47-55.1 Master Cylinder/Booster HELP!!

[dsraven]

If your pedal has a coiled style return spring on its pivot and the pedal always returns to its top position then that should be fine. If not then you will need a return scoring of some sort to keep the pedal at the top of its stroke whenever your foot is off the pedal. The larger bore master cylinder will displace more fluid which will make pedal effort a bit more for the same stopping power as well as have an effect on the amount of pedal travel required. It does, however need to be seized properly for the calipers. An adjustsble prop valve is nice to dial in the brake bias front to rear. Just mouht it under the truck because once set you don't usually need to mess with it.

[NeoJuice]

Originally Posted by dsraven

bench bleed the master before install. they usually come with some plastic fittings you can screw into the ports and some line that you plug into those fittings and the other end goes back into the top of the reservoir. you would push the piston with a screwdriver or some kind of tool like that. when you stop getting air bubbles the master is bled. sometimes you gotta walk away for a bit because the master keeps picking up the fluid from the reservoir that is already full of bubbles from pumping it.
install a return spring on the pedal to keep the pedal at the top of it's stroke. make sure there is a rubber stopper on the arm so the pedal stops at the same place every time. otherwise you adjust the booster and then something moves a bit and the pedal height changes, then the brakes act up again because the free play on the pedal is either gone or more than it used to be. the original pedals had a stopper on the arm that bottomed against the firewall for this purpose and also so the brake light switch worked properly.
you need to start by getting the pedal height adjusted so it doesn't interfere with the master cyl to booster adjustment. you could even take the pedal off for now just to ensure it isn't interfering. then when the master to booster is correct install the pedal and get the pedal to booster adjustment done.it is kinda important to have the pedal stopper and return spring on there so you can be sure the pedal isn't slightly pressing on the booster but also doesn't have a load of free play either and is also returning completely every time.

DSRaven,

That's a good idea. I will remove the pedal from the back of the booster then I can hopefully find a depth gauge tool to set the gap between the Master and the booster. After that is done then I can hopefully adjust the pedal properly. I'm not sure about the return spring though what your talking about.

[1project2many]

I will apologize in advance for the long post. I take brakes seriously...

I've read online that some people have no problems with there pedal with low vacuum around what I'm running and others that do. I guess could that be due to where they altitude wise? Some people have reserve canisters and some people have the vacuum pump kits. I mean it's a SBC 350 not a blown out 454 with a supercharger that produces no vacuum. I guess I will need to see once I get the new Master installed.

There are many variables that factor into pedal feel and stopping power. Whether or not a particular level of vacuum is enough to allow easy stopping and to prevent creeping at a stop can depend on the type of booster (hydraulic or vacuum) (single or double), size of the diaphragm, master cylinder bore size(s), caliper bore size(s), rotor diameter(s), auto vs manual transmission, engine idle rpm, torque converter stall speed, and even the final drive ratio of the axle. To read internet forums and decide that your one-off build will behave the same as someone else's vehicle takes some experience and some precision guesswork imo.

From what I've read online and how I had the old MC plumbed the larger front bowl is for the front brakes and the booster side is for the rear brakes.

If there is one fact the internet will argue over until artificial intelligence displaces us, it is which port connects to which half of the vehicle. There is no standard answer. But there are clues. Yes, if the master cylinder is from a disc/drum car and the reservoirs are divided, the larger reservoir is for the disc brakes. If the master cylinder is from a disc/disc car expect a shared reservoir or both reservoirs the same size. If you have a quick takeup master cylinder the port closest to the booster is front brakes. Next step requires knowing the bore sizes. In almost all vehicles a port connected to the larger bore is almost always for front brakes. If both bores are the same size like in the Corvette master, the OEM application often routed the forward port to the front brakes.

Issue of not having a disc/disc master cylinder instead of a disc/drum master cylinder.

I'm going to be a little tough on ya here, but master cylinder and caliper sizes need to be selected to work together, not based "disc/disc" or "disc/drum."

