What could this be?

[Emew]

So I have discussed in my tune thread, and also with @SonicNutrition how my Speed seems to within the first 3-4 miles make a decently audible pop noise when coming to a stop after driving from cold boot. The pop does not reoccur this is a 1 time instance upon every cold boot session. My local mechanic drove it and said if I am not seeing anything on my AP logs, to forget it and that it can't be anything huge. I recently described the situation to Sonic and he says potentially my master cylinder. Upon inspection from his recommendation, I have noticed the brake fluid is at the 1/2 way point. So my question would be, and the point of this post. What may be going wrong, or what actions should I take next/look into?

Conditions:
1. Cold Boot
2. 3-4 miles driving.
3. Pop heard from center console vicinity upon braking to a stop.

Heat on or off has no effect on the occurrence and again the problem does not come back after the initial pop upon braking from a cold boot state.

As usual, all input is appreciated!

[Dirk McGurck]

I'm getting small backfires on these cold days, could it be something like that?

[Emew]

I was thinking something like that but thought it would show in AP logs if that were the case. Could be though.

Sent from my dial up phone

[jm211]

If you fluid is low, it went somewhere.

You are at, may I assume 60,000-90,000 miles. At that age, it is likely your master cylinder and/or system is leaking, albeit slowly as your note seeing any leak; this is quite normal.

I would recommend, at this time anyways to replace your master cylinder (located under you fill hole), your slave cylinder, your choice brake fluid and pick up a stainless steel clutch line for good measure.

It is in your interest to go OEM for the cylinders, or rebuild.

http://onlinemazdaparts.com for your OEM parts

http://www.edgeautosport.com/techna-...utch-line-ms6/ for you SS clutch line

http://support.corksport.com/instruc...LUTCH-LINE.pdf - Replacing to SS clutch line.


I have the service manual if you need it. 1000 pages of How-To's from Mazda.

[Emew]

I think it's definitely the master cylinder or related to it. I attached a picture from september when I got my new intake, the brake fluid is over the max line. Yesterday? Half empty below max.

Sent from my dial up phone

[scubasteve711]

Where does it sound like it is coming from? I've been working on cars a long time and never come across a pop under stopping that came from a master cylinder. 6's are somewhat known for the lower control arms needing to be replaced...

[Final Impact]

As the pads wear the fluid will drop so it not unusual to see the fluid down and NOT be a fluid leak. Why it would go up and down so much is beyond me unless its the level being checked and the difference in temperature.

As for the noise itself; from cold with high idle it could have a tad more vacuum. Could more vacuum assist be related to the noise? Something that happens once per start up cycle is indeed strange. Can you describe it with more detail perhaps?

[IHeartGroceries]

Originally Posted by Final Impact

As the pads wear the fluid will drop so it not unusual to see the fluid down and NOT be a fluid leak. Why it would go up and down so much is beyond me unless its the level being checked and the difference in temperature.

As for the noise itself; from cold with high idle it could have a tad more vacuum. Could more vacuum assist be related to the noise? Something that happens once per start up cycle is indeed strange. Can you describe it with more detail perhaps?

Indeed! As pads wear, more fluid is displaced in the caliper bores. So, it wouldn't be unusual to see level drop over a period of time.

You should feel something in the pedal, and likely lose brake performance if the MC wasn't functioning correctly. I can't think of what would pop either, unless a piston is getting hung or something.

I have a very similar sound occur randomly in my car. Has done it for a while now. However, mine seems directly correlated with the HVAC system. For example, I might turn the defrost on, and after it has been running for a couple minutes, I hear a thud from behind the HVAC bezel. Sometimes, I will have had the system on, then off again, and when I brake, the centrifugal forward force from braking will result in the popping sound. I decided it was the vent behind the dash sticking for some reason, and I pretty much ignore it now.

[Final Impact]

Originally Posted by Final Impact

As the pads wear the fluid will drop so it not unusual to see the fluid down and NOT be a fluid leak. Why it would go up and down so much is beyond me unless its the level being checked and the difference in temperature.

As for the noise itself; from cold with high idle it could have a tad more vacuum. Could more vacuum assist be related to the noise? Something that happens once per start up cycle is indeed strange. Can you describe it with more detail perhaps?

Should have said: "Why it would go up and down so much is beyond me unless its changed by HOW level the vehicle is when its checked and the difference in temperature.

O/T: Anyone with Auto Climate control have whistle through the core of the HVAC when the temperature reaches the set temp? Example: set at 77F and as the cabin is fully warmed to 77F, it whistles. Less fan, less whistle, more fan more whistle - adding vehicle speed adds even more! Move dial to colder or hotter and it stops until it hits the new set point. A volume of 12 on the Bose Radio will drown it out somewhat. lol


OP Just curious; have you looked under the dash for cracks around the clutch pedal and brake mount? I think its unlikely but for know you have go for what it "isn't vs what it is!"

[oh_yeams6]

Originally Posted by IHeartGroceries

Indeed! As pads wear, more fluid is displaced in the caliper bores. So, it wouldn't be unusual to see level drop over a period of time.

You should feel something in the pedal, and likely lose brake performance if the MC wasn't functioning correctly. I can't think of what would pop either, unless a piston is getting hung or something.

I have a very similar sound occur randomly in my car. Has done it for a while now. However, mine seems directly correlated with the HVAC system. For example, I might turn the defrost on, and after it has been running for a couple minutes, I hear a thud from behind the HVAC bezel. Sometimes, I will have had the system on, then off again, and when I brake, the centrifugal forward force from braking will result in the popping sound. I decided it was the vent behind the dash sticking for some reason, and I pretty much ignore it now.

I thought the thud was from animals dying of heat or cold, and then hitting the back of your face plate when they come through the ventilation system?