Don't manually bleed your brakes. It might damage the booster - PeachParts Mercedes-Benz Forum

alamostation · #1 11-12-2007, 10:33 PM

I'm in the middle of replacing the power brake booster in Guderian. It quit working when I replaced a front caliper.

While looking for an easy way to replace the booster, I found a bunch of threads that start out "after replacing my master cylinder, caliper, brake pads, etc., my booster doesn't work." After the obligatory posts saying that the person must have knocked off a vacuum line and further testing, yes the booster went bad. Sounds familiar. But everyone was amazed at the coincidence of two brake components going bad at the same time.

I happened to look at my "new" 300SD and it had a booster with a junkyard date of 9-25-07. When I got it, the PO said it just had new brake pads front and rear and gave me the receipt. Got it out. 9-21-07. Too much for coincidence.

Theory: A twenty to thirty year old booster diaphram isn't as flexible as it used to be. It can stand a limited range of movement very well, but when the brake pedal is pushed all the way to the floor, it is more than the old diapham can stand.

From now on, its only pressure or vacuum bleeding for me. In one of the posts, I did see a great idea. If you have to do the pumping method, put a block of wood under the brake pedal to keep it going further than it usually did.

I hate to be a Chicken Little, but if I can spare someone the torture of replacing a power brake booster in a 300SD, it seems worth it.

BTW. There is no easy way to replace the booster on a 300SD.

Stevo · #2 11-12-2007, 10:42 PM

I think the pressure bleeder was one of the most useful tools for the money I've ever invested in. I could never "go back"

dieseldan44 · #3 11-12-2007, 10:59 PM

If the booster is so shaky that pedaling it to the floor ruptures it, then I'd be happy to replace it rather than having it give out when it *really* counts.

My $.02.

dd

PS - yes Ive replaced mine :-)

Mustang_man298 · #4 11-12-2007, 11:07 PM

Don't get me wrong, I'd love to have a pressure bleeder, god knows its sooo much easier to do the job.
But I feel I should raise the flipside of this, I know some people work on a budget and such, been there and understand that. However, if there is one thing I won't scrimp on on a vehicle it is the braking system, and you have to weigh it, yes, the booster may or may not be affected by this, and may or may not last years more if not stressed by that procedure. In perspective though, is it really worth saving a questionable booster that much? To risk compromising yours and others safety unexpectedly when that near ready to go booster you saved suddenly fails on you when you most need it as that child or deer runs out in front of you, and you smash those brakes instinctively before you think and push that pedal beyond normal use? I'm not trying to create a war here, only asking you to weigh and consider it all in perspective. My thought on it is if that booster was that tired and ready to go that it failed from doing the brakes, then it already needed replaced as a matter of PM's and safety.

dmorrison · #5 11-12-2007, 11:47 PM

Quote:

Originally Posted by dieseldan44

If the booster is so shaky that pedaling it to the floor ruptures it, then I'd be happy to replace it rather than having it give out when it *really* counts.

My $.02.

dd

PS - yes Ive replaced mine :-)

Have to agree with dieseldan44. If it's going to go bad. Do it while I'm not driving down the highway or in a panic stop situation.

Another consideration. If the other brake parts are failing due to age, old rubber, etc. Then the booster is not far behind.

But you may have made an interesting observation.
Dave

#6 11-13-2007, 12:10 AM

Quote:

Originally Posted by dieseldan44

If the booster is so shaky that pedaling it to the floor ruptures it, then I'd be happy to replace it rather than having it give out when it *really* counts.

Exactly what I was thinking too.

Hatterasguy · #7 11-13-2007, 12:26 AM

If bleeding the brakes causes it to fail it was on the way out anyway.

Shawn D. · #8 11-13-2007, 09:32 AM

A brake booster failing (supposedly) because you did manual bleeding is why shops don't change fluid or do repairs on really old transmissions -- something you do will blamed for the already-imminent failure of the other part.

pdxwaker · #9 11-13-2007, 11:34 AM

Quote:

Originally Posted by alamostation

when the brake pedal is pushed all the way to the floor, it is more than the old diapham can stand.

I've always heard that you shouldn't press the pedal all the way to the floor... something about moving the piston in the master cylinder beyond the travel it sees in normal use... this releases 'gunk' that has build up and can damage the master cylinder. Perhaps the same holds true for the booster.

I've always put a block of wood under the brake pedal to limit travel.

lkchris · #10 11-13-2007, 12:01 PM

You're not supposed to push pedal "all the way to floor" when manually (sic) bleeding brakes.

Whether or not it damages booster diaphragm, it will for sure put master cylinder piston into place it doesn't normally go, damaging seals in master cylinder.