help, bad brake master cylinder need advice
 

I need to replace my brake master cylinder on my 85 300cd. Any advice.

I have found some online for around $85 plus shipping. Anyone done this job before.

any info would be greatly appreciated.

BTW Pedal travels to floor 3x so far. and will recharge with a few quick pumps.

Pretty easy job, just messy with brake fluid getting everywhere. Just be careful with the brake lines that feed into the master cylinder, they are pretty soft and easy to strip. Make sure not to cross thread one like I did :mad:

You might want to bench bleed the MC, or at least use your fingers to bleed it.

You'll be pretty pleased after you install it and get all the air out of the lines, your brakes will be far, far more effective.

Good opportunity to flush the entire system with fresh DOT 4 fluid. Also an eye dropper is helpful for bleeding the MC, squirting brake fluid into passages of the MC before hooking up the lines. And last time I replaced a Master Cylinder also took advantage of the exposed rusty brake booster to sand and paint it to look like new. Cover the brake line ends with tin foil to prevent crap from getting into em if/when doing this.

Remember to bench bleed the MC first!

Also, I'd get one from the local McParts. Lifetime warranty and all.

Thanks guys.

Things to remember..
 

1. If you don't have them, a set of Metric line wrenches are awesome. Basically they wrap about 3/4 of the way around the flare nut fitting so that you won't round off the fastener when you try to loosen the metal brake lines leading into the Master Cylinder. Sears has a set for $20-$30 it think.
2. When reinstalling the lines, it sometimes helps to leave the M/C a little loose on it's mounting bolts so that you can wiggle it a little to get the lines back in the holes dead on. If you feel any unusual resistance, STOP and try lining it up again. If you get it in there crooked, it will crossthread and leak.
3. After you install you will obviously have to bleed the brakes. If you don't bench bleed the M/C, it will be really hard to get the fluid going. It's not impossible though and there is the "stick trick" which is currently being discussed in the Yahoo diesel mercedes group. Basically you just put a big stick pushing all the way down on the pedal and leave it overnight, somehow it allows enough air out so you can bleed the brakes. I've never tried it but al lot a people swear it works for hard to bleed brakes.
4. While you have the system open why not check for hoses that need to be replaced? Also don't drive on this thing- I had one that would pump up but it blew out completely right when I needed to stop for a red light! Good thing no one way coming the other way. Of course this was in a 1962 VW crew cab with a single circuit M/C.
Don't forget to wash the brake fluid off your paint! Have fun.

job completed
 

I did this job with a friend last week and taking our time installing and bleeding the brakes... it took just under two hours....

Bench bled the MC, and everything was just as smooth as can be. I did make a momentary mistake eyeballing the brake fluid resevoir (didn't look at both sides of the split resevoir until one side was near empty...)

I am only a beginner mechanic, and the job was easy, saved about $100 in labor...Thanks to all that advised...

Where'd you get the MC? Seems like a good price.

Did my daughters 240D. Got the MC at Oreilly's. Lifetime warranty.

1. Turkey baster to remove as much brake fluid as possible. Garbage bag to install under the MC to catch any dripping fluid.
2. Remove the vacuum line from the vacuum pump to the booster so you don't brake the two nipples coming off it.
3. Once the MC is removed, determine if the rear seal on the MC was leaking. If so then fluid is in the booster and may be ruining it.
4. Replace the reservoir if the warning light switches are bad, test them.
5. A cover for the wheel fender to prevent the brake fluid from destroying the paint.
6. New brake fluid for bleeding the system and flushing it.
7. Check your rubber brake lines and if old replace them while the fluid is being replaced.
8. New Orings between the reservoir and the MC. You'll have them apart.
9. New Oring ( its actually flat) between the MC and the brake booster.
10. Flare nut wrenches so you don't strip the brake line connectors.
11. Bench bleed the unit.
12. If the paint is bad under the MC, POR-15 would be a good idea.
13. Someone to help bleed the brakes. Keep an eye on the rear reservoir.
14. Road test the unit and then check for leaking connectors at the MC.

Dave

ebay
 

Got it on ebay... it was the lowest price for new I could find....

beer bottle trick [or little plastic bottle from the parts store]
hook a clear plastic tube to the bleed nipple
put the other end in a clean bottle with a inch or two of brake fluid in it
put hose below the fluid level, open the nipple and pump away on the brakes
intill no more bubbles just donot forget to top up the master rez and empty the bottle before it over flows

I've got a few gpd used MC's