Car:

1978 Mercedes Benz 240d, 4-speed manual transmission.
manufactured 12/77, model 123D, vin 123.123 10 057918

History:

Replaced the bendix front calipers with Fenco rebuilt ATE calipers (part numbers C9106 and C9107) and new pads. New rubber lines all around the system, and a new Fenco rebuilt Master Cylinder (part #M52326).

Bench bled the Master Cylinder (rebuild kit came with threaded nipples that would pump the fluid back into the reservoir)

It was difficult to install the brake lines once the MC was installed due to the angle of the solid metal lines... maybe significant air got in at this point?

Did the tedious and slow 'girlfriend in the car' 2 person brake bleed on a level surface with the engine off, and in this order: RR, RL, FR, FL

After extensive bleeding and no more air bubbles the pedal still goes down to the floor and the front calipers will not extend far enough grab the rotors. The rear brake calipers activate.

Next day I ditch the girlfriend and build a contraption to move pressurized brake fluid up from the bleeder valve at each wheel into the reservoir. I move about a quart and then some through the system this way. Marginal difference (percieved only?) in pedal pressure.

When I drive the car the back wheels will lock, but the front's still don't activate.

What do I do now?
Is it possibly air in the Master Cylinder? In the Brake Lines or Calipers?

Would the car possibly benefit from doing a regular two person bleed with the engine on to have the assistance of the brake booster?

If there is air in the Master Cylinder should I jack the car up in a way that the the master cylinder is level (the ass end is in the air?)

Thanks guys,
Perplexed and Vexed,
Tyler

Hyper,

Might be a bad master cylinder. Wouldn't be the first rebuilt part that didn't work.

P E H

Somewhere in here is a thread relating to installation of calipers on the correct sides of the car......they are side specific, and if they are on on opposite (wrong) sides the bleed screws wind up on the bottom of the caliper rather than the top.....

SB

__________________

Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG

YOu definately still have air in the system. Are you sure the rear of your master cylinder res is not dry?

Not to insult but maybe you are not doing the bleeding correctly.

YOu need to pump the pedal until you build up some pedal with the bleeder shut. Then holding a foot on the brake pedal you open the bleeder until the brake pedal is pushed near the floor. Shut the bleeder and pump the brake pedal again til you get a good pedal and repeat. Never let the brake pedal rebound with the bleeder open cause it will suck air back in.

Good luck.

Tom W

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Shorebilly: Good advice, both of my bleed valves are on the top of the caliper, I'm confident they are installed on the correct sides of the vehicle.

t walgamuth: No offense taken, I ensured during the entire bleed process that both tanks inside the reservoir had plenty of fluid, realizing that the only way for fluid to enter the tank for the rear calipers is through the little whole just below the neck on the reservoir cap.

I didn't know to build pedal pressure by pumping prior to opening the bleeder valve.
Is this with the engine running to provide brake boost?

I'll go try this tonight if I can enlist my girlfriend

Thanks!
Tyler

Hello again,

I've bleed the system according to the instructions provided in this thread, I had the car fairly level on jacks with all wheels off, engine running and proceeded to do a 2 man bleed starting from rear right, then rear left, then front right, then front left. Procedure was simply person on the pedal pumping a few times, holding the brake down, then man on the bleeder valve opening, and closing when the brake pedal was down. We used a simple container with hose attached to the bleeder nipple.

After going through about a quart of brake fluid, the pedal is a bit stiffer.
However, there is so much play in the pedal, she sinks almost to the floor before the brakes activate, and even now, the rear brakes are activating more then the front brakes. (If i stand on the brakes to lock the tires, it's solely the rear wheels that lock and skid).

I'm lost... is there air someone still trapped in the system? How do I get it out if so?

Is my Master Cylinder toast? It's a Fenco rebuild... how can I tell if it's toast?

Thank you guys.
Your help is much appreciated.

sounds like a poorly bled mc... also, DO NOT BLEED BRAKES WITH THE MOTOR RUNNING!!! way too dangerous, plus you can damage the booster this way. pull the lines off the MC and hook up the bench bleed tubes and re bleed it. then go through the pressure/bleed/hold/tighten procedure again... report back.
did you replace the soft lines at the wheels?

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

vstech - thank you... i bled the brakes with the motor running based on recommendations in another thread. Could I inquire as the reason for or against such an action?
I have new soft lines at all wheels.

Remove the master cylinder completely from the car to blench bleed it?
Will try, and post my response on the forums.

I see no reason that having the engine running would contribute to the problem. Off or on should work fine, imho.

Also bench bleeding the mc at this point would not be of any benefit. This only helps the beginning of the process.

Were the brake pads free to move when you installed them? If you perhaps had to hammer them in they might be hanging on the sides of the caliper.

If that is not the case, then you may still be doing a part of the process a little wrong. YOu always must close off the bleeder valve before the pedal person lets the pedal up.

It is a fairly simple process but each step must be done correctly or it will not work.

Good luck.

Tom W

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

simple reason not to bleed brakes with the motor running, YOU ARE UNDER THE CAR!!! really, it's not safe. unless you are in a nice garage, with a full lift securely attached to the car, don't do it! I suppose if the tires are still on the car, and it is up on ramps, and the car is securely attached in some way, it would be safe in that case, but not me... anyway, the amount of travel the pedal makes with no pressure (due to you opening up the bleed screws) while the motor is running, giving the booster full power, will certainly damage the MC. anyplace you read about bleeding brakes, states clearly do not have the motor running while bleeding.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

NO NEED TO PULL THE MASTER TO "BENCH BLEED"
in fact it is eazyer and quicker on the car on most cars
you just remove the brake line one at a time and loop back to the rez
pump intill no bubbles rehook the line and do the next one
after that bleed from the calipers

and YES you can bench bleed any time the lines are airlocked

I once bought a car with mystery bad brakes after the owner had done a replacement of most bits [ inc a new master] but didnot bench bleed the car
the sellor was pissed to watch me go to the store and beg a plastic nipple and buy a buck's worth of clear tube and ''bench bleed'' the car in his D/W in a few minites
that alone was enuff to get a hard petal to drive the car home in a safe manor that the sellor dumped for "BAD BRAKES"

we are definatly closing the bleeder valve before the pedal goes back up.

I'll try blench bleeding the the mc in the car, removing one line at a time, hooking up the nipple and tube, and pumping that line.

Should I pump the pedal multiple times in rapid succession or one steady slow pump - pause - pump?

After talking with a qualified and competent mechanic he explained how there is a component that can get stuck in the brake system that will direct the pressure to the rear wheels like as was happening in my car. He advised me to replace the master cylinder.

So I pickup up a replacement master cylinder and before I had a chance to install it and go through the whole bleeding process AGAIN something miraculous happened...

As I was driving the down the street I went to use the breaks and heard/felt a "pop" and suddenly my pedal was no longer mush and needing to be pressed all the way to the floor... it was FIRM and responsive just like it should be with new parts.

So, case closed. Thank you everyone for your support.
Moral of the story - if you value your time and want to actually enjoy wrenching on your benz - buy quality parts.

No wait, so what happened, divine intervention, what do you spoz popped in the system? Do you mean the master cyl, not being a quality part, was plugged?

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"