Brake Pedal Hissing AFTER Replacing Brake Booster!

[cutlassman]

I'm stumped and hope someone can help me out. I had a hissing brake pedal on my 1992 Cutlass Supreme Convertible (3.1L) so I replaced the brake booster with a reman unit. This video is after the replacement was installed. I still have hissing when applying the brakes. The stopping power isn't what it should be...or was when everything was fine...but I can drive the car again as it stops okay. I was able to get the old booster out and the new one in without doing anything other than disconnecting the master cylinder, so I may or may not have to bleed the brakes. Regardless, I can't figure out why I still have the hissing. Any thoughts?

 

https://photos.app.goo.gl/HUz4UKgLuVeIOaz73

[cutlassman]

I can't get  the video to upload...I'll keep trying...

[55trucker]

Which end of the booster are you hearing the hiss from?

 

front end (engine bay) or back end (passenger compartment at the pedal linkage)

[cutlassman]

Only at the pedal itself in the passenger compartment.  I can't hear anything from the engine compartment.

[55trucker]

It sounds as tho the seal around the reaction piston is leaking, does the leak occur foot off pedal as well as foot on pedal?

[cutlassman]

Just a tiny leak with the foot off the pedal.  Much more obvious when pressure is applied to the pedal.  Maybe I got a bad reman unit.

[55trucker]

When you installed the booster did you loop the eye in the pushrod around the pin on the pedal arm BEFORE you fastened the booster to the firewall?

 

The pushrod arm can only swivel so much, too much side pressure on it can dislodge the seal that closes the atmospheric port that allows air into the booster from the passenger compartment.

[Imp558]

Wow! So it may be atmospheric pressure hissing in, not vacuum hissing past the diaphragm. I'm really interested in seeing how this unfolds.

[55trucker]

The booster is a tanden design, when the brake pedal is at rest there is a vacuum (supplied by the engine) on boths sides of the two diaphragms, when the brake pedal is pressed the plunger valve opens to allow atmospheric air into the booster to fill the backside of both diaphragms, this added *normal* air pressure increases the force on the front side of the two diaphragms to overcome the return spring pressure.

 

As soon as one lifts off the brake pedal the plunger valve closes off the inlet port and the air inside the diaphragms is sucked out thru the port on the front of the booster to the engine.

 

When the engine is running & one presses on the brake the *whoosh* you hear is the air being drawn into the booster. There is a filter around the pedal pushrod that silences the sound of the air passing thru.

[cutlassman]

Come to think of it, I did attach the pushrod to the pedal before securing the booster to the firewall. Your explanation sounds spot-on - that seal may be the problem. Is that something I can fix, or do you think I need another booster unit?

[55trucker]

There's probably nothing wrong with the booster but finding a shop to disassemble it to relocate the o-ring seal might be problematic depending on where you live.

 

Disassembling the booster is not something that the average individual finds themselves doing.

 

It's not rocket science, but one needs a walk-thru to show them how it's done.

 

a picture's worth a thousand words......or better yet ....a good video

[cutlassman]

Thanks so much for your insight and expertise!

[vipmiller803]

Or just R&R with another unit under warranty, this time with better installation practices? Why reman the remanned unit when the remanners will give you another remanned one?

 

Sort of shady, I know, but worse has certainly been done.

[Imp558]

When you pull the booster again could you snap some pictures of the firewall and the back of the booster? A lot of us have never seen how they fasten or what the linkage looks like.

[cutlassman]

I'll take some pictures.  I'm getting another reman unit and will swap it out.

[mfewtrail]

When you pull the booster again could you snap some pictures of the firewall and the back of the booster? A lot of us have never seen how they fasten or what the linkage looks like.

 

Here's a picture of the part of the firewall the booster spins to lock into(though it's not on the firewall, but cut out from it in this picture, lol). Best I could find quickly that's from a w-body. That picture came from "shurup." He swapped his PMIII car to vacuum brakes without having to remove the entire firewall plate by cutting out that piece and doing a few other mods.

Edited November 11, 2017 by mfewtrail

[Imp558]

So it's a bolt in panel with a quarter turn pill jar kind of mounting? One would think we can run a lot of different gm boosters.

[vipmiller803]

Let's face it... anything can be done if we go the fab route. Are there are gm boosters that follow that bolt pattern though without the locking ring thing?

Edited November 10, 2017 by vipmiller803

[55trucker]

The *plate* that the booster locks to is a large multi cornered piece (5 or 6 corners) that is bolted to the firewall. You cannot see it as it is hidden on both sides by the insulation applied. It's not unique to the 1st gens, GM has used this same method on the later cars to follow as well. One removes the plate and there is a gaping hole in the firewall. The cam-lock is not unique to the 1gen cars.

[Imp558]

Okay so a smaller second gen isn't going to lock onto a first gen plate. I wonder if a second gen has a similar bolt pattern firewall plate. I've theorized about trying to bolt an early non-abs MC to a second gen booster but haven't gotten serious enough to measure things.

[55trucker]

It's not impossible to do, the mounting bolt centers for the masters are all the same where all W bodies are concerned.  

 

The master on my 91 will bolt to the booster on my sons 02 GTP.

 

The foot pedal pushrod would have to be altered to the same working length as the 1st gen cars foot pedal pushrod.

 

I stand corrected on one point, my son informs me that his booster on his 02 is also a cam-lock design. Only having researched the 1st gen cars I overlooked the 2nd gens as an alternative.

 

Now knowing that I too want to explore the possibility of upgrading to a later designed booster, the brakes on his car are so much better than mine (he does have ABS). Originally I was going to settle on the 94-99 1st gen booster.

[Imp558]

There was some discussion in another thread about smaller boosters, which is what gave me the idea. The diameter is smaller on the Gen II but the length is consistent over the years.

ABS is unnecessary on my next build since the car will be a summer only vehicle so I want the early non-ABS MC. The smaller booster and early MC advantages from my perspective are smaller and neater to make less clutter, a bit lighter for the power / weight ratio, simpler and less expensive to repair.

[cutlassman]

I swapped out the defective reman booster with another one and the hissing is gone! Back to normal operation. Tip...pressing in the protruding tab on the left side of the booster a little helps when mounting.

[cutlassman]

Here's a look at the firewall where the booster mounts.  This is a 1992 CS Convertible 3.1L. https://photos.app.goo.gl/f8ubrEU56JsRjiXK2