My '69 F-bird has power brakes with disks up front and drums in the back. All brake components at the wheels are new as is the booster. There are no leaks so I did not run new lines. The car does stop but feels much more like manual brakes with very slight power assist. The car does have a big cam and I've been told that can effect vacuum but I've had other cars with big cams where the brakes felt OK. Not really a brake guy so I'm looking for some insight on what to check to the problem.

Did you bleed the air out of the system?
What kind of brake fluid did you use?

Brakes are bled. Not sure of the type of fluid. What should it be?

FWIW...I had to go to manual brakes after my rebuild, was only pulling about 10 psi with the bigger cam. You have access to vacuum gage to check?

Yeah my buddy has a shop. What kind of pressure reading should I be looking for in a normal situation?

FYI: They market vaccum cannisters that "collect" enough vaccum to work with power brake boosters for cars with low manifold vaccum.

I'd say at least 15 for power brakes.

Nah, you can go lower than that. My gauge reads about 11-12 lbs at idle and I have plenty to run my stock booster. You don't need much for brakes at idle though and when you do need them you usually have plenty of vacuum anyway with the RPMs up.

OK put a vacuum gauge on it and I've got 15-17. Doesn't seem to be an issue. What else should I check?

9 times out of 10 it seems to be a system bleeding issue when I have had trouble with mine. There's been times when I've had to pull the MC off a couple of times to bench bleed and then do the whole system several times before it felt right.

Thanks Bob I'll bleed them again and see how it works out. Would be real nice if that's all it is.

are the soft lines new also? They can collapse internally and cause problems bleeding.

No I did not replace the brake lines. They seemed to be OK at the time I redid the other components as they weren't visibly damaged or leaking.

Last but not least check the inside diameter of the drums. If they are far over the max dia it will cause excessive pedal travel

Did you adjust the star wheel to adjust brakes lining to come close to contacting the drums?

How are you bleeding? Back to front? Do you have a plastic tube going from bleed screw into a bottle of brake fluid?

Yes we used the tool to adjust the brake linings close to the drums. We have been bleeding back first but are just bleeding into and old drain pan.

If you drain into clean bottle then air cannot get back into the system. Also, top up master, if it goes empty then air is back in system again and you have to do full bleed again.
So your pumping up the brakes, hold, release fluid into bottle and close before foot hits the floor?

Reason I asked about the fluid is because you won't want to mix new type with old. I believe we use Dot 3 for the old cars (if memory serves me right).

If that all checks out I'm not sure what else it could be. I had a very radical cam on my car years ago with no issues with the brakes. Maybe try remove vac line from booster and plug of vac connection and test to see how they perform without vac assist. If there is little or no change then sometime wrong in the assist side.

Back in the day I would run a long vac line to my windshield so I could monitor it while I was driving. Try it on yours and see what it's pulling when your braking while driving.

I would 2nd changing out the soft lines, if for no other reason then to eliminate it as a possible issue.

Appreciate everyone's input. I will try these suggestions over the weekend and let you guys know how it turns out.

Yep the rubber lines can do weird things, best to replace. But the way you described it "feels like manual brakes" sounds like a hard pedal not a soft pedal. Definitely suspect the new booster as 15" of vacuum is more than enough.

I had a hard pedal on my manual drums. One problem was that my return spring on the pedal was weak, so when I had adjusted my brake light switch I had adjusted it out to far and was actually putting slight pressure to the brakes constantly. Also had a rear brake cylinder that was hung up. Fixed the break cylinder and backed off the brake switch and no more hard pedal. Trying to find the will power to take out brake pedal assembly to replace the spring, but for now just pulling back on the pedal gently with my foot so the break lights go off.

Definitely a very hard pedal. Probably something I should have noted to begin with-might have gotten different responses. Think I'm going to start with a good bleeding and then work to the booster and lines.

Hard like it is when the car is shutoff and you try to use the brakes? That sounds like a bad booster or bad valve.

Almost the same just marginally different with the car running. What valve would you be referring to?

There is your problem Dave, something wrong with your booster or the vacuum supplied to it. The valve is the plastic 90 degree fitting on the booster that the vacuum line connects to. It is a one-way valve so the booster should hold vacuum for some time even if the engine is not providing any. For example, after you turn off the car you should usually get one application of the brake pedal with power assist, after that you've lost that vacuum and no more assist.

Thanks man. I guess I should start with replacing that valve, bleeding the system and see what happens.

test the valve by running the engine and shutting it off without using the brakes. then pull the valve out of the front of the booster, you should hear the vacuum being released as you break the seal. If you don't hear it then check to make sure it is getting vacuum(start the engine with line disconnected and put your hand over it). If there is vacuum at the valve the booster should be working even if the valve has failed.

Appreciate that. I will test that tonight when I get home from work. If I have vacuum when I remove the valve and feel vacuum when covering up the end of the disconnected valve I guess the issue would be with the booster itself?

yes, but I have been lucky enough to not face the failed booster thing yet so I can't answer stuff about pushrod length, travel etc. It seems to me that those issues might cause a good booster to not work but not sure. good luck.

do you have a part number for what master cylinder is on the car?
does it have a 1.125" bore

I'm checking. It is a Delco-Moraine so its something decent, but the guy I got the car from put it in, not me.

This is weird but it was the problem. I recently put a TA hood on the car and when trying to get it aligned properly found that the hood was hitting the top of the booster. We changed the angle of the booster so the hood would close and found that it also made a big difference in how the brakes function. I would have never thought this would be the problem but seems like it was.