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Thread: Fintail brakes

  1. #1
    56 & 60 sl & 67 Sedan 230 Andre Hudon's Avatar
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    Fintail brakes

    The brake booster on the 1967 Fintail is linked directly to the master cylinder like most cars. The master cylinder on the 190sl brake system is separate from the brake booster. Also a bit different the way to work on it.
    My problem is the brake pedal is soft going low, near the floor to stop the car. When pumping the pedal, it improves a bit, but for a very short time. I disconnected the vacuum line off the brake booster, near no brakes at all. Booster is working. No reasons to have air in the brakes' line, the system was not opened. No oil leaks, the reservoirs still full, I suspect the master cylinder to be defective.
    Am I right?
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    André Hudon

  2. #2
    Registered User tommd's Avatar
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    Re: Fintail brakes

    Andre, am am not familiar with the fin tails, but what do you mean by goes soft? Typically a spongy pedal is air in the hydraulics or something mechanical in the drum area. If the pedal drifts to the floor and there are no leaks, it would be a master cylinder. Keep in mind if the master cylinder is bolted directly to the vacuum booster, it could be leaking into the vacuum booster.
    Tom D.
    1961 190SL

  3. #3
    56 & 60 sl & 67 Sedan 230 Andre Hudon's Avatar
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    Re: Fintail brakes

    Thanks Tom,
    The pedal is not only spongy, but goes near the floor with little brake capability. Because the oil reservoirs are still full, it seems the master is not leaking thru the booster.
    First move will be to bleed the lines to eliminate any air and if no improvements are noticed, I will remove the master cylinders with booster.
    Will let you know, but for now I have to repair the laundry washer making a lot of noise.
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    André Hudon

  4. #4
    Administrator JimVillers's Avatar
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    Re: Fintail brakes

    Tom is correct to suspect the master cylinder; you can peal back the rubber on the master brake shaft, if it is full of fluid, the cylinder is leaking and is bad.

    Poorly adjusted brakes can also cause some of the symptoms you describe. Check the brake adjustment on each wheel (I do not know if they had automatic or manual adjustments and I assuming that it has drum brakes). If it has disk brakes, the master cylinder is probably the cause of your problem.
    Jim Villers
    1961 190SL, 230SL 5-speed, MGB 5-speed, Porsche 356C; 1967 Porsche 911; 1950 Jeep CJ3A

  5. #5
    56 & 60 sl & 67 Sedan 230 Andre Hudon's Avatar
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    Re: Fintail brakes

    I removed the master cylinder and dismantled it. No corrosion, everything seems normal. The check valve looked not very tight, also I changed it. After installation and bleeding, nothing changed, also I ordered a new master from Rockauto. Shipping to Canada is very reasonable.
    I was pleased to have bought a new wise grip tool last winter, I had rounded connectors on the master, being unable to unscrew them with the standard 11 mm key. Very easy with the one on the picture. Good also on any damaged nuts.
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  6. #6
    Registered User tommd's Avatar
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    Re: Fintail brakes

    Andre, unless they were damaged previously, I would suggest using a line wrench. Also, when I asked if the pedal was drifting to the floor, you indicated no. If a master cylinder is bypassing, one would expect it to do so all the way to the floor. Of course, corrosion could cause it to drift past the corrosion, then hold at the good section. But there is usually more corrosion the further down the cylinder. And you indicated little corrosion anyway. If not, I would think it may not be bypassing and there is something mechanical, as suggested above. Little braking capability, pedal not to the floor, indicates poor booster or bad lining. But in my opinion, brakes are not as predictable as one may like. Since you have a new master cylinder on order, go ahead and try it, hopefully it will solve the problem. If not, in my view it may be time to redo the entire system, cylinders, hoses, booster, and checking all mechanical parts. You could have stuck wheel cylinders, and any number of broken, worn or misaligned mechanical parts.
    Tom D.
    1961 190SL

  7. #7
    56 & 60 sl & 67 Sedan 230 Andre Hudon's Avatar
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    Re: Fintail brakes

    Quote Originally Posted by Andre Hudon View Post
    Thanks Tom,
    The pedal is not only spongy, but goes near the floor with little brake capability. Because the oil reservoirs are still full, it seems the master is not leaking thru the booster.
    First move will be to bleed the lines to eliminate any air and if no improvements are noticed, I will remove the master cylinders with booster.
    Will let you know, but for now I have to repair the laundry washer making a lot of noise.
    Misunderstanding, the pedal does not go to the floor, but it is stopped by the booster travel. Also it is equivalent to the floor.
    This means like Tom said, that the master is bypassing. The new one should solve the problem.
    Tom, I do not know what is a line wrench! Could you show us a picture?
    I use a round wrench on which I cut a slot large enough to slide it thru the line.
    My line fittings were damaged previously.
    Last edited by Andre Hudon; 06-22-2016 at 12:59 PM.
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    André Hudon

  8. #8
    Registered User tommd's Avatar
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    Re: Fintail brakes

    Andre, it sounds like you made your own line wrench! I believe some call it a flare nut wrench. It would be stronger and flex less than a box wrench cut.
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    Tom D.
    1961 190SL

  9. #9
    56 & 60 sl & 67 Sedan 230 Andre Hudon's Avatar
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    Re: Fintail brakes

    As an update, I received the new master cylinder and installed it today. After bleeding brakes, system is working fine.
    ________________________________
    André Hudon

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