

Think of blowing through a straw and then through a garden hose the same length with the same amount of air. The straw will have more pressure and less flow due to it being a restriction whilst the garden hose will not have much pressure and flow more since it is less of a restriction. Similar to boost on a turbocharger, boost is a measurement of restriction so on an efficient piping setup more power can be made with less boost since there is less of a restriction, whereas a poorly designed cold side will take more boost to make the same amount of power due to it being restrictive. It is all based around Bernoulli's principles.

 

[Blue Ox]

So restricting flow to the rear brakes will increase the pressure on the rear brakes?

That doesn't seem to add up.

 

[bucket]

Think of blowing through a straw and then through a garden hose the same length with the same amount of air. The straw will have more pressure and less flow due to it being a restriction whilst the garden hose will not have much pressure and flow more since it is less of a restriction. Similar to boost on a turbocharger, boost is a measurement of restriction so on an efficient piping setup more power can be made with less boost since there is less of a restriction, whereas a poorly designed cold side will take more boost to make the same amount of power due to it being restrictive. It is all based around Bernoulli's principles.

Added pressure before the restriction point does not mean added pressure after the restriction.

Brake line sizing and master cylinder bore sizing needs to match the requirements of the caliper/wheel cylinder AND the desired pedal travel and feel.

 

[bucket]

Also, many master cylinders appear to have a shared reservoir, but they are only shared to a point. There is usually a divider wall that separates the two circuits, with a slot in it near the top. It allows fluid travel between the two circuits until the level gets down to a certain point.

 

[Blue Ox]

Also, many master cylinders appear to have a shared reservoir, but they are only shared to a point. There is usually a divider wall that separates the two circuits, with a slot in it near the top. It allows fluid travel between the two circuits until the level gets down to a certain point.

I don't advise re-engineering, but I guess he could get a similar effect by milling the divider between the two reservoirs down partway.

I still think he's going to need to look at a lot of parts lists and see what size masters get used with what size calipers.