Film-Tech Forum ARCHIVE: Car Repair: Farting Brakes

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Posted by Randy Stankey (Member # 64) on 06-18-2011, 12:03 AM:

Just had my car repaired and I'm having some strange symptoms afterward.

2001 Mazda 626. 5-speed. Has 109,000 miles on the odometer but it will still make the Kessel run in less than twelve parsecs.

The clutch master cylinder was replaced because it was hard to shift into gear and one of the brake lines to the rear wheel was replaced because there was a crack in the jacket.

Each repair was done by a different mechanic. The clutch was done by a transmission shop and the brakes were done at a general car repair shop.

The clutch was repaired on Monday. Everything was good. I had to add some fluid because it was low but, after that, it was normal.

The brakes were repaired on Thursday. When I got the car back, the brake pedal was spongy and it made a funky noise when I stepped on the pedal. A groaning or "farting" sound instead of the familiar "woosh" as the engine vacuum activates the cylinder.

I only drove the car around the block and went right back to the shop. The guy looked at it and tightened the brake adjusters on the rear drum brakes. The problem got better but it didn't go away completely.

I drove out to a country road where there were no other cars around and did some "maximum braking" tests. Accelerate up to about 40 MPH then step on the brakes hard until the car stops. Repeat five or six times.
This is something I always do whenever I get new pads or rotors because, as I understand, you need to "set" the new pads into the rotors.

Afterward, the problem got better but still not 100%.

I'm wondering whether there is some air or water in the brake lines causing the problem.

The mechanic at the shop that did the brakes says that it can't be air in the brake lines because, if there was, the pedal would go all the way to the floor. I want to believe him but I also think it would be a simple thing to bleed the brakes again just to be sure. I also wonder whether draining and replacing the brake fluid would be a good thing to do.

The fly in the ointment is that on this car, the brakes and the clutch share the same supply reservoir. It is conceivable that the guy who repaired the clutch could have introduced some air or moisture into the system which eventually "floated" over to the brake system.

I'm supposed to take the car back to the shop (the guy who worked on the brakes) on Monday to have him check it over again but, maybe, I should be calling the transmission shop.

An alternate possibility would be that there is a pin hole in the vacuum diaphragm inside the master brake cylinder but I'm skeptical of that. The problem would have shown up before. Wouldn't it?

What do you guys think?

Which shop should I be calling back on Monday? The transmission shop or the guy who worked on the brakes?

Posted by Monte L Fullmer (Member # 2797) on 06-18-2011, 01:18 AM:

Odd that both systems uses the same container holding the same fluid.

Odd is that when a master cylinder gets changed out, it's usually a good practice to change out the slave as well for the clutch..but an unrelated topic pertaining to your conversation dealing with the brakes.

Pinhole will kill the vacuum needed for power brakes, yet have you checked the vacuum line coming from the intake manifold?

Was the system totally flushed out and returned with new fluid?

Usually to set the autoadjusters on drum brakes is to go into reverse, then mash down on the brake pedal.

..and I wouldn't worry on doing the fast "set in" on the front brakes for if you do that, it's like breaking in a motor too quick and with disc brakes, you could get warped rotors and quick glaze spots on the rotors. I'd just let them get broken in normally with normal braking procedures.

Posted by Chase Pickett (Member # 5975) on 06-18-2011, 01:19 AM:

Because you only had to replace only that one brake line, the pedal wouldn't necessarily go all the way to the floor when braking. The 'spongy' feeling of the brake pedal is tell tale sign that there is air in your lines, but it seems just the tiniest bit. I'm assuming that you don't have abs brakes, which makes life so much easier with bleeding if you choose to do it yourself. On another note, you would have felt a difference in the clutch if there was originally air in the clutch system. I hope that when you had to add fluid, it wasn't sucking in air in the time between getting your car back from the shop and you adding the fluid. In my honest opinion it's air in the brake lines. Ask the shop which did your brake line to bleed them again, and if they won't, try it yourself. It's a very easy process, and if that isn't it THEN talk to the transmission shop. But like I said, I'd start at the shop that did the breaks. -Chase

Posted by Monte L Fullmer (Member # 2797) on 06-18-2011, 02:55 AM:

..to answer the question: the brake man since the clutch thing is okey.

