1966 Mustang aftermarket brake booster issues... Please help

Thanks for the reply Michael. Yes they do feel spongy, and the pedal travels nearly to the floor before the brakes really start to engage. And no, the master cylinder was not bench bled... can you tell me what this is?

The system had been bled at all 4 wheels after the initial installation, then again when the proportioning valve was replaced, then again by the mechanic who was trying to overcharge me. After the third bleed, I noticed a large improvement. If this is just trapped air and I don't have the option of doing a bench bleed, do you have any recommendations for getting the air out at this point? Thanks again. -Ken

This might sound funny, but I was just doing research on the booster and realized it is not connected to a vacuum source. There is a black plastic plug over the connection on the booster now with no hose connecting it to the manifold. I'm guessing this might have something to do with it... though the brakes still work somewhat without the vacuum connected. Does anyone know where I can connect the vacuum for the brake booster? I have a 289 with an Edelbrock manifold...

Drummer, Mike 76 is absolutely right, you MUST bench bleed the MC first. We're talking a dual MC right? Are your brake lines/hoses in could shape, rusty old steel ones, orignals? I converted from a I6,original MC, Auto, all drum brakes to a V8 302, AOD, dual MC, all disc brakes and a brake booster.

My brake booster never really worked becasue it didn't get enough vacuum. The chowder head that charged me a fortune put a way overhead stock cam in, put in junk yard rotors and other parts that were out of tolerance, so the rear brake pads never contacted, froze them up for years before I found out. After installing a more reasonable cam and new brake calipers/parts we continued on to bleed the brakes, farthest one away first, always keeping brand new fluid in the dual bowls. I pumped the brake pedal and made sure the bowl(s) kept full. (You don't want to bleed them dry and get air back into you lines again and have to start all over). The mechanic would have me pump the pedal and then he would say "hold down", (meaning for me to keep my foot down on the pedal) and he would tighten the bleeder screw, (after seeing a steady stream of clear brake fluid and no air out of bleeder screw. At first all kinds of discoloration and water came out. Eventually clean new fluid came out of each bleeder screw. You have to be really carefully too, not to over tighten and break them off. Well, my brake pedal raised up a bit, but I still had to push down about 3" before they were solid. Anyway, we had to take the MC off after draining the fluid out first. Make sure you put plenty of towels all around and below the MC if you do. Brake fluid will take your paint off in a heartbeat. We determined that the break booster was working fine. We could see the rod coming straight out during travel when the pedal was depressed. We determined that the MC was somehow defective inside and that it was a rebuilt from Argentina, not remanufactured or new. I went to SSBC, receiving twice, MC's that did not work because the cylders inside where to short. Same problem with two other popular Mustang suppliers and all the MC's they sent me did not work with the brake booster either. The cylinder in the MC was not flush with the connecting side that the booster rod makes contact with like the original. Even Autozone couldn't find the right one. In other words the brake booster rod traveled but was almost completely at the end of travel before it made contact with the recessed MC cylinder which was about 1/2" below "flush". Not enough to engage the brakes. I had to buy another complete MC/brake booster kit, more money. The new MC had to be bench bled, all the brakes had to be bled again and use all brand new fluid again. Also the proportioning control valve to balance control the front/rear brakes was part of the SSBC kit I had installed and was new at the time, not out of a junk yard. It still worked. Problem solved, done. I just went through this tough experience last month. I only know what I just learned, but brakes have to be at the top of the safety list. No fudging or cutting corners. I hope you find someone that really knows brakes. Good luck.

Michael and Tony, thanks for the advice. I found a very reputable brake shop and have had it there the past 3 days for troubleshooting. He has taken the MC off to prep for the bench bleed, which we will be doing in the morning. He had bled several times and put almost a quart of fluid through it with no change to the pedal. He thinks it is likely air trapped in the MC due to not bench bleeding prior to install, so we will see after tomorrow.

Tony, the MC is a dual, and all new stainless lines and hoses up to the rear, and this car is also an i6 conversion to a 289, front Versaille disc conversion and factory drum rear. Sounds like you were in nearly the EXACT same boat last month as I'm in this month... This brake guy mentioned just today the possibility that the MC might be too short, but he's going to see what kind of response he gets after the bench bleed. I'm not sure I have much faith in this booster yet either... It came from the previous owner who has no recollection where he got it or who manufactured it (conveniently), so I'm crossing my fingers that I won't run into having to replace it also. I did just replace the Chinese-made lower control arms that he had on there.... If these Chinese parts I keep finding on there are any indication, I may be looking at replacing this booster very soon. I do agree that I don't want to mess around with the brakes, problem is I inherited these parts from the previous owner and was hoping I could make it work with what it has, but I don't know what it has! I'm uncovering many things that he was less than honest about. I'm walking on eggshells here.