Your rear calipers came from a vehicle with:
2.5" diameter rear caliper pistons on 11" rotors
3" diameter front caliper pistons on 11" rotors
1.125" X 1.125" bore master cylinder

Discounting the proportioning valve, more pressure will be generated at the front pads creating more braking force at the front wheels. This makes sense because more of the vehicle weight is on the front wheels.

As best I can tell, your front calipers came from a car with:
3/4" diameter rear wheel cylinders in 9.5" drums
2.50" diameter front caliper pistons on 10.5" rotors
7/8" X 7/8" bore master cylinder

Discounting the proportioning valve, more pressure will be generated at the front pads creating more braking force at the front wheels. This makes sense because more of the vehicle weight is on the front wheels.

If I'm reading correctly your system with the Corvette master will be:
2.5" diameter rear caliper pistons on 11" rotors
2.5" diameter front caliper pistons on 10.5" or 11" rotors
1.125" X 1.125" bore master cylinder

Discounting a proportioning valve, this system will either generate the same pressure at both front and rear calipers and similar brake torque at all four wheels, or will generate more braking on the rear wheels. This DOES NOT make sense because there is substantially more weight on the front wheels. Additionally, your caliper bore to master cylinder bore ratio is 2:1 which is on the "stiff" side. This may be ok depending on booster configuration but most folks tend to enjoy something in the neighborhood of 3.0:1 with a vacuum booster.

Although the picture you posted shows several different part number m/cyls I cannot tell which you have. Some are the same bore size as the Corvette master, some are smaller. Without measuring the bore size the only way to judge whether or not you will see a change is to swap the master cylinder.

If I were building this vehicle I would look for a master cylinder with a stepped bore. I would connect the rear brakes to the larger bore to reduce pressure at the rear brakes. I would connect the front brakes to the smaller bore to provide increased braking at the front wheels. I would look for a 1" X 7/8" first. I would probably opt for a 1.125" X 1" last.

I was thinking about it yesterday I think I might know what my issue's with my brakes might be.

Anyone who spent time in repair shops when the vehicles regularly using that style rear caliper were still on the road will probably remember fighting with insufficient brake pedal. The park brake has to be adjusted properly and be able to apply and hold the rear rotors or you will not get a good brake pedal. The apply screw in the caliper works as a ratchet to push the piston out toward the rotor. It can take several applications of the park brake to "auto adjust" the rear caliper pistons. Once the park brake holds you can do a final bleed of the rear brakes.

I will need to source one of these tools. https://www.amazon.com/Power-Brake-B.../dp/B079QGXY55 but no one seems to have one locally or even know what it is.

Also, as far as that special tool goes, you probably don't need one. An old brake booster push rod will work. Cut off the master cylinder end square then drill and tap a hole in the center for a #10 machine screw. You can adjust the screw in or out then use trial and error to determine what length pushrod is needed.

IME you can usually look at the amount the pushrod is protruding from the booster then compare it to the depth of the hole in the master to determine whether or not you have the correct pushrod. They're usually either close or very wrong.

What are peoples thoughts on vacuum and boosters? I'm hoping that swapping out the MC for the corvette one will fix my issue.

Before changing the master I would use hose pinch pliers or vice-grips with fuel line over the jaws to pinch the rear brake hose. If the pedal apply height improves then I would investigate the possibility that the rear brake caliper pistons are not adjusted properly or that there is still air trapped in the rear brakes. Based on the caliper sizes alone, I would not expect that a 1.125" bore master cylinder is required to provide good pedal application height. In fact the application height for that combination may be "right at the top."

[NeoJuice]

Originally Posted by 1project2many

Before changing the master I would use hose pinch pliers or vice-grips with fuel line over the jaws to pinch the rear brake hose. If the pedal apply height improves then I would investigate the possibility that the rear brake caliper pistons are not adjusted properly or that there is still air trapped in the rear brakes. Based on the caliper sizes alone, I would not expect that a 1.125" bore master cylinder is required to provide good pedal application height. In fact the application height for that combination may be "right at the top."

