Clutch Master Cylinder question - Page 2 - Mercedes-Benz Forum

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post #11 of 14 (permalink) Old 07-22-2013, 12:06 PM
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since DOT 5 [ silicone ] does not absorb moisture , you are safe .maybe replace at 10 years interval .
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post #12 of 14 (permalink) Old 07-23-2013, 08:00 AM
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"since DOT 5 [ silicone ] does not absorb moisture , you are safe .maybe replace at 10 years interval ."


How did you find that out? I've been looking for authoratative information on that subject for decades without success.

Back in the early 1980s GE was trying to create a market for their silicone brake fluid. Part of the marketing strategy was selling it at Pep Boys with a rebate equal to the purchase price. I got a bunch of it that way, well over a gallon. It has worked well, after learning how to bleed it effectively. Learning the bleeding technique was trial and error because there is so little published information on DOT5. All I've seen in writing is love it and hate it personal opinions.

On my street rod the front brake braided steel hoses connect to a bulkhead fitting that passes through the boxed frame rails. Any leakage of DOT 3 brake fluid at those locations would strip the paint.

Eying the compact size of engine in this roadster and having experienced its torquey power delivery has prompted my wife to ask me what it would take to put an identical small block Chevy in her 190SL. My answer was that it wouldn't take much. The downsides would be that 2 things would get destroyed, the value of the car and any original power train components left in place. Tapping the throttle of a warmed over Chevy 350 would probably turn the original transmission/U-joints/differential into shrapnel. That would be a lot of "Bang!" for the buck, literally.

Ray W
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post #13 of 14 (permalink) Old 07-23-2013, 08:46 AM
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Vehicle: 1959 220S cabriolet, 1983 240D original owner, 1999 E300 turbo diesel, 1988 560SL, 2003 SLK320
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Originally Posted by Waldbaum View Post
"OTOH DOT3/4 absorbs any moisture and is flushed out during routine service that is supposed to be done every two years. I do service mine every two years and at a cost of maybe ten bucks a pop, I'm comfortable with that. I guess if someone never services his brake system, the moisture in the DOT3/4 fluid will also allow rust to form."


Since I first put DOT5 in my '36 pickup in about 1995 I have been concerned about the issue you raise. I have looked at the recommended maintanance intervals in various owners manuals and I have not found brake fluid flushing recommended. Do you know of a discussion on this subject? It's definitely something I don't want to ignore any longer.

Thanks for bringing that issue up.

I have seen specific recommendations that DOT5 not be used in ABS equipped vehicles. My anecdotal observation is that whenever DOT5 is agitated it forms what I call "microbubbles". My theory is that until the "microbubbles" coalesce into bigger bubbles bleeding is futile. That's why I wait a couple of days after filling a system to do the final bleeding. Obviously a professional mechanic cannot do that for various reasons.

Ray W
Ray - interesting observation about the bubbling of the DOT5 fluid. Never used the stuff myself, so that's the first I've heard of that. With the DOT 3/4 that isn't an issue.

The maintenance sheets for all of my Mercedes have the brake fluid service listed as a time required interval. Was one year on my ponton and 240D and two years on the 210 and SLK. I have gone to two years on all of them for the following reasons. I put very few miles on the one year cars, often under 1000 miles a year and also since those recommendations, both the fluids and the rubber in the brake systems have improved, so I figure every two years is plenty.

'59 220S Cabriolet - for sale -
'83 240D original owner 351,500 miles - for sale -
'88 560SL 41,000 miles being parted out -
'99 E300 turbo 196,000 miles
'03 SLK320 34,500 miles
'14 Smart electric
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post #14 of 14 (permalink) Old 08-07-2013, 09:17 AM
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My 220S always had clutch cylinder issues. So I threw out the manual tranny & got auto gear swap. Never been happier since. I think ur 16 yr old would benefit if u do the same or she might get bad feeling about old car n refuse to drive it!

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