Brake vacuum

[Steeveedee]

Backing down the driveway in neutral is in your future.

[forestb]

Originally Posted by Steeveedee

Backing down the driveway in neutral is in your future.

[theastronaut]

Delete the booster, use a smaller bore master cylinder (1" or 7/8") for more line pressure, move the master cylinder pushrod to the upper hole for more leverage on the master cylinder, swap to a semi-metallic pad that has a higher coefficient of friction.


The "need" for boosted brakes is one of the biggest wives tales in the C10/classic car world. Manual brakes can be more than strong enough with the simple things I listed.


When you swap from manual to power brakes, do people realize that a lot of what is involved with swapping to power brakes actually takes away the leverage that your foot would normally convert into braking power? Examples-

The stock master cylinder is 1" but the typical boosted system uses a 1.25" M/C. Basic hydraulic principles tell us that a larger bore will make less pressure at the caliper/wheel cylinder than the same amount of pedal pressure would make with a smaller stock 1" bore.

The pedal ratio is changed when you move the pushrod to a lower hole on the brake pedal- leverage that could be making more line pressure is taken away when you lower the mounting point.

Some brake kits, and all parts stores will tell you that ceramic pads are an "upgrade". They are, but only in terms of lifespan and amount of dust they make. Ceramic pads actually have the lowest coefficient of friction of all normal pad types. That requires you to press the pedal harder to create the same amount of friction between the pad and disc. Pad compound can make a huge difference in how well the brakes work; the last car I bought had fairly terrible braking performance- borderline unsafe. Everything was 100% stock and in good condition so it should've stopped just as well as my other identical car. I deglazed the rotors and swapped out the unknown pads for semi-metallic pads, did the procedure to bed-in the pads (this makes a big difference just by itself), and the brakes went back to performing like normal.


So... you take away significant braking power in 2-3 ways depending on what pad type you pick, than add braking power back with a booster. Makes a lot of sense... when you're a vendor selling parts.


Sticking with a small bore master cylinder for more line pressure (simple hydraulic principle at work there), leaving the pushrod in the top hole so that more of your applied pedal pressure makes it into the master cylinder, and using brake pads that are actually good at making friction (semi-metallic) will go a long way in making the truck stop really well without excessive pedal pressure. The pedal will also be more responsive and have better feel, boosted brakes usually feel fairly vague or are overly sensitive to pedal pressure. And if you still need more braking power or prefer less pedal pressure, you can drop down the master cylinder bore size for more line pressure.


My own C10 has a 1" bore dual circuit master cylinder to convert it to a split system, the stock/upper pushrod hole is used, stock rear drums, and the front has been converted to disc using CPP's standard drop spindle/disc kit that uses plain squarebody rotors and calipers. The pads are semi metallic. Nothing fancy. The pedal feel is excellent and pedal effort is normal. The brakes are easily powerful enough to make full use of the tire's grip well above any legal speed without needing excessive pedal pressure. Since the pedal is responsive I can modulate the pedal and hold the brakes at the limit of tire grip right before lock up in an emergency stop situation- something that is harder to do with less responsive boosted brakes.

[The Rocknrod]

That seems so counter intuitive in the hydraulics world because Area X Pressure = Force.

[theastronaut]

Originally Posted by The Rocknrod

That seems so counter intuitive in the hydraulics world because Area X Pressure = Force.

That is true at the caliper (output force), but not the master cylinder (input force).

https://www.joesracing.com/master-cylinder-math/

[SkinnyG]

Yes. A smaller master cylinder piston raises pressure IN the system. A larger caliper piston raises force OUTSIDE the system. You can, of course, do both.

[AcampoDave]

I run a manual disc/drum set up. It was easy. I bought a '71 manual disc/drum MC from the parts store and bolted it up. My brake pedal only has one hole for the push rod and I used it. My proportioning valve is from a squarebody.
It all works fine and takes no more effort to stop than any other manual brake vehicle, in fact pedal effort feels stock except I get the increased stopping power with less fade from the discs....and no heavy unactractive booster to stick my MC out over my valve cover.

