I'm down to the last step of my full width axle swap before it'll run again.

I've bleed brakes many times, both alone with a vac bleeder and using the 2 man approach. This time it just won't seem to give up. I'm using a vac bleeder and can't seem to get a firm pedal.

I'm running a 99 Mustang (not Cobra, noone listed a different part number for Cobra vs nonCobra- please explain if you can) hydroboost & M/C, I bought used from a salvage yard & had shipped to me. I installed it a couple years ago, with absolutely no problems. I used the same vac bleeder then, and had the brakes bled in no time. I didn't even have to open the bleeders on the M/C.

The brakes worked great when I took on this project, but there are some things that are worrying me:

#1: there does seem to be some seepage from the h-booster, between the M/C & h-booster & under the dash, there is p/s fluid around the firewall/h-boost stuff. I wasn't loosing brake fluid, so I assume its p/s fluid, and its not much of a leak, but it is wet.

#2: the M/C drained when I disconnected the lines at the axles. I guess this means there is a bad oring in the M/C. I disconnected the brake pedal to make sure there was no pressure on the system, there was none. I never took the M/C off the h-booster so I'm guessing there wouldn't be anything wrong between the two.

I've bled at each wheel, starting furthest from the M/C, and even at the M/C, multiple times, I've burned through over a quart of brake fluid, and really don't know what to address next. Take off M/C & bench bleed? New M/C? Rebuild h-boost? The pedal will feel firm with the truck off, when I start it, I loose the firm pedal, and it drops about 1/2 way before feeling firm. Before this, there was no pedal drop, really at all.

Anybody know if opening the bleeders on the M/C is like bench bleeding? or what?

Calipers on right, looked at my old axles w/F150 brakes & all is the same. No leaks from brake system.

Ran truck, turned steering from lock to lock, no problems. Thought maybe the leak @ h-boost allowed air into h-boost unit while the truck was sitting.

Chad

Check to make sure your brake pedal is returning all the way. I ran into a clutch that would not bleed because the clutch pedal would not return all the way to the top. If your brake pedal or hydro boost is not allowing the mc piston to return all the way it will never bleed right.

The pedal seemed to return just fine. When I go back tomorrow, I'll check. I guess I'm not going to spend a lot more time on this. I've been reading a lot, looking for the magic bullet that will save me more time & money, but I don't think it exists. My only real hope is that this is because I haven't adjusted my new rear brakes. Maybe the extra throw in the pedal is because the shoes are too far from the drums.

I think I need to accept that the M/C is leaking and needs replaced and the hydroboost is leaking and needs rebuilt. It looks like there is no point in doing one without the other, as the leaking h-boost may damage a new M/C. I'm hoping to find the rebuild kit at Carquest or Napa, or I do work for a GM dealer, and it looks like the kit may be available through them. I'd rather not wait 5+ days for Piratejack to ship me one.

Try pulling the pedal back up manually. Not just letting the normal force return it. Hopefully it is as simple a the rear brake adjustment though!

I am not an expert with the hydroboost, but remember that all brakes hydraulic systems work the same. you said the master cylinder drained down when your bleeders at the liunes are open. Or did I read that wrong? anyway if I read it right, that's fine. I gravity bleed all brake systems before doing an actual bleed.

One of my pet peeves is to NOT pump the brake pedal excessively when bleeding, when you do this, it aerates the system making it even harder to bleed. (those big air bubbles moving around inside the lines turn into a bunch of smaller lines and spread all throughout the system) < Just a little technical help.

If you have a good solid pedal when there is no boost then start engine and pedal drops excessively you may be over powering your master cylinder and that will force the seal at the back bore of the master to start leaking. The other and more common problem is the adjustment between pushrod and booster. you also do not want pressure on the booster when pedal is released, there should be a tiny amount of play there before applying pressure. Remember you are applying power assist to the master cylinder and that will force power causing the pedal to drop some.

Am assuming there are no leaks within the system.

I hope this helps some.