Hey Drummer, It'll get worked out. I could write a book on what I found out about my conversion that was done totally wrong and dangerous in 2003. Yah, finding the correct MC match to the booster became the problem for me. No Mustang supply house could find or provide the correct MC to match the booster. I had originally purchased the mc/booster kit from MustangsPlus, (They've been good for me). They were great working with me in the search, but we just couldn't find the correct one. They get their MC from SSBC, so I called them and THEY couldn't provide me with the correct one either. Either the part numbers are recorded wrong in their computers or nobody is checking the parts box, etc. I ended up going to NPD, National Parts Depot, located in Ocala, Florida (and other states), because my car was there and they were able to ship the next day to my mechanic. I ended up buying the complete MC/booster kit. Done. We bled the air all out and the brakes work great. If I had to do it all over again, I would of replaced my steel brake lines with SS like you have. I have already replaced 95% of all steel screws, studs, fasteners with SS.. No more rust, broken rusted out fuel lines etc. If you still have the MC off, could you post a pic of the faceside that connects to the booster? Take a slight angled close up. I want to see how far that inner cylinder comes out or if its recessed or flush with the face. Our cars are basically the same and would use the same kit. But matching separately a MC to a booster is the devil. (I ended up wasting 2 months searching for a match until I bought the kit). Also, did you hook up the vacuum hose? (I think) you have to get it from a particular port off the manifold. BTW, I have a Edelbrock High-rise manifold, so almost the same as you. Let us know how you make out with the bench bleed, etc.:bigthumbsup

Thanks again for the help. I just got a call from the mechanic... He can't get a pedal after bench bleeding and 2 quarts of fluid. So it looks like I'll need to do the same as you Tony. I made the mistake of buying the booster off the guy who sold me the car, but he has absolutely no recollection of where it came from, just that he got it off ebay. So I'm stuck with a $200 booster that's scrap. I'll post a couple pics I took of the prop valve and booster that I took a couple weeks ago but I'll take more when I go pick up the car.

I suppose, on the bright side, I can pick up a booster and MC for a manual that makes room for a hydraulic clutch, since I plan to do a T5 conversion soon. Do you (or anyone) know if there would be any issues using this on the automatic in the meantime, without the clutch in place or the swap started yet yet?

Hi Drummer, I have an AOD.Yeah, that was fun. The first guy left out the TV cable. Luckily, I went to Lokar and got the necessary linkage/cables and a good transmission place to set it up correctly otherwise I would have destroyed my new transmission. I don't know the answers to your T5 questions. Sometimes I go to Mustang Monthly. They have a lot of good tech "how-to" w/pics articles. And of course there are some really experienced folks replying on this forum too.

Yea Tony, seems half our time working on our car is spent trying to correct someone else's mistake. I inherited a lot of problems from the previous owner (I replaced the Chinese-made lower control arms the other day), and found many things that he actually lied about. Fact is it would be easier just to KNOW what they did wrong... I wouldn't even hold it against them just to hear them say, "I screwed this up" or "I totally half-assed this" just as long as I know what it was...

I'm curious to know your experience with trying different MC's with your booster... after seeing the pricetag for a full booster setup compared to some MC's, I thought maybe there's a possibility I could just replace the MC since it appears to be the only thing that's not working properly. My limited understanding of this problem is that the piston is not making a full travel inside the length of the valve to allow enough pressure to be distributed out to the brakes. What I was told is it may be "too short," meaning it needs to travel further within the valve to fully engage the brakes, and for whatever reason this MC valve is not correctly engaged by the press of the pedal. Is this correct?

It seems to me (in my lack of knowledge) that maybe if there were a longer rod that connects the pedal to eventually engage the MC valve, that would push the piston farther into the valve, allowing it to engage fully and not come up "short." Forgive me for trying to form an understanding on my own, I'm just trying to figure out what is actually causing this... it seems to me that there's nothing mechanically wrong with the booster or MC, just the way it's working with this car... and I'd really hate to go spend $500 toward a new booster out of the T5 fund...

