There's a snake in my brakes! (hissing noise)

[brucecooner]

My brake pedal is hard to press, I'm not getting any help at all.

I've heard the XJ's weren't known for the stopping prowess, but I have to think about a half mile ahead about upcoming stoplights.  And don't even think of follow distances less than a quarter mile.

 

If I press the brakes to or past a certain point, there's a hissing noise from under the dash that I suspect is air rushing in to fill the vacuum in the booster.

 

There's been a couple of times when I pressed the brake very hard, and the engine revved.

Now, those were panic braking situations (think a stale green light taking me by surprise) and since the gas and brake pedals are close together I might have had my foot partway on the gas.  But, if that wasn't it I'd guess it means somehow the vacuum line was open to the atmosphere and it was basically like the throttle being opened.

In which case, isn't the check valve supposed to prevent air going back out?

 

So obviously I figured the first thing I would do is just check the check valve.

But the dang thing doesn't want to come off the booster body.

I pulled on it, to no avail.

So I twisted it, thinking it had tabs to align, but apparently it don't.

 

Is there a trick to pulling the vacuum line off the booster?

You can see in the picture my fingerprints where I was fumbling with it.

 

Any further tips for debugging the brakes are welcome.

 

I've heard there are other flavors of more powerful booster one can upgrade to, are they worth the effort? Things are TIGHT in that engine bay.  My tires are slightly oversized but the suspension setup is otherwise stock, so I don't know if I really need the extra oomph.

 

 

 

[cruiser54]

Check the booster valve from the end of the hose at the manifold. 

You shouldn't be able to blow through it. 

 

But I bet it's your booster. Go back with a stock one for your needs. 

[gogmorgo]

X2 on a bad booster.

As far as upgrades go, I’ve had no complaints about stock brakes as long as they’re maintained and working correctly. All an upgraded booster does is push the pedal harder, it doesn’t really improve braking performance all that much. 
The valve/fitting just pushes into a rubber grommet. Pull harder and it *should* pop out. Careful putting it back in that you don’t push the grommet into the booster. 

[Minuit]

X3 on a bad booster. X2 on the factory braking system being fine as long as everything is working as it should. I have rear discs on my '91 and the stock booster and master cylinder drive those just fine. Yes, the pedal effort is higher than more modern cars, but the pedal in my truck is very firm, easy to modulate, and the stopping performance is just fine. I actually kind of like it, to be honest. In a non-ABS system, requiring a deliberate effort to induce lockup is good IMO.

 

An upgraded booster will lessen pedal effort. It will make it "easier" to stop quickly. If your stock system is capable of locking up the wheels, that's all it will do. A lot of people interpret this easier pedal action as an improvement in braking performance, but it ultimately comes down to the traction between the tires and the road.

[brucecooner]

10 hours ago, Minuit said:

X3 on a bad booster. X2 on the factory braking system being fine as long as everything is working as it should. I have rear discs on my '91 and the stock booster and master cylinder drive those just fine. Yes, the pedal effort is higher than more modern cars, but the pedal in my truck is very firm, easy to modulate, and the stopping performance is just fine. I actually kind of like it, to be honest. In a non-ABS system, requiring a deliberate effort to induce lockup is good IMO.

 

An upgraded booster will lessen pedal effort. It will make it "easier" to stop quickly. If your stock system is capable of locking up the wheels, that's all it will do. A lot of people interpret this easier pedal action as an improvement in braking performance, but it ultimately comes down to the traction between the tires and the road.

 

All through high school I drove a '66 Mustang without power anything and the brakes were never an issue.  Stopped when I needed it to.

I would think that at the point that you lock the brakes you're at the upper limit of "braking performance", in regards to boost anyway.

 

I see cheap-ish reman boosters at the usual culprits (Autozone, O'Reillys, etc.), is there a particular brand I could seek out for better durability?

 

 

 

 

 

 

 

[cruiser54]

It's a crap shoot on brands. I'd rather have a good used one.