Bus master cylinder replacement

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anotherbluebus
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Bus master cylinder replacement

Post by anotherbluebus » Thu Sep 22, 2011 10:32 am

I'm starting a new thread specific to my brake repair journey.

I have a '69 bus with manual brakes. When we bough the bus, we knew it had a leaky rear wheel cylinder. Got replacement cylinders, new shoes, etc. When we tried to bleed the brakes, I noticed a leak in the MC as well. Got the recommended German MC. I didn't read all of the online resources about bench bleeding or any prep for installing the MC. Bentley and Muir shrug it off with "install just like you took it out," so that's what I did. Now it's in I can't get the $*% thing to bleed properly. I can get fluid to both front wheels, and they bleed okay, but nothing in the rear. I don't have access to a vacuum bleeding system, but I suspect that's what it's going to take to suck fluid down those lines to the rear. Any suggestions on what's next for me? I would love not removing the MC. I am hoping there is an ancient germanic druid ritual involving a dead chicken and some kind of chant that makes it all good.

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hambone
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Re: Bus master cylinder replacement

Post by hambone » Thu Sep 22, 2011 10:40 am

I have a vacuum bleeder, but I will bee a needin' it soon for the back brakes on my Square.
After I'm done? It may be a couple weeks tho.
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anotherbluebus
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Re: Bus master cylinder replacement

Post by anotherbluebus » Thu Sep 22, 2011 12:08 pm

hambone wrote:I have a vacuum bleeder, but I will bee a needin' it soon for the back brakes on my Square.
After I'm done? It may be a couple weeks tho.
thanks for that offer. Mi esposa is breathing down my neck to get this project done. I just found a $25 hand pump bleeder at Harbor Freight. Looks like I should pick that up and get it over with!

steve74baywin
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Re: Bus master cylinder replacement

Post by steve74baywin » Thu Sep 22, 2011 12:25 pm

You probably know this, but I once spent hours attempting to bleed brakes in my bus.
You need to adjust them first, or you will just be spinning your wheels.

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anotherbluebus
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Re: Bus master cylinder replacement

Post by anotherbluebus » Thu Sep 22, 2011 1:35 pm

steve74baywin wrote:You probably know this, but I once spent hours attempting to bleed brakes in my bus.
You need to adjust them first, or you will just be spinning your wheels.
yup. Did that as part of the original brake job. Thanks for checking though.

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hambone
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Re: Bus master cylinder replacement

Post by hambone » Thu Sep 22, 2011 2:01 pm

Do not exceed 5-6 PSI (according to Colin. I followed his advice.)
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RSorak 71Westy
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Re: Bus master cylinder replacement

Post by RSorak 71Westy » Thu Sep 22, 2011 4:26 pm

The rubber hose to the rear brakes is probably swollen and clogged internally. You need a new rear brake hose I bet.
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Rick
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Amskeptic
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Re: Bus master cylinder replacement

Post by Amskeptic » Fri Sep 23, 2011 7:18 am

RSorak 71Westy wrote:The rubber hose to the rear brakes is probably swollen and clogged internally. You need a new rear brake hose I bet.
Wait. Let's not explode the variables with speculations.

anotherbluebus,

Fill your reservoir. Get thee under the bus where you can smartly pull down on the brake pedal lever. Find the rear brake line connection at the master cylinder. Get the wrench so you can pull fitting loose and tighten in one short easy movement. Crack it loose with your 11mm wrench. Wait for a dribble of brake fluid. Once evident, proceed. Pull the brake lever down when fitting is loose, tighten the fitting, then release the brake lever. Again, loosen fitting, pull lever, tighten fitting, release lever.
Let me know if you get some spits, some dribbles, and eventually, a good indication of pressure. If you do, go to the back of the bus and open a bleeder and sit there a while contemplating the miracle of brakes. If a dribble starts, you may bleed the brakes normally. Got assistant? Assistant must shove down on the pedal with verve when you yell "hold!" Assistant must pump pedal deliberately and slowly with time at the top to allow fluid to enter circuit. Some people get all huffing and pumping and the poor circuit never gets time to replenish between bleed events.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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anotherbluebus
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Re: Bus master cylinder replacement

Post by anotherbluebus » Fri Sep 23, 2011 8:00 am

Amskeptic wrote:
Fill your reservoir. etc....
Thanks all for the responses. Assistant and I did get 3 of 4 corners functional. The right rear is being stubborn, but it is spitting some old fluid out at the bleeder screw. It was sporadic and that may be our fault. I think we were the enthusiastic brake pumpers & probably took 6 months off the life of the new master cylinder with an enthusiastic sewing machine like pump method. Going to try again with the method you describe, Colin. I'll report back.

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anotherbluebus
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Re: Bus master cylinder replacement

Post by anotherbluebus » Mon Sep 26, 2011 8:48 am

Got back to the brakes (almost) on Saturday. I noticed a drip that could only be brake fluid under the master cylinder. I got under the bus and poked around a little. The leak seemed to be coming out from under the reservoir. I checked the connection where the filler hose goes into the reservoir, and it was okay (dry and still connected). Could only be the connection between reservoir and MC. Ugh. I didn't replace the 2 grommets because they looked good when I inspected them before installing onto the new MC. The leak turned ugly after that. My wife came unglued about the large brake fluid puddle. I set a container underneath to catch the rest. At least I don't have to syphon out the reservoir line. Pretty sure it's drained by now. Beaverton Imports tells me they have the grommets, so at least replacements are close by. Any chance I can replace those grommets without removing the MC?

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RSorak 71Westy
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Re: Bus master cylinder replacement

Post by RSorak 71Westy » Mon Sep 26, 2011 12:50 pm

Tell the wife to chill, brake fluid is water soluable and it wont leave a stain.

As far as the grommet goes I'm sure its possible or not with the master bolted in.
Take care,
Rick
Stock 1600 w/dual Solex 34's and header. mildly ported heads and EMPI elephant's feet. SVDA W/pertronix. 73 Thing has been sold. BTW I am a pro wrench have been fixing cars for living for over 30 yrs.

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anotherbluebus
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Re: Bus master cylinder replacement

Post by anotherbluebus » Mon Sep 26, 2011 2:54 pm

RSorak 71Westy wrote:Tell the wife to chill, brake fluid is water soluable and it wont leave a stain.

As far as the grommet goes I'm sure its possible or not with the master bolted in.
Thanks, I'll let her know.

I decided to pull the MC out just so I could confirm to myself that there wasn't any other cause for this leak. No problem pulling it out & putting in new grommets on a long lunch break. I got it mostly back together except for one brake line fitting that isn't lining up to thread on correctly. I decided to come back inside and do some of the work that pays for VW parts. Hopefully it stays dry outside so I can go back to wrestle with that last fitting. Then re-bleed the brakes, etc etc etc.

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grandfatherjim
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Re: Bus master cylinder replacement

Post by grandfatherjim » Mon Sep 26, 2011 8:36 pm

After replacing shoes, then replacing them again with the correct shoes (ahem), the wheel cylinder did not operate. Even put it in a vise and tried to squeeze the pistons in and couldn't move them.
OK, new wheel cylinder. No action. Rubber hose was acting as one-way valve...I don't know how many times I have heard this over the years, and always thought it must be pretty rare. Maybe it isn't.
Beauty of it is, now the parking brake is quite effective. I had to think about that one a bit.

A trