Is there a break-in period for a new brake booster?

[MaximRecoil]

My original brake booster had a vacuum leak, though it still worked fine. I replaced it with a rebuilt one (A-1 Cardone 54-73501), and it doesn't leak, but it doesn't work nearly as well as the original. You have to push on the brake pedal about twice as hard compared to the original. It is getting plenty of vacuum (~18 inHg). I was wondering if the new diaphragm inside might be stiff and need to "break in". Or maybe Cardone just doesn't know what they're doing.

[303 Mopar]

I have that booster and it works fine, although I would say it may have a different feel to the original.  You may need to bleed your brakes.   

[MaximRecoil]

I have that booster and it works fine, although I would say it may have a different feel to the original.

Mine must be defective then.

You may need to bleed your brakes.

Brakes that need to be bled don't result in a brake pedal which is harder to push. Air is compressible, so air in the brake lines results in a soggy pedal that goes to the floor or almost to the floor before fully activating the brakes. In my case, the brakes work the same as before; they just require about twice as much leg muscle to activate. Also, all I did was change the booster; I didn't touch the brake lines.

[ws23rt]

No
You may have  18 in hg vacuum but not the required volume.  
What is the vacuum drop (at booster) when braking?

[MaximRecoil]

No
You may have  18 in hg vacuum but not the required volume.  
What is the vacuum drop (at booster) when braking?

If I apply 18 inHg of vacuum to the booster with a hand-operated vacuum pump, then press the brake pedal down as far as it will go, the pressure drops about half. The fact that the original power brake booster worked fine (even with its leak) eliminates the vacuum source as an issue though. Nothing has changed except for the booster.

[b5blue]

You got crap. That thing should over boost so bad you could knock your teeth out braking with the tip of your toe! Same thing happened to me long ago just as your describing, put in one from NAPA and drove fr a year that way. Happened to visit a shop that had one in old stock for 80.00 so I bought it and first test drive damn near busted my lip open on the steering wheel.

[ws23rt]

No
You may have  18 in hg vacuum but not the required volume.  
What is the vacuum drop (at booster) when braking?

If I apply 18 inHg of vacuum to the booster with a hand-operated vacuum pump, then press the brake pedal down as far as it will go, the pressure drops about half. The fact that the original power brake booster worked fine (even with its leak) eliminates the vacuum source as an issue though. Nothing has changed except for the booster.

IMO --with what is given here. The new booster is not seeing the vacuum needed.  Maybe the check valve is stuck?

[MaximRecoil]

No
You may have  18 in hg vacuum but not the required volume.  
What is the vacuum drop (at booster) when braking?

If I apply 18 inHg of vacuum to the booster with a hand-operated vacuum pump, then press the brake pedal down as far as it will go, the pressure drops about half. The fact that the original power brake booster worked fine (even with its leak) eliminates the vacuum source as an issue though. Nothing has changed except for the booster.

IMO --with what is given here. The new booster is not seeing the vacuum needed.  Maybe the check valve is stuck?

If you tried to apply a manual vacuum to a brake booster with a stuck check valve, the pressure would rise to 18 inHg in just a few pumps of the handle, because there is hardly any air volume in a check valve. However, it takes a lot of pumps to get this booster up to 18 inHg, so I know it's pulling the air out of the booster and not just a plugged check valve. I suppose it could be partially stuck, but it's definitely not fully stuck. The brakes are getting some vacuum assist, just not nearly as much as they should be getting. I do have a known-good check valve that I can try in it tomorrow.

You got crap. That thing should over boost so bad you could knock your teeth out braking with the tip of your toe! Same thing happened to me long ago just as your describing, put in one from NAPA and drove fr a year that way. Happened to visit a shop that had one in old stock for 80.00 so I bought it and first test drive damn near busted my lip open on the steering wheel.

That's what I'm thinking too, which really sucks, because it is such a pain to change those things out. It took me 6 hours. If not for that upper right-hand corner nut, it would be a lot easier. Because of that nut I have to take the instrument cluster out and go through the dash with a socket on a long wobble extension, and getting that nut started again after putting in the new booster was the worst part, because I couldn't get a straight shot at it due to things in the dash being in the way.

[rebby]

If you're talking about that top nut on the door side, you can get at it with a long extension with a wobble fitting. That's how I did the R&R when I added my hydroboost system last week. It's a tight fit but you can get in there. For the inner side, I found that's there is plenty of room to get at it with a wrench. Good luck!

[MaximRecoil]

If you're talking about that top nut on the door side, you can get at it with a long extension with a wobble fitting. That's how I did the R&R when I added my hydroboost system last week. It's a tight fit but you can get in there. For the inner side, I found that's there is plenty of room to get at it with a wrench. Good luck!

