500psi T-Bird Calipers

[ksagis]

I can measure from the centerline of the mc up to the top of the reservoir tomorrow for ya if you want Chuzie. Make sure it fits. I think the lower profile AstroVan reservoirs fit on it also as another option... I think??? Not even 68% sure tho... lol

Rockauto shows both of these MCs for diesel with HB, you running one of these MCs? If so, do you know if they have the usual 3.4" bolt spacing for GMs?

ACDELCO 18M742

ACDELCO 18M949

 

[ba123]

I'm not gonna say don't bother going large, but that's the whole point of the HB unit...you shouldn't need to.

I have the Wilwood that came in the WH kit and pretty sure it's only 1-1/8" if that and my Bronco stops on half a dime. You could breathe on the brake pedal and it's stopped.

Whatever you go with just make sure you're not gonna give yourself more of a headache getting it to match up.

 

[nvrstuk]

ksagis- Bolt spacing is the same as the GM/ AstroVan HB unit.

The positive benefit of the slightly larger mc with the HB is that you have more brake pedal feel with the larger dia bore mc. It's not breathe on it and you are stopped and by no means is it as much pedal pressure to stop as a larger vacuum boost unit- it's just not so touchy.

What's important is that we all get used to whatever pedal pressure and pedal stroke we have and they work great. I'd go either way but like previously mentioned the rusty, potentially leaky, heavy cast iron one was my last choice.

I'll get a pic and measurement in a bit.

 

[chuzie]

I have the Wilwood that came in the WH kit and pretty sure it's only 1-1/8" if that and my Bronco stops on half a dime. You could breathe on the brake pedal and it's stopped.

That's actually part of my concern. On the rocks, a sudden brake application could send me end over end. I'd prefer something with more finesse.

I can measure from the centerline of the mc up to the top of the reservoir tomorrow for ya if you want Chuzie. Make sure it fits. I think the lower profile AstroVan reservoirs fit on it also as another option... I think??? Not even 68% sure tho... lol

That would be super helpful just to be sure. I have a 2" body lift and placed a piece of 1" square stock on top of the Corvette MC. I have the clearance, but extra eyes on this would be great.

BTW- As expected, my rear brakes are only achieving 1500psi whereas before they were showing over 2,000. The issue definitely resides on that rear port.

Just got off the phone with CPP.
- Confirmed rear port is for rear brakes and front port is for front brakes
- Stroke + Bore both 1-1/8"
- Asked why front vs rear ports matter if it's a 50/50 MC - Said it wasn't 50/50.
- Asked what the proportions were - Had no data available.
- Couldn't explain the lack of volume, but assured me if I had 2500 at MC, everything was fine.
I laughed and we parted ways.

 

[ksagis]

One thing we haven’t touched on with respect to pedal “touchiness” is the the piston size in the hydro. They come in a ~1.6” and ~1.8” diameter power piston.

 

[ksagis]

That would be super helpful just to be sure. I have a 2" body lift and placed a piece of 1" square stock on top of the Corvette MC. I have the clearance, but extra eyes on this would be great.

Don’t think body lift plays into MC to hood clearance since firewall that the MC is bolted to goes up with body lift and so does the hood?

 

[chuzie]

Don’t think body lift plays into MC to hood clearance since firewall that the MC is bolted to goes up with body lift and so does the hood?

Crap! I totally forgot about that minor detail

 

[chuzie]

One thing we haven’t touched on with respect to pedal “touchiness” is the the piston size in the hydro. They come in a ~1.6” and ~1.8” diameter power piston.

Maybe WH will chime in for clarification

 

[ksagis]

The positive benefit of the slightly larger mc with the HB is that you have more brake pedal feel with the larger dia bore mc. It's not breathe on it and you are stopped and by no means is it as much pedal pressure to stop as a larger vacuum boost unit- it's just not so touchy.

I'll get a pic and measurement in a bit.

Agreed on larger bore will help with pedal feel. And getting my on pedal ratio sandbox - I think getting pedal ratio down from factory 6:1 is another knob to turn.

 

[Apogee]

The two easiest ways to increase y

That's actually part of my concern. On the rocks, a sudden brake application could send me end over end. I'd prefer something with more finesse.

That would be super helpful just to be sure. I have a 2" body lift and placed a piece of 1" square stock on top of the Corvette MC. I have the clearance, but extra eyes on this would be great.

BTW- As expected, my rear brakes are only achieving 1500psi whereas before they were showing over 2,000. The issue definitely resides on that rear port.

Just got off the phone with CPP.
- Confirmed rear port is for rear brakes and front port is for front brakes
- Stroke + Bore both 1-1/8"
- Asked why front vs rear ports matter if it's a 50/50 MC - Said it wasn't 50/50.
- Asked what the proportions were - Had no data available.
- Couldn't explain the lack of volume, but assured me if I had 2500 at MC, everything was fine.
I laughed and we parted ways.

