MN69Grande 203 Report post Posted February 13, 2017 3-4 years ago, in the final rush to get the car back on the road, I swapped out the old Midland Brake boosters with the Bendix style. Simply because I couldn't find the Midland style in stock with anyone and sending it out for 10 weeks to be rebuilt seemed too long as we were so close to getting on the road. I'm not sure what Master Cylinder we got, but knowing the person that ordered the part I'm assuming he did it by using the part number stamped on the one we pulled from the vehicle. Looking at Napa's site tonight I see different listings for W/ and w/o Bendix Casting. The brakes have a ton of travel on the pedal before stopping, and they've been bled a number of times to every wheel. I'm thinking I need to at a minimum adjust the power brake booster pin. But now looking at Napa's website, would it be stupid to pay $45 dollars and make sure I'm matching a W/ Bendix Casting to the Bendix Booster? They stop OK but the pedal feel is horrible. Also to note I did the CSRP Kelsey Hayes style swap but they stop great you just have no feel. I mean a panic stop will put anyone not wearing a seat belt into the windshield. 5 yapedVem, uapedVem, ncdruroSor and 2 others reacted to this Quote Share this post Link to post Share on other sites
1969_Mach1 333 Report post Posted February 13, 2017 West Coast Classic Cougars has a video with information on Brake Boosters, differences and a little on master cylinders. The Bendix booster does not use a space/filter assembly between the master cyl and booster like the MIdland booster. Did you accidentally install the spacer/filter assembly on the Bendix booster? 1 RPM reacted to this Quote Share this post Link to post Share on other sites
MN69Grande 203 Report post Posted February 13, 2017 West Coast Classic Cougars has a video with information on Brake Boosters, differences and a little on master cylinders. The Bendix booster does not use a space/filter assembly between the master cyl and booster like the MIdland booster. Did you accidentally install the spacer/filter assembly on the Bendix booster? The problem is, this isn't one of the things I did myself so I don't know exactly what happen. I did run out and take a look and the MC is installed directly to the booster. So I think no spacer/filter. I pretty sure I'm going to separate the MC and the Booster to check the pin length. But I figured if the MC was the wrong one it would be a good time to swap. Quote Share this post Link to post Share on other sites
Brian Conway 264 Report post Posted February 13, 2017 Might want to compare your brake pedal to the examples on the mustang steve site ? Brian Quote Share this post Link to post Share on other sites
MN69Grande 203 Report post Posted February 13, 2017 Might want to compare your brake pedal to the examples on the mustang steve site ? Brian The pedal is original to the car. Do you mean the hookup on the back of the booster? Quote Share this post Link to post Share on other sites
1969_Mach1 333 Report post Posted February 13, 2017 Might want to compare your brake pedal to the examples on the mustang steve site ? Brian Good point. If it was originally a power brake car it should be the correct brake pedal. But who knows. Look at the rod attaching the pedal to the booster. Make certain it has the downward offset and is not straight like the 1970 and newer Bendix boosters. If that looks okay, remove the master cylinder and double check the rod length. Compare that to the bore depth in the master cylinder. According to my reproduction Ford Service Manual the rod should extend out of the Booster 0.980" to 0.995". I've used those specs on my Bendix booster and it works fine. It's also possible you simply have a bad master cylinder. For the price of a new master cylinder, if you are removing the old one to check the push rod length, you might as well reinstall a new master cylinder. Quote Share this post Link to post Share on other sites
pinexcorp 1 Report post Posted July 31, 2021 It would be nice to find out how this issue was resolved as I am having exactly the same problem. I have now replaced the master cylinder twice and have bled the line 5 times with same result. Pedal feel awful and goes all the way to the floor before stopping. Quote Share this post Link to post Share on other sites
aslanefe 333 Report post Posted July 31, 2021 12 minutes ago, pinexcorp said: It would be nice to find out how this issue was resolved as I am having exactly the same problem. I have now replaced the master cylinder twice and have bled the line 5 times with same result. Pedal feel awful and goes all the way to the floor before stopping. If you have smaller diameter master, your pedal will go down more compared to bigger dia master before stopping. Need to know your master diameters (the old/original one and the one you have now). Quote Share this post Link to post Share on other sites
det0326 179 Report post Posted July 31, 2021 As aslanefe said we would need more information. If you have drums on rear or all four could be a shoe adjustment problem If you converted to power assist and didn't change the pedal that could be a problem. Need to confirm all parts are correct for power assist. Quote Share this post Link to post Share on other sites
Brian Conway 264 Report post Posted July 31, 2021 Pictured is a (Mustang Steve Picture) 67-69 brake pedal w/booster. You should check the measurement against what you have ? All of our 69 master cylinder bore diameters are 1inch. Is yours ? Brian Quote Share this post Link to post Share on other sites
