Brake issues (thinking brake booster)

Kline224

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May 29, 2019
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Merritt Island, Florida
I posted a while ago about a Jeep that I'd been working on after it having sat for many, many years. It's a 2004 wrangler 4.0. Thanks to a previous post I made earlier this year and a bunch of info I found just searching the forums, she's alive and running well!

But, there's still one issue left to fix. When I finally got everything else good to go, I got in and pushed down on the brake pedal. Went straight to the floor, didn't matter if it was off or on. So I picked up some brake fluid and completely flushed the brakes. Brake pedal was much, much better. Feels like there could still be some air in the lines, but the brakes work and it doesn't go to the floor.

Now, if it's on, the pedal goes down a good bit before the brakes kick in. I can hear sort of a quiet "whoosh" sound when pressing down on the pedal (If I'm not imagining things). I let the Jeep idle for about a minute or so, pressed down on the pedal and turned off the Jeep. The pedal started slowly coming back up after just a few seconds, almost immediately. I tested the check valve (Blew into it/sucked air from it) and it seems to be working.

Any thoughts? I'm assuming the brake booster is toast, but, if someone else with more experience has any input it'd be greatly appreciated before I put the order in for a new booster. Could it be the O ring between the booster and master? Or more likely to be the booster? Thanks!

(I'll be posting before/afters of the Jeep once I finish fixing up everything and fixing the paint job)
 
I posted a while ago about a Jeep that I'd been working on after it having sat for many, many years. It's a 2004 wrangler 4.0. Thanks to a previous post I made earlier this year and a bunch of info I found just searching the forums, she's alive and running well!

But, there's still one issue left to fix. When I finally got everything else good to go, I got in and pushed down on the brake pedal. Went straight to the floor, didn't matter if it was off or on. So I picked up some brake fluid and completely flushed the brakes. Brake pedal was much, much better. Feels like there could still be some air in the lines, but the brakes work and it doesn't go to the floor.

Now, if it's on, the pedal goes down a good bit before the brakes kick in. I can hear sort of a quiet "whoosh" sound when pressing down on the pedal (If I'm not imagining things). I let the Jeep idle for about a minute or so, pressed down on the pedal and turned off the Jeep. The pedal started slowly coming back up after just a few seconds, almost immediately. I tested the check valve (Blew into it/sucked air from it) and it seems to be working.

Any thoughts? I'm assuming the brake booster is toast, but, if someone else with more experience has any input it'd be greatly appreciated before I put the order in for a new booster. Could it be the O ring between the booster and master? Or more likely to be the booster? Thanks!

(I'll be posting before/afters of the Jeep once I finish fixing up everything and fixing the paint job)
A dead booster produces a hard pedal that doesn't change how much force it takes to move the pedal with the engine on or off.

Sounds like you have a vacuum leak. If the check valve is in fact viable, then check the o-ring at the back of the master. Don't overlook any plugs or vacuum fittings on the manifold.
 
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A dead booster produces a hard pedal that doesn't change how much force it takes to move the pedal with the engine on or off.

Sounds like you have a vacuum leak. If the check valve is in fact viable, then check the o-ring at the back of the master. Don't overlook any plugs or vacuum fittings on the manifold.
I believe Mrblaine is correct. Vacuum leaks are common

Thanks! I think I'll try a smoke test tomorrow and if I can't find it I'll check the O ring at the booster/master. I'll report back with what ends up being the fix
 
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Cleaned the hose to the check valve/the ends of the check valve itself and the grommet in the brake booster, reseated it in the grommet and hose, and vacuum leak is gone. Tested the brake booster and it seems to be working well. Spongey brake issue persisted though, even after I just re-bled the brake lines about 25 minutes ago.

I'm guessing that either the master is bad or it has to be bench bled, as when I first flushed the brakes the fluid level was very very low in the resevoir and the old fluid came out milky/opaque. Probably doesn't help that on the last bleeder I accidentally let the res. run out of fluid for one press on the pedal during the flush (woops).

But, the pedal goes about 1/3 to half way down very easily before real braking power gets applied and it stiffens up a bit - much better than it completely going to the floor like it was in the beginning. I don't suppose brake pads/shoes could be the culprit? Or should I go ahead and pick up a new master?

Edit: Found both Dorman and Centric master cylinders, if I need a new one, any difference between the two quality wise? Dorman is about $30 cheaper.
 
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Cleaned the hose to the check valve/the ends of the check valve itself and the grommet in the brake booster, reseated it in the grommet and hose, and vacuum leak is gone. Tested the brake booster and it seems to be working well. Spongey brake issue persisted though, even after I just re-bled the brake lines about 25 minutes ago.

I'm guessing that either the master is bad or it has to be bench bled, as when I first flushed the brakes the fluid level was very very low in the resevoir and the old fluid came out milky/opaque. Probably doesn't help that on the last bleeder I accidentally let the res. run out of fluid for one press on the pedal during the flush (woops).

But, the pedal goes about 1/3 to half way down very easily before real braking power gets applied and it stiffens up a bit - much better than it completely going to the floor like it was in the beginning. I don't suppose brake pads/shoes could be the culprit? Or should I go ahead and pick up a new master?

Edit: Found both Dorman and Centric master cylinders, if I need a new one, any difference between the two quality wise? Dorman is about $30 cheaper.
Just bench bleed it and see what happens. No need to replace a part until you know it is bad. I'm a Centric Dealer, I don't use Centric masters.
 
Just bench bleed it and see what happens. No need to replace a part until you know it is bad. I'm a Centric Dealer, I don't use Centric masters.


Sorry for the (extremely!) late response but the brakes are sorted, the mushy pedal and what not came down to 2 things, one of the bleeders seemed to have been ever so slightly leaking regardless of how tight it was and one of the calipers was bad. I went ahead and replaced both front calipers along with new rotors and pads, brakes perfect now.

Thanks for the help!
 
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