Morning Sickness

[firstq]

Guys - my brakes are giving me trouble and I am stumped.

Brakes literally do not want to come on when the car is cold in the AM. we are still talking Phoenix AZ weather cold - probably still 50-60 degrees.

As soon as the car warms up, the brake engages exceptionally well. If I do not warm the car and drive it cold my braking power is orders of magnitude worst to a point that it may be literally unsuable.

If anyone can help triage this one, it will be really helpful. one thing to focus would be that this is a problem only in cold, when it warms up the car breaks w.o any effort.

The brake pedal is very heavy and requires too much force when cold, when warm it glides as knife thru butter...

- Synthetic brake oil flushed less than 12 months- new pads and rotors - less than 12 months- car har some idling vibration, but that is all the times - cold or warm

Why bad brakes only when cold? why why why?

Thanks for any pointers

[PalmerWMD]

What kin dof pads are you running?W/o knowing one migth speculate maybe a racing pad set-up?

But I guess if it was non OEM pads you would have mentioned it?

Fred...

[911/Q45]

Check your power brake system for cracked hoses, booster leaks, etc. I'll bet it's something that leaks vacuum when it's cold.

[firstq]

Fred - the pads are not OEM, no racing either - some Autozone stock. Please do not flame for that, I was in there on a Sunday and that was my only choice -

Regardless, this could not be brake pads, right? As we are not talking about that the brakes start to work after the pads are warm after driving in the morning or anything.

I can keep the car parked, let the engine get warmed up and then move the car with excellent braking right from the beginning. It is the engine warming up that matters. Does not matter a bit if the car is physically moving or not (or if the brrakes have been used in the morning or not). As soon as the engine temp needle goes to 3 o clock, the braking is normal and as expected.

Thanks

[DAEDALUS]

I had the same problem once. Check the booster hose check valve as well as looking for cracks. It might be sticking. It's a cheap enough part, you could just replace it without any diagnosis.

[firstq]

I did the check this mornign and the check valve checked out okay. The valve appears to be functioaning as explained in the service manual (BR section) - vaccum in one direction and none in the other - the hoses from the booster to the plenum got no cracks either.

I think it is something to do with the vaccum coming from the plenum part - is not there a different pathway when the engine temp is cold and another when the engine temp reached the 176 or wahtever mark for the blow by gases?

I am thinking that when the car is cold the vaccum thing is not correct (the cold pathway is busted, leak or whatever...) and when the car gets hot (the hot pathway is sealed and the vacuum corrects).

Does this make any sense?

Thanks

[firstq]

Besides the hose from the Brake booster to the plenum (thru the check valve) - anything else to check?

Thanks

Check your power brake system for cracked hoses, booster leaks, etc. I'll bet it's something that leaks vacuum when it's cold.

[911/Q45]

I'd just replace the hoses and checkvalve like Daedelus suggested and go from there if it's not fixed. I don't believe there is a hot and cold path.

[squeefoo]

Maybe there's a bunch of "crap" in the manifold, that melts or expands enough when its warm. There could also be "crap" in the vacuum passages inside the booster. Ya never know---Squee

[firstq]

I have hand cleaned the plenum about 1 year back - so it should be relatively clean (only about 8K miles since then).

I will try to replace the hose and the check valve - are these hoses any special or a quick trip to AutoZone will be okay (knowing these are easy to replace, I do not see much harm - unless there is a safety issue - was going to match the specs on the q45 hose with what I will take from AutoZone as a replacment)

Thanks

[DAEDALUS]

Autozone may have a replacement, but I don't think you can use generic hose. It has to be specifically for the brake booster and designed for that capacity. A generic hose may collapse suddenly under vaccum, cutting off your brakes unexpectedly. When my check valve failed, it still passed air the right way, but it was a little sticky. It would open at 3-4 psi, which isn't much vacuum, but enough to stay closed sometimes. The factory valve opens at very close to 0 psi.

[firstq]

Sold - trip to Autozone got switched to trip to the dreaded dealership.

BTW - how much were these at the dealership, do you remember?

Thanks

Autozone may have a replacement, but I don't think you can use generic hose. It has to be specifically for the brake booster and designed for that capacity. A generic hose may collapse suddenly under vaccum, cutting off your brakes unexpectedly. When my check valve failed, it still passed air the right way, but it was a little sticky. It would open at 3-4 psi, which isn't much vacuum, but enough to stay closed sometimes. The factory valve opens at very close to 0 psi.

[DAEDALUS]

I always go to Scottsdale for my parts...they can overnight if you're in a hurry, as can Pinnacle I'm sure. The booster hose price I can't recall...I'd guess $30-40. The check valve was pretty cheap, maybe $5-8. It really helps to have a handheld vacuum/pressure gauge to check these things.

http://www.toolsource.com/ost1...L8618

[Chally]

See if you can blow back into the Plenumn when all is cold. Just hook up a piece of tube to the manifold vacuum outlet & you should be able to blow freely. If not, a cleaning you must go.

I have a feeling you may fix it with the Check Valve though...

[Q45tech]

". It would open at 3-4 psi, which isn't much vacuum, "

The typical idle vacuum on a warmed up Q is 18" HG [mercury column] which is roughly 8.8-9 psi negative.WOT is roughly 0.6 psi negative........17" of water column 1/15th less.