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Old 07-09-2013, 03:52 PM   #1
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04-Alpine Coach-40',3 Slides Brake Question

The Coach has a Bosch Master Cylinder with a 50-80 bore size. Brakes
have been very good with full pedal . On a trip from the East Coast to
Gillette, Wyo. - after crossing Powder River Pass 9666', brake pedal started
going down half way and I would have to pump one time to bring pedal to
full pedal (sounds like air in system to me). Brakes did not get hot or stinky
hot, also, both Stemco Oil Caps on front wheels began leaking. Upon checking brake fluid level , it felt like honey but full. I am thinking about
flushing and replacing brake fluid with Dot 3 Synthetic. Should I consider
changing the master cylinder or not?
Any help on these questions would be very much appreciated!

Jim and Pat Sinsel
Baltimore, Maryland
04, Alpine , 40', 3 slides
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Old 07-09-2013, 04:23 PM   #2
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Does your 04 have the adjustable pedals under the dash or does the brake pedal come thru the floor by the steering column? If adjustable pedals, you can, perhaps should, do the master cylinder replacement but it doesnt sound like you had any issues before the recent incident. "Honey" in the brake fluid reservoir isnt good so brake fluid should probably be flushed [suggested every 3-4 years, sooner if you want] To do it correctly, requires taking the wheels off so both calipers on each wheel can be flushed. If the front hub plugs are leaking, it probably means they are getting old [lost their flex] and you probably rode the brakes a bit too much on your last mtn pass. New plugs [red caps] are cheap. Since its an 04, you might consider changing the oil in the front hubs [more of an exchange unless you take the hubs off] and having the pre-load on the bearings checked.
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Old 07-09-2013, 09:00 PM   #3
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04 Alpine - 40', 3 Slides - Brake Questions

Thanks, Old Scout for your reply,
The Brakes are adjustable pedals under the dash. I am trying to get the
right part no. for the 0-4 Master Cylinder. The brakes were excellent
before loss of pedal. Should I use Silicon fluid or regular brake fluid?
I will replace red caps and change the wheel bearing fluid to silicon also.
I would also like to know what size cylinder bore is 50-80?
I am trying to find what the proper bore size for the correct cylinder
replacement. Any help on these questions is greatly appreciated.

Jim and Pat Sinsel
04, 40' 3 slides Alpine
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Old 07-09-2013, 09:57 PM   #4
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Do a search on this forum--I'll try to find the link if I can. In the interim, someone with the part numbers may chime in. I have helped a fellow Alpine owner swap out their master cylinder--not very difficult to do. As I recall, the OEM cylinder has a 2 inch piston [your 50-80] while the replacement is a 1.5 or 1.75 inch--results in somewhat more pedal travel but significantly increases the mechanical advantage to the calipers. Most brake fluids are synthetic now [DOT 3]. Synthetic in the hubs is fine but probably not necessary. Most of the oil [80w-90] in the hubs is in the hollow of the hub itself so even if you take the 6-bolt Stemco cover off [requires new gasket], you only change out maybe half the oil in the hub. Again, if its not been checked recently, this would be a good time to check the pre-load on the bearings.

Do a search on "Meritor Braking Improvement" Part number listed in thread is MC131759. Saw several listed on Ebay and Amazon for less than $200 w/free shipping.

PS--not all coaches with adjustable brake pedals seem to have the same degree of brake issues. Some owners have not had any problems while others have had major concerns about required pedal pressure. Not sure why the differences.
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Old 07-11-2013, 07:04 PM   #5
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50-80 is 50.80 millimeters, which = 2"
Meritor Braking Improvement thread link

There was another "pedal going down half way" problem a few years back. Owner would fire up the engine and the pedal would automatically depress visually a half inch or more; it was applying brake pressure & heating up the front wheels. Turned out it was an over-amping hydraulic pump creating an overpressure at the master cylinder boost input; new (or maybe rebuilt) pump fixed it like new. You can have the pressure input at the M.C. checked by a hydraulics shop, or they can tap at the exit from the steering gear if that's more convenient (that's what I did per post# 12 of the above linked thread). Cost me $90. Good insurance to see that the pump is on spec or not at the brakes.
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Old 07-17-2013, 11:20 PM   #6
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And FWIW-Annually or at least every two years, the brake system in Alpine Coaches equipped with hydraulic brakes need to be power flushed. Brake fluid loves water, water in the air, water in the rain/snow. To be safe Power Flush them. You can do it, if you have a lift to get the rear off the ground, and a power torque wrench which can torque to 450 ft-lbs, as the rear wheels have to be removed to get to both bleeder screws on the brake unit. See other threads on this issue, lots of good information concerning how this should be done and safely. Or you can take it too a good Motorhome shop, Detroit diesel or Navistar service centers can do it for you. Last time I had it done was not much more than 100 dollars, cheap insurance in my case.
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Old 07-18-2013, 08:46 AM   #7
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Having just done a wheels-off, 4-corner myself, I can pretty much tell you that if a repair shop charges you less than a $100 to "flush" the system, they didnt take the wheels off. At best you got the inside calipers flushed--if they did all 8 calipers you got the deal of the century.
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Old 07-18-2013, 01:25 PM   #8
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I specifically told them to take the rear wheels off, which they did. They are very accommodating, since they were doing a transmission service at the same time. They changed my coolant (I Provided the coolant) and only charged me 120 for that one, great place to have work done of a non engine nature. Detroit Diesel-Allison Transmission Facility, Exit 14 North Bound on I-5 in Washington State, go left at the exit, turn left past the Chevron dealer. You can get their contact information from the Allison's website as an authorized dealer/service center. Great Place to Have work done.
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Old 07-19-2013, 05:56 PM   #9
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Monte,
I second your comments regarding that place at exit 14.
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