Stopping is a state of mind
August 19, 2010 9:34 AM Subscribe
Carfilter: I have a 2003 Ford Explorer (2WD, 2-wheel ABS) with 98k miles whose brake pedal requires more travel and pressure to get the vehicle to stop. I've checked the fluid--as has the repair shop every time it gets its oil change--as well as the pads and booster pump compression. My gut says to change the master cylinder.
The "booster pump compression" test I mentioned comes from the Haynes book: Start the engine, then depress the pedal and stop the engine. Hold for 30 seconds and make sure the pedal holds steady. Second, run the engine for a little while, then stop it and press the pedal, making sure it gets progressively harder to push.
It looks like I could replace the master cylinder myself. Yet again, I curse the builders of this house for putting the driveway on a steep slope, which would make removing wheels for the bleed process difficult. Before I haul it into the repair shop, or up to a relative's house that does have a flat surface, I wanted to see what the HiveGearMind thought.
The "booster pump compression" test I mentioned comes from the Haynes book: Start the engine, then depress the pedal and stop the engine. Hold for 30 seconds and make sure the pedal holds steady. Second, run the engine for a little while, then stop it and press the pedal, making sure it gets progressively harder to push.
It looks like I could replace the master cylinder myself. Yet again, I curse the builders of this house for putting the driveway on a steep slope, which would make removing wheels for the bleed process difficult. Before I haul it into the repair shop, or up to a relative's house that does have a flat surface, I wanted to see what the HiveGearMind thought.
Are you sure you need to remove wheels to bleed the brakes? I don't think that's typical. Usually the nipple is accessible from under the car behind the wheel. For a truck you probably don't even need to lift it.
But I agree with tmt. I was surprised how much firmer the brakes were when I had a flush and brake fluid change on my 80kmile '03 VW. You'll get a bleed done that way too.
posted by fritley at 10:48 AM on August 19, 2010
But I agree with tmt. I was surprised how much firmer the brakes were when I had a flush and brake fluid change on my 80kmile '03 VW. You'll get a bleed done that way too.
posted by fritley at 10:48 AM on August 19, 2010
Bleeding the brakes is never a bad idea-if it is done properly. And given your description bleeding the brakes might cure the problem and is probably the cheapest thing you can do that might cure it, and you are gonna have to bleed them anyway if you replace a master cylinder.
You either need 2 people somewhat familar with the process and a lot of time or buy a brake buddy pressure bleeder. You do not need to remove the wheels technically, although taking them off sure makes it easier. It can be quite difficult to get to the bleeders if the wheels are on for a lot of vehicles (I have no idea if this is true for a ford explorer).
There are lots of guides out there on how to do it right and it isn't a hard procedure, just tedious. I would suggest doing it for a full round twice if you are doing it for the first time and by hand-and then be really careful and cautious the first time you drive the vehicle, and if you don't like the brake feel when done, just do it again-after all you can kill yourself or someone else if you get it wrong.
posted by bartonlong at 3:24 PM on August 19, 2010
You either need 2 people somewhat familar with the process and a lot of time or buy a brake buddy pressure bleeder. You do not need to remove the wheels technically, although taking them off sure makes it easier. It can be quite difficult to get to the bleeders if the wheels are on for a lot of vehicles (I have no idea if this is true for a ford explorer).
There are lots of guides out there on how to do it right and it isn't a hard procedure, just tedious. I would suggest doing it for a full round twice if you are doing it for the first time and by hand-and then be really careful and cautious the first time you drive the vehicle, and if you don't like the brake feel when done, just do it again-after all you can kill yourself or someone else if you get it wrong.
posted by bartonlong at 3:24 PM on August 19, 2010
Best answer: Sometimes, it can be hard to tell if the master cylinder is bad with the car running. Often, the power booster makes the pedal so soft, it can be hard to pick up the subtleties of a bad master cylinder.
I usually test them with the engine off. With the engine off, pump up the pedal until it's high and firm. Then apply firm pressure. If the pedal sinks even in the absence of power assist, you surely have a bad master cylinder.
Replacing the master cylinder is usually a pretty easy process. You'll want the correct size line-wrench for the steel brake hose going to the master cylinder. Trying to brake the fittings loose with a regular open end wrench will be less than ideal. Also, get a whole box of gloves, a bunch of rags, some brake-clean spray, and a couple quarts of brake fluid. Be prepared to make a mess.
