AL_BOS

Hi All, My brake pedal has been feeling very soft lately. Have to push it almost to the floor before the brakes bite. All 4 brake pads have been replaced within the last 4 months. Had the lines flushed, still same problem. Any thoughts?

losiglow

iTrader: (1)

I had the same problem which started happening after I flushed the lines. I reflushed but it didn't help. I ended up replacing the master brake cylinder but it also didn't help. The only thing left was the vacuum booster. That's what did it. Once I did that the firm pedal feel returned to normal.

It didn't make a lot of sense to me since the only purpose of the brake booster is to provide the braking assist. I don't see how it would be responsible for a soft pedal. I may have been the master cylinder sort of "breaking in" and nothing to do with the vacuum booster. Dunno. Either way, it worked for me.

I'd probably start with the master cylinder. How many miles do you have on the car?

AL_BOS

Thanks. Mileage is just over 80k.
I had been under the impression that if it was the master cylinder the pedal would stay down.
Are the master cylinder and vacuum booster expensive to replace?

losiglow

iTrader: (1)

The master cylinder can result in a soft pedal, not necessarily the pedal staying down. The latter would only happen if was completely shot.

I did the work myself so I can't comment on labor. The master cylinder was about $90 new. I got a brake booster for $40 used on eBay. With brake fluid to do another flush, which you should do if you replace the MC, it was maybe a total of $150 or so in parts.

I suspect a shop would charge at least 3 hours of labor.

AL_BOS

Great info. Thanks, much appreciated. Its been driving me crazy trying to figure this out. I'll look into replacing the MC. How difficult is it to DIY?

losiglow

iTrader: (1)

The master cylinder removal isn't too bad. It's pretty easily accessible and only held on by two bolts to the vacuum booster. They can be reached with a ratchet extension. The two brake lines will need to be removed as well. I believe those are 10mm connections. Be careful with those because they're on pretty tight and can strip relatively easily. I can't remember what I propped them against but I raised and propped them to reduce brake fluid leaking. You're inevitably going to leak some brake fluid so it's a good idea to stuff some old towels or something under the master cylinder so the brake fluid doesn't drip all over the lower components in the engine bay. You then remove the master cylinder and collect or scrap the brake fluid. You'll need to bench bleed the new master cylinder prior to installing. It's relatively easy but can a little messy. Just google "bench bleed master cylinder". Some have said you can just fill it with fluid, let the fluid start to drain from the outlets, then install. But you'll risk getting more air in the system than necessary, which can cause bubbles that won't flush out very easily.

At that point it's just the opposite to removal. Make sure the reservoir is full of fluid since some will spill out of the outlets during install and you don't want it to empty resulting in air getting in there. It can be a bit of a messy job so just make sure to have some towels around and place something on any painted surfaces like your drivers side fender and front bumper cover. Brake fluid can ruin paint. I'd also wear some nitrile gloves during the whole process. Get at least two 1qt. bottles of brake fluid. I prefer DOT 4 since it's not much more expensive than DOT 3, and DOT 5.1 is much pricier and not really necessary for our cars unless you're tracking them and need the higher boiling point.

Edit: Like I mentioned though, the master cylinder replacement didn't solve my problem. I think it would in most situations but it didn't for me. I had to replace the vacuum booster. That's a bit more of a pain in the neck because you have to remove the master cylinder, then somehow finagle the stupid booster out which is not particularly easy. Unbolting the booster is easy. It's just a couple of bolts under the dash and a pin connecting it to the brake pedal. But it's a pretty big component and not easily removable. Luckily it's readily accessible there at the top of the engine bay on the drivers side. But I found myself having to remove a fuse box, some tubing and the sway bar in order to get the big ol' thing out.

AL_BOS

Thanks again. Thinking I'll try replacing MC myself and see how it goes from there.
Is the vacuum booster the same as the "Master Power Set" ?

losiglow

iTrader: (1)

Assuming that's #1 then yes