Help with Hard Pedal after Adding Power Booster

[HOWDY69]

TLDR: Brake pedal is hard. Not sure if added power booster is bad or just the wrong booster for my truck.

(Edit: I found this post which is helpful.

http://www.fordification.com/forum/view ... hp?t=38068 )

I had a power brake booster added over ten years ago. At the time I thought it helped a little but now the pedal is just plain hard.

I did the standard tests sitting in the cab and the pedal doesn't do any of the things described in the manual, it is just plain hard. I did the test to see if the pedal dropped a little when the truck is first started and the test to run the vehicle and then turn the vehicle off and pump the pedal three times.

I disconnected the vacuum hose at the check valve and connected a vacuum gage. I read 22 while warming up on high idle and 18 on low idle in park when warm. In drive with brake depressed and engine warm I read 17-18.

I tested the check valve and air goes in but not out.

I removed the master cylinder (MC) and compared the pushrod length to the depth in the master cylinder and there is about a half mm gap based on my measurements.

The brake light comes on when starting the truck and then goes right off again so there doesn't seem to be a problem with the pressure valve.

I am trying to figure out if I have a bad booster or maybe the wrong booster for my application. Some manuals say 15 in Hg is enough but others say you need a solid 18 or better.

The brakes are drums all around (7500 GVW). The engine is a modified 360FE (edit stroked to 428) with a low rise aluminum intake manifold, Melling RV cam, and mild porting of the heads. It has stock exhaust manifold with dual exhaust but the builder said it is still exhaust limited.

I can't remember where I got the booster but it looks similar to the LMC replacement. I am trying to decide if I should try the same type of booster or a larger diameter or a dual membrane booster. From what I have read the drums can get pretty grabby if you add too much assist.

I am looking for advice from folks that have added a power booster to a four drum truck with a mildly modified FE, or similar situations.

I need to solve this brake issue because my right ankle just can't take the abuse anymore.

[two-bit]

If i am understanding you correctly, the pedal has always been hard ? and has gotten harder over the years ?
If that is correct. heres my next question.
The rod that is attached to the brake pedal, goes thru the firewall, and pushes into the booster. Is that the same rod that was on your truck when it did not have the booster ?
If so, that rod maybe/probably is to long. It is partially, or almost completely depressing the booster all the time. So you are not getting any stroke of the booster to assist your braking.

I ran into this when i put power brakes on my 69 F-100. I unbolted the master, bolted on the bracket for the booster, bolted on the booster, (had to shove it onto the bracket to get the fasteners started), bolted on my master, and fired it up. Pedal was rock hard, harder then when i had no booster. Scratched my head for a while. Pulled it all back off. Next weekend went back to the salvage yard where the donor truck was and looked at stuff. It was then i realized that the rod coming thru the firewall was a different length then what i had on my truck. Grabbed that one, went home, swapped everything over again and TADA i had power brakes.
(Donor was a '70 F-350)
I have heard of a few others over the years having this problem also.
Solved it on a few others by unbolting the rod from the pedal, letting the booster relax, pushing the rod into the cab, and then finding the length difference, by using the pivot point on the pedal as a reference. Got the correct length rod, and TADA. Problem fixed.
Can i guarantee this is your issue. No. But i had the same problem when adding power brakes years ago and this was the solution that worked for me.
Good luck, hope this helps.
Two-bit

[HOWDY69]

If i am understanding you correctly, the pedal has always been hard ? and has gotten harder over the years ?
If that is correct. heres my next question.
The rod that is attached to the brake pedal, goes thru the firewall, and pushes into the booster. Is that the same rod that was on your truck when it did not have the booster ?
If so, that rod maybe/probably is to long. It is partially, or almost completely depressing the booster all the time. So you are not getting any stroke of the booster to assist your braking.

I ran into this when i put power brakes on my 69 F-100. I unbolted the master, bolted on the bracket for the booster, bolted on the booster, (had to shove it onto the bracket to get the fasteners started), bolted on my master, and fired it up. Pedal was rock hard, harder then when i had no booster. Scratched my head for a while. Pulled it all back off. Next weekend went back to the salvage yard where the donor truck was and looked at stuff. It was then i realized that the rod coming thru the firewall was a different length then what i had on my truck. Grabbed that one, went home, swapped everything over again and TADA i had power brakes.
(Donor was a '70 F-350)
I have heard of a few others over the years having this problem also.
Solved it on a few others by unbolting the rod from the pedal, letting the booster relax, pushing the rod into the cab, and then finding the length difference, by using the pivot point on the pedal as a reference. Got the correct length rod, and TADA. Problem fixed.
Can i guarantee this is your issue. No. But i had the same problem when adding power brakes years ago and this was the solution that worked for me.
Good luck, hope this helps.
Two-bit

I had the booster installed about 13 years ago so my memory is a little fuzzy. What I recall is the brake pedal was higher and the brakes were not much better.

