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Discussion Starter · #1 ·
Bought the 04 2.5t awd with 117,000 on the odometer; records from 50,000 showed no brake problems, but there has never been what I would call adequate boost at the brake pedal.

Soon after purchase I replaced the front rotors with Brembos: no change in braking effect noted. More recently, at 134,000, I replaced front pads - also with Brembos - and bled at each caliper until new fluid was flowing. Still no change was noted.

Just to make sure, I re-bled the rears and pulled the rear pads. Since they still have 5-6mm of material and the rotors are over 11mm, I just cleaned it all up, applied lube at the usual spots, and re-assembled. On the test drive, I could not get the ABS to engage on a dry road from about 40 miles per hour. Braking is straight and pedal force is linear, but it just requires very heavy pressure to slow down in anything like a hurry.

There are lots of deer around here; when one jumped in front of me last week, I hit the brakes at 25-30 miles per hour and ended up having to change lanes to avoid hitting it. Clearly something is not right.

As per a recent thread [on Matthews] by dna316, I performed a static test of the electric vacuum pump: turned on ignition, applied brake, pump cycled on for a few seconds and then off; applied brake again, and pump cycled for a few more seconds. This leads me to suspect that the problem is inside the booster/mc unit.

Could someone please provide or link to a testing protocol to isolate the proper operation of the booster and master cylinder? Throwing parts at a problem has no appeal.

tia, 686Sport

Ps. On the plus side, almost three years' ownership and not the first code! ARD Green and 16t gives boost to 14psi and still 30+mpg is easy to achieve on trips.

Location: SW VA
Model and Year: 2004 V70 2.5T awd
 

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I'm on 12" Slotted rotors front, blanks on the rear, w/Hawk HPS semi-metallic pads all around, running stock tires 215/65R16 Scorpion STR. In dry hot conditions with hot tires my brakes will not lock up in a panic stop situation, but will slow the XC down fast and predictably.

Vacuum pump cycling is normal when pushing the brakes with the engine off, key in position II. There's an issues if the vacuum pump runs on and on.

http://www.volvoxc.com/0/resources/how-to/pdf/power-brake-booster-replacing.pdf
Checking the power brake booster
Depress the brake pedal several times until it feels stiff.
Hold the pedal down. Start the engine. The pedal should travel and feel softer.
Release the brake. switch off the engine. Wait 1 minute. Then depress the pedal. The pedal should still feel soft but should become stiffer when it is depressed several times.
There should be no leakage between the vacuum hose and the terminal at the power brake booster.
There should not be any leakage between the master cylinder and the power brake booster.
Check that the stop lamp functions.
If the stop lamp switch has been modified or changed after installation of the master cylinder and power brake booster it must be readjusted.
Similar test with the vacuum pump. Instead of starting the engine, you turn the key to position II.
 

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Discussion Starter · #3 ·
Mine's crystal, too. Nice color. We have 2 other vehicles: a 2000 Tacoma 4x4 and a newer 535i. The Tacoma's brakes engage quicker and seem to stop quicker than the V70, and the BMW is just in a different time zone brake-wise.

Honestly, I think our clapped-out 1970 145S stopped quicker. Very few other cars had 4-wheel discs back then.

Had a 240Z race car that ran through brakes at a frightening rate, since it was in a class that required stock rotors and calipers. To be competitive, one had to service the brakes after every practice session or sprint race, and we changed pads at every pit stop in longer races. Many and many are the calipers I've rebuilt or exchanged after a race or two. Yet in all that time plus 50 years driving, I've never had to rebuild or replace a booster or master cylinder - hence the request for help.

686Sport
 
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