I will give this a try. Thank you for the tip. Here or there the master will need to be replaced because I dont know if it's a disc-drum or drum-drum.

[NeoJuice]

1project2many,

I thank you for all the information in the post. That's allot of information to absorb. Now I'm really confused. I'll try to respond to some of your information.

1. The new Master is a NUP 39052 with information attached.
2. As for the front end all I really know is it's a TCI mustang II front end. I would need to measure the front disc's or call them to find out what calipers they used and disc size.
3. The rear calipers if I remember correctly without going to my receipts I believe is off a 1980 eldorado/Seville.
4. With the corvette master I dont believe both ports are the same size. I will plumb the larger bowl to the front breaks as I did before. But your stating that I should plumb them opposite?
5. The kit that was on the truck states 7" Dual Diaphragm Booster.

Here is a link to the kit. http://mbmbrakes.com/pbufmct4754-194...er-brake-unit/

I dont have disc-drum or drum drum I have disc-disc.

As always everyone that you for your help. I mean I'm mechanically inclined but this is a little more tricky then I thought.

[1project2many]

2. As for the front end all I really know is it's a TCI mustang II front end. I would need to measure the front disc's or call them to find out what calipers they used and disc size.

You should do this. It can be a big safety issue if the rear brakes lock up too quickly.

4. With the corvette master I dont believe both ports are the same size. I will plumb the larger bowl to the front breaks as I did before. But your stating that I should plumb them opposite?

The factory assembly manuals I viewed for some early Corvettes show the front port connected to the front brakes.

Here or there the master will need to be replaced because I dont know if it's a disc-drum or drum-drum.

It might be easier if you stop thinking of the master in terms of disc/drum or drum/drum. I realize many people describe them this way but there are disc/drum masters that are configured very close to your Corvette disc/disc master. The differences are going to be in bore size(s) and in the reservoir setup (large/small for disc/drum). And small reservoir masters can work for the rear brakes of a four wheel disc car, but you may have to check the fluid more often.

[NeoJuice]

Originally Posted by 1project2many

You should do this. It can be a big safety issue if the rear brakes lock up too quickly.




The factory assembly manuals I viewed for some early Corvettes show the front port connected to the front brakes.


It might be easier if you stop thinking of the master in terms of disc/drum or drum/drum. I realize many people describe them this way but there are disc/drum masters that are configured very close to your Corvette disc/disc master. The differences are going to be in bore size(s) and in the reservoir setup (large/small for disc/drum). And small reservoir masters can work for the rear brakes of a four wheel disc car, but you may have to check the fluid more often.

I'll call TCI and get the information from them on what make/model the calipers are and disc size.

So you mean the front port being the 9/16 in. - 18 port? the 1/2-20 port is next to the booster.

ill post back once I have more information.

[dsraven]

the TCI MII front end could have the smaller, S10, style calipers with 2 1/2" pistons or the larger "big bore" calipers with the 2 3/4" pistons. it would be fairly easy to measure yourself. the same goes for the front discs. you can also do the same for the rear brakes with a simple "crawl under and look" with a tape measure. once you know this you can figure out better what you will need for the master cyl bore diameter. I would say though that the corvette master should work. the old master may work as well, like 1project says, it would mean possibly checking the fluid more often because one reservoir is smaller than the other. I do that on every oil change anyway, just me though. a lot of the disc/drum masters have a built in residual valve in the port for the rear brake line which, if you're gonna chuck the old master anyway, can easily be removed and used for the disc/disc set up. here is a link to a camaro site with instructions on how to remove the tube flare seat and then get at the residual valve underneath that. the seat would need to be used again so be careful doing the remove/install. this link explains it pretty well using a tube flare nut and a small screw with some washers.

http://www.camaros.org/forum/index.p...19259#msg19259

or just strap on the corvette master cyl, bleed it, and try it.