I don't know if the mechanic used the same rod to the brake pedal. They would usually give me any spare parts. I don't recall them giving me a connector rod.

I'll check the connector rod. I assume I mark it, unbolt it from the pedal, and then see if it returns further into the cab.

Did the 69 F-100 you put the 70 F-350 booster in have front drum brakes? If I end up buying a new booster I am trying to decide which one to get. I posted a link to Robroy's post about the two different boosters.

Thanks for the help.

[two-bit]

Yes F-100 and the F-350 were both front drum.
I have heard that there is also a difference in the shape of the pedal in relation to the mounting point of the pivot bolt. Not sure if that is true. If there is, i have never seen it.
My f-100 had a healthy build 390 (340hp). Never had any issues with vacuum operating the booster.
Good luck
Two-bit

[HOWDY69]

Two-bit,

I started to check the push rod but the AC makes it very congested around the brake lever. As I was considering if I wanted to remove the AC from the cab (I removed the parts from the engine compartment long ago) I decided to check the master cylinder.

The larger (rear) reservoir is down about 3/4 inches and the smaller (front) reservoir is normal at about 3/8 inched below the top. When I depress the brake pedal fluid flows into the smaller front reservoir but no fluid flows into the rear reservoir.

As I was pushing on the brake pedal I could here a noise like those toy cans that would moo when you turned them over.

I'm not sure how to interpret these results. Does it mean the push rod isn't allowed to return all the way (as you described in your previous post) or the splitter valve or rear cylinders are frozen?

When I removed the master cylinder the other day the pushrod was not longer than the space in the master cylinder, I could put the MC back on and slide it up against the booster without using much force.

Edit: Is it possible the push rod is holding the primary piston past the compensating port which would explain why there is no fluid return in the rear reservoir. It may have been like this so long that it won't return all the way even when I removed the MC.

[two-bit]

Two-bit,

I started to check the push rod but the AC makes it very congested around the brake lever. As I was considering if I wanted to remove the AC from the cab (I removed the parts from the engine compartment long ago) I decided to check the master cylinder.

The larger (rear) reservoir is down about 3/4 inches and the smaller (front) reservoir is normal at about 3/8 inched below the top. When I depress the brake pedal fluid flows into the smaller front reservoir but no fluid flows into the rear reservoir.

As I was pushing on the brake pedal I could here a noise like those toy cans that would moo when you turned them over.

I'm not sure how to interpret these results. Does it mean the push rod isn't allowed to return all the way (as you described in your previous post) or the splitter valve or rear cylinders are frozen?

When I removed the master cylinder the other day the pushrod was not longer than the space in the master cylinder, I could put the MC back on and slide it up against the booster without using much force.

Edit: Is it possible the push rod is holding the primary piston past the compensating port which would explain why there is no fluid return in the rear reservoir. It may have been like this so long that it won't return all the way even when I removed the MC.

HHHMMMM.
I like the can/moo reference. I am not sure why its happening though.
I keep thinking its that rod length.
You even stated that pedal sat higher when you first got the work done. Just like it was getting "pushed" into the cab.
If it was the splitter valve stuck to one side or the other your brake light would be on all the time. If its stuck in the middle, it should not make any difference. Thats its normal function spot.
If it was my mess. I would unbolt the master, and then unbolt the booster from the mounting bracket. I would pay really close attention to how much tension is on the fasteners that hold the booster to the mounting bracket. If you unbolt the booster and it "pushes" into the engine compartment that would be a red flag for me.
With the brake pedal pulled all the way into the cab. (Bungee cord around the pedal hooked to the steering wheel), does the brake booster sit flush against the mounting bracket, or do you have to push it towards the bracket to get it bolted back up ?
Unbolting the booster from the bracket, with the pedal pulled all the way towards the inside of the cab, should have the inside of the booster completely relaxed. You should not have to compress anything inside the booster in order to bolt it on with the pedal in this position.
Its hard not being there, to see and hear everything its doing.
This is what i would do to verify that rod length.
BTW, that vacuum line from the booster to the intake. Any scent of brake fluid there ? By the test results you posted from vacuum testing i would guess there is not.
I'm throwing out ideas. Maybe we can get someone else to chime in ?
Two-bit

[HOWDY69]

... I would unbolt the master, and then unbolt the booster from the mounting bracket. I would pay really close attention to how much tension is on the fasteners that hold the booster to the mounting bracket. If you unbolt the booster and it "pushes" into the engine compartment that would be a red flag for me.
With the brake pedal pulled all the way into the cab. (Bungee cord around the pedal hooked to the steering wheel), does the brake booster sit flush against the mounting bracket, or do you have to push it towards the bracket to get it bolted back up ?
Unbolting the booster from the bracket, with the pedal pulled all the way towards the inside of the cab, should have the inside of the booster completely relaxed. You should not have to compress anything inside the booster in order to bolt it on with the pedal in this position.
Its hard not being there, to see and hear everything its doing.
This is what i would do to verify that rod length.
BTW, that vacuum line from the booster to the intake. Any scent of brake fluid there ? By the test results you posted from vacuum testing i would guess there is not.
I'm throwing out ideas. Maybe we can get someone else to chime in ?
Two-bit

I really like the idea of unbolting the booster from the bracket to see if it is under compression.