You'll also need a bench vise (or improvised alternative). The new master cylinder will need to be "bench bled" before installation. In the box with the new master, there'll be a couple plastic fittings and some plastic hoses. Install the fittings where the brake lines used to be, and then route the hoses from the reservoir to the fittings. Clamp the master cylinder in the vise and fill the reservoir with brake fluid. Then actuate the m.c. with a screw driver (where the rod sticks out of the booster, as though you were pumping it with the pedal) until there are no more bubbles in the clear plastic hoses. Don't be lazy or skip this step. If you think it's just "good enough" you could still spend a horrendously long time bleeding the system if the master cylinder is insufficiently bled before installation.
When installing the m.c., another tip is to install the brake hoses before you tighten up the two bolts holding it to the booster. Without wiggle room, it'll be really hard to thread the brake fittings back into the m.c., especially with the inevitable quantity of brake fluid on your hands/gloves.
Once you're sure they've threaded in correctly, bolt down the m.c. then tighten up brake hoses.
Then, be prepared to do a quick re-bleed of the m.c. . Top it up with more brake fluid, have your assistant pump up the pedal, then (with pressure on the pedal) crack open one of the brake lines at the m.c. If you've done a good job of bench bleeding, only a little air should come out of each line. Crack each line in sequence, individually, just like bleeding brakes.
Then, bleed the brakes as usual.
I remember when I was younger and just getting started, I asked an older mechanic, "How can I tell if it's bled all the way." I never forgot his reply. "Well kid, it should come out in a strong, clear stream. Like when you take a piss." So, I pass that nugget of wisdom to you.
posted by Jon-o at 3:49 PM on August 19, 2010
I usually test them with the engine off. With the engine off, pump up the pedal until it's high and firm. Then apply firm pressure. If the pedal sinks even in the absence of power assist, you surely have a bad master cylinder.
Replacing the master cylinder is usually a pretty easy process. You'll want the correct size line-wrench for the steel brake hose going to the master cylinder. Trying to brake the fittings loose with a regular open end wrench will be less than ideal. Also, get a whole box of gloves, a bunch of rags, some brake-clean spray, and a couple quarts of brake fluid. Be prepared to make a mess.
You'll also need a bench vise (or improvised alternative). The new master cylinder will need to be "bench bled" before installation. In the box with the new master, there'll be a couple plastic fittings and some plastic hoses. Install the fittings where the brake lines used to be, and then route the hoses from the reservoir to the fittings. Clamp the master cylinder in the vise and fill the reservoir with brake fluid. Then actuate the m.c. with a screw driver (where the rod sticks out of the booster, as though you were pumping it with the pedal) until there are no more bubbles in the clear plastic hoses. Don't be lazy or skip this step. If you think it's just "good enough" you could still spend a horrendously long time bleeding the system if the master cylinder is insufficiently bled before installation.
When installing the m.c., another tip is to install the brake hoses before you tighten up the two bolts holding it to the booster. Without wiggle room, it'll be really hard to thread the brake fittings back into the m.c., especially with the inevitable quantity of brake fluid on your hands/gloves.
Once you're sure they've threaded in correctly, bolt down the m.c. then tighten up brake hoses.
Then, be prepared to do a quick re-bleed of the m.c. . Top it up with more brake fluid, have your assistant pump up the pedal, then (with pressure on the pedal) crack open one of the brake lines at the m.c. If you've done a good job of bench bleeding, only a little air should come out of each line. Crack each line in sequence, individually, just like bleeding brakes.
Then, bleed the brakes as usual.
I remember when I was younger and just getting started, I asked an older mechanic, "How can I tell if it's bled all the way." I never forgot his reply. "Well kid, it should come out in a strong, clear stream. Like when you take a piss." So, I pass that nugget of wisdom to you.
posted by Jon-o at 3:49 PM on August 19, 2010
Response by poster: Follow-up: I took the car into my usual repair outlet, and they gave it back saying they couldn't find anything wrong with the brake system. The fluid, pads, and lines all checked out. According to the service writer, the tech who test-drove it on regular roads and the highway said even the pedal didn't feel weird. I may try for a 2nd opinion, but for now I'm going to leave it alone. Thanks for the detailed answers!
posted by fireoyster at 1:21 PM on August 29, 2010
posted by fireoyster at 1:21 PM on August 29, 2010
This thread is closed to new comments.
It retains water (which lowers the boiling point of the fluid), which can cause weird pedal feel once the water-retained percentage gets too high. Also check the flexible lines at the wheels. Have someone push on the pedal while you observe the rubber hoses. A worn or damaged hose will bulge more in comparison to hoses at the other corners of the vehicle.
posted by tmt at 10:01 AM on August 19, 2010