69 Bronco 69,

You are correct that the m/c drained with the lines disconnected. I was thinking that shouldn't happen. If you are correct, then that is very good news, it'll save me a bunch of money. When I said the m/c was "leaking" this is what I talking about. If the m/c is fine then hopefully, adjusting the rear shoes will take up my long pedal. Or maybe I need to bench bleed the m/c? Does anyone know how the bleeders on the side of the Mustang m/c work?

mastercyl.jpg

I"m using a vacuum bleeder, so there is no pedal pumping.

I'm not sure about what you mean by overpowering the m/c causing the seal to leak. Again, the m/c is not leaking. When I said "leaking" I meant I THOUGHT there was a bad oring that was allowing the m/c to drain. Also the m/c and booster came from the same car as a "set". I've never separated the m/c from the booster, so there shouldn't be any problem with the pushrod to m/c clearance. Its run fine for the last 2+ years in my truck.

I hope you are right & I just need to bench bleed or adjust the rear brakes. I'm keeping my fingers crossed. I'd much rather shell out $40 for a hydroboost rebuild kit, and save the extra $120 for a new m/c.

Thanks
Chad

Gunni - I have the same set-up and had the same problems. I have a 98 Cobra hydroboost and it was a bear to bleed.

1. you definitely have to bench bleed the MC to get it primed. I did this by using clear tubing from the MC bleeder valves routed back into the top of the MC reservoir. This is critical...make sure it's pumping good before you put it back in the truck. This was my point of failure in getting mine to work...once I finally got the MC primed and bench bled then I was able to get the lines cleared when I bled at each wheel.

2. Buy some speed bleed valves for each wheel if you don't have them. That way you can do it with one person, or do it more reliably if you have two people. I literally bought the big ass gallon jug of brake fluid I was so determined to get mine to work. If you pumped through a quart, then man-up and get a gallon. Keep trying, it's really frustrating but I just pumped the hell out of mine and finally got it clear.

3. I also tried to do the gravity bleed on mine. Leave a speed bleeder open on the wheel and let the system set for 3 hours or more. THen close it and move to the next wheel. You have to keep checking it to fill the reservoir. Research this on the internet...some guys believe this is the easiest and only effective way to get it to work. The theory is that gravity continually draws the fluid through the system and forces the air out over time. This might have been the trick that got mine working good...it was definitely the last thing I tried before I determined it worked good.

Good luck - pm me for a phone number and call me if you have questions. I'm not a guru but I went through the same frustrating problem you have. I was ready to punch my hydroboost in the nose it was so frustrating. But when you get it done it will be sweet.

Dave

Thanks,

I'm really hoping my problems are caused by poorly adjusted rear brakes. Looks like I was wrong when I thought the m/c draining was an indication of a bad m/c. So I thought I had a bad part, until 69 Bronco set me straight. I've bled the system from the ports at the side of the m/c using the vac bleeder, but without pumping the pedal. I figured that when the m/c drained, it could have trapped air. If adjusting the brakes doesn't work, then I'll move to bench bleeding.

I'm not even sure there is anymore air in the lines. Using the vacuum bleeder is nice, its a one man job, without the special bleeders. The thing I've noticed with the vac bleeder is that, I think, it pulls air into the tubing from the around threads of the opened bleeder valve. So you see bubbles, even though they aren't coming from the brake system. I've successfully used the vac bleeder before, getting great brakes, even though you still see air bubbles. If you "jiggle" the bleeder screw, while under vacuum, you'll get a big burp of a bubble. I'll call in a favor for help this afternoon, if I need it, if I have to "2 man bleed".

Gravity bleeding will be my last resort. I really don't want to sit around "work" all Sunday refilling my m/c. If tomorrow comes & I'm still struggling, I'll try that. I can work while the system bleeds.

Great advice. On CB.com, the first/only advice I got was: "Just replace the m/c." I fixed hottubs for 10+ years, and I know that blindly throwing parts at a problem is a waste of time & money. If I had followed that advice, it would have cost me $120+, 2 days of waiting for the new part, all the work of changing the m/c & rebleeding the system. All because of an incorrect ASSUMPTION that I had a bad part. And I would have had the same problem in the end.

