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Old 08-22-2012, 08:19 PM   #1
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Master Cylinder Part #

Does any one have a Master Cylinder Part # The one one the coach has very few markings on it. It has 'Bosch' and '50.80 Bore' cast in the side.
Took the coach in this morning to have the Brake Fluid flushed and when the finished, no brakes.
I tried searching but there are so many posts about brakes but couldn't find anything identifying the part.
Any help will be greatly appreciated.

PS I can post pictures if you think that will help.
Bob
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Old 08-22-2012, 09:36 PM   #2
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Bob- you can learn more than any sober motorhome owner can stand about master cylinders in this thread about braking improvement. Down the thread you'll see master cylinder part #'s for the 1.75" (it will say 45.45 Bore) on it, vs the 50.40mm (2") unit that came standard on Alpines. Not sure if there was a part# mentioned for the 2" bore.
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Old 08-23-2012, 01:09 PM   #3
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Thanks Mike for the info. I told the mechanic about using the 1.75" bore but Bosch is saying that it is not compatible with the ABS system. I guess I'll have to let them install the 2" unit (if they find one) as I'm running out of time and need to get home sometime soon. It's kind of hard driving the rig with just the parking brake to stop.
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Old 08-23-2012, 04:06 PM   #4
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Bob--I havent [yet] but quite a few folks have installed the 1.75 master cylinder with no apparent problems [eg not compatible with ABS]. The 1,75 is a perfect bolt on replacement for the older 2.0 MC. Was a bit curious about compatibility issues but figured the only real difference might be slightly higher fluid pressure to the calipers. One thing is for sure, appears those that have converted to the 1.75 are very happy with the improvement in braking.....

Would be curious to hear what and why your current MC "failed" after a routine fluid flush--realize you are up again time and at the mercy of the techs currently working on your coach, but there are a few things that dont add up here. My next concern will be how much they intend to charge you for what they have done for you/to you!!!!!
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Old 08-23-2012, 08:28 PM   #5
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The brake master cylinder subject came up in today’s gearhead session @ the Indy pre-rally. Louie Burch trotted out his portable filing cabinet with the file folder on master cylinders. Per Lou some members have replaced the OEM 2” bore master cylinder with the Wagner 1.75" bore master cylinder p/n MC131759. Around $200.00?
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Old 08-27-2012, 12:05 PM   #6
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Hi Old Scout:
The problem the MC appears to be a stuck or bad equalizer valve that allows the fluid to circulate around inside the cylinder without going to the brakes. When they pulled the MC out, there was some stringy substance in the brake fluid that may have caused the valve to stick.
I'm not a mechanic and can only hope the one who explained it to me was knowledgeable. At least I have brakes now. Wish I had the time to get the 1.75" MC. I know it was too expensive but at least the labor rate was only (?) $72.00 an hour, and they spent 4 hours. Had to flush the system a second time after the MC change.
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Old 08-27-2012, 03:07 PM   #7
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Bob--sounds like you came out ok....MCs arent that expensive and it is one part on your coach that you dont want to take any chances with. As more and more folks change out the 2.0 for the 1.75, we as a group will get more feedback on how good an idea this is in the longer-term. My primary thought was that since you were in the market for a new MC anyway, you should consider the 1.75. Bottomline--you are back on the road and your brakes are working....
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Old 08-27-2012, 06:02 PM   #8
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Bob- 4 hrs is lightning fast!! Did they remove the wheels to get at all 8 bleed screws? There is an inner (easy to reach on all 4 corners) and an outer (next to impossible on fronts & actually impossible on rears) bleed screw on each caliper & both have to be bled or you leave the bad fluid in the outer half of the caliper.

The second round bleed & a full gallon of Dot3 is common to get the feel for the process; once you let one tank side get low you suck air easily, and have to start over.
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Old 08-27-2012, 06:11 PM   #9
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Engineer Mike.
They claim they got all eight bleed screws without pulling the wheels and they did use over a gallon of brake fluid. One of the problems of age is that it is hard to check really close on what they are doing under there. I now have the ABS light on all the time and am going to try to check the sensors to be sure they are clean and properly installed. I hope it is just one that got displaced or something simple. At least I am home now and can get to these problems.
I do think they actually spent more than four hours but the time was spread over two days.
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Old 08-28-2012, 01:40 AM   #10
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There was a game in my crass youth called B_ _ _ S_ _ _, readily abbreviated B.S. I'm calling B.S. on those outer rear bleed screws. The inside wheel is steel, has only two oval cutouts, is cupped fully around the caliper to the inside of the coach frame, and there is no way to reach the bleed screw from the outside. I've been under mine many times to check things out, and there is likewise no way to get a wrench on the bleed screw to open it, no room to turn it if you could, and then you'd need another hand to deal w/the bleeder tube (on & off) since it has to rotate while you're turning the bleed screw.
Yeah, I think B.S. was the name of that game.

I was in a Sacramento shop, pretty good joint all told. However when flushing fluid on an 05 I was next to, they didn't pull the wheels either. After I asked about the outers, was told: "Don't need to touch those, the fluid bleeds thru."
Also B.S.

I don't think its fatal in your case Bob, but you still have old fluid in the outer caliper unless I'm full of, well, er, you know.
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Old 08-28-2012, 03:23 PM   #11
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Quote:
Originally Posted by EngineerMike View Post
There was a game in my crass youth called B_ _ _ S_ _ _, readily abbreviated B.S. I'm calling B.S. on those outer rear bleed screws. The inside wheel is steel, has only two oval cutouts, is cupped fully around the caliper to the inside of the coach frame, and there is no way to reach the bleed screw from the outside. I've been under mine many times to check things out, and there is likewise no way to get a wrench on the bleed screw to open it, no room to turn it if you could, and then you'd need another hand to deal w/the bleeder tube (on & off) since it has to rotate while you're turning the bleed screw.
Yeah, I think B.S. was the name of that game.

I was in a Sacramento shop, pretty good joint all told. However when flushing fluid on an 05 I was next to, they didn't pull the wheels either. After I asked about the outers, was told: "Don't need to touch those, the fluid bleeds thru."
Also B.S.

I don't think its fatal in your case Bob, but you still have old fluid in the outer caliper unless I'm full of, well, er, you know.
I agree with EM that those outer bleeders are not accessible without the wheels coming off. Been a couple of years since I bleed out the rears but I recall spending quite a bit of time trying to get to the outer bleeders and I say it can't be done.
I have 25 plus years as hvy equipment mechanic and still don't like taking wheels off, but that is the only way to do it.

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