Brake booster?

[supton]

Last few times I drove my 99 Camry I noticed that the brake vacuum was discharged when starting. Brakes fine, but the system seems to suddenly bleed down quickly: I moved the car today, had to start it, shut it down and an hour later it was again discharged (brake pedal has no assist). I see that there is a check valve on the booster, should I try that first, or is this a sign that the booster is on its way out?

Last couple times driving it, maybe the pedal goes down a bit further, hard to say, it is not my daily anymore and I have been alternating between other vehicles, so I want to say it has not changed the pedal feel, as long as the engine is running.

 

[bullwinkle]

The check valve would be cheaper, but a bad booster on a 20+ year old car wouldn't be surprising. Do you hear any weird hissing noises when you apply the brakes (while engine is running)? Most bad boosters seem to be pretty obvious.

 

[supton]

I think I see the problem—cold weather and old vacuum lines. When I grabbed them, they were too loose. Am going to add some clamps and see if it holds.

 

[Nick1994]

I had to put a booster in mine last summer. The symptoms I had were after braking a couple times in a short period of time (like a parking lot) the pedal would go hard. After waiting 10-20 seconds it was usually boosted again but then the next braking shortly after was hard.

It isn’t too hard to replace. Just have to be a little bit of a contortionist, and I’m a big boy so it wasn’t too fun, but do-able.

 

[Lubener]

I think I see the problem—cold weather and old vacuum lines. When I grabbed them, they were too loose. Am going to add some clamps and see if it holds.

Not likely, the check valve and its grommet should maintain the vacuum within the booster when the engine is off.

 

[supton]

Not likely, the check valve and its grommet should maintain the vacuum within the booster when the engine is off.

It appears you are correct, no change. Worth a try.

I did another check. In park, mash down on the pedal. Engine bogs down a bit, and the lights dim (lower engine rpm?). So it sounds like the booster is on its way out. Wonder how long I can limp it, car needs a steering rack too at some point, and something is leaking oil (again).

 

[Tomioka]

I've seen leaking brake boosters where short and long-term fuel trims throw positive values, but not bad enough where it will throw a lean code. If you have access to a scan tool that can read fuel trims, check before and after removing the vacuum hose and plugging it.

I've had a brake booster fail on a 01 Tundra before so it's probably a coincidence.

 

[Lubener]

It appears you are correct, no change. Worth a try.

I did another check. In park, mash down on the pedal. Engine bogs down a bit, and the lights dim (lower engine rpm?). So it sounds like the booster is on its way out. Wonder how long I can limp it, car needs a steering rack too at some point, and something is leaking oil (again).

If it's leaking that bad, I would believe a hissing sound should be heard all the time. The grommet or check valve are more likely candidates than the booster itself. Always try the cheapest part first.

 

[supton]

Finally got around to it. Removed check valve, applied 5psi to booster. 1ps loss in 5 minutes? something like that. I tried first with the check valve in place, same result, so it sounds like it’s the booster. Very slow leak. Starting to look into how to replace, looks like loads of fun (not).

 

[Marcozi]

It appears you are correct, no change. Worth a try.

I did another check. In park, mash down on the pedal. Engine bogs down a bit, and the lights dim (lower engine rpm?). So it sounds like the booster is on its way out. Wonder how long I can limp it, car needs a steering rack too at some point, and something is leaking oil (again).

What's happening is you're inducing a vacuum leak, which alters the fuel-air mixture.

 

[supton]

What's happening is you're inducing a vacuum leak, which alters the fuel-air mixture.

Possible. I don't think I've noticed it much lately, so maybe it's altered itself again. It certainly hasn't altered my driving for the last 10 months, lol (it's been a crappy year, I make no excuses for not staying on top of this issue).