I know parts can go bad, at weird times. But it seemed very strange, that the m/c & hydroboost would crap out while the truck sat for the last 5 or 6 weeks. I just kept saying to myself "I never touched the m/c, why would it go bad? I was working on the axles."

Chad

1. CAUTION: Use only bleed screws on the engine side of the brake master cylinder. The hydro-boost bleed screw, located near the dash on the hydro-booster casting, is for the booster cavity filled with power steering fluid, not brake fluid.

Connect a clear waste line to the bleed screw closet to the booster first and the other end in a container partially filled with recommended brake fluid.

2. Open the bleeder screw, have an assistant push the brake pedal down slowly through full travel, close the bleeder screw, then return brake pedal slowly to full released position. Wait five seconds, then repeat operation until air bubbles cease to appear.




3. Repeat Step 2 for bleeder screw farthest from hydro-booster.
this is the procedure to prime your master cylinder. Sometimes I am too stubborn top ask for help, so I use my long pry bar and vise grips and push pedal down and clipp vise grips on the bar and let it hold against the seat. There is a tool for this on the alignment rack but I like my way. then Go close the valve and release pedal, usually after the 3rd or 4th try its clear. Where I work now we have a sweet pressure bleeder and I can clean the sludge inside the reservoir out and pressure bleed the system without using anything but the machine and a 9/16" wrench.

I just spent a few hours working. I'm getting closer, and the truck ran, up & down the street. There is definatly still something wrong with the front brakes. The rears are ok, but I found something very interesting.

One set of the new brake shoes I bought for the back end has about 1/2 the material of the other set. I left the measurements at work, but the thick ones were like .27" thick and the thin ones were like .16" thick. Pics aren't that obvious. I had to open the adjuster foreever before it made contact with the drum. This will be returned to Carquest & replaced tomorrow.
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IMG_1543.JPG

So that was part of the problem. I kept bleeding w/the vac bleeder, and then wanted a little better control, so I made a system like you said you have. Except I used my hood prop rod. Great minds think alike
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IMG_1546.JPG

I've gotten more air out of the m/c, especially the rear most bleeder (NOT on the h-boost). I must still have air in the front system, I'm locking up the rears like crazy, but don't have much up front. I've added t-bird calipers & slotted/drilled rotors, because I had a little too much rear bias before, with my standard F-150 brakes.

Thanks
Chad

Something just crossed my mind. I think the problem is still air, but think about this:

The T-bird calipers have a larger piston & therefore use more fluid to move the piston. I've also changed from 10" 1974 drums to 11" 1979 drums in the back. If there is no more air, I think I may need a proportioning valve. What if I've screwed up my front to rear volume ratio and the Mustang m/c can't keep up? I'm using the stock proportioning block.

Just a thought, I'd like to get some opinions on.

Chad

I've got no air, but still locking up rear brakes. I pm'd Cortez, to check his install. I've got the front outlet from the m/c feeding my rear brakes, and the rear outlet feeding my front brakes. I never checked before, and can't find specific info anywhere. Can someone confirm the outlet configuration to the Mustang m/c?

I think it was noticeable, but acceptable with the standard F150 calipers, but with these huge t-bird calipers, I'm not getting enough front brake.

Chad

If I'm remembering correctly, there is a wheel cylinder for the late '70s F-350 that will balance the system back out. I think that Zoso was the one who told me about it.

Sounds like you are disproportioned alright, is that even a word disproportioned. LOL now if you were to speak with an automotive engineer he would have to calculate how much volume you need to operate your front and your rear brakes, then figure out how much volume the master cylinder sends to the front and the rears. Then determine what needs to be done which more than likely would be a P. Valve.

I would first take the vehicle out to drive and get heat in the brakes then measure how much heat is in the fronts and then the rears. With a good working disc front Drum rear system youll have about 350-400 F front and about 180-280 rear. Sometimes more in the drums but not usually. If your not getting more heat up front then your not proportioned correctly.

Drums out of adjustment and not correct fluid travel will cause this.