for comparison, from what I can find on rock auto, to compare apples to apples, the cadillac that your rear disc set up came from had front calipers with a piston size of 2.48", so likely the same size as the set up you have, more or less, unless you have the big bore kit up there. the rears had a piston size of 2.12". so that tells me the rear calipers you have are 2.12 piston size unless somebody did a big brake upgrade. the eldorado master cylinder spec'd with a 1" bore. the front and rear discs were 10.5" diameter. so this tells me your rear discs are 10.5" diameter and likely match the front discs you have for diameter, same as the eldorado your rear set up is from. you could do a "for sure" measure of what you have and go from there.
the rock auto site may be some help if you are doing a comparison of vehicles that come with the same size rotors as you have, the same size caliper pistons as you have and then compare the master cylinder bore and try to figure it out from there. if you go with the larger bore master cyl your pedal travel will be less but the effort will be more for the same amount of brake application pressure as the smaller 1" bore master cyl. with the smaller bore master the pedal travel would be more but the effort would be less. make sense?

[1project2many]

So you mean the front port being the 9/16 in. - 18 port? the 1/2-20 port is next to the booster.

I would say yes. The "front" port is farthest from the booster and closest to the front of the car in the original configuration.

This is the master and original style booster in a '75 Corvette:

[NeoJuice]

Ok, I just got off the phone with TCI. Here is the information I got from them.

Rotors has two options:

10 3/4" - 82-87 Camero
11" - 78-84 Ford Granada rotor with Chevy bolt pattern. (can be purchased at places like summit, jegs, speedway motors)

-78-80 ford Granada inner race bearing (for both rotors sizes)
-78-80 ford Granada outer bearing for the 11"

-82-87 Camero outer bearing for the 10 3/4" rotor

Calipers:

78-80 GBody Malibu or Buick Regal (uses same pads)

[1project2many]

Neojuice, I believe this is almost the same as was posted in your build thread. The difference is the "small" rotors are 1.75" instead of 10.5". So you could replace 10.5" rotors in my evaluation with 10.75" rotors.

I believe it's a good idea to use a stepped bore master and connect it such that the front brakes receive greater pressure than the rear brakes. This will provide for better braking in light and heavy braking. A proportioning valve can still be used to reduce rear brake pressure in panic stops, but the balance and the "around town" feel would be better imo with higher pressure in the front. If you try the Vette m/cyl and still want improvements this would be the direction I would go.

[NeoJuice]

Originally Posted by 1project2many

Neojuice, I believe this is almost the same as was posted in your build thread. The difference is the "small" rotors are 1.75" instead of 10.5". So you could replace 10.5" rotors in my evaluation with 10.75" rotors.

I believe it's a good idea to use a stepped bore master and connect it such that the front brakes receive greater pressure than the rear brakes. This will provide for better braking in light and heavy braking. A proportioning valve can still be used to reduce rear brake pressure in panic stops, but the balance and the "around town" feel would be better imo with higher pressure in the front. If you try the Vette m/cyl and still want improvements this would be the direction I would go.

1project2many,

I appreciate all your time and knowledge & expertise answering my questions. I will try the vette m/c and use the bigger 9/16 front bowl for front and 1/2' bowl for rear.

When I'm doing the bleeding I'll measure the rotors. I'm not pulling the calipers off to measure the inner pistons.

[paintman]

Can I step in here with a pertinent question. I see someone posted about quick uptake MC's. I basically have the same setup although it is disc/ drum,, with GM metric calipers. Does anybody know of a quick uptake MC that fits into a 7" booster. I tried an s10 quick uptake, but the nose of that MC would not fit into my 7" booster. I can only assume that it would fit into an 8" but I have no room as my MC and booster are mounted under the cab. I guess my next move would be non low drag calipers?

[1project2many]

Does anybody know of a quick uptake MC that fits into a 7" booster.

Hmmm... Interesting question. Not off the top of my head. Most of the quick takeup masters I've seen are paired with large boosters. I would suggest looking at Dodge products though. They also used the quick takeup system in the '90s and their engineers seem more likely to mix n match parts.