pinexcorp 1 Report post Posted July 31, 2021 Thanks for your comments. Unfortunatelly I returned the MC core that was on the car and no longer available for me to see if any different from what I got now. My mustang is original power brakes with disc brakes in front and was running great brakes were good until I noticed my MC leaking at the seat and possibly into the booster. I dont think the booster has been damaged. So I set out to replace and have gotten units from Oreillys and autozone and both do the same where the pedal goes all the way to the floor before breaks. I have read and seen videos where they describe two types of booster on the 69 a Bendix and an midland.. I believe the booster in my car is a bendix since the vacuum port is on the side and not infront of the MC... Oreillys had a call out for a MC for Bendix which is not available anymore and so I am now wondering if there is a physical difference in the two MC and I need to find one. Maybe my old MC was a Bendix?? I think one of the lessons learned here is if you but a part for which you need to return the core dont return until you install the new part and all is well. kind of lost know as to not sure how to proceed. Quote Share this post Link to post Share on other sites
pinexcorp 1 Report post Posted July 31, 2021 Core diameter of the MC I have now is 1" Quote Share this post Link to post Share on other sites
Brian Conway 264 Report post Posted July 31, 2021 Lesson learned on the core. The way I read your post ; everything was fine until you exchanged the master cylinder ? Making the MC the focus ? Again the way I see it; When your exchanged MC was re-built a shorter, and incorrect ' piston ' was installed. Happens. Thus making the Booster push rod to short. The 69 Shop Manual has a description and instructions for adjusting the Booster push rod. The other guys will help you out with this, I could be all wrong, and the more questions you answer the better. My brakes and booster operate at about 18-19 hg's of vacuum. Do you know what yours is ? Brian Quote Share this post Link to post Share on other sites
pinexcorp 1 Report post Posted July 31, 2021 Thanks Brian. Yes I think the MC is the focus. I had no Idea the push rod out of the booster had adjustment. I will check lengths. Quote Share this post Link to post Share on other sites
aslanefe 333 Report post Posted July 31, 2021 Booster does not affect the pedal height where the brakes stop the car. Booster only reduces the effort your foot excerts on the pedal. MC diameter change changes how far down the pedal goes to stop the car. If your original MC diameter was bigger (let's say it was 1 1/16) and now that you have 1 inch MC, the pedal needs to go down more to move the same amount of fluid to the calipers (and rear cylinders). After you fill the calipers then the pressure in the caliper goes up and stops the car. MC dia goes up, the brake pedal travel goes down but effort goes up. MC dia goes down, the effort goes down but pedal travel goes up. Booster makes the effort go down, but not affect pedal travel. Above is assuming your push rod is adjusted correctly. Quote Share this post Link to post Share on other sites
pinexcorp 1 Report post Posted August 3, 2021 I am totally dumbfounded. Four days working on this issue and now nothing makes sense. No matter how much I bleed the brakes I can not get them to come up insted they go all the way to the floor. They do stop the car when it hits the pedal hits the floor. Removed the MC and checked the stud sticking out of the booster and measures about 1" Next I suspect the booster was bad so I placed a 3/4 inch wood board and braced to test out how much force the stud was pushing out with.. pressed the pedal and force was strong enough to actually break the board and stick out an additional 4-5 inches? Bench testing the MC and pushing on the piston the action of piston fully depresses is only like 1 1/4 " so the booster is working... or so I think. Next I installed the MC back on the booster.. filled with fluid.. bled the MC and plugged the ports tight. With engine and vacuum the brake pedal was so hard barely moved. This tells me the MC is developing pressure and booster is working.. Next I reconnect the brake lines and bleed system and bleed and bleed going thru about a quart of brake fluid... Checking for leaks. Pedal still goes to the floor.. same thing. Nothing makes sense where is the pressure going? Anybody want to buy a mustang before I burn it? Quote Share this post Link to post Share on other sites
aslanefe 333 Report post Posted August 3, 2021 59 minutes ago, pinexcorp said: I am totally dumbfounded. Four days working on this issue and now nothing makes sense. No matter how much I bleed the brakes I can not get them to come up insted they go all the way to the floor. They do stop the car when it hits the pedal hits the floor. Removed the MC and checked the stud sticking out of the booster and measures about 1" Next I suspect the booster was bad so I placed a 3/4 inch wood board and braced to test out how much force the stud was pushing out with.. pressed the pedal and force was strong enough to actually break the board and stick out an additional 4-5 inches? Bench testing the MC and pushing on the piston the action of piston fully depresses is only like 1 1/4 " so the booster is working... or so I think. Next I installed the MC back on the booster.. filled with fluid.. bled the MC and plugged the ports tight. With engine and vacuum the brake pedal was so hard barely moved. This tells me the MC is developing pressure and booster is working.. Next I reconnect the brake lines and bleed system and bleed and bleed going thru about a quart of brake fluid... Checking for leaks. Pedal still goes to the floor.. same thing. Nothing makes sense where is the pressure going? Anybody want to buy a mustang before I burn it? I hear your frustration; that is why I bought a brake pressure gauge that I connect to bleeding ports to test the pressures at each corner individually. On a side not, what year, model, engine etc is the Mustang you are going to burn or sell? As if I need an other Mustang. Quote Share this post Link to post Share on other sites
