So on my 70 Newport there is a pretty audible hissing sound coming from the brake pedal when it is stepped on. Upon further investigation , I see that there is a "boot" type rubber thing that seems to be part of the brake booster between the firewall and the brake pedal itself. If I reseat the boot in a certain postion the hissing stops . The hissing is due to vacuum loss at the point where the boot ends connect. Does anyone know if I have to replace the entire brake booster or is there a way to reseat /install a new "boot". Whatever that part may be. I hope I am not being to vague, im seeking someone who has had this issue chime in maybe to shed some light for me.
Hissing noise coming from power brake booster interior boot.
- Thread starter NWPT70
- Start date
75LandYacht
Yank Tank
I have the same hissing from under the dash, It goes away when I accelerate though, which I assume is the motor compensating for the vac lose. I assumed the same as you that I have a Vac leak involving the brake booster. I haven't investigated it though. I too would like to see what the forum can offer.
GregG48203
Active Member
It may be necessary to pull the booster off of the firewall to see if it's rusty. Otherwise, the boot may be leaking due to the age of the rubber. Some boosters can be rebuilt; for others it's better to find a replacement.
My booster on the 78 Newport was hissing.....I replaced it.
You're gonna end up replacing it.
Major pain in the *** to get the booster off....
traintech55
Senior Member
You have a leak in the booster, better replace it now before it gets worse. Good time to do the master cyl. also.
Have it rebuilt and keep it for a spare.
75LandYacht
Yank Tank
Great info.. Thanks all.
69_topless
Member
Continue with the old thread, I have the same problem on my 69 Polara. Last night when cruising, enjoying one of the last warm nights with the top down, I have noticed this hissing sound when stopped at the lights. Further, I started to have feeling the brakes are not working proper way, requiring more power applied on the pedal to slow down.
I did check today these parts:
Car sitting all day, 1st thing I tried was to push the brake pedal couple of times and kept it pressed, when started the engine. No pedal position has changed
intake manifold hose - OK, no damage
power brake booster valve - seems working properly, not leaking the other direction
fluid in master cylinder - full level as it should
Hissing noise with engine running and brake pedal pressed - still there
When engine is running, I can move with the brake booster valve installed in the sealing on the booster, like when the engine is OFF. I would expect it would be sealed well due the vacuum? Vacuum test port on the valve worked but have no experience how much strong the vacuum press should be, tested with just with the finger as a plug. Original rubber plug seems to be OK.
Is there something else to check, before placing order for the refurbished "new" power brake booster?
Recalling there might be early symptom of the brake booster going bad:
the brake lights stayed ON if I switched the engine OFF prior releasing the brake pedal. I had to start the engine again to have the brake pedal returned to standard position
Thanks for any comment, appreciate your help.
I did check today these parts:
Car sitting all day, 1st thing I tried was to push the brake pedal couple of times and kept it pressed, when started the engine. No pedal position has changed
intake manifold hose - OK, no damage
power brake booster valve - seems working properly, not leaking the other direction
fluid in master cylinder - full level as it should
Hissing noise with engine running and brake pedal pressed - still there
When engine is running, I can move with the brake booster valve installed in the sealing on the booster, like when the engine is OFF. I would expect it would be sealed well due the vacuum? Vacuum test port on the valve worked but have no experience how much strong the vacuum press should be, tested with just with the finger as a plug. Original rubber plug seems to be OK.
Is there something else to check, before placing order for the refurbished "new" power brake booster?
Recalling there might be early symptom of the brake booster going bad:
the brake lights stayed ON if I switched the engine OFF prior releasing the brake pedal. I had to start the engine again to have the brake pedal returned to standard position
Thanks for any comment, appreciate your help.
traintech55
Senior Member
Everything you describe is an indication of a bad diaphragm in the booster. Get a new one or have yours rebuilt.
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