[arachnidmagnet]

I was driving my Alfa spider for a few hours and everything was fine running smoothly. All of a sudden the brake pedal felt like it was thumping. If I press hard enough on the brake pedal there is a rhythmic thumping. The brake pedal does not seem to apply as much pressure to the brakes as it used to. What could the issue be? Thanks in advance

 

[m3_tom]

could be brake drag caused by a sticking caliper(s) or a bad hose or hoses, overheating, and then glazing the rotors. Check for heat buildup at each wheel after your next drive, and repair/replace faulty parts as needed. If the fluid is old, the hoses are hold, problems such as this can arise.

 

[vf31rhill]

There is a check valve in the intake manifold end of the big vac line going to the booster. Could this be an oncoming failure of this check valve? What year and model is your Alfa?

 

[arachnidmagnet]

I checked the hoses and there are no leaks. The brake fluid level is normal and is a few months old. I have a 74 spider. The brake pedal makes a whooshing sound when I press it all of the way when I drive

 

[arachnidmagnet]

Is this the check valve that you mentioned?

 

[arachnidmagnet]

I'm thinking it's the booster but how do I check if it's faulty?

 

[Gubi]

I'm thinking it's the booster but how do I check if it's faulty?

That hose in your picture is the vacuum line for the booster. Disconnect it and plug the rubber hose, leaving the booster port open. If that solves the problem your booster is likely bad.

 

[vf31rhill]

Is this the check valve that you mentioned?

No, the check valve is on the other end of that big vac hose, where it attaches to the intake manifold. The fitting in your photo is just an elbow, hollow inside. The check valve looks pretty much like an enlarged pipe nib. But it has a check valve inside it to keep the vac in the booster from dropping when the engine slows down or goes to idle. Sorry I do not have a photo of it.

 

[vf31rhill]

Here is a photo of the vac check valve. Follow the big fat hose under the hood catch/release to the intake manifold. It is that rusty looking hose nib at the end of the fat hose. Bottom left hose connection in the photo. THAT is the check valve. Follow Eric's instruction to test the booster vac system.

 

[alfaparticle]

To check the booster: with the engine stopped push down hard on the brake pedal then start the engine. The pedal will go down some more if the booster is good.

 

[arachnidmagnet]

It looks like it might be the booster. The pedal did not go down when I turned on the car. And when I plugged the hose. The pedal stopped thumping. Should I go on and check the valve also?

 

[arachnidmagnet]

The brake boosters are a bit pricey. Is there a way to fix it or should I go the used route?

 

[vf31rhill]

Buying a used booster is OK but you should try to get one off an Alfa owner who is parting out a known Alfa, one which the seller has driven prior to selling the booster and can vouch for the performance of the booster.

 

[alfaparticle]

It is possible that the booster is not working because it is not getting a vacuum. Disconnect and unscrew the check valve where the booster vacuum hose connects to the intake manifold and clean the internals with carb cleaner. After it has dried out you should be able to blow through it from the manifold side but not from the booster side.

 

[arachnidmagnet]

Would this be the check valve? Do I remove the whole thing?

 

[alfaparticle]

Would this be the check valve? Do I remove the whole thing?

Yes. It screws into the rear of the intake manifold.

 

[arachnidmagnet]

I cleaned the check valve and it seemed difficult to blow any air through the valve. I'm not sure how much force is supposed to be blown. It is still making the whoosh sound as I press all of the way and I noticed the the engine idles more roughly when I step on the brake pedal. Would it be the check valve not working properly or the booster?

 

[vf31rhill]

If the engine idle changes when you hit the brakes, then it is most likely that the rubber diaphram inside the booster can has a hole in it and it bleeding off vac to the other side of the diaphram. This is the kiss of death for your booster assembly. I have seen on rare occasions repair kits offered to rebuild these boosters. But they are rare and expensive. Also a bit of trouble to install. If it were me I would hold out for a KNOWN good used booster. They are pretty easy to remove and replace. And while you have the replacement booster on the workbench is a wonderful time to repaint a booster which has become rusty and scratched up, prior to re-installing it.

 

[arachnidmagnet]

Okay thank you and everyone else who helped me resolve this issue. I'll be on the lookout for a booster and will be repainting it

 

[vf31rhill]

There was a very recent post by someone who wanted advice on parting out a later Graduate, about a 86 if I recall correctly. I am thinking that he mentioned that he knew the car. Look at recent posts in this forum, or in the "parts for sale and wanted" forum. It was only a week or two ago.