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dillon772
10-25-2015, 08:53 AM
hi guys i own an Audi A4 B5 1.9tdi with 115 bhp 2000 reg. i am having terrible trouble with the brake system. i suspect it is vacuum pump related. when the car is trying to stop there's like there is no there at all, the brake effort does not match the brake force. The lower the rpm the worse the brakes get. the brakes are not as bad when the revs are high but are still pretty bad. in my opinion this car is not safe to drive on any public road as the brakes are dodgy. I checked the vacuum lines and i cant not find any cracks or erosion in the lines. is this a known problem or has anyone had this problem before? any information would be very helpful and much appreciated.

p/s this car has been to a mechanic and he could not find anything.

bhusted
10-25-2015, 11:04 AM
When you say that the braking force does not match the effort, do you mean that it is very easy to push the pedal and the car doesn't slow down or is it that the pedal is very difficult to push and the car doesn't slow down? If the former I would be looking at the brake fluid, master cylinder, and brake lines. The latter could indicate an issue with the brake booster. This is the round black part between the firewall and the master cylinder. How does the brake pedal feel when the engine is not running? If you press the brake pedal while starting, can you feel it get softer when the engine starts?

I'm not familiar with the vacuum hoses on the TDI applications, but you should see a larger vacuum hose going to the booster. If you pinch off the hose and notice no difference in the braking it could be that the vacuum connection at the engine is leaking or that booster is going out.

dillon772
10-25-2015, 11:36 AM
hi sorry for the missing information. when the car is driving the brake peddle feels very soft (easy to push) and the harder you push the peddle the car doesn't slow down any more. the car will slow down but not as fast as it should. when I start the car with my foot on the brake peddle it will push down to the ground slowly but not all the way down about 70% or so. when I turn off the car and press the brake peddle 3 time each time I press it the peddle comes up a half inch or so till it gets to the top and gets stiff (hard to push down).

bhusted
10-25-2015, 12:30 PM
It sounds like you may have a some air in the brake lines. hydraulic braking depends on the incompressible fluid transmitting the force from the pedal to each caliper. If there is air trapped in the system, the air compresses before the caliper pistons move. The fluid is hygroscopic and should be changed with some frequency. As the fluid absorbs more water from the air, the boiling point of the fluid drops dramatically.

Brake fluid is cheap and fairly easy to change, before replacing any other parts, I would flush out all of the brake fluid in the system. The fluid should be clear as water and a light honey color. Brown or black and opaque is a good sign that it has been a long time since the system was flushed. Pickup 1.5-2L of DOT 4 fluid and flush all of the old stuff out. I bet you'll see a dramatic improvement.

dillon772
10-26-2015, 03:32 AM
I take what your saying on bored but I don't see how bad brake fluid could cause the brakes to be like this, the reason why I'm saying this is because the brake force is dependent on the rpm of the car. when the car is slowing down on a idle there is very little braking force but when the car goes over 1500 rpm the brakes start to improve there still not 100% but it does be a lot better. if the brakes were not rpm dependent then I would fully agree with you. to me it sounds more like a booster or master cylinder. is there any way to tell is the brake booster or the brake master cylinder is bad?

SN95Audi87
10-26-2015, 01:25 PM
Let me see if I can shed some insight. I've owned the B5 for almost 6 years now and seen my fair share of problems. A few months ago my braking system became severely degraded because of a sticking caliper. One night while I was driving my fiance home to her apartment I lost most of my braking force like you mentioned in your post. I neglected to change the caliper because I thought it was just frozen pins that the caliper slide on but to my surprise it was more than that. The caliper seals were on its way out and lower pin was frozen so basically it got the caliper so hot one night that it bubbled the line or partially ruptured the seal in the caliper causing air to get in some how. The outcome was when I tried to slow down it would grab the brakes like normal but when the brake pedal started to get closer to floor it got worse to almost no braking force. I pulled into a supermarket parking lot and pumped the brakes unknowingly that is proper procedure to get some brake pressure back into the pedal and it worked. I limped it home and parked it for a few weeks until I had enough money to buy all right parts to fix it. I would inspect all brake lines and brake calipers to see if they are in proper working order. Hope this helps.

ECS Tuning-Audi
10-26-2015, 02:24 PM
Sounds like you have a vacuum leak somewhere. The brake booster is driven by vacuum so if it sees little to no vacuum you'll get hardly any power assist.

Check for vac leaks through out the engine bay.

Jason