Hello All,

I am about to install new front calipers and bleed the system on my 84 245. I have a Eezi bleed pressure bleeder, and two thoughts on ways to do this.

(1) pressurize the system and blow all the old fluid and crud out, front and rear, then change the calipers add fresh fluid and bleed the system. The idea being the new calipers would only see fresh fluid, and mixing of old and new fluid would be held to a minimum. The question is if the system is filled with air and I add fluid and pressurize it will the air stay ahead of the fluid and come out first? Or will the air and fluid mix creating a foamy nightmare that will require me to flush twice as much fluid to clear it?

THE OTHER OPTION

(2) Change the calipers, losing as little fluid as possible. Add new fluid and pressure bleed. This way I introduce the least amount of air possible to the system.

Give me your thoughts, Thanks

When you remove the old calipers, you will leak out old fluid no matter how you try to prevent it. The Bently manual says to replace the vented resevoir cap with a non-vented cap. Well, I don't have one of those and I suspect you won't, either.

I have had limited success stemming the flow by sealing the resevoir bottle using some plastic bad material under the vented cap. It slows, but does not stop fluid loss out the broken or undone line(s).

In one sense, this is good because gravity is draining out the old fluid. But do you want to let the master cylinder run out of fluid?

Mine did (long story).

Since getting things back together with the rebuilt calipers in place on the front, I have bled my system three times. The pedal still goes to the floor until it is pumped several times. The car will stop, but braking is spongy.

On previous attempts to flush the system for fluid changes (past three cars, including this one) I had much better luck leaving fluid in the system from the MC - down.

Typically, I remove the fluid and fluid bottle. Clean out the bottle and replace it on the MC. Then I bleed with the EZ-Bleeder.

If you want to flus out the old fluid before it gets into the new calipers, try doing so with out draining the MC. I believe you'll come out well.

Tips on the EZ-Bleeder...

DO dry test the system for air leaks before filling the bottle. You can use slightly higher air pressure (up to 35psi), but secure the fluid resevoir onnto the MC by using a plastic electrical tie sound it so the bottle dosn't pop off!

And in case you forget, the cap on the fluid resevoir goes in the front position on the MC.

Don't be surprised if you need to bleed 2 or more times. Try tapping on the calipers with a small hammer as you open each bleeder screw. This loosens small air bubbles clinging to the walls of the fluid chambers.

*

Hi Bruce,

Here's what I do: Buy a large turkey baster at a supermarket, the largest one you can get. Then buy some Havoline synthetic brake fluid - I recommend it because it's clear like water. Now then: Using the turkey baster, suck out the dirty brake fluid from the resevoir. Pour in the Havoline fluid. Cap the resevoir, start the engine, and pump the brake pedal slowly to the floor a dozen times. Repeat the process until the brake fluid is as clear as you can get it to be.

I've used synthetic brake fluid on my last four cars, including two Mercedes, and I've never had any caliper problems, because I flush the brakes using this method three time a year! You won't believe how much higher your pedal is with clean brake fluid, especially the synthetic fluid, which resists boiling off. Good luck!

Bob Glotzer

/// There is an SAE paper on brake bleeding that says to disconnect the "wheel cylinders" before flushing old brake systems to avoid sediment being pushed in to the new parts. I think the last date on that paper was 75? 77? This has come up before.

Remember that air bleeds from the top and fluid from the bottom of the caliper. Any thing that flushes into a caliper stays there. There have been posts for older cars that recommend denatured alcohol as a flush for old brakes. If the system has been flushed at two year intervals that should not be necessary.

I only use DOT 4 fluid to flush. I blow out the system with air if there has been a problem. They start empty at the factory.

Your power bleeding system should be able to handle the empty system. Just start with everything closed tight.

Bruce:

I like your first approach best. The idea of having the new calipers seeing only fresh fluid makes sense. Plus, I wouldn't think you'd need to open the rears back up to bleed again after the new front calipers are installed.

Given the age of your vehicle, I'd take a close look at the rubber flex hoses while I had things apart. The ones on my '85 245 were starting to go when I replaced them last year. They get sort of spongy and bulging out a bit at the ends where the metal fittings attach.