I suspect my brake booster is faulty... idle issue

[StefanLee]

Hi guys.

I have a problem with my idle and in connection with that I think my brake booster is kaput...

My idle has gone up quite a bit the last few days, now the car idles at 2000 rpm just just under that. When I depress the brake pedal, the idle increases about 500 rpm, quite a lot.

I suspected a vacuum leak somewhere, with the brake booster being a hot tip. All the vacuum lines seem okay, I can´t find any leaks. I used starter spray on the suspected areas while the engine was running and no leaks.

The master brake cylinder appears to be ok, I did the mc test by depressing the brake pedal with the engine off, it did not sink. When I started the engine though, it didn´t sink any further as it should have... So the brake booster isn´t doing it´s work if I understand everything correctly.

So, could there be something else wrong, or am I barking up the right tree for once? What else should I look for?

Stefan

[ungermm]

Work your way from the carb to the booster. Start by plugging the fitting of the vacuum inlet at the carb and see if that lowers the idle. Then disconnect and plug the booster hose at the booster. If you have an original booster hose, it probably leaks to some degree even though you can't see any problems. If these two check out OK, then you probably have a booster leak.
Jerry

[jvandyke]

I got a hose from a John Deere tractor place. Needs be the right kind. Could be the diaphram in the booster is shot. Or the seal between the booster and the M/C?

[StefanLee]

thanks for the replies. I´ll plug the hose tomorrow and check that out.

as jvandyke said, the diaphragm is probably shot. I´ll try to find a complete new unit, most likely something with better capacity to handle larger calipers. What master brake cylinder and brake booster would you use in that case? I have better access to european parts than american, since I am in europe.

Stefan

[StefanLee]

Besides, I have found out that I lack a one-way valve on my brake booster line. How serious is that? An aquiantance of mine is digging through his stash of opel parts for one, better be safe than sorry!

Stefan

[George]

Originally Posted by StefanLee Besides, I have found out that I lack a one-way valve on my brake booster line. How serious is that? An aquiantance of mine is digging through his stash of opel parts for one, better be safe than sorry! Stefan

I don't think the booster will work without the one way valve.

[baz]

look at BMW even some mercades i think they all use pretty much off the shelf ATE bits in there cars so you should be able to up the system easy but dont go too far over the top or you can over brake the car so it locks up at a touch of the pedal
there are threads here on using bmw pits have a look for it

[StefanLee]

now I´m confused. I went out to test the hoses and lo and behold the idle was a steady 700-750 rpm cold. Not 2000 like yesterday.

The revs went up when I depressed the brake, but not as much as before. Looks like it has to do with hot motor somehow...

I pinched off the vacuum hose to the brake booster, and nothing happened except the revs went up for a second when I removed the pliars. I assume that means that the brake booster leaks and collects air which is then released into the plenum when the pliars are removed and therefore increases the revs. Correct?

Any ideas why the idle goed up when the engine is hot (normal running temp)? I suspect something is causing a lean condition.

Stefan

[baronbors]

When my booster went south- the engine would idle fine until I hit the brake. The idle would decrease, not increase, to the point of stalling the engine. I didn't have a one way valve on the line so I added one but it made no difference. You might have a leak other than your booster.

[Turbo X]

if I am not mistaken the one way valve is there to prevent a backfire from the carb from over pressurizing the booster, rupturing the diaphragm.
if you experience a lean condition with a hot engine (high RPM) can be several things, one a crack in the aluminum intake and it open up when it get hot, gas boiling in the carb bowl, vapor lock, throttle sticking, a split in a vacuum hose, your distributor advanced diaphragm going bad.or sticking. a host of things can make a problem. now that it's back to normal, I would run it again and see if I can repeat the problem and put my test equipment to it..
good luck...let us know what happens..