47-55.1 Master Cylinder/Booster HELP!!

[NeoJuice]

Hello fellow forum members,

I really hit a road block yesterday when it comes to my brakes and I need some help with what to do with my master cylinder/booster in my truck. I was getting ready to plum all my break lines and thought I would pull out the MC/Booster last night to bench bleed it before getting started.

As some of you might know I purchased this truck from a guy who started the build but lost interest and I wanted to make sure I had the correct unit in the truck for my disc/disc setup.

Here is the link to my build thread just in case along with pictures of my rear disc setup on the last page.

http://67-72chevytrucks.com/vboard/s...d.php?t=723325

I finally got in all my break parts like copper/nickle break line & all my fittings organized to start the job. I also got in my flaring tool from eastwood tools & 2lb residual valves, 3 way splitters & frame clips so I was totally ready to start the job.

The only part I havent figured out yet is what I was also going use for a proportioning valve. I was thinking about using this one from wilwood because it also has a built in brake switch.

http://wilwood.com/MasterCylinders/M...emno=260-11179

Ok so here is the problem. The MC/Booster he put in the truck was for as far as I can tell for Disc/Drum setup. On the MC/Booster the only informaiton I can find is on the rubber plunger it says MBM and then on the bracket MBMPRAFMCT4754.





So looking up MBMPRAFMCT4754 on the MBM site says that its the frame bracket but it also lists all the MC/Boosters being only disc/drum or drum/drum.

http://mbmbrakes.com/search.php?Sear...MBMPRAFMCT4754

So what do I do now? Can I just replace the master cylinder and keep the booster? Should I call MBM and see what they say? Also I noticed when i tried to push in the rod on the booster it wouldnt move in/out. Is that because there is no vacuum or fluid in the booster? looking at the fluid bowls i believe the front one was larger then the rear if I recall correctly.

Or I could just be freaking out over nothing and it has this MC on it but i would need to find a stamping of some sort or model number.

http://mbmbrakes.com/mc2912h-gm-univ...er-1-1-8-bore/

Or scap it for a underhood booster/pedal assembly?

Thank you for your help and time.

[OrrieG]

I do not think the booster makes any difference but you will need a disc/disc MC. I think most kits use a GM one for earlier Corvettes. You can tell because the reservoirs and outlet fitting are the same size. Ideally the MC is mated to the correct calipers so the fluid volume being pumped is correct. I would start with IDing the calipers and make sure the MC is correct.

[NeoJuice]

Front end is TCI Mustang II and the rear calipers are 1980 Cadillac Seville.

If you look at the second image on the MBM link below I believe the front reservoir is larger like in the picture. Now I just need to find a stamping of what MC it is. I'm going to try and phone MBM today and find out

http://mbmbrakes.com/mc2912h-gm-univ...er-1-1-8-bore/

[dwcsr]

I see you have the clevis in the wrong hole or the brake arm , It goes into the other one, The part number is for the bracket only, its for 55-59 trucks, the booster is universal works with almost any master, The master you need is for disc/disc so just get a master

the wildwood prop valve works well on these systems

[Rude Dude]

The booster doesn't have a thing to do except use vacuum to aide in the pressing of plunger in M/C. Your master cylinder looks like corvette style so the determination weather it is disc/drum or disc/disc would be in the proportioning valve and I noticed you do not have one on.

[NeoJuice]

I called MBM today and to say the gentlemen I talked to was quite rude. But from the little bit of information I could get out of him was this.

- did it have two ports or four. I said it had four ports so he said that is not a disc disc MC and would need one with ports.
- I would need two 2lb valves which I have and a MBM PV4 proportioning valve. I think I might go with the wilwood instead.
- the master cylinder I have he said is a 1" bore and I need 1 1/8" bore.

That's about all the information I got out of him. I'm going to try and see if I can get there GM one. But I will update the post later when I have more information.

Hopefully this one will swap onto the booster.

http://mbmbrakes.com/mc2912h-gm-univ...er-1-1-8-bore/

[NeoJuice]

Originally Posted by Rude Dude

The booster doesn't have a thing to do except use vacuum to aide in the pressing of plunger in M/C. Your master cylinder looks like corvette style so the determination weather it is disc/drum or disc/disc would be in the proportioning valve and I noticed you do not have one on.

