Hi all I have another thread that is shoebox ford specific but figured maybe this is a generic enough question. I changed out my old unknown 7" booster (likely chinese junk) with a 7" one made by TUFF STUFF 2222NA (made in america). I bought it on ebay and it was said to be "new" open box but only paid $83 for it including shipping. I couldn't find any others since they were out of stock (when I checked in November). It looks immaculate nonetheless when I got it. I installed it and when I step on the pedal there is no more hissing noise. With the engine still a little cold I can hear a slight change in the engine RPM when I let off the brake pedal after pressing it. It is slight and way less than with the old one and I didn't see the oil pressure change at all on my gauge. With the old booster I remember seeing the oil pressure change when I let off the brake pedal along with a moderate change in rpm/engine tone. Does that seem fine? Is it likely I should expect some level of change in the rpm/tone when I press and let off the pedal? It's slight but I repeated many times to make sure it wasn't a coincidence. Curious if anyone else experiences this as well with a similar booster. If it helps I have a SBC 350 with headers and flowmaster and not sure what cam is in it.
Figured that's the case but how perfectly do universal 7" boosters work even the ones made in america? Just curious if I should expect a small amount of change in the engine rpm when stepping on the pedal. It's slight.. nothing as noticeable as with the previous chinese made junk booster that was in there. Thanks!
Plug it off. It will not affect the engine. Reconnect it. It will affect engine RPM for a second or so. If the diaphragm is bad, it will affect RPM as long as the pedal is pressed (vacuum leak).
Thanks! Yep I agree with that. I had already tried this with the old booster and it was apparent it had a leak inside the valve or diaphragm assembly. It also made a hiss when pressing the pedal. With this booster replacement I'm getting no hiss at all when pressing the pedal and a slight change in engine RPM when letting off the brake pedal. Its slight, I can notice it since I'm paying special attention to it. I guess my question is how perfect are these universal (even american made) boosters supposed to work? Should there be not even a slight change in the engine tone/rpm when letting off the pedal? It could also be I bought a booster from ebay that was sitting for a while even though claimed to be in new condition.
Perfect is how it's working. If you don't want it to affect idle at all, don't hook it up! That's WHY it is connected to the intake, it uses the vacuum to assist (power) the brakes. When to turn the wheel with power steering, it also uses engine power and will drop the idle. If you have A/C and the compressor cycles on and off, it will affect idle.
Oh ok, I don't mind the engine rpm change at all! I just want to hear from others if my setup is fine and its normal to expect a little rpm change when letting off the brake pedal. In others words just a sanity check I don't have yet another bad booster. The old one was making a hissing noise and had a very noticeable rpm drop so it was obvious to me that one needed to be replaced.
oh ok so when I put my vacuum pump on it with the pedal pushed in and at 15 in hg of vacuum it holds well. When I do the same with the pedal not pushed in I also see it holds ok with 15 in hg vacuum. During the actual pressing in or releasing of the pedal I see vacuum drop a lot on the vacuum pump. It makes sense the vacuum drops when I let the pedal go as the valve opens a passage so both sides of the diaphragm will have vacuum again to reduce stress on the diaphragm when not braking and this could (in my case does) cause a change in the engine rpm. I also am not sure why vacuum drops on my gauge as I’m pushing the pedal in but the engine rpm doesn’t. Maybe it’s a small leak in the poppet design as the seals are moving position and that’s how these work and it’s enough for me to see it on the gauge but not hear any change on engine rpm. I was just looking for others to say “oh yeah my engine rpms also change when I let off the brake pedal” to give me a sense it’s normal. The video does help! maybe my old booster was fine minus the hissing noise it made when I push on the pedal.
Do you have a one way check valve in the vacuum line? The check valve will keep vacuum in the chamber and won’t open until you let up on the pedal.
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