Master cylinder bore size for hydroboost brakes

[bigmuddy]

Any thoughts on 1" vs 1 1/8 bore sizes being used with hydroboost?

Picked up a Wilwood that has a 1" bore and I am running 79 bronco front discs, with the 77 largest rear drums.
I also have a new Wilwood adjustable prop valve to install so maybe I can dial out the front and rear well enough?

I had been running a stock type master cylinder and I do not recall the bore size but it worked well enough, the issue was that I needed more clearance as it hits the new hood, ugh always something.

Anyway, I don't want to get this bled and then find out it's inadequate for the job and I have wasted a good chunk of cash....

TIA. Looking for anyone but I know Yeller and Todd Z have a lot of the brake knowledge...

 

[bigmuddy]

Never mind, I did a quick search and came up with a min 1-1/8 bore but 1-1/4 is better.
Unfortunately, Wilwood only makes the compact in 1-1/8 from what I can find online.

 

[Madgyver]

Smaller bore equals higher pressure.
I used a 77 corvette MC 1.125" bore with an astrovan Hboost. T-Bird front caliper and cady rear discs brakes.
It's been on my yellow77 all these 20+ years working great.

 

[Broncobowsher]

Mine was pretty dang good with a 15/16" master (GM front, 11" rear, 33" tires, stock pedal ratio)
Choice of brake pad material also makes a HUGE difference in braking performance. Look at all the possible compounds that Wilwood offers. That is one of the reasons I went with GM brakes, larger pad material selection. They have added more since I did mine (and also removed the Polymatrix-D compound I was running). Rear shoes were new from the parts store when I bought it, never changed them, no idea what they were.

 

[bigmuddy]

Smaller bore equals higher pressure.
I used a 77 corvette MC 1.125" bore with an astrovan Hboost. T-Bird front caliper and cady rear discs brakes.
It's been on my yellow77 all these 20+ years working great.

Fairly similar to mine, but I have a different front discs. I will post a pic of what I am working with later.

 

[1969miller]

1-1/8" works best in my opinion

 

[ntsqd]

GM calipers, Vanco H-B kit, stock FSB brake pedal ratio, Saginaw P-Pump built for use with H-B, Ø1.25" bore m/c. No way would I consider going smaller. Not only not necessary to generate more pressure, it would also make the pedal feel mushy to me.

Pedal feel is highly subjective, I want a firm pedal with good modulation, and I don't like the longer travel that a smaller m/c bore creates.

By doing it this way I don't need to buy racing pads, I can buy generic Fleet Service pads and get the brake performance that I want. No doubt that the racing pads are overall a better pad, they also cost more.

Try this: wrap your hand around a rubber brake hose. Have a helper simulate a panic-stop while you're doing that. Have he or she cycle thru a couple of times. Brake systems have an upper pressure limit and you just felt what happens when you get close to it.

 

[bigmuddy]

I am really thinking about shipping this back and getting the 1-1/8, ugh I hate buying the wrong shite and stalling progress!

 

[bigmuddy]

Ok, so this is what I am working with. Little cramped.

The wilwood unit fits size wise under the hood as it's a "compact unit"

Hydroboost and master are not bolted together on the offset bracket either, FYI.

 

[ntsqd]

IS there an overall length constraint, or just a height constraint? If height only I'd expect that you can find something OEM that will fit. Sometimes the "Extra Info" page on Rock Auto will give dimensions that are useful. Just because one brand of some specific application m/c does have them doesn't mean that another brand won't either.

 

[bigmuddy]

length and height both. I would prefer something stock, perhaps one of the small corvette masters, but I think most all are made for disc/disc.

Thanks for the tip on Rockauto, I didn't realize they showed dimensions.

 

[ntsqd]

Not all brands do, but some do. Example: https://www.rockauto.com/en/moreinfo.php?pk=112979&cc=1125021&pt=1836&jsn=832
As it happens that's the stock application m/c for a '96 F-250 5.8L and it is a Ø1.125" bore. A different brand for the same application has a Ø1.06" bore (& few other dims), so I'm in the habit of always checking those pages under the "Info" button.

 

[Broncobowsher]

That offset bracket, I can't tell, does it change the pedal ratio?

 

[bigmuddy]

That offset bracket, I can't tell, does it change the pedal ratio?

I am not sure about that? There was some conversation about this unit awhile back but haven't tracked down the thread yet.

What's your concern about pedal ratio?

 

[ntsqd]

It directly affects both braking force and pedal feel. IF it increases the ratio over stock then you'll probably want a larger bore m/c. If it decreases the ratio under stock then you'll probably want a smaller bore m/c.

 

[bigmuddy]

It directly affects both braking force and pedal feel. IF it increases the ratio over stock then you'll probably want a larger bore m/c. If it decreases the ratio under stock then you'll probably want a smaller bore m/c.

Roger that. That said, couldn't I manage that with changing the length of the pedal and in this case rod that goes to the boost unit?
What a pickle...

 

[ntsqd]

Changing the length of the pedal will change the pedal ratio. Changing the length of the operating rod only changes the start position of the pedal. Adding new operating rod holes to either or both of the levers on the bell-crank will change the pedal ratio.

 

[toddz69]

I am not sure about that? There was some conversation about this unit awhile back but haven't tracked down the thread yet.

What's your concern about pedal ratio?

That looks like one of @catfan's brackets. Maybe he can tell us whether it changes the pedal ratio or not.

Todd Z.

 

[toddz69]

Any thoughts on 1" vs 1 1/8 bore sizes being used with hydroboost?

Picked up a Wilwood that has a 1" bore and I am running 79 bronco front discs, with the 77 largest rear drums.
I also have a new Wilwood adjustable prop valve to install so maybe I can dial out the front and rear well enough?

I had been running a stock type master cylinder and I do not recall the bore size but it worked well enough, the issue was that I needed more clearance as it hits the new hood, ugh always something.

Anyway, I don't want to get this bled and then find out it's inadequate for the job and I have wasted a good chunk of cash....

TIA. Looking for anyone but I know Yeller and Todd Z have a lot of the brake knowledge...

It is somewhat dependent on what brakes you're running (and perhaps the bracket too depending on what we find out about your bracket). I ran a 1.125" master from ~2000/2001 until about 2 years ago and was pretty happy with it but the brakes were touchy and the pedal a little lower than I liked. Then I switched to a 1.25" bore unit and I've been a lot happier with the pedal feel and pedal height. I've had an OEM hydroboosted truck (01 PSD) in my driveway for 23 years now as a baseline for what I *think* a hydroboost system should feel like.

Todd Z.

 

[Oldtimer]

There was some conversation about this unit awhile back but haven't tracked down the thread yet.

This thread?

Hydroboost Installation question

Can someone with a hydroboost that has "great braking" tell me how much pedal travel you get in your early bronco? With the engine running, can I get a measurement from the pedal to the floor, before and after applying the brakes. My new Hydroboost with an AstroVan HB, and a 1-1/8 Corvette MC...

classicbroncos.com