I think I'm going with the wilwood one. That's why there is nothing there. I'm basically building the brake system from scratch.

[NeoJuice]

Originally Posted by dwcsr

I see you have the clevis in the wrong hole or the brake arm , It goes into the other one, The part number is for the bracket only, its for 55-59 trucks, the booster is universal works with almost any master, The master you need is for disc/disc so just get a master

the wildwood prop valve works well on these systems

In the picture the brake pedal is not connected to the booster plunger arm it's just sitting there. Is there any reason why I can't move the plunger in/out? Could it be seased? Or does it need to be under vacuum to work?

[59chev]

I have the CPP kit based on the corvette master that i purchased from KMS tools. According to them the Master is identical in a disc - disc or disc-drum situation, the only difference is the proportioning valve. My holes on one side are blocked. I believe the extra set of holes allow more flexibility to swap the lines over to the other side for certain applications.

[NeoJuice]

Originally Posted by 59chev

I have the CPP kit based on the corvette master that i purchased from KMS tools. According to them the Master is identical in a disc - disc or disc-drum situation, the only difference is the proportioning valve. My holes on one side are blocked. I believe the extra set of holes allow more flexibility to swap the lines over to the other side for certain applications.

59Chev,

That's interesting that you say that about your MC/Booster. I guess I could just put it back together and see what happens. Do you have any pictures of your setup I could look at? Do you have a link to the CPP website with the part number?

What proportioning valve are you using? I was thinking about using the wilwood one because it also has a break light switch in it. I'm sure it's not going to be cheap but I think the MBM PV4 wont be either. Or I go to the wreckers and pull one off another vehicle.

Looks like Photobucket changed there hosting. Now all the images are broken probably for every thread on this forum LOL.

[59chev]

Here is the kit that I have:

http://www.classicperform.com/Store/...ks/4754BBD.htm

[NeoJuice]

Originally Posted by 59chev

Here is the kit that I have:

http://www.classicperform.com/Store/...ks/4754BBD.htm

Thanks for the link. And is yours under floot mount or under hood? and I'm assuming your using the proportioning valve from the kit.

[59chev]

Mine mounts under the floor, using the original pedal. When I purchased it, they had a bunch of the disc-disc kits on sale, and just sold me the disc-drum proportioning block separately. They said the kits where identical except for the proportioning block and all I needed to do was swap it out for a disc-drum application.

[NeoJuice]

Originally Posted by 59chev

Mine mounts under the floor, using the original pedal. When I purchased it, they had a bunch of the disc-disc kits on sale, and just sold me the disc-drum proportioning block separately. They said the kits where identical except for the proportioning block and all I needed to do was swap it out for a disc-drum application.

Do you still have the disc disc proportioning valve? Could save me $125 bucks on the wilwood one.

[NeoJuice]

Is it necessary in every application to have the Adjustable Proportioning Valve plummed into the system? or can you just get away with a standard proportioning valve like the PV-4

[NeoJuice]

So I just talked with a guy and he said I should be fine. He said to re-install the MC and get the wilwood proportioning valve and put in my 2lb residual valves in the front/rear and everything should be good. Plum the larger front bowl to the front brakes and the smaller bowl to the rear brakes.

Anyone have any other thoughts? crossing my fingers everything works out ok.

[dsraven]

here is a link to the caddy rear calipers and how they work/look on the inside. have you done the park brake adjustment on the calipers?

https://www.youtube.com/watch?v=ojo2hmOLSMk

and another showing one way of how to adjust and fine tune the park brake on the caddy calipers so they work properly. they should be done along with the brake bleed etc once you get the master cylinder figured out.

https://www.youtube.com/watch?v=opjdu8DdVeA

[NeoJuice]

Originally Posted by dsraven

here is a link to the caddy rear calipers and how they work/look on the inside. have you done the park brake adjustment on the calipers?

https://www.youtube.com/watch?v=ojo2hmOLSMk

and another showing one way of how to adjust and fine tune the park brake on the caddy calipers so they work properly. they should be done along with the brake bleed etc once you get the master cylinder figured out.

https://www.youtube.com/watch?v=opjdu8DdVeA

DSRaven,

Thanks for the video links. I've watched both of those many times. Also a good one which I found was this video which really helped with the adjustment.

https://www.youtube.com/watch?v=k9FVCMFTXpA

If I recall after I adjusted the rear calipers they lock down with about 1/8".

