Defective new master cylinder? (long)

[joshhol]

Regarding '76 300D with tandem master cylinder, second version from 029142

You might be able to add me to the ranks of suckers screwed by that guy bigbabbo, or whatever his name is. After spending 1500 some odd dollars on Fastlane for the front end rebuild, I thought I might check competitors prices and save a few bucks. Based on a thread here, I found a site with better prices, ordered and installed the new looking master cylinder in ATE packaging.
Now after much bleeding, I cannot get proper braking or pedal feel. I've used the manual method with an assitant and opening and closing the bleed screw. Then I bought an eezibleed and ran fluid through each wheel. That didn't work, so I again attached the eezibleed, raised the rear end, then opened both rear bleed screws while pumping vigorously several times on the pedal, then did that on the front. With only slight improvement, I repeated it only opening one bleed screw at a time with the pressure bleeder attached and pumping the pedal. Still, braking is very minimal with brake effect only taking place when the pedal is mashed to the floor, very weak braking at that. I've made SURE that both compartments of the resevoir have been full while doing this.

The pedal should pump up and become firm even if there is air in the lines, only my pedal pumps up reluctantly and then sinks to the floor right away. I beat on the master cylinder a couple times with a brass hammer in case the floating piston may have gotten stuck. Another thing is the brake warning light will not go off, even after "resetting" the fluid level sensor switch.
The fluid level does not drop after repeated pumping of the pedal and no wetness is observed around the calipers indicating no malfunction of the wheel cylinders in my mind. However, there may be the possibility that the rear calipers froze while the car was being worked on over the last three months, while at the same time my front caliper reseal job may have been defective.
The pistons in the front caliper moved fairly easily after I rebuilt them, and I feel confident in my work. The shame about it is that my old master cylinder was probably fine, no pedal fade noticed. I'd throw it on and check but I submerged it in a vat of ATF thinking I would keep it from rusting not know that oil contamination in the brake system was forbidden. (Still new at this $*#!)

What would you do next? I'm considering removing the master cylinder and taking it to my indy for inspection, or should I tow the car to him and let him have a go at the bleeding?
I do have a strong feeling that had I shopped with Phil, I wouldn't be having any of these problems.
Thanks for reading this rant. After 3 months of work and being so close to driving the old 115 again, I'm very annoyed at this delay.

[Tomguy]

I think you're going about the bleeding process all wrong. When you pump the pedal, fluid will come out of the bleed screw, but air will go back in when you release it! I just opened the bleed screw, made sure the resevoir was full, and let it drain by gravity until the res was halfway down. Refilled it, did the other rear, then did the same on the fronts (all 1 at a time). You're sure you dont have a leak between the master cylinder and brake booster (the rubber gasket is tight)? You're testing with the car's engine running I assume.

[joshhol]

I only cycled the pedal with the bleed screw open with the pressure bleeder attached. I assumed this would prevent the air from returning to the lines. The pressure bleeder's instructions even recommended this. Besides, I should be able to build pressure with the pedal if it's just air in the lines. Also, the booster seal looked good and is sitting properly. If the vacuum was being lost, the car would A) not shut off properly and B) the pedal should get harder, not sink to the floor.
I've been bleeding with the engine off.
A parallel thread has been going in the diesel discussion. Seems to be the lack of directions in the box caused me to forgo bench bleeding.

Crossing my fingers this is the cause.

[ctaylor738]

Test the MC like this:

- Open a bleeder and have someone push the pedal down, and watch that you get a good squirt of fluid

- Close the bleeder, hold constant pressure on the pedal and observe that the pedal does not sink slowly to the floor.

If the MC is OK, then bleed. If not, get a different MC.

Get some clear plastic hose to attach to the bleeders. Go RR LR RF LF with the power bleeder (pump to 20 psi before each wheel) and watch for tiny bubbles in the tube. Go at least a minute after the last bubbles that you see.

If this doesn't do it, then you probably have a caliper or brake hose problem.

