It's a good possibility that the one on my '72 Supreme is bad, and dunno if they're vehicle specific.

 

I don't know if they're universal. I've only ever replaced one (on an old Dodge Dart I had back in the '70s). I'd surely get the correct one for the model brake booster you have on the car. Did you pull the valve and have a look-see? It might be possible you'll find a yard of gunk, debris & sludge you can clean out. Just a thought.

 

I haven't pulled it yet Norm, but from what I've read on the innerweb, cleaning them is only a band-aid.

 

They are "generally" universal for the GM Abody (and other GM models) models. 68 or 69 at least through 72 will be the same. Pre-68 are a different design compared to yours.

Auto parts stores carry these for your car and then you can go from there if the more exact original look is a concern.

They should either hold suction or not....not really any "in between" on these valves.

 

Is this the one you're looking at? Supposedly it fits a 1972 7.5L/455.
Raybestos PG Plus Professional Grade Power Brake Booster Check Valves CV89000

 

What are the symptoms of one that's bad?

 

I didn't come across that one yet, but it has my attention.

 

Remove the valve from the hose and booster and.....wait for it......suck and blow (from both openings while you're at it). You should be able to blow air through one end and then suck on the same end and not get any air. Same thing from the other opening on the valve. Sorry about the description but that best describes it. This can be done with a Mighty Vac vacuum tool as well (with proper sized hose).

$18 (+ shipping I assume) seems like a ridiculous price for one of these. Check around....I see a black plastic one at AutoZone (Dorman) for less than $10.

Heck - I have a new one from Inline Tube or NAPA I'll sell you if these are for some reason hard to find (which they shouldn't be). EDIT: Maybe not.....just found the new NAPA valve I bought a few years ago (stored in my house) and it doesn't seem to pass the suck/blow test completely. Have a lot of nice originals that pass the test...but that style isn't repro'd as far as I know.

It does look like the Raybestos valve is "out of stock".....jeez......this crap never ends.

 

Is this the one you saw at Auto Zone?

 

Yes, that particular brand is out of stock in several places. It wasn't my intention to suggest Dave purchased it from Summit, I was only interested in suggesting this might be one to consider (wherever he buys it).

Shipping from some of these places is just stupid.

 

Web search shows Dorman 80189 is available from numerous sources for around $8. Check with your local auto parts store.


But test yours as noted above before doing anything else. In 40 years of driving my car the check valve has never failed.

 

Yeah that 80189 fits your buggy, also. Probably the delta is manufacturer(s) and claims of better quality.

Applications for RNB-80189

 

Whatever "Professional Grade" represents/means. You have to be a Professional Race Car driver, maybe? LOL

 

I'll run that test tomorrow and scoop up the one from Auto Zone just in case.

 

I didn't mean to imply anything Norm.....and yes, shipping can get stupid sometimes. Summit seems to have generally reasonable prices but as you mentioned, maybe it's a "perceived" quality deal with the price. And yes, you MUST be a "professional" to qualify for purchasing and installing these Raybestos parts.....

 

Patton - Unless someone runs an automotive service garage/shop & is dependent on weekly shipments of a large quantity of items, the last place I'd buy an item would be RA. Their shipping prices are stupid.

 

I've personally used the Dorman valve. It works just fine, if not optically correct.

 

And, as Kenneth suggested the Dorman Check Valve is most likely available from any auto parts store.

 

So I did the test on the old one, and while it functioned accordingly, it seemed more "restrictive" than the new one, so I replaced it. Also, the grommet for the old one was no longer soft and pliable, so that got replaced as well.

Hopefully that fixes my issue.

 

I never did see what was your issue.

 

That's because I didn't mention it...lol.

When I step on the brakes, the pedal is a bit spongy, but if I let off and step on them again, I get a good pedal. This started after I replaced the driver side rear shoes about 2 weeks ago. Before that all was good, and here's what I know:

1-I didn't crack the system open when I replaced the shoes.
2-Shoes were installed correctly.
3-No leaks, and fluid level is good.
4-Rear shoes are adjusted properly (I checked them for for wear).
​​wear.
5-No uneven braking or pull to one side or the other.

When I did the research, my symptoms pointed to a bad booster check valve. The only other thing I could think of is the new shoes need to 'bed in".

 

Hmm. My experience is loss of vacuum at the booster results in a hard pedal.

 

And once again proving why "research" on the interwebs is the fastest way to get incorrect information.

Sorry, but there is absolutely no way that a bad booster check valve can cause a spongy pedal, period. The only thing it can do is cause the booster not to provide boost, so a hard pedal as noted. Sorry, but this is where learning the theory behind how the systems in your car work allow you to correctly diagnose problems (as well as being able to filter the online bullshit).

Your symptoms indicate a bad M/C. When the internal seals go bad, leakage is dependent on piston velocity. Push slowly and the pedal is spongy or goes to the floor. Push quickly or in rapid succession and the seals can't leak fast enough so the pedal feels hard.

 

Hmmm...is Classic Oldsmobile (includes yourself) "on" the interwebs?

 

So if pushing it slowly would cause the seals to leak, where is the fluid going?, because I have zero leakage.

 

You have zero external leakage. The fluid goes around the seals, so back to where it was originally instead of being forced in front of the seals and creating pressure in the system.

 

So if the internal seals were bad, and you pushed slowly on the pedal, it would eventually go to the floor, correct?

 

Your M/C is leaking INTERNALLY. Keep in mind that the piston seals need to push fluid from the reservoir into the lines. If the seals are bad, that fluid just stays in the reservoir (or worse, goes out the back of the M/C, into the booster).

 

Yes, depending on how bad the seals are.

 

It could be air in the system, poor brake adjustment, in addition to a bad wheel cylinder or master cylinder.

 

Everything was good until I replaced the driver side rear shoes, so I'm not understanding how it could be the seals.

 

Wheel cylinders are good, and brake adjustment is good, and I didn't crack the system open, so I'm pretty sure there's no air in the system.

 

Maybe it's coincidence that they started leaking at the same time you replaced the shoes? Then maybe it's not the seals leaking? These things are hard to diagnose over the internet.

 

Understood, that's why I'm starting with the easy stuff first. It took me all of 5 minutes to change the check valve.

 

Joe, if it were leaking into the booster, wouldn't the fluid be low in the master cylinder?

 

What Joe is trying to say is the leak is internal to the master cylinder, leaking past the seals inside the unit. Not leaking into the booster.

 

So what was the result?


Yes, but initially it can leak internally before it gets bad enough to leak into the booster.

 

I haven't had a chance to check yet...weather hasn't been in my favor.


I've driven it almost 300 miles since the issue started, and the fluid level hasn't changed. Would that be enough to determine of it's leaking into the booster?

 

Maybe. If it’s leaking internally there won’t be any fluid loss.

 

Update
So after replacing the valve and driving to work last Saturday, it seems to be doing better. Maybe it was the valve, or maybe the new shoes are finally starting to "bed in". I plan in taking it out for drive tomorrow and then I'll make the final call.