[Old Radio Tech]

I have an 11" brake booster on my 65 Suburban 283. Every time I stepped on the brakes the booster stole all of my vacuum (15"). the booster wanted 18", so bad brakes and vacuum advance swung all over the place resulting in a bad running engine. installed a separate vacuum pump for the booster and now everything works fine. Vacuum for the timing is manifold vacuum. No other vacuum demands except PCV

[Cohi]

Originally Posted by forestb

This is the motor that I am running.

https://blueprintengines.com/product...ads-roller-cam

Im currently running the same engine at 5280 ft. I couldn't get more than 11 out of it when running a carb and ended up adding a pump.

[forestb]

Originally Posted by Cohi

Im currently running the same engine at 5280 ft. I couldn't get more than 11 out of it when running a carb and ended up adding a pump.

How much does elevation make a difference. I am at around 607’

[Steeveedee]

Elevation variation will yield less boost when the atmospheric pressure is lower, so at your elevation, you're pretty much getting the full benefit of that. Something else must be going on with your braking system.

[88Stanger]

Just want to throw this into the mix here.
I have had issues with brakes and vacuum on two different engines, my "69 C10 with 5.3 LS - it has maybe 10" to 11" of vacuum at idle (note Idle is set to 800-900rpm or so). I have tried every possible idea for vacuum brake booster I could imagine, size of booster, different size bore masters (note I am running Wilwood brakes and master) even tried a vacuum cannister and then out of frustration I bought a damn electric Vacuum pump.. and well the noise from that alone was not working for me... anyways, I spoke with Wilwood and basically came to the understanding that they require a min. of 15" but prefer 17" of vacuum. So, I was told to consider a Hydro-boost brake system. Needless to say, I got one and DAMN what a difference! It is not cheap, but works great!
So on my "66 I am running a 383 stroker with a cam that produces maybe 10" if lucky, so I have already purchased a full Hydro-boost system for it, I am convinced they are they are great.
Now just to add 1 more idea, I have learned about an electric stand alone Brake system that is now offered. Not sure on these, never tried it but those that have love it, but be ready to pay for it.
Anyways, just wanted to toss these ideas into the mix also. I am not sure but as some have mentioned they have great luck with min. vacuum but I am unlucky in this. LOL Wish you luck!!

[forestb]

Originally Posted by 88Stanger

Just want to throw this into the mix here.
I have had issues with brakes and vacuum on two different engines, my "69 C10 with 5.3 LS - it has maybe 10" to 11" of vacuum at idle (note Idle is set to 800-900rpm or so). I have tried every possible idea for vacuum brake booster I could imagine, size of booster, different size bore masters (note I am running Wilwood brakes and master) even tried a vacuum cannister and then out of frustration I bought a damn electric Vacuum pump.. and well the noise from that alone was not working for me... anyways, I spoke with Wilwood and basically came to the understanding that they require a min. of 15" but prefer 17" of vacuum. So, I was told to consider a Hydro-boost brake system. Needless to say, I got one and DAMN what a difference! It is not cheap, but works great!
So on my "66 I am running a 383 stroker with a cam that produces maybe 10" if lucky, so I have already purchased a full Hydro-boost system for it, I am convinced they are they are great.
Now just to add 1 more idea, I have learned about an electric stand alone Brake system that is now offered. Not sure on these, never tried it but those that have love it, but be ready to pay for it.
Anyways, just wanted to toss these ideas into the mix also. I am not sure but as some have mentioned they have great luck with min. vacuum but I am unlucky in this. LOL Wish you luck!!

What brand of Hydro-boost did you get?

[Steeveedee]

There are solenoid-assist brake systems in some of the newer cars. Old tech, in a way, like and electric rack and pinion. If I had this much trouble, I'd go to a manual system. It's always disconcerting when the engine stalls. My wife was driving our Astrovan (long gone) when the fuel pump quit. She managed to coast off the freeway and off an offramp with no hydra-boost or power steering.

[forestb]

I have a bad knee. Would switching back to manual breaks require more force than hydroboost breaks?

Also when I had my truck painted and my firewall shaved I had a captain fab bracket installed and I have no idea what things look like underneath it and what was done with my original bolt holes.

[theastronaut]

Originally Posted by Steeveedee

There are solenoid-assist brake systems in some of the newer cars. Old tech, in a way, like and electric rack and pinion. If I had this much trouble, I'd go to a manual system. It's always disconcerting when the engine stalls. My wife was driving our Astrovan (long gone) when the fuel pump quit. She managed to coast off the freeway and off an offramp with no hydra-boost or power steering.