[dsraven]

roger that on the caliper. cpp also has instructions online for their caddy caliper kits.
on the brake pedal return spring, just ensure the pedal doesn't put any pressure on the booster as you go over bumps etc and the pedal tends to bounce. a little bit of pressure there will cause a slight brake application. the pushrod from the pedal to the booster should have a little play in it. there is usually also a diagonal support brace to keep the bracket at a continuous angle so it doesn't bend when the brakes are applied. a bending bracket will also change the pedal adjustment as well as not be all that good from a safety standpoint. not sure if you have that or not. usually came with the booster kit.

[dsraven]

on the "which line goes where" I would connect the front brakes to the larger threaded port. smaller threaded port would be the rear. also check how the prop valve you have works as some have metering valves that restrict flow/pressure to the rear brakes on hard brake applications. this is to stop rear wheel lock up and keep the rear of the car where it is supposed to be, behind the front. if the master had 2 different sized reservoirs the larger res would normally be the front brakes. masters with 2 hugely different sized reservoirs are usually for disc/drum brakes because the rear wheel cylinders don't vary as much, fluid wise, as the front calipers do as the brakes wear out. caliper pistons are usually much bigger diameter than the wheel cylinders so they displace more fluid and as the brake linings wear they require more to top up. hopefully this didn't confuse you more.

[NeoJuice]

Originally Posted by dsraven

roger that on the caliper. cpp also has instructions online for their caddy caliper kits.
on the brake pedal return spring, just ensure the pedal doesn't put any pressure on the booster as you go over bumps etc and the pedal tends to bounce. a little bit of pressure there will cause a slight brake application. the pushrod from the pedal to the booster should have a little play in it. there is usually also a diagonal support brace to keep the bracket at a continuous angle so it doesn't bend when the brakes are applied. a bending bracket will also change the pedal adjustment as well as not be all that good from a safety standpoint. not sure if you have that or not. usually came with the booster kit.

I've read the CPP adjustment procedure over many times as well as the videos. My emergency brake works great when applied. I even have it hooked up to the original floor pedal.

[NeoJuice]

I'm going to re-open this thread from back in 2017. Now that the truck is running, seat belts are in I'm again left with little to no break pedal. As I mentioned in my "Whats going wrong inside my 350" Thread the truck is currently running 10-12" vacuum and 32 degrees total timing and 10 degrees base timing. The low vacuum is because of the cam.

I have my 2 lb residual check valves in the front and the back. I also have Wilwood Adjustable Proportioning valve installed.

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

1. Issue of not having a disc/disc master cylinder instead of a disc/drum master cylinder. The master that is currently on the truck has four ports (see attached image for MBM referance). So I went to the parts store and picked up a 1980 corvette master cylinder as suggested by DSRaven NUP 39052. It is a disc disc master so I will get that swapped into the truck. I need to do some re-plumbing of the lines with some unions because the lines are on the opposite side from where I previosly plumbed them into the old master. Picked it up for $65 because I said i could get it cheaper on rockauto lol.

2. When I assembled the master cylinder/Booster I didn't check the push rod adjustment on the booster. Since the pedal is soft I can also feel a big gap between when I start to push the pedal and the actual contact with the master cylinder. So that will need to be checked. 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.

3. Check to make sure the booster check valve is functioning correctly. Replace if necessary.

4. Re-bleed brakes and test for pedal travel. At this point once I verify all the air is out of the system and when the truck is running to see what kind of pedal I have. If the pedal is still pretty soft I will either need a vacuum reserve canister or something simular to a vacumm pump kit.

https://www.speedwaymotors.com/Mr-Ga...ter,61773.html
https://leedbrakes.com/i-23439165-el...it-series.html

5. 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.

6. 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. This should be how GM did it as well. I just want to be sure its the same before I make some new lines.

