Brake booster replacement

[austex360]

So the brakes in my explorer went kaput recently and when I went to a ford dealer he showed me that there was bubbles bubbling up through the fluid reservoir then I pumped the breaks. The mechanic said it was the break booster that was shot and to grab a new one from a wrecker.

So, that's all said and done, now it needs to go in. Anybody familiar with this give me a rundown of the tools I'll need and anything I should watch out for when replacing it?

if it helps, its a 96 explorer, LTD

 

[Turdle]

Bubbles in the fluid would be from a seal leak in the master cylinder, or brake line.


The vacuum booster going bad would create a hard pedal. I see no way the booster could pass air to the master cylinder.

Either there is a hole in a brake line, or the master cylinder is bad. There could be a leak in the ABS pump also, but I doubt that.

 

[koda2000]

Bubbles in the fluid would be from a seal leak in the master cylinder, or brake line.


The vacuum booster going bad would create a hard pedal. I see no way the booster could pass air to the master cylinder.

Either there is a hole in a brake line, or the master cylinder is bad. There could be a leak in the ABS pump also, but I doubt that.

+1. no way a bad booster is gonna cause bubbles in your master cylinder.

 

[austex360]

So the Ford mechanic was wrong? It's not the booster, it's probably the master cylinder?

I don't think the breaks need to be bled because they went from A-OK to almost nothing in a matter of a day of driving. Also, the first "break" of every engine startup is fine and powered, but then the pedal goes squishy after that. The truck does have 300,000 on it so I wouldn't be surprised if it needed a couple new pieces

 

[Cranmaro99]

So the Ford mechanic was wrong? It's not the booster, it's probably the master cylinder?

I don't think the breaks need to be bled because they went from A-OK to almost nothing in a matter of a day of driving. Also, the first "break" of every engine startup is fine and powered, but then the pedal goes squishy after that. The truck does have 300,000 on it so I wouldn't be surprised if it needed a couple new pieces

Yeah, the Ford mechanic was probably wrong. Don't be too surprised

 

[delexploder]

Look at the line that is clipped to the rear axle housing at the top of the diff cover and work your way forward looking for leaks if no leaks then master cylinder

 

[budwich]

I believe one of the tests for the booster function is with the car running (in neutral or park), depress brake for "firmness" (hold at his level). Then increase engine speed to say 2k-3k rpm, the pedal should fade a bit as the loss of vacuum at the higher rpms results in less boost.... and loss of "firmness". Of course, this assumes that you don't have a fluid leak in the system that has allowed air in the lines. In your case, it is likely you have a leak in the hydraulics not a vacuum boost issue which you won't see as as bubbles... there is no "non-mechanical" path between the booster and the master cylinder / fluid tank.

 

[snoranger]

Seeing as how a vacuum brake booster doesnt create air pressure, it just increases force, there's no way it could form bubbles. It uses vacuum on 1 side of the diaphragm (lower pressure) and atmospheric pressure on the other side (higher pressure) to increase force that the rod pushes on the master.

^ Ford mechanic proven wrong by a simple understanding of how a component works. ^

Your bubbles are from air getting into the system somewhere else... A leak someplace in the system. (calipers, lines, master, etc.)

 

[koda2000]

Seeing as how a vacuum brake booster doesnt create air pressure, it just increases force, there's no way it could form bubbles. It uses vacuum on 1 side of the diaphragm (lower pressure) and atmospheric pressure on the other side (higher pressure) to increase force that the rod pushes on the master.

^ Ford mechanic proven wrong by a simple understanding of how a component works. ^

Your bubbles are from air getting into the system somewhere else... A leak someplace in the system. (calipers, lines, master, etc.)

+1 again. no doubt in my mind. just because someone gets paid to repair cars, and calls himself a mechanic, doesn't mean he's any good at his job. i've never met many that have impressed me with their skills.

 

[austex360]

Thanks for the feedback guys! I'm plannin to bleed the breaks tomorrow, top off the fluid , and then drive around a bit until the problem returns to be sure . I wasn't the one driving when it went so maybe it'll be more obvious if I'm around to hear any noises or see any leaks . I'll let ya know how this goes

 

[koda2000]

for what it's worth, if you don't find any leaks - my guess is the seal on the master cylinder is the problem. if so you'll need to replace it.

 

[austex360]

UPDATE:
Bled the rear breaks with acceptable results. no air in the lines, fluid squirts out. with the rear tires in the air, breaks applied, the tires don't spin. everything is OK in the back.

Bled the front breaks with poor results. almost no fluid poured out. if anything it "oozed" and there was no pressure there at all. with the breaks fully applied and tires in the air, I could still rotate the tires. there was a LITTLE bit of breaking power but not much at all. (both sides the same).

SO, brought it to the best mechanic in town, who told me its the ABS box between the master cylinder and the calipers (connected to both through break lines). apparently those are reaaaaally expensive, and if the wrecker doesn't have one for dirt cheap, the truck's probably going to be sold to a junkyard for whatever i'll get for a working engine and tranny.

UPDATE:
Bled the rear breaks with acceptable results. no air in the lines, fluid squirts out. with the rear tires in the air, breaks applied, the tires don't spin. everything is OK in the back.

Bled the front breaks with poor results. almost no fluid poured out. if anything it "oozed" and there was no pressure there at all. with the breaks fully applied and tires in the air, I could still rotate the tires. there was a LITTLE bit of breaking power but not much at all. (both sides the same).

SO, brought it to the best mechanic in town, who told me its the ABS box between the master cylinder and the calipers (connected to both through break lines). apparently those are reaaaaally expensive, and if the wrecker doesn't have one for dirt cheap, the truck's probably going to be sold to a junkyard for whatever i'll get for a working engine and tranny.

 

[budwich]

Wow.... This is even more suspicious than your "first diagnosis" that you got about the booster. I think I would move if that's your best mechanic in town...

 

[Runnin'OnEmpty]

......Bled the front breaks with poor results. almost no fluid poured out. if anything it "oozed" and there was no pressure there at all. with the breaks fully applied and tires in the air, I could still rotate the tires. there was a LITTLE bit of breaking power but not much at all. (both sides the same).......

I believe you have a bad seal in the master cylinder
end that pressurizes the front brakes.
It's an easy and relatively cheap fix, under $50 for
a rebuilt master cylinder...

 

[koda2000]

yeah, you need to move... before you do, get your master cylinder replaced.

 

[my98nnj]

I agree, it's the Master Cylinder that's gone bad. The ABS isn't activated during normal braking, it's just a pass through for fluid. The Master Cylinder is divided into 2 sections, front/rear. This is for safety reasons, if one side goes, you still have brakes, just very poor but you can limp home. Which is exactly what has happened to you.

Replace the Master Cylinder, bench bleed the cylinder first, then install it and bleed the system again.

 

[budwich]

This thread started with "my brakes went kaput"... :-( what does that actually mean? did your brake light go on and you had no brakes? or just poor braking? If you had no brake warning light, it is unlikely that you have a master cylinder issue. It is more likely that your front brakes were having an issue like frozen caliper or like on one or both sides and eventually stopped working almost completely. Your "check" of the "bleeding" of the front probably just shows a poor / rusted caliper on both sides... not unusual for a canadian 96 IF little or no maintenance was done on it. Further, I suspect that if you actually disconnect the lines at both front brakes, they will "flow" normally. IF your calipers aren't the issue and even if they are, odds are also high that the rubber connecting hoses on each side have an issue also.