I'll also check the vacuum hose to see if it smells like brake fluid.

Thanks for the ideas!

[HOWDY69]

Photo test

1609727091820~2.jpg

[68fe360]

TLDR: been there done that. Cheek that the entire system flows,, and Replace the booster.

I had a very similar issue. The pedal was hard, and had to press harder then I should have to bring it to a stop. This would get worse slowly over time.

Due to time constraints I took it to a shop.

Vacuum was fine, and everything checked out good. So they replaced the master cylinder.

Part of thier inspection they unbolted the MC to check for a piston seal leak. Bingo found the problem. After replacing it resolved the problem. Except that it came back over the next 6 to 12 months.

Recently I redid everything break related. Lines booster, etc. You name it I replaced.

Guess what I found when I unbolted the MC? The piston seal was leaking again. Apparently the shop never checked why it was leaking. The booster rod to MC seal was leaking, and drawing manifold Vacuum on the MC piston and seal. Which was causing the apparent leak.

I bet if you replace that booster the problem will go away. But it's also a good idea to attempt a quick bleed on all wheels. This will ensure fluid flows through the entire system, and you do not have a clog of one type or another. Do the method of having someone press the brake. This replicates everything, and prevents accidentally missing a potential problem.

Important lessons learned.
1.) Never trust a shop to trust a shop, even a trusted shop, to determine why a part failed.
2.) Always do a postmortem to determine the cause of a failure. Knowing why can uncover a more complex failure.

[68fe360]

Found my screen shot of an old insert Cardone includes with thier master cylinders that explains the problem with a good diagram. It's possible this vacuum induced piston seal leak to be small enough that it gets sucked into the booster. Then into the manifold to be burned up. Thus leaving no external sign of a leak. Only visible when you remove the MC, or when it's bad enough will it seap out between the MC and booster. There should be zero fluid in that area of the booster.

This booster seal leak will cause a hard pedal due to reduced, or no assist from the booster.

Plus I just got a look at the pic of your MC fluid. Seems rather dirty. It is possible you have a clog or restriction some ware in the system. Specialy if there is grime at the bottom of the reservoirs. Even though you stated your brake light proves out, and turns off. It should not be relied on if it is pretty much assumed to be original, or older then my 1992 Canaro. Lol

That grime can cause the shuttle in the valve assembly to become stuck in the normal position. Not just in the one of extreme positions. Rendering it inoperable. Periodic cleaning and resealing these valves is required for proper operation, and safty. Which makes testing for good flow at all 4 wheels a must if you have grime at the bottom of the reservoirs. If one or more doesn't flow, or doesn't flow close to the same amount as the others, you at the very least have a restriction. Possibly a full on clog

Check the condition of the MC gasket. If it is becoming swollen this is a sign of petroleum contamination, and is the cause of the grime. Replacement of all rubber componets will need to be done. As well as flushing the system with denatured alcohol to clean the contamination out of the system without breaking down the rubber parts, hoses, gasket, etc. Then drain and flush with clean break fluid.

Not sure if you have done so or not, but visually check each wheel cylinder is not frozen on one or both pistons. It's a P.I.T.A. but don't just look at it and pop the wheel back on. Remove wheel cylinder to brake shoe pin and look in the boot. Moisture will rust the piston to the bore. Making it solid, or drag pretty bad. If you can carefully pop the boot off to get a better look if it is questionable. This may require removing the hold down springs, but the shoe retracting springs should hold the shoes together so you don't have to do a full disassemble of the shoes.

Even one stuck piston will cause significantly reduced breaking effort. On the rear it can cause the parking break to remain partially engaged by not letting the shoes retract. This in turn overheats the drum, leaving you to rely on only your front breaks.

Even though the main culprit is likely your booster, you did originally state your breaks were requiring increased effort before adding the booster. That the booster had only improved it some, and eventually progressed to ware you are today. This indicates a prior cause that needs to be addressed to prevent resisting the problem in a few months.

The leaky booster I replaced had that leak out of the box. As I was having the issue after installing a new one to replace one with an unmistakably torn diaphragm. So your booster being bad as well as the preexisting problem is not just possible, but probable.

I hope this is helps track down the root cause. It sucks having safety issues like this.

-Will

Screenshot_20210114-094621_Drive.jpg

[two-bit]

Any update on this ? Any luck so far ?

[Wes]

Hard Glazed shoe linings will cause hard braking effort, even when the master and booster are working as designed. Inspect your linings and drums.