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

[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]

on some of these style brake set ups the weight of the pedal, with no return spring, is enough to take away the free play that you built into the adjustment when you set it all up. no free play in the pedal can mean the brake master cylinder isn't allowed to return fully so the brake "charge" in the system is never fully returned back to the reservoir and also the piston is not allowed to uncover the fluid supply ports in the cylinder. that is sometimes why the brakes feel like the pedal goes down a long way before there is any brake effect. to check, simply remove the reservoir cover and look as the brakes pedal is pressed down. the first little bit of pedal travel should result in a small fountain of fluid or at least a disturbance in the fluid inside the reservoir. this is because the piston seals are actually behind the fluid supply ports in the brake cylinder. as the piston travels forward it displaces fluid and the path of least resistance for the fluid is back up into the reservoir resulting in that little fountain. as the piston travels further forward those supply ports get covered up and passed by the piston and as soon as that happens fluid is moved down the lines to the calipers or wheel cylinders and the brake actuation cycle starts. on a disc brake set up the caliper pistons are sealed with square O rings which roll in their respective grooves as the piston moves outward. yes, the piston can slip on this o ring to take up slack from a new brake job but once that has occurred the piston doesn't really slip on the O ring much except a small bit as the pads wear. the piston moves out until the brakes are eventually applied and pressure in the system builds as the operator applies more leg pressure on the pedal. then the pedal is released and the caliper piston would stay where it is, resulting in brake drag, if it weren't for the square O ring wanting to go back to it's original shape in it's groove. when the O ring rolls back to it's normal shape it also brings the caliper piston along which results in a small gap between the brake pad and the rotor. if you have done many disc brakes you will have seen systems where the outside pad is worn distinctly more that the piston side of the disc. it is usually due to tight or seized caliper mounting hardware. the rolling square O ring moves the free moving caliper piston to retract which allows the pad on that side some slack so it doesn't drag but the pad on the other side of the disc is held against the rotor by the stuck caliper slide/mount mechanism.
anyway, hopefully you get this figured out and you get the STOP working as well or better than you have the GO working.

[NeoJuice]

Originally Posted by dsraven

on some of these style brake set ups the weight of the pedal, with no return spring, is enough to take away the free play that you built into the adjustment when you set it all up. no free play in the pedal can mean the brake master cylinder isn't allowed to return fully so the brake "charge" in the system is never fully returned back to the reservoir and also the piston is not allowed to uncover the fluid supply ports in the cylinder. that is sometimes why the brakes feel like the pedal goes down a long way before there is any brake effect. to check, simply remove the reservoir cover and look as the brakes pedal is pressed down. the first little bit of pedal travel should result in a small fountain of fluid or at least a disturbance in the fluid inside the reservoir. this is because the piston seals are actually behind the fluid supply ports in the brake cylinder. as the piston travels forward it displaces fluid and the path of least resistance for the fluid is back up into the reservoir resulting in that little fountain. as the piston travels further forward those supply ports get covered up and passed by the piston and as soon as that happens fluid is moved down the lines to the calipers or wheel cylinders and the brake actuation cycle starts. on a disc brake set up the caliper pistons are sealed with square O rings which roll in their respective grooves as the piston moves outward. yes, the piston can slip on this o ring to take up slack from a new brake job but once that has occurred the piston doesn't really slip on the O ring much except a small bit as the pads wear. the piston moves out until the brakes are eventually applied and pressure in the system builds as the operator applies more leg pressure on the pedal. then the pedal is released and the caliper piston would stay where it is, resulting in brake drag, if it weren't for the square O ring wanting to go back to it's original shape in it's groove. when the O ring rolls back to it's normal shape it also brings the caliper piston along which results in a small gap between the brake pad and the rotor. if you have done many disc brakes you will have seen systems where the outside pad is worn distinctly more that the piston side of the disc. it is usually due to tight or seized caliper mounting hardware. the rolling square O ring moves the free moving caliper piston to retract which allows the pad on that side some slack so it doesn't drag but the pad on the other side of the disc is held against the rotor by the stuck caliper slide/mount mechanism.
anyway, hopefully you get this figured out and you get the STOP working as well or better than you have the GO working.

Ill keep the thread updated. Probably wont be able to tackle the master install until the weekend. In the mean time I might be able to get it bench bled and some new lines bent up.

Going back to my other question and the attached images 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. This should be how GM did it as well correct?

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