I guess my next move would be non low drag calipers?

Yeah, about that. Lots of scary warnings about low brake pedal when putting "regular" master with quick takeup calipers. I warn people of the same potential problem. But I've tried it a few times and in my case the pedal has ended up slightly lower but not low enough to feel like something is wrong. Currently I have a '99 suburban using stock rear brakes, 2013 Silverado front brakes, and a 1.125" bore master that was used on many GM vehicles (Autozone NM1521). Front brakes are dual piston quick takeup style and the pedal apply height is about halfway down. Getting rid of the quick takeup master was one of the best things I've done. The sluggish response of the old system is completely gone now. I have to be careful not to apply the brakes to quickly if someone stops short.

[NeoJuice]

Update- I got the corvette master cylinder bench bled and re-installed in the truck. I flared up some new lines and used the joiners to connect them to the existing lines. I pumped the pedal a couple times to check for leaks and none found at this time.

I haven't had the chance to bleed the lines yet because I was waiting for my vacuum pump to arrive. It arrived yesterday from Jegs. Before I proceed with bleeding the lines I want to verify that I have all the lines plumed correctly. See attached image. This is how I have it plumbed in the truck.

I'll get a plug for the back of the carb and plum the hose directly from the vacuum pump to the booster.

[NeoJuice]

One thought that just occurred to me. Should the 2lb residual valves be closer to the proportioning valve or like in the image further away.

My rear 2lb valve is near the back of the truck currently. I put it up near the rear b/c the rear calipers could possibly be higher or at the same elevation as the master cylinder and I didn't want a possibility of loosing some pressure on the brake pedal.

Thoughts?

[paintman]

Alot of people say the res. valves are supposed to be as close to the MC as possible. Although, the same people that say this can't give any good explanation as to how the location makes any difference. If you do a google image search you will see that they are place all over. I placed my front res. valve about 3 inches away from the MC. My rear Res. valve is about 24" away, and after the prop valve.

[paintman]

Curious to know why you think you need a vacuum pump. Not trying to be a smart ass. Just going through some brake issues myself.

I have also been told I need a vacuum pump. However, It seems to me that if after you bleed the brakes and have a rock hard pedal, you should still have a rock hard pedal once engine is running if you have low vacuum. No? After all the booster is there to help pull the pedal down for you. Thus making the pedal easier to depress.

[NeoJuice]

After I got the truck tuned by a buddy it's running 10-12" vacuum and 32 degrees total timing and 10 degrees base timing. The low vacuum is because of the cam the previous owner put in the truck. When the truck was running I had little to no brakes at all. You need at least 18 inches of vacuum to properly operate the booster as far as I'm aware. The Leed pump does 25"hg

Between swapping out the master cylinder for the corvette MC and adjusting the booster push rod and adding the vacuum pump I hope to resolve all my brake issues.

I went with the LEED pump b/c it's quiet. I could have got another style and paid less but I didn't want a noisy a$$ pump and I also wanted a simple two wire hookup in a self contained unit. I didnt want to deal with something like this https://www.performance-world.com/El...p-p/841001.htm

I hope this weekend to get the pump installed and all the brakes bled. Then I can test from there.

Thinking about it after the fact I should have spent that money on a OEM style CAM, I had it all ripped apart earlier when I did the timing chain & I would probably be ahead in the $$ dept lol.

As you can see in the video it's got a pretty good lump in the idle.

https://photos.app.goo.gl/BCa9hN5qPyCJ6zU37

[NeoJuice]

Originally Posted by paintman

Curious to know why you think you need a vacuum pump. Not trying to be a smart ass. Just going through some brake issues myself.

I have also been told I need a vacuum pump. However, It seems to me that if after you bleed the brakes and have a rock hard pedal, you should still have a rock hard pedal once engine is running if you have low vacuum. No? After all the booster is there to help pull the pedal down for you. Thus making the pedal easier to depress.