Posted by Rick Raskin (Member # 1561) on 06-18-2011, 07:18 AM:

quote: Randy Stankey
The mechanic at the shop that did the brakes says that it can't be air in the brake lines because, if there was, the pedal would go all the way to the floor.

That's nonsense. That would be symptomatic of a defective master cylinder, a leaking system or low brake fluid. As Chase said, its most likely air in the brake system. Go for the re-bleed.

Posted by Randy Stankey (Member # 64) on 06-18-2011, 09:43 PM:

Yes, the brakes and clutch feed off the same reservoir.
When the problem with the clutch began the first thing I did was go looking for the clutch fluid filler but couldn't find it. I had to look it up.

When I took the car in for the clutch job I did plan to have both cylinders replaced but the mechanic inspected everything and said the slave was still good.

After that repair was done the fluid was low enough to trip the warning light on the dash but it was still above the "MINIMUM" mark on the reservoir. I added some fluid and it was fine.

Funny thing is that it took me a couple of days to get used to driving a car with a good clutch for a change. I often had to double pump the pedal and wiggle the shift to get it into gear. It took a day or two to break bad habits. I've been driving it since Monday and it's working fine.

The problem did not start until after the second mechanic took the brakes apart.

What if a drop of water or dirt got into the system when he took the car apart? Would that cause such slack when you step on the brakes?

I'm thinking that I should have the entire system flushed, refilled and bled out just for safety.

What do you think?

Posted by Monte L Fullmer (Member # 2797) on 06-18-2011, 10:37 PM:

quote: Randy Stankey
I'm thinking that I should have the entire system flushed, refilled and bled out just for safety.

What do you think?

I would - be your safest bet....I'm glad I did it with my hydraulic clutch system in one of my cars when I had to replace the slave cylinder. Went through a pint of fluid when I did my own flush job, but it was worth it.

amazing how junky looking and smelly old fluid can get.. - Monte

Posted by Chase Pickett (Member # 5975) on 06-18-2011, 11:21 PM:

Monte, the fluid in your brakes shouldn't get too gunky looking. After all it IS a closed system (or should be) that the brake fluid lives in. I wouldn't recommend doing an entire flush unless you want to bleed your brakes for days. Bleed each corner until no more air bubbles come out, and inspect the fluid that came out. If it's really terrible, then your problem is probably more severe.

Posted by Randy Stankey (Member # 64) on 06-19-2011, 07:54 AM:

It is DOT-3 fluid. Polyethylene Glycol. It hasn't been changed since the car was new. (Going on 11 years.)

By now the stuff should be pretty worn out. Yes, the top has been secure on the reservoir but, in more than 10 years, you've got to imagine that the fluid has absorbed some water by now, especially since the clutch cylinder has been leaking.

My rationale is:
1) The system has been opened twice in the last two weeks.
2) The system has recently sprung a leak.
3) The fluid in the system is more than 10 years old.
4) The brakes are not behaving as I expect.

I think it's high-time the system was flushed out. At minimum, a good bleed.

Posted by Monte L Fullmer (Member # 2797) on 06-20-2011, 09:49 AM:

I would..esp when the two systems uses the same reservoir (rather retarded, wouldn't you say and hope that Mazda got smart and separated the two systems by now) - do a total flushout.

I've done total flushouts by replacing master cylinders before - ain't that all hard to do .. just time consuming and it's interesting how the fluid can look when aged since when one takes the cap off to fill the reservoir and brake fluid, which it alcohol based can absorb water and discolor and weaken the viscosity of the fluid.

My last clutch job (replaced slave cylinder), the fluid came out coal black from age and possible moisture absorbing from the many times the cap was removed.

Clutch worked tons better with new slave and new fluid.

Posted by Louis Bornwasser (Member # 3063) on 06-20-2011, 11:16 AM:

Rick & Monte are spot on. Only trouble is a brake shop that doesn't understand how to routinely bleed brake lines.

(Print out this thread!) Louis

Posted by Monte L Fullmer (Member # 2797) on 06-20-2011, 12:59 PM:

lol...even a 12 yr old can be taught how to flush and bleed lines...(must be 10yr olds in this shop if they don't know howto bleed any hydraulic lines then...)

...just have plenty of fluid handy when doing the flush to push out the old and replace with the new..

..just like doing tranny flushes...