Getting better, but still not great.

I told Carquest about the problem brake shoes. We pulled another set off the shelf & then, I learned a lesson. Rear brakes have a front shoe and a rear shoe, they are different. The metal plates are the same, but the front shoe has less material. Both less thickness & less material lengthwise, with more exposed metal at each end. That last part might not make any sense, I don't know how to explain it, should have taken pics. Anyways, I felt more than a little dumb.

I got the pressure bleeder from our main shop today & a quick how-to schooling. I hooked the bleeder up & got one more air bubble from the rear m/c bleeder (running my front brakes). Then, bled at each corner & had no more air at all.

After the brakes were bled, I swapped the shoes around to the correct positions. Put the drums back on & adjusted the rear brakes. The truck drives better, no lock up from the rear end. Probably, due to fixing the shoes. It still doesn't stop as well as my old set up & the pedal is long & soft (that's what she said).

I did pick up the adapter fittings needed to swap the lines for when I find out I've plumbed the m/c wrong. Our Carquest has always had a great selection of brake line adapters, so I'm blessed, it's 4 block away. Cheap too, less than $9.00 for both.

Chad

Oh I see you had your primary and secondary shoes on in the wrong position. dont feel dumb, it happens all of the time with drum brake systems, more now than ever since the majority of commuters today have 4 w disc. My suggestion to anyone doing drum shoes on the weekend to do one side at a time and make sure the shoes you take off are in the correct position before hand. When I bought my 67 mustang it had the primary shoes on the driver side and secondary on the passenger side. Threw me off at first.

Chad - I put a proportioning valve on the rear and it's about 2/3 open...seemed to do the trick for me. It sounds like you are close.

Thanks a ton, I've been reading and reading, looking at picture after picture. Couldn't find the answer. That is really good news. I think I'll try it without the proportioning valve, first. See what I get. Now that I know about the pressure bleeder, bleeding doesn't sound so terrible.

I must have missed the notice, & I just posted the question @ CB.com.

I don't know why I hooked it up the way I did, but I think it came down to what fittings were the easiest. I guess I didn't think it through & it worked ok till now.

I plan on having it swapped & rebled tomorrow.

Chad

REEDIT: "All m/cs are plumbed the same". The rear line from the m/c (closest to the firewall) feeds the front brakes, the front line (furthest from the firewall) feeds the rear brakes. This is now corrected with the info BC Broncos gave me.

I swapped the lines, per Cortez's install. And rebled the system again. The brakes, over all, are better, but now are able to lock up both the rears very easily. I can't get the fronts to lock no matter what I do. The pedal is longer, and I guess that is to be expected. It'll sit overnight & I'll try to bleed again. I did a whole extra "lap" around the truck, bleeding m/c & all 4 corners, even after I came up with no air. If there is really no air in the system, I think its time for a proportioning valve.

I'm still not 100% on the plumbing, although switching the lines, now has the front brakes, being fed by the larger line, which makes sense. Cortez's set up is a 98 Mustang, which used a different m/c. 99-04 all used the same masters, so if someone can confirm plumbing, it would be appreciated.

Chad

Oh, I'd be interested in the F-350 wheel cylinder info if someone has that.

Chad

Well I was able to confirm, from a Mustang shop in San Diego, that the 99 m/c is plumbed the same as the 98 m/c. I've ordered a proportioning valve, and will install it on the rear line next week. I'm sure that will fix the bias problem.

Thanks for the help.

Chad

Well, I've installed the proportioning valve, and bled the system. I've run the proportioning valve all the way out to minimize the rear brakes. I don't lock up the rears anymore, but the fronts don't lock up either. I push the pedal down a couple inches, the pedal gets rock hard & stopping is not great.

When bleeding the front brake system, open a bleeder & the brake pedal only drops a couple inches & stops- about even with the clutch pedal. When bleeding the rear brake system the brake pedal drops to the floor when a bleeder is opened. The pedal drop when bleeding the fronts stops about where the pedal gets hard when driving. What is wrong?

