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VWDog
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Joined: June 24, 2005
Posts: 617
Location: Ladysmith, BC
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 Posted: Fri Apr 27, 2012 10:22 am Post subject: How to tell if Master Cylinder hooped,broken(how to test?). |
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I have a 70 Deluxe that has sit for a couple of years and I am trying to get it back on the road. I have replaced the wheel cylinders(front and rear) that were definitely leaking and there is no sign of any moisture on the ones I left on. I replaced the front shoes and rear were okay. Bleeding the brakes both the Bentley method or the way I was taught(furthest from master first) yields erratic results. I have gone thru quite a bit of fluid, but still I seem to get pedal that is only 1/3. The rear brakes still seem to produce some air bubbles, but only after leaving them for a bit and only occasionally(ie sometimes I get pedal and sometimes it falls to the floor easily(that is when I see an air pocket)).
Could this just be a bad master?
On a related note, my Bus was produced 02/70 and it has wiring to two switches where the master is, but only one connection on the Master that is there now and only one connection on the master recommended by CIP.
Any thoughts on that would be appreciated too.
Thanks very much.
Don |
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onion456
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Joined: September 09, 2006
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Location: Houston, TX
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| Posted: Fri Apr 27, 2012 10:28 am Post subject: |
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are the brakes adjusted well? that can make a big diff in how much throw is in the pedal...
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'76 Creamsicle 7-passenger 2.0 CS FI
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VWDog
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Joined: June 24, 2005
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Location: Ladysmith, BC
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| Posted: Fri Apr 27, 2012 10:32 am Post subject: |
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| onion456 wrote: |
| are the brakes adjusted well? that can make a big diff in how much throw is in the pedal... |
I feel as though I have that covered with all of them scraping just a little bit. I have the wheels off and maybe when I get them back on I might be inclined to give the stars a bit more, but for now they are locking the hubs easily(when the pedal is 1/3 from the floor though).
Also, when I pump, don't seem to get any more pedal, which says to me that there is not a bunch of air in the system. Am I wrong on that point? |
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busdaddy
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Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Fri Apr 27, 2012 11:58 am Post subject: |
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Back off both brake cables at the handle so they are loose and then turn the stars equal turns until they won't turn any more, then back them off until the wheel barely scrapes. Adjust the brake cables last.
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onion456
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Location: Houston, TX
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| Posted: Fri Apr 27, 2012 1:17 pm Post subject: |
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pedal to the floor occasionally does make me wonder if the MC is bad too, as long as youre confident the brakes are adjusted properly and you feel like youve bled the system adequately...
i poked around and found this video, its for a bug MC but i think it applies, some fairly tricky stuff at around 7:00, about bleeding the master. i thought it was pretty cool, and if youre getting to the point where youre ready to replace the MC anyway, you might be inclined to give it a try.
http://www.youtube.com/watch?v=0DcY5iQMtg4&feature=related
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VWDog
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Joined: June 24, 2005
Posts: 617
Location: Ladysmith, BC
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| Posted: Fri Apr 27, 2012 1:19 pm Post subject: |
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| busdaddy wrote: |
| Back off both brake cables at the handle so they are loose and then turn the stars equal turns until they won't turn any more, then back them off until the wheel barely scrapes. Adjust the brake cables last. |
I did this, except for the hand brake, already as I eluded to in my post above(just didn't put it so succinctly  ). I have left the hand brake cables loose since starting this whole procedure, knowing they would be last, after bleeding.
I know air must have entered the system as the Bus sat, but I would have thought that could be bled out during the bleeding procedure, but maybe not. It just seems to be so erratic, sometimes good pedal, sometimes none. Maybe I need to get a pressure bleeding done at a shop? |
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VWDog
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Joined: June 24, 2005
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Location: Ladysmith, BC
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| Posted: Fri Apr 27, 2012 1:32 pm Post subject: |
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| onion456 wrote: |
pedal to the floor occasionally does make me wonder if the MC is bad too, as long as youre confident the brakes are adjusted properly and you feel like youve bled the system adequately...
i poked around and found this video, its for a bug MC but i think it applies, some fairly tricky stuff at around 7:00, about bleeding the master. i thought it was pretty cool, and if youre getting to the point where youre ready to replace the MC anyway, you might be inclined to give it a try.
http://www.youtube.com/watch?v=0DcY5iQMtg4&feature=related |
I guess that is part of my question because I still get air sometimes. I have never had this happen before(in recent memory anyway  ). Thanks for the link to the vid, though. I think I will take a closer look at the MC for leaks. Checked it before bleeding but not since. Duh! I am sometimes prone to jumping to conclusions and the vid you sent has reminded me of this work inducing problematic behaviour. Cheers!
Update:
Okay, the MC is dry. Rusty, but dry. There are no leaks under the vehicle anywhere. The MC pushrod is adjusted to spec. Hmmmm  |
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busdaddy
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Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Fri Apr 27, 2012 2:47 pm Post subject: |
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I you're up to it take the master cylinder apart and look for rust spots inside the bore, sounds like one of the pistons may not be returning fully.
 If you've never been inside a master disregard this as it's not something you want to learn from your mistakes on.
As for the missing switch the replacement many lesser vendors sell lacks the third hole for the early style warning switch, it'll work but the warning light won't unless you upgrade to 3 terminal switches and do a minor rewire at the cylinder.
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Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
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SGKent 
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Location: Citrus Heights CA (Near Sacramento)
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| Posted: Fri Apr 27, 2012 6:30 pm Post subject: |
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It doesn't take much to get air in the lines - just a pinhole anywhere in the system but my best guess is that if all the wheel cylinders were rusted the master is too. When we did our bus we just assumed all the cylinders would be bad and the master and the hoses and did them all.
Usually the best test of a non-abs master cylinder when you have replaced everything else is you step on it and see if it slowly falls to the floor. If so it is bad.
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