I've had the engine stall in two different hydroboost trucks, once while halfway through turning into a driveway- lost power steering and brakes in a heavy C30 flatbed towing a trailer and really had to crank on the wheel and pedal to keep it out of the ditch beside the driveway. The other time was on the interstate in a crewcab dually pulling a trailer with a car on it and the truck starting having fuel issues. It didn't have a lockup torque converter so the engine would completely stop and the steering and brakes were totally unassisted even though the truck was still going 65-70 mph.

Originally Posted by forestb

I have a bad knee. Would switching back to manual breaks require more force than hydroboost breaks?

Also when I had my truck painted and my firewall shaved I had a captain fab bracket installed and I have no idea what things look like underneath it and what was done with my original bolt holes.

The pedal effort/force depends on the total mechanical advantage (hydraulic and pedal ratio combined) your foot has on brake pads, and how much bite the pads have. You can use a smaller bore master cylinder for more pressure in the system and calipers with more bore area so the pressure the master cylinder makes is multiplied more.

The one "drawback" to a low pedal effort manual system is that making the master cylinder smaller bore, or increasing the caliper's bore area (or both) will mean that you have to push the pedal farther since the master cylinder's volume is pushing less fluid for a given amount of travel. Brake fluid isn't compressible so it's not like the pedal will go to the floor before it makes pressure, but it's something to consider if you're trying to make a really low effort pedal.

[MT65]

Originally Posted by 88Stanger

Just want to throw this into the mix here.
I have had issues with brakes and vacuum on two different engines, my "69 C10 with 5.3 LS - it has maybe 10" to 11" of vacuum at idle (note Idle is set to 800-900rpm or so). I have tried every possible idea for vacuum brake booster I could imagine, size of booster, different size bore masters (note I am running Wilwood brakes and master) even tried a vacuum cannister and then out of frustration I bought a damn electric Vacuum pump.. and well the noise from that alone was not working for me... anyways, I spoke with Wilwood and basically came to the understanding that they require a min. of 15" but prefer 17" of vacuum. So, I was told to consider a Hydro-boost brake system. Needless to say, I got one and DAMN what a difference! It is not cheap, but works great!
So on my "66 I am running a 383 stroker with a cam that produces maybe 10" if lucky, so I have already purchased a full Hydro-boost system for it, I am convinced they are they are great.
Now just to add 1 more idea, I have learned about an electric stand alone Brake system that is now offered. Not sure on these, never tried it but those that have love it, but be ready to pay for it.
Anyways, just wanted to toss these ideas into the mix also. I am not sure but as some have mentioned they have great luck with min. vacuum but I am unlucky in this. LOL Wish you luck!!

I have used those “electric “ brake booster setups, works great, still driving it daily…actually bought 2 for the next project which never materialized …

[Old Radio Tech]

I tried the Dracarys 28146 electric vacuum pump first. It was cheap. Noise level was greater than my exhaust, and the vibration was so great I thought the inner fender sheet metal was going to start cracking. Spent the extra money and got the AC9001K Silent drive from Master Brakes. Very happy with the result. It runs for a few seconds after I turn off the engine due to a small leak at the booster/brake pedal piston, but not a bother. Brakes work great, good vacuum engine wise. I recommend.

[Cohi]

Originally Posted by forestb

How much does elevation make a difference. I am at around 607’

Not sure on the vac. I was getting 11inches with a 600cfm holley (from blueprint) on the same motor you have.

I believe I lose a 16% loss in HP due to elevation.

Best, Jon

[forestb]

Originally Posted by Old Radio Tech

I tried the Dracarys 28146 electric vacuum pump first. It was cheap. Noise level was greater than my exhaust, and the vibration was so great I thought the inner fender sheet metal was going to start cracking. Spent the extra money and got the AC9001K Silent drive from Master Brakes. Very happy with the result. It runs for a few seconds after I turn off the engine due to a small leak at the booster/brake pedal piston, but not a bother. Brakes work great, good vacuum engine wise. I recommend.

