Can I "bench bleed" the Master Cylinder in place? - Page 2 - PeachParts Mercedes-Benz Forum

Chad300tdt · #16 04-14-2008, 11:58 AM

Quote:

Originally Posted by Ken300D

The master cylinder does have to be bled before use in order to purge it of air. However, it is not necessary to "bench" bleed the master cylinder if you can meet the same bleeding requirement with the assembly mounted in the car.

Note how the master cylinder normally sits in the car - it is tilted upward at the forward end (the end away from the vacuum booster). All you have to do to bleed the master cylinder properly in the car is eliminate that tilt. Face the car down hill enough to make the master cylinder sit level. Now you can bleed it properly with something like the Motive Power Bleeder. Using a Power Bleeder, you can go ahead and hook up the brake lines to the master cylinder before you start bleeding the system - just bleed air out the calipers as in a normal brake bleed. With the master cylinder level, it is exactly the same as a bench bleed.

This is what I have done in the past with perfect results. Its a lot less messy to do it this way, and I believe less likely to induce air bubbles as you try to transfer the master cylinder from the bench to the car.

Ken300D

Thanks, I think I'll bleed it this way before I take the rear off the jack stands. I was thinking this would be a much cleaner way too.

Knightrider966 · #17 04-14-2008, 12:05 PM

Quote:

Originally Posted by tangofox007

The master cylinder needs to be level when bled. You won't get all the air out of it if it's not horizontal.

Those who insist on taking short cuts when working on brakes might do well to reconsider.

That's why you back the car up onto an incline or ramps with a carpenters level fixed to the MC.

This is how I did mine.

Chock your wheeels if this is your first rodeo!

ctaylor738 · #18 04-14-2008, 01:59 PM

I would add the following.

If the budget allows it, replace the reservoir at the same time as the MC. I have had a couple where the various o-rings and seals leaked under the pressure from the bleeder.

Always replace the seals between the MC and the reservoir.

Before attaching the Motive bleeder to the reservoir, turn the fitting/hose counterclockwise a couple of turns. That way, when you screw the fitting on to the reservoir the hose will be straight and withour kinks.

Be sure to release the pressure on the bleeder before disconnecting it from the reservoir.

Have a small fluid pump handy because the reservoir will be completely full when you are done bleeding and you will need to siphon some fluid off.

Chad300tdt · #19 04-14-2008, 02:03 PM

Quote:

Originally Posted by ctaylor738

I would add the following.

If the budget allows it, replace the reservoir at the same time as the MC. I have had a couple where the various o-rings and seals leaked under the pressure from the bleeder.

Always replace the seals between the MC and the reservoir.

Before attaching the Motive bleeder to the reservoir, turn the fitting/hose counterclockwise a couple of turns. That way, when you screw the fitting on to the reservoir the hose will be straight and withour kinks.

Be sure to release the pressure on the bleeder before disconnecting it from the reservoir.

Have a small fluid pump handy because the reservoir will be completely full when you are done bleeding and you will need to siphon some fluid off.

Thanks for the tips ... I'll have my old turkey baster handy.

Fallinggator · #20 03-15-2017, 03:58 PM

Quote:

Originally Posted by ForcedInduction

Just do it any way you like. Replacing the MC is about a 30-45minute job, in the time you've spent with this thread you could have bench bled the MC and installed it on the car already.

Responses like this are so unhelpful. The guy just wants to understand the situation. He's not arguing against doing it. He just wants to know what is actually being done and why. Instead of telling him off, you should praise him for trying to better understand what's happening.

BillGrissom · #21 03-16-2017, 01:58 AM

Agree. But that post was 9 yrs ago and that guy may not be around anymore. Seems like there were more M-B purists here in those days, many who fussed a lot but never touched a wrench. Today I see more "git 'er done" bottom-feeders like me with these cars.

I always install the MC in the car first, so I can use the pedal to stroke the MC. Seems silly that these guys worry how level it is. Don't connect the car's tubing yet. Instead, install clear "bleed tubes" which curve back to flow the fluid from the ports back into the reservoir. These sometimes come in the box w/ a rebuilt MC or can buy cheap at any auto parts. Pump the pedal until you see no more air bubbles in the tubing, might take 50 strokes. Then connect to the car's tubing. And watch the youtube's. I use silicone fluid so no corrosion and doesn't remove the paint.

Junkman · #22 03-16-2017, 10:40 AM

That post was from Forced Induction. He's a little abrasive and sometimes his advice is from further out than way past the fence in left field. Other times not. He periodically gets banned.

I have a cap for each vehicle that I use my bleeder for. I have the hose from the cap extend into the reservoir at or slightly below the level I want in the reservoir after bleeding. Releasing the pressure then pulling the trigger will let the reservoir siphon down to the correct height (when all goes as planned).

compress ignite · #23 03-17-2017, 12:58 AM

Using the Brake Pedal to "Bleed" Always has the risk of damaging the MC's
elderly components ('Not used to the Wild DISTANCE gyrations your assertive foot may Force them into.)

I've made my own Pressure Brake Bleeder using a inexpensive "pump up"
garden sprayer and directions from our friends online.
Most difficile part was sealing the pressure gauge threaded orifice into the
plastico Jug (And RTF always saves the Day)

AFTER ordering and receiving the aforementioned "Power Bleeder"
and discovering that they used Ferrous metallic securing nuts on the Inside
of their "Jug" which would have sooner or later Corroded (AKA Rust)
AND Rust inside a Brake system only spells trouble!
I actually went to the trouble of calling the Noodleheads whom own the
"Power Bleeder" outfit AND they said they were aware and not concerned.
"A bunch of stainless steel nuts would Hurt our bottom line."

A friend,who still turns wrenches professionally, swears by Gravity Bleeding
BUT all it takes is once forgetting to keep the MC "Topped Up" during the
process to sour you on it.

However it does work!Even on ABS equipped systems.

cho · #24 03-17-2017, 05:10 AM

Quote:

Originally Posted by compress ignite

However it does work!Even on ABS equipped systems.

It does, I do it all the time... patience is the key

cheers

ur20v · #25 03-17-2017, 10:31 AM

I bench bled a master cylinder once, about 20 years ago. Then I spent the money on a proper pressure bleeder and have replaced hundreds of brake and clutch master cylinders, and never had a mushy pedal (unless the calipers on the vehicle had significantly more piston surface area than stock, but that's a completely different discussion).

yuke · #26 03-17-2017, 11:47 AM

Quote:

Originally Posted by Chad300tdt

I asked this question in the tech forum, but wanted to ask it here since a number of knowledgeable people only view this forum.

I just replaced all the rotors and calipers and I'm getting ready to replace the master cylinder. I plan to use a Motive Power Bleeder once the master cylinder is in.

Do I need to do a bench bleed prior to installing the MC if I am pressure bleeding the system anyway?

If you already have the master off yes bench bleed it you can do a better job and are right next to it to watch what is happening. You can get a bench bleeding kit for under $10. I just did it on my SD couple months ago have great brakes now.