Brian Conway 264 Report post Posted August 3, 2021 Well I don' have a ready answer for your problem. My immediate response is if the pedal goes all the way to the floor there is a disconnect in the system. You say the system functioned correctly prior to the MC replacement. Is the car an original factory power disc brake car ? I am guessing you adjusted the booster push rod to come up just short of the MC piston Cup when installed ? Yet the pedal still goes to the floor ? You never did reply to my questions: do you have the correct pedal and do you have the correct booster with the pedal turned down connection ? Honestly without a hands on inspection I don't know what to suggest. Brian Quote Share this post Link to post Share on other sites
pinexcorp 1 Report post Posted August 3, 2021 Yes Brian.. Thanks. The Car is all original with power disc brakes.. Correct pedal , correct booster. What I dont get is why if the pedal when pushed all the way to the floor pushes the boosted push rod like 5 inches.. and the MC max travel is 1 1/4" any adjustment on the stud only positions the pedal higher or lower... Maybe I still dont understand how a booster works but looking at cross sections it looks like is a straight connection to the MC with the diaphragm in between and vacuum on one side assist to help with the pushing..I am starting to think that the booster is only effective in a certain range.. so I need to adjust the push rod to see it makes any difference.. Maybe an incorrect booster was installed and only worked with the MC I removed.. I think that makes sense... My Mustang is a 1969 Mach I original S code 390 and C6 trans. Originally Raven black. Quote Share this post Link to post Share on other sites
Brian Conway 264 Report post Posted August 3, 2021 Got the vacuum hose connected ? Tried the ' Power Brake Functional Test ? Quote Share this post Link to post Share on other sites
aslanefe 333 Report post Posted August 3, 2021 Pedal movement (for example 5 inches) moves the MC piston a lot less (for example 1 1/4 inches) due to the fulcrum of the pedal. Fulcrum is different between power and non power car pedals. Yes the booster has a straight rod (connection) to MC piston. The diaphragm in the booster converts the vacuum to force and reduces pedal effort needed to press the pedal when you press the pedal. When you release your foot from brake pedal, the vacuum on one side equalizes to other side (if it does not equalize, the brakes will be kept applied). If when the engine is off (and brake was applied a few times to spend the vacuum in the system) and you press the pedal, it should stop higher and with more effort. If the brake pedal goes down more and takes less effort when the engine is running (and providing vacuum to the booster), your booster is doing it's job. I put a booster on my 70 with non-power front disc brake car almost 30 years ago. The MC and brake pedal are for non-power cars and I installed a Fiat booster in between. Brakes work good with minimum pedal effort but full braking power comes on with pedal closer to floor (more pedal travel) compared to my 69 with booster, power MC, and power pedal. If it is 390 car, don't burn it, I'll try to make room in my shop for it while wife is not looking. Quote Share this post Link to post Share on other sites
aslanefe 333 Report post Posted August 3, 2021 I would put in a 1 1/16 MC on it, it should stop the car before pedal goes all the way down. Quote Share this post Link to post Share on other sites
Midlife 814 Report post Posted August 4, 2021 Let me understand the problem: without connecting to the brake lines, the pedal is hard and firm. Once the brake lines are connected and brakes bled, the pedal is soft and goes to the floor, right? I would first suspect a rubber brake line section is expanding under pressure due to it being old and about to fail. Have you replaced every single bit of brake lines? If so, is there any brake fluid leaking from any of the calipers or drum cylinders? No? Are the rear drums adjusted so that there is a very slight drag when the rear is off the ground? All of the above can explain your symptoms (if I understand them right) without resorting to the MC or booster. Quote Share this post Link to post Share on other sites
Brian Conway 264 Report post Posted August 4, 2021 On 2/12/2017 at 9:09 PM, MN69Grande said: Went back and picked up something I missed on the first pass... See below. No idea what "the CSRP Kelsey Hayes style stop " is ? As whatever ' it ' is didn't come as original equipment in this power brake system it could be responsible for your problem ? " Also to note I did the CSRP Kelsey Hayes style swap but they stop great you just have no feel. I mean a panic stop will put anyone not wearing a seat belt into the windshield. " Quote Share this post Link to post Share on other sites
aslanefe 333 Report post Posted August 4, 2021 15 minutes ago, Brian Conway said: Brian, you are quoting a post from 2017 by MN69Grande who has Kelsey Hayes style (early 4 piston calipers). Pinexcorp says he has original power disc brake car so he should have single piston calipers. Kelsey Hayes style is a common retrofit disc brake you can install on drum brake spindles; I put a set (with booster) on my 69 Grande which was a non-power front/rear drum brake car. Quote Share this post Link to post Share on other sites
