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Discussion Starter · #1 ·
I've been noticing more travel in the brake pedal lately. Checked the brake fluid and it's still full. I haven't done any recent work on the brakes.

Are the brake boosters known for going bad on these cars? Hard to tell if I get pedal travel with steady pressure. I think there is some.

2004 V70r manual trans, 159k miles.

Any suggestions? Booster is likely fairly expensive so I don't want to just guess.

Thanks!
 

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Probably a master cylinder rather than booster, I've replaced a lot more master cylinders than boosters.

Usually when the boosters fail on these cars the pedal just becomes stiff.
 

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Usually when the boosters fail on these cars the pedal just becomes stiff.
On cold startup my brake pedal feels like no brake assist. Very little travel with a lot of effort. Booster need replaced or just check valve?
Once it warms up, braking is normal.

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Neither, your vacuum pump isn’t working.


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Discussion Starter · #6 ·
A new brake master cylinder wasn't that expensive so I put one in...No improvement. I'm at something of a loss.

Symptoms are more pedal travel than I remember (haven't been driving the car much) and the pedal will sink some with constant pressure with the engine running. I don't seem to be loosing any fluid. The pedal is firm until the ignition is turned on and the vacuum booster runs, then the pedal will start to sink. Possibilities:
  1. Air in the system somewhere. (I don't think this would explain the sinking pedal) I haven't done any recent work on the brakes prior to installing the master cylinder.
  2. Internal leak in the ABS block. I found one reference to this on the web, but not much discussion.
  3. Bad check valve? The electric vacuum pump does cycle with the key on and engine not running. Where is the check valve located? Seems like a cheap guess.
  4. Brake booster? I think a bad booster just gives a stiff pedal, not excessive travel. Right?
I'd welcome any guesses!
 

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A new brake master cylinder wasn't that expensive so I put one in...No improvement. I'm at something of a loss.

Symptoms are more pedal travel than I remember (haven't been driving the car much) and the pedal will sink some with constant pressure with the engine running. I don't seem to be loosing any fluid. The pedal is firm until the ignition is turned on and the vacuum booster runs, then the pedal will start to sink. Possibilities:
  1. Air in the system somewhere. (I don't think this would explain the sinking pedal) I haven't done any recent work on the brakes prior to installing the master cylinder.
  2. Internal leak in the ABS block. I found one reference to this on the web, but not much discussion.
  3. Bad check valve? The electric vacuum pump does cycle with the key on and engine not running. Where is the check valve located? Seems like a cheap guess.
  4. Brake booster? I think a bad booster just gives a stiff pedal, not excessive travel. Right?
I'd welcome any guesses!
A bad wheel bearing/hub can cause low pedal. If wheel bearing is loose then when you release brake the motion in wheel bearing lets rotor tip over and push pistons into caliper bores. It takes more pedal travel to move the pistons out to take up the slack. Like the pedal travel you initially after a brake pad replacement but less.
Loose wheel bolts can let rotor move and do the same.
 
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If you need a brake booster I've got one sitting in my closet, purchased from Tasca, never installed.
 

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Discussion Starter · #10 ·
Thanks cattlecar for the suggestion. I can see how a bad wheel bearing or warped rotor could give excessive pedal travel. I've replaced 3 out of 4 of the wheel bearings on this car so I've had some experience what they sound and feel like as they go bad. I think everything is ok there. In my case, the high pedal travel happens even if the car isn't moved. I think the problem is somewhere in the hydraulics. When I get a chance, I'm going to hook-up Vadis and try actuating all the ABS solenoids while bleeding the brakes. Maybe there is air trapped in there somewhere.

Fetend, I'm still optimistic that it's not the booster. I seem to get good vacuum assist, just excessive travel. I'll send you a PM and make an offer if I get to the point of trying a new booster.
 

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I've been noticing more travel in the brake pedal lately. Checked the brake fluid and it's still full. I haven't done any recent work on the brakes.

Are the brake boosters known for going bad on these cars? Hard to tell if I get pedal travel with steady pressure. I think there is some.

2004 V70r manual trans, 159k miles.

Any suggestions? Booster is likely fairly expensive so I don't want to just guess.

Thanks!
I thought brake booster makes hissing / buzzing noise if bad...

Never had brake pedal go to the floor but similar issue solved 100% last yr after all 4 calipers fluid drain refill. Also clutch fluid can be reverse pumped out reservoir. Theres a post on here somewhere showing how
 

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Exactly what I knew of brake booster failure JCN
Like I said earlier I've seen it discussed that the Check valve on the booster can cause this issue and to 10 dollars people have solved this similar issue
 

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Neither, your vacuum pump isn’t working.


Sent from my iPhone using Tapatalk
Fuse was burned out, replaced and pump is working. Vacuum switch appeared to be working. Pump kept cycling so now it's time to find the leak.

Sent from my Pixel 4a using Tapatalk
 
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