That looks nice and probably a better option than a hydroboost system. I just ordered a vacuum canister from comp cams and see if that works first. I am tempted to go back to a manual system but I fear that my fire wall is butchered under my existing bracket. I will also look into semi metallic pads. I have rear drums. Do they sell semi metallic pads for those also?

[forestb]

Originally Posted by theastronaut

Delete the booster, use a smaller bore master cylinder (1" or 7/8") for more line pressure, move the master cylinder pushrod to the upper hole for more leverage on the master cylinder, swap to a semi-metallic pad that has a higher coefficient of friction.


The "need" for boosted brakes is one of the biggest wives tales in the C10/classic car world. Manual brakes can be more than strong enough with the simple things I listed.


When you swap from manual to power brakes, do people realize that a lot of what is involved with swapping to power brakes actually takes away the leverage that your foot would normally convert into braking power? Examples-

The stock master cylinder is 1" but the typical boosted system uses a 1.25" M/C. Basic hydraulic principles tell us that a larger bore will make less pressure at the caliper/wheel cylinder than the same amount of pedal pressure would make with a smaller stock 1" bore.

The pedal ratio is changed when you move the pushrod to a lower hole on the brake pedal- leverage that could be making more line pressure is taken away when you lower the mounting point.

Some brake kits, and all parts stores will tell you that ceramic pads are an "upgrade". They are, but only in terms of lifespan and amount of dust they make. Ceramic pads actually have the lowest coefficient of friction of all normal pad types. That requires you to press the pedal harder to create the same amount of friction between the pad and disc. Pad compound can make a huge difference in how well the brakes work; the last car I bought had fairly terrible braking performance- borderline unsafe. Everything was 100% stock and in good condition so it should've stopped just as well as my other identical car. I deglazed the rotors and swapped out the unknown pads for semi-metallic pads, did the procedure to bed-in the pads (this makes a big difference just by itself), and the brakes went back to performing like normal.


So... you take away significant braking power in 2-3 ways depending on what pad type you pick, than add braking power back with a booster. Makes a lot of sense... when you're a vendor selling parts.


Sticking with a small bore master cylinder for more line pressure (simple hydraulic principle at work there), leaving the pushrod in the top hole so that more of your applied pedal pressure makes it into the master cylinder, and using brake pads that are actually good at making friction (semi-metallic) will go a long way in making the truck stop really well without excessive pedal pressure. The pedal will also be more responsive and have better feel, boosted brakes usually feel fairly vague or are overly sensitive to pedal pressure. And if you still need more braking power or prefer less pedal pressure, you can drop down the master cylinder bore size for more line pressure.


My own C10 has a 1" bore dual circuit master cylinder to convert it to a split system, the stock/upper pushrod hole is used, stock rear drums, and the front has been converted to disc using CPP's standard drop spindle/disc kit that uses plain squarebody rotors and calipers. The pads are semi metallic. Nothing fancy. The pedal feel is excellent and pedal effort is normal. The brakes are easily powerful enough to make full use of the tire's grip well above any legal speed without needing excessive pedal pressure. Since the pedal is responsive I can modulate the pedal and hold the brakes at the limit of tire grip right before lock up in an emergency stop situation- something that is harder to do with less responsive boosted brakes.

I have the cpp drop spindles also. Do you remember which brake pads you ordered for them?

[forestb]

This is what I was thinking of for the front

https://www.summitracing.com/parts/ado-17d52mh

And these for the rear

https://www.summitracing.com/parts/pwr-b228

Do these seem right?

[geezer#99]

Originally Posted by forestb

My engine is currently detuned for the breaking in process. I need to go another 200 miles before I can adjust the timing for better performance. It sounds like that might help increase vacuum.

Have you finished the breaking in and fine tuned your motor with more initial timing?

[Gconroy]

You can use manual brakes just fine. I was running disk in the front and drums in the back with 15 inch rims but changed to 20 all the way around and now it will not stop at all in a panic stop. I have an aggressive cam with 8 inches of vacuum and a vacuum power brake booster calls for 14 inches. So I purchased a right stuff hydro boost kit to cure the stopping problem. Few more days until it gets here.

[forestb]

Originally Posted by geezer#99

Have you finished the breaking in and fine tuned your motor with more initial timing?

Yes and it didn’t improve the vacuum.