I'm talking about the upper right-hand one (right-hand from the perspective of sitting in the driver's seat); the position indicated by the "X" below:

O X
O O

There's no way to do it with a wrench that I could see. My car originally had AC, so things are a lot more cramped under and behind the dash than a non-AC car. I can get at all 3 of the other ones easily enough without having to remove the instrument cluster.

[Mopar Nut]

If you're talking about that top nut on the door side, you can get at it with a long extension with a wobble fitting. That's how I did the R&R when I added my hydroboost system last week. It's a tight fit but you can get in there. For the inner side, I found that's there is plenty of room to get at it with a wrench. Good luck!

I'm talking about the upper right-hand one (right-hand from the perspective of sitting in the driver's seat); the position indicated by the "X" below:

O X
O O

There's no way to do it with a wrench that I could see. My car originally had AC, so things are a lot more cramped under and behind the dash than a non-AC car. I can get at all 3 of the other ones easily enough without having to remove the instrument cluster.

You'll need a universal joint socket with an extension.

[rebby]

If you're talking about that top nut on the door side, you can get at it with a long extension with a wobble fitting. That's how I did the R&R when I added my hydroboost system last week. It's a tight fit but you can get in there. For the inner side, I found that's there is plenty of room to get at it with a wrench. Good luck!

I'm talking about the upper right-hand one (right-hand from the perspective of sitting in the driver's seat); the position indicated by the "X" below:

O X
O O

There's no way to do it with a wrench that I could see. My car originally had AC, so things are a lot more cramped under and behind the dash than a non-AC car. I can get at all 3 of the other ones easily enough without having to remove the instrument cluster.

It was a tight fit but I was able to get on that one with an open ended wrench. My car is an A/C car as well. The vast majority of the factory firewall insulation has been replaced with dynamat though and the factory A/C box has been replaced with a Vintage Air system. I know that the factory A/C box is pretty big, sounds like it goes further into the driver's side than I remembered.

[MaximRecoil]

You'll need a universal joint socket with an extension.

You can use a wobble extension to remove the nut. It may be possible to get the nut back on using just a wobble extension, but I wasn't able to do it. I ended up using a U-joint socket to get the nut back on, though it still wasn't easy. It was a matter of "keep trying until you get lucky", which is the same approach you have to use for plugging the speedometer cable back in (sometimes it plugs back in on the first try, but not very often for me).

It was a tight fit but I was able to get on that one with an open ended wrench. My car is an A/C car as well. The vast majority of the factory firewall insulation has been replaced with dynamat though and the factory A/C box has been replaced with a Vintage Air system. I know that the factory A/C box is pretty big, sounds like it goes further into the driver's side than I remembered.

Yeah, it was the factory AC box that prevented me from getting my hand anywhere near that upper right-hand nut. It could probably be done with a very long wrench with a series of custom bends in it.

[Mopar Nut]

You'll need a universal joint socket with an extension.

You can use a wobble extension to remove the nut. It may be possible to get the nut back on using just a wobble extension, but I wasn't able to do it. I ended up using a U-joint socket to get the nut back on, though it still wasn't easy. It was a matter of "keep trying until you get lucky", which is the same approach you have to use for plugging the speedometer cable back in (sometimes it plugs back in on the first try, but not very often for me).

You can also remove the gauge cluster to have a straight shot.

[MaximRecoil]

You can also remove the gauge cluster to have a straight shot.

That's what I did. Here's what I said earlier:

That's what I'm thinking too, which really sucks, because it is such a pain to change those things out. It took me 6 hours. If not for that upper right-hand corner nut, it would be a lot easier. Because of that nut I have to take the instrument cluster out and go through the dash with a socket on a long wobble extension, and getting that nut started again after putting in the new booster was the worst part, because I couldn't get a straight shot at it due to things in the dash being in the way.

And I can only get an almost straight shot that way, which is why I need the wobble extension to take the nut off and the U-joint socket to get the nut started again. There's no way to do it without removing the instrument cluster (or without removing the AC box, which would be a lot worse) that I could see.

[ws23rt]

I replaced a brake booster on my 70 charger rt (ac car) in the late 70s.

At the time I had not yet had the instrument cluster out of one of these cars and needed the car badly for work the next day.

I used a fine pawl ratchet (1/4" drive) with a deep socket for the passenger side upper stud.  Getting the wrench on the stud was not so tough. The room to move the ratchet was limited and I needed to move the socket on the ratchet one square to gain the movement needed to get a click on the ratchet for each movement of the wrench.---(remove the wrench,turn the socket on the wrench and gain enough to move forward to the next wrench click)---

It worked. --The down side was the threads on the stud were not loose. It took several hours and a skinned up hand to get the old booster out.
To put the new booster in I made the pilot end of that stud a bit longer to make starting the nut a breeze.

This thread just happened to bring back that memory.  Sometimes if we don't know any better and need to get something done it can happen.
BTW I would say--take the instrument cluster out for this task.  I know why.