Chad

Chad, im starting to wonder if you may have a bad master cylinder that is bypassing the front seal. What I would do now is pick up some brake line clamps at the parts store.


Now what you do is apply these to your front lines and rear lines, then without actually driving it, the pedal should be rock hard and not move at all. Take the rears off one by one and pedal check at each corner. If it drops more at one pedal than the others, you know where the air or leak is. If the pedal does not get rock solid, then you may have a bad master. With the lines on only the front and not the rears and it seems normal, youll know the master is bad as it is not applying pressure to the fronts, does this make sense?

I think I've got you.

Clamp off the soft brake lines that drop to each axle. Brake pedal should be rock hard, because there is no calipers or wheel cylinders to fill. If the pedal is soft at all it indicates a possible bad master. Or I guess a leak or air between the master & clamp.

I'll see what I can find around town tomorrow & give it a try.

I guess you can't really clamp off individual rear wheels, because there is no soft line to each wheel. But, I can see how you can ID where a leak or bubble is.

I'm also going to try bedding in the brakes and hope for the best.

I think its weird that the brake pedal won't press to the floor when bleeding. Makes me wonder if the master really is plumbed right. I saw a 2000ish GT Mustang the other day & I may find the owner and see if I can track down how the brakes are really plumbed.

Last ditch effort, I'll give it to the real mechanics at the shop and let them go over it.

Thanks, more stuff to track down
Chad

I spent some good time this morning (no real work to do) bleeding. I did get more air, mostly from the m/c, some from the front left caliper. I keep bleeding, and bleeding, till there is no air, only to return 1 or 2 days (or 10 minutes) and get more air. There are no leaks, I keep checking. Still no front brakes.

Scheduled the truck with our mechanics. I'm over it. If they can assure me there is no air, then they are to test my m/c. If there is no air & the m/c is good, then I'm going to switch back to F150 calipers.

Chad

Ok I have done some research on this subject since I wanna go Hydroboost. You'll need to go back to the other calipers for them to work properly. The mustang M/C only has a 15/16"s bore. The t bird calipers need about a 1-1/8 bore for the volume. Thats why the brakes get hard and a poor job at stopping. If you want to keep the t bird calipers you'll need to find a M/C with a larger bore to handle the needed volume for the bigger pistons.

That is interesting, maybe there should be a single thread on these types of issues for Brake modifications to help people find the information.

I think you are right. On rockauto.com, the 99 Mustang lists a 1" or 1-1/16" master bore, depending on the brand of part. There doesn't seem to be any upgraded m/c for the Mustang h-boost. The m/c mounting tabs are at 1 o'clock & 7 o'clock, instead of the traditional 3 o'clock & 9 o'clock. So unless I change my h-boost I'm stuck. I pulled my old F150 calipers & hoses off my old axle & am ready to put them on. I'm going to order new stainless steel hoses & new calipers, but want to fix my problem & be ready to go camping by next week. I have to put the old calipers back on the old axle, since it is "sold" and hopefully will be paid for & picked up in the next month.

Since I've got an Explorer motor to install someday, it might interfere with the h-boost, so I may be changing that again. I'll hang on to the calipers & hoses, so if I end up with a new m/c I can swap back. Actually, I'll probably hang on to them for a couple years, then get fed up & sell them at a huge discount, only to realize I need them 4-6 weeks later. Oh, well.

69Bronco69, I think I just stumbled on a combo that won't work together. I have been combing CB.com, and think I'm the first guy to have this problem, just my luck. I didn't do much reading about the upgrade. I was told it fit & found the parts, I never thought about the side effects. I never considered m/c volume, flow, etc. Looks like most guys are finding truck masters that work, just not with my h-booster.

Chad

It's all in the research. LOL When I did the tbird calipers on my 79 I found that in order to make it all work I had to run a M/C and booster off an f350. 1" bore vs. 1-1/8" bore. Its the needed volume. Thats the only reason I figured that one out. You will need to run the proportioning valve on the rear for sure since it's designed for rear disc's. Disc's take more volume and less pressure than drums. There are a lot of things that come into play when messing with brakes and to get them to work properly.