There are several ways to improve modulation of the brakes, where we're talking about the amount of pedal force required to achieve any given brake torque. A larger bore master cylinder will require more pedal effort, but will also have less pedal travel, so it will improve brake modulation if they currently feel too touchy. Similarly, a lower CoF brake pad will require more caliper pressure to produce any given brake torque, so reducing the brake pad coefficient of friction can be another relatively inexpensive way to improve modulation. Another option, albeit not necessarily an easy one to accomplish, is that you can numerically lower the pedal ratio, thereby giving yourself less mechanical advantage over the booster/MC, and producing lower input forces for any given pedal force. Last but not least, you can reduce the caliper piston area, thus requiring higher pressures to achieve similar clamping forces and therefore brake torques for any given input.

As for the conversations regarding "proportioning" on master cylinders, they don't have any proportioning functionality. Most tandem master cylinders consists of two piston sliding in the same bore, so they both push the same amount of fluid and produce the same amount of pressure. The 50/50 you see advertised on various websites for MC's is referring to the volumtric ratio of the reservoirs, meaning they hold the same amount of fluid front and back. The amount of fluid used is determined by the piston diameter/bore and stroke, not the reservoir, which merely accounts for pad wear and the associated piston extension to account for it.

For the record...I disagree with the CPP tech...everything is not fine.

 

[ntsqd]

FWIW, because there's an exception to nearly everything, the OEM m/c on my '96 FSB and the F trucks of similar age have the proportioning valve built into the inverted flare adapter between the m/c body and the rear brake tube. As those p-valves aren't always easy to find I suggest NOT using one of those m/c's on anything.

 

[nvrstuk]

That's actually part of my concern. On the rocks, a sudden brake application could send me end over end. I'd prefer something with more finesse.

That would be super helpful just to be sure. I have a 2" body lift and placed a piece of 1" square stock on top of the Corvette MC. I have the clearance, but extra eyes on this would be great.

BTW- As expected, my rear brakes are only achieving 1500psi whereas before they were showing over 2,000. The issue definitely resides on that rear port.

Just got off the phone with CPP.
- Confirmed rear port is for rear brakes and front port is for front brakes
- Stroke + Bore both 1-1/8"
- Asked why front vs rear ports matter if it's a 50/50 MC - Said it wasn't 50/50.
- Asked what the proportions were - Had no data available.
- Couldn't explain the lack of volume, but assured me if I had 2500 at MC, everything was fine.
I laughed and we parted ways.

Just saw this post, sorry Chuzie. I'll go out in the shop tonight and measure it for ya

 

[nvrstuk]

Here ya go...

Since my HB/MC is over 8" offset to the DS these measurements should be more relevant to you since my hood is darn close to stock ht where this is mounted in relation to the fender.

The steel rule measurement (3rd pic) is probably the most inaccurate pic I have for ya. The steel rule laying on top of the lid is not quite level but it shouldn't be because the mc mounts at an angle to the ground so really this pic doesn't help at all.

Hope the others do. Width of the level might help huh?? Level is 1 9/16"

 

[ksagis]

Here ya go...

Since my HB/MC is over 8" offset to the DS these measurements should be more relevant to you since my hood is darn close to stock ht where this is mounted in relation to the fender.

The steel rule measurement (3rd pic) is probably the most inaccurate pic I have for ya. The steel rule laying on top of the lid is not quite level but it shouldn't be because the mc mounts at an angle to the ground so really this pic doesn't help at all.

Hope the others do. Width of the level might help huh?? Level is 1 9/16"

Your inner fender liners are long gone!

 

[nvrstuk]

Your inner fender liners are long gone!

Easily one of the most appreciated mod's ever done!! Required cause my tires travel up a couple inches higher than the stock fenders would allow.

 

[chuzie]

Here ya go...

Thanks brother! Looks like I should have enough space. Ordering now. Will report back in a few days.

 

[ZOSO]

I stopped reading around page 4. But 1 thing I can see is too small of a bore on MC or too short of a stroke. Are you getting the full travel out of the pedal and HB? When I did the tbird swap on my 79 back in 03 it was a lot of trial and error getting the correct volume to the tbird calipers. 1-1/8 could be enough volume if the stroke on the MC is long enough. If you cant get the stroke for volume, up the piston size. The larger pistons need more volume and less pressure to do the same amount of work. Now with that being said it may have an affect on rear brake performance.

 

[ksagis]

Here ya go...

Since my HB/MC is over 8" offset to the DS these measurements should be more relevant to you since my hood is darn close to stock ht where this is mounted in relation to the fender.

The steel rule measurement (3rd pic) is probably the most inaccurate pic I have for ya. The steel rule laying on top of the lid is not quite level but it shouldn't be because the mc mounts at an angle to the ground so really this pic doesn't help at all.

Hope the others do. Width of the level might help huh?? Level is 1 9/16"

In the pic with the steel rule, is the 5.5" from top of MC measuring to centerline bore of MC?

And one more, look's like the pot closest to the firewall is the bigger one, is that the one you ran to front brakes?

 

[chuzie]

Are you getting the full travel out of the pedal and HB? When I did the tbird swap on my 79 back in 03 it was a lot of trial and error getting the correct volume to the tbird calipers.

I'll know for sure once I pull the MC and manually test the stroke.

And one more, look's like the pot closest to the firewall is the bigger one, is that the one you ran to front brakes?

Yes, firewall port was initially going to front brakes.

 

[ZOSO]

See you just answered this question

Another question is did you pull the master off and measure the stroke of the hydroboost? If master is 1-1/8" stroke HB should be close to that. If not I'd start there.