Weird Brake Issues

[nono0044]

I upgraded my brakes to the Macan ones a while back, but I think the problem may have existed prior, but is now exaggerated due to the new calipers.

I can't tell if I have air in the lines, or if my MC/brake booster. The pedal is rock hard after a few pumps when the car is off and it doesn't move, but the moment I turn the car on the brakes start sinking to the floor. Obviously I understand that the pedal is supposed to be a bit softer due to the brake boosting when the car is on, but my pedal is REALLY soft when the car is on. Usually I can let go quickly after the initial braking and the pedal is firm again, but doesn't seem to be working anymore. Should i be trying to replace the MC or the booster first, or is the problem elsewhere?

I'll try to activate the ABS via some braking on gravel, and try to see if there's any extra air.

Thanks.

 

[jimlloyd40]

Air in the lines or a vacuum leak.

 

[nono0044]

Air in the lines or a vacuum leak.

Are vacuum leaks common? Where should I be checking?

 

[jimlloyd40]

Are vacuum leaks common? Where should I be checking?

Can be difficult to trace with so many vacuum hoses. It sounds more like air in the lines though.

 

[victorofhavoc]

Try rotating the order of bleeding. The Mc in these cars can be weird and likes the front brakes to be bled first. I had a really stuck bubble and after bleeding Front Left, FR, RL, RR it was out. Supposedly the shop manual states for stuck bubbles in the Mc to bleed the two front at the same time.

 

[odessa.filez]

correct on both front at same time according to my copy

 

[nono0044]

Try rotating the order of bleeding. The Mc in these cars can be weird and likes the front brakes to be bled first. I had a really stuck bubble and after bleeding Front Left, FR, RL, RR it was out. Supposedly the shop manual states for stuck bubbles in the Mc to bleed the two front at the same time.

I always go by the manual order, but I haven't tried bleeding both at the same time. I'll give that a try

 

[billbadass]

if you can pump the brakes and they get more firm the 3rd or 4th time you push down it is almost always air in the brake line somewhere.

 

[tmw2442]

At this point I would say it is much more likely you have air in the system, than a bad master...

Pressure bleeder...set at 30 psi...per VW service manual....cycling the ABS pump...like you used to in the mk5/mk6 days...doesn't remove the air from the mk7....

https://www.amazon.com/Abn-Manual-E...ywords=pressure+bleeder&qid=1599691318&sr=8-9

crack the bleeder nipples on the calipers with the pressure bleeder attached and lightly tap them with a small rubber mallet to encourage any air in the crossover tubes out.

remove the pressure bleeder....

followed by a normal 2 person bleeder method pumping the brake pedal should ensure you have removed as much air as possible from the system

If you are really into it you could pressure bleed one last time....to remove any tiny amount air pumping the brake pedal may have dislodged in the master...

Most think they made things better by doing some ABS stops...but what really happened is your butt was fooled by into thinking you made it better by putting some heat in the brakes and made the pedal slightly stiffer do to the fact you ratcheted the parking brake adjuster on the rear caliper a little closer to the disc taking up a little slack in the system giving you a stiffer pedal..../end run on sentence....

 

[nono0044]

Yeah I'm going to try to work on the brakes with my friend tomorrow. He has a pressure bleeder, so we're going to pump it to 30psi, open the fronts at the same time with tilting and tapping.

Then manually pump bleed as well. Just going to use some crap fluid and flush with better stuff once I know the air is out

 

[jmason]

Resurrecting this thread. I'm in a similar situation.

I have bled the brakes using a power bleeder followed by the two-person manual method. (As an aside, VW supposedly recommends 30 psi with the VW brake bleed tool, while the Schwabben bleeder cautions not to exceed 20 psi. I used 20 psi.) Bled in the VW-recommended order (LF, RF, LR, RR). Fresh ATE 200 brake fluid. Tapped the calipers to dislodge air bubbles. At no time since I have had the car has the system run low enough on fluid to allow air to enter.

With the ignition off and the handbrake not engaged, the pedal is high and rock solid. I can't push the pedal to the floorboard. With the car running, the brake engagement point is the same, but with some effort, I can push the pedal to the floorboard. It doesn't feel squishy, just that through continuous application of pressure on the pedal, it will settle to the floorboard.

As a check, I found that on my wife's Acura, I can push the brake pedal to the floorboard when the engine is running. To me, this suggests there is nothing broken on my car.

To recap, there is not a long push (deadspot) of the pedal to engage the brake (so pressure valve suggested in another thread will not address the problem) and the pedal is rock hard when the engine isn't running. I have not tried the VCDS ABS bleed technique. (I don't know how.)

I don't understand how I am able to push the pedal to the floorboard. Can anyone explain?

 

[victorofhavoc]

It has to be a bubble somewhere. I can't stand the brake system on these cars and the power bleeder does not make things easier. If you have even the slightest leak in your power bleeder, then bubbles may move upwards in the system as the slow release allows air to flow through the fluid to get to the evacuation point. My gti I have found to trap air somewhere high in the system, and it requires my wife pumping and holding down the brake for me after I'm done with the majority of fluid flush with the power bleeder. It's almost always somewhere north of the front left caliper and a couple times required bleeding both fronts with three people, one on each end, plus a person on the brake. This is why I think it's somewhere high in the system and not really near a caliper or end line, and also why I believe a slow leak in the power bleeder ends in frustration with the bubble moving up and down.

 

[jmason]

Thanks Victor. I guess I need 5 people because I have a BBK with two bleeders per wheel! Don’t know what to try next other than the VCDS ABS technique. Do you know how it is performed?

I’m not disagreeing with you. What I don’t get is that the pedal is solid when the engine is off. Seems like that suggests no air in the system. Or there is air in the ABS circuit that is isolated from the rest of the system when the engine is off.

 

[victorofhavoc]

Thanks Victor. I guess I need 5 people because I have a BBK with two bleeders per wheel! Don’t know what to try next other than the VCDS ABS technique. Do you know how it is performed?

I’m not disagreeing with you. What I don’t get is that the pedal is solid when the engine is off. Seems like that suggests no air in the system. Or there is air in the ABS circuit that is isolated from the rest of the system when the engine is off.

I had the same issue in my z recently. Rock hard when off, but when on pedal goes to floor and virtually no brake. On the z it was a stuck few bubbles on the inside side of the caliper. Correct order for calipers with multiple bleeder is out then in (furthest to closest). You might have a bubble stuck there.

I think you can use obd11 to kick off the abs pump, but you'd need ignition on for it to get power, and at that point it should be on anyway and release the pressure before/after the pump. I really don't know where it is though.

If a manual, gravity bleed doesn't solve it, check for leaks in your system (usually bleeder or brake line fittings). I've had ss brake lines go loose on a fitting and a tiny leak cause the pedal to go totally out.

 

[jmason]

Thanks again. I did go outer to inner.

Wish I could find a diagram of the VW ABS, not some generic version. I’m just guessing without the insight a diagram would provide.