[joshhol]

ctaylor38, here is the link to the diesel discussion if you care to read it all: http://www.peachparts.com/shopforum/diesel-discussion/112993-defective-new-master-cylinder-long-post798995.html#post798995

In summary: after bench bleeding the master and bleeding the lines, the brakes will not function correctly.

[nachi11744]

Hello,
I have not had this problem myself, but a friend that renovated a W116 450SEL brake system in Raleigh could not get a firm pedal even after running almost two gallons of brake fluid thru the system
He borrowed an EAZIBLEED from me and had to do the whole thing again before he got a good pedal, er, I mean useful brakes.
Did you replace the flex hoses? I always keep the old hoses to compare the hydraulic coulpings(flare, I believe)with the new parts, MB makes so many production line changes that even the hood star is not the same for all years of the W114/115 AND the *bent back* star on my car that was a production line fitment on 1976 W114/5 cars is NOT avaliable as a spare part
Quick test for duff m/c:Crack open the lines at the m/c one at a time and have an assistant press the brake pedal gently. Keep a bucket of water handy for all brake work. Brake fluid has a nasty habit of spilling or dripping in the middle of a hood or very visible part of the bodywork.Don't ask me how I know
Hope that helps

[ctaylor738]

So I read the Diesel post, and my advice remains the same: get some clear tubing and make sure that you are getting all the air out before you condemn the MC. I have resolved several clutch and brake problems with this technique.

[joshhol]

I've been advised that you cant bench bleed on the car as the master sits at an angle. I will remove it and level it and bleed.
I've run 5 liters through it, using clear tubing so I think I'm getting the air out. It shouldn't be that difficult if it's just air in the lines? Using an eezibleed too. I replaced the front hoses, (Fastlane) they went in with no problem although I didn't inspect them next to the old ones. The rear hoses are older, about 10 yrs but I didn't have any issues with brakes before doing this work. It has to be air in the MC or the MC is defective.

Thanks for reading.

[yakerz]

Attach a tube of any color to the bleed screw. Put tube inside old cup partially full of new brake fluid. have a friend push brake pedal and hold it down. Once you notice fluid enter the cup close bleed screw immediatly. The fluid in the cup keeps air from flowing back into the line. Do this one wheel at a time . there may be a order to do this , But the rule of thumb is to start from the furthest tire from the brake fluid reseviour. If this doesn't work you probably have a leak somewhere or the master cylynder is faulty. I basicly told you the same thing as everybody else just a little easier to comprehend.
The car must be running when you bleed the system!!!

[joshhol]

Greetings.

I finally found relief from the annoyance of this headache. I stopped by my indy again to discuss. He gave me a new ATE master cylinder to throw on the car and see if the results were any better. I did a messy bench bleed, put it on and power bled it. While I got better results than the other one (many more tiny bubbles being evacuated), the braking was still unsatisfactory. I limped it over to my mechanic and they bled it, now the pedal is as hard as a rock.
I asked them if they got a lot more air out of it, they said no, not much.
The sweet part is he said he'd return the questionable MC on warranty through his shop. I don't have to deal with bigbaboon. So, I can't trash the guy cause he never had a chance to correct the problem. It could have been an honest mistake.
Anyway, I still wonder if that other one was bad. After I did the second master, the braking sucked but the pedal DID NOT drop as the other one did.
So thanks very much for the help.

[nachi11744]

Hello,
Not the first time a new m/c could have been defective. The rubber *cups* are easily damaged , eg. if you have itchy hands and push on the piston with the m/c dry, it can easily reverse the lip of any one of the cups or cause small tears.
This has happened to me with a new ATE m/c for another car, the supplier pushed on the end of the exposed piston to show me that it was not *stuck*, but when I installed it, it gave up after a week, the pedal would slowly sink and no amount of pumping would improve it.
When taken apart, one circuit main cup had a small tear, letting fluid pass thru.
I guess you live and learn.
At least you got around the problem, sounds like your indie is one of the *good guys*.
Take care and have a good week.
Oh, BTW, all you guys freezing right now in the US, it is 100F here today