From Wiki:

A brake booster is an enhanced master cylinder setup used to reduce the amount of pedal pressure needed for braking. It employs a booster set up to act with the master cylinder to give higher hydraulic pressure to the brakes and/or lower force applied on the brake pedal through a brake booster push-rod. The brake booster usually uses vacuum from the engine intake to boost the force applied by the pedal onto the master cylinder or may employ an extra vacuum pump to enable it. Without the engine running the brake pedal feels very hard and ineffective on the braking capability. An "active" booster is a non "conventional" booster where a solenoid is used to open the booster air valve to automatically push the master cylinder forward to perform some forms of dynamic stability control.

[paintman]

Thanks Neo! I guess I need to invest in a vacuum guage and see whats going on. I also have a lumpy cam in my 292 six banger. Although, even with the wiki explanation of how a booster works, I just can't get my head wrapped around...........How can it be when the engine is off, and you have a hard pedal, logic would say if when the engine is running and there is not enough vacuum, you should still have a hard pedal. Not a soft pedal.

[NeoJuice]

Best thing to do would be to get a vacuum gauge hooked up and see what your pulling.

My buddy who set the timing & carb adjustments on my truck came to my house with a timing light and vacuum gauge. I know there are lots of videos on you tube about troubleshooting engine issues with just a vacuum gauge.

[NeoJuice]

Originally Posted by paintman

Thanks Neo! I guess I need to invest in a vacuum guage and see whats going on. I also have a lumpy cam in my 292 six banger. Although, even with the wiki explanation of how a booster works, I just can't get my head wrapped around...........How can it be when the engine is off, and you have a hard pedal, logic would say if when the engine is running and there is not enough vacuum, you should still have a hard pedal. Not a soft pedal.

DsRaven? he might be able to chime in on this. I'm no expert or claim to be one and my advice should not be used to operate a motor vehicle in any way lol.

[1project2many]

It seems to me that if after you bleed the brakes and have a rock hard pedal, you should still have a rock hard pedal once engine is running if you have low vacuum. No? After all the booster is there to help pull the pedal down for you. Thus making the pedal easier to depress.

Sort of. You can probably imagine drinking soda through a straw. You create a vacuum at one end of the straw and air pressure at the other end forces your drink up the straw and into your mouth. Now pinch the straw in the middle. Create the vacuum on one side but nothing goes through the straw. Release the pinch and what happens? Well it depends on how much vacuum you're creating. If you create a little vacuum then the drink will flow slowly. If you create a bunch of vacuum the drink flows quickly.

In a booster there is a valve which seals the booster off from air pressure like like your hand pinching the straw. The engine creates vacuum on the master cylinder side of the valve and air pressure applies the brakes when the valve is opened. If the engine is only producing a small amount of vacuum then you will get assist, but it will be very little and the brakes will feel like they apply slowly. Things can get a little more complicated because the brake booster has a check valve on the vacuum side which "stores" vacuum. If you were to rev the engine and snap the throttle closed you would create high vacuum for a very short time. This increased vacuum will get "trapped" in the booster and when you apply the brakes they will apply just fine. But if you release and apply the brakes again the "trapped" vacuum will be depleted and the brakes will again apply slowly. So the pedal may not be rock hard after startup, but pressing the pedal two or three times in a row would cause it to apply slowly and with very little assist.

How can it be when the engine is off, and you have a hard pedal, logic would say if when the engine is running and there is not enough vacuum, you should still have a hard pedal. Not a soft pedal.

Both logic and experience tell me the same thing. If I started the engine and the pedal was substantially easier to apply after two or three applications I would not say there is insufficient vacuum for the brakes. I would look elsewhere for the cause of a too-soft pedal.

[mick53]

I bought my vacuum pump from Master Power Brake. They say it doesn't need a reservoir but I will probably put one in. It came with a gauge for testing or you can leave it on there. It's not a very nice gauge.I plan on taking the engine out of the loop. I'm running a 4-71 blower on my 292 so vacuum is a problem. I think it was about $600.