Hi Drummer, Your first paragraph, I totally agree...let's start a club:shigrin. Your 2nd. Your are totally correct. My mechanic said there might be a good brake shop around where they can actually replace that inner "rod" in the MC to the correct the "short" lenght. We never checked and I didn't want to take what I thought was a high risk of failure, time and money. When I spoke with reps at SSBC, NPD, MustangsPlus, gave them the part number of the full mc/booster kit, they ALL, sent me an MC, and each one from all those companies, including SSBC, had a different length "rod" in the MC. The bottom line: the "rod" inside the MC was as much as 1 1/2" - 2" short, not allowing the booster rod to extend a full reach. I wish I had the pics on my notebook here overseas to show you, but the MC that originally came with the MC/booster kit had that "rod" flush with its surroundings at the opening end, (that end that connects to the booster). Yes I bit the bullet, but it was finally installed after two months of screwing around trying to find the right match. Now, I still have the other booster, and there's nothing wrong with it. I might be able to sell to someone for a discount. So not a total loss. Hmmm, I could call SSBC tomorrow on my lunch break, as I am only 4 time zones away. Maybe I can talk to the one guy who seems to know what's going on there. There not easiest customer friendly up there. I tell them your dilemma. My mechanic told me NOT to fool with the brake booster rod or try to adjust it. Someone else here might be able to join in and tells us what will/could happen if you do. Hang in there:bigthumbsup, I had over 60 really bad things done to my car over the years from "part changers", (not Professionals), and I just found all this out between last Christmas and the end of May. I have a hole in my wallet the size of Grand Canyon. Feel free to ask as many questions as you want. I'm learning so much reading all the forums here. I'll be picking your brain regarding something in the future, I'm sure.:gringreen

Yea we'd probably have the biggest car club in the world. I've been looking into it and might just do the same by replacing the entire setup. I found a place called Classic Performance Products (CPP) out here by me in Anaheim. They say they have a full booster kit for the 66 that includes the MC and proportioning valve for $360. Biggest advantage I see is that they seem to have a great reputation, manufacture their own products as brand new not refurbished, and offer a lifetime warranty on everything they make. So I'm thinking if I bite the bullet and buy their kit, I'll never have to worry about my brakes again... or at least I'll know where it came from and can return it if it doesn't work. And it's the same price as NPD's, which only has a 5 year warranty. I'm gonna try one last thing tomorrow, and that's to connect the vacuum to the manifold and see if that helps. The brake guy told me that if he can't get the pedal first, there's no use connecting the vacuum because it would just make the pedal lighter and not improve the stopping power. I've been reading things that contradict that, so I'll tinker more while it's up on jack stands. If it doesn't work, I'll be making the trip to CPP. Thanks again. Where are you at overseas?

Hi Drummer, everything you said makes sense, about that place close by to you, lifetime warranty and all. Once installed, tested and adjusted your done. Everything purchased together and backed up by a local vendor. :bigthumbsup
You can drive with confidence that the brakes are going to do the job, no guessing or hoping they will stop your ride. One question though, how far back inside is the "rod" in the MC, 1-2 ", when you look inside at the end which attaches to the booster? Yah, I'm working here in West Africa(again). Just a month to go. No TV, so I really spend most of my time surfing on the Net when I get home from work. I hope you get your brakes installed soon. Maybe you could show everyone a pic of your install if you end up going that route.

hey drummer, I bet jetset is right on, I just went through this. I must have vacuum bled a gallon of brake fluid with no pedal, how frustrating! Finally took the MC off and realized the push rod wasn't contacting the MC piston. I measured it got the correct length bolt to screw into the booster, bled it again and now the pedal is high and firm, just the way I like it!! Give it a try and maybe ya can save some money, good luck!

Tony and Tooms, thanks again. You guys are pacing me for everything I'm doing to troubleshoot. After messing with it more this weekend, trying a couple more bleeds, still no pedal. I spoke to a couple brake guys and they told me the same, take off the MC. One guy told me the piston inside is adjustable for the length it travels, but I'm not familiar with adjusting it. Guess I'll find out when I jump in, but that will have to be next week.

Has anyone heard of, or had experience with, the Phoenix systems reverse brake bleeder? I found an ad during my search and it seems like a great way to be positive there is no air in the system... But it's kind of expensive.

Low Pedal pressure after Booster Mod on a 66 Mustang

I know this is a reply to an old thread but it's still good knowledge.
You must re-use the 64-66 push rod on the new master cylinder. It is longer then the rod that comes with the 67 style dual master cylinder. If the 67 push rod is used, a low brake pedal condition will exist.

I think I have the same problem after converting my 64.5 from drum to 4 wheel disc. No amount of bleeding will bring the pedal up to a normal height. Can the rod be changed from under the dash or does the m/c and booster have to be removed from the car to change it. I still have the old rod from the original pub drum setup.

Appreciate all input.

Gary

glmarker said:

I think I have the same problem after converting my 64.5 from drum to 4 wheel disc. No amount of bleeding will bring the pedal up to a normal height. Can the rod be changed from under the dash or does the m/c and booster have to be removed from the car to change it. I still have the old rod from the original pub drum setup.

Appreciate all input.

Gary

Click to expand...

I have the SSBC mini-booster too. I had to "adjust" the bolt in the front of the booster that contacts the plunger in the Master Cylinder.

Too short, and there will be too much pedal travel. Too long and the brakes won't fully release, so be careful!

There exists a special tool/jig to measure and set it, but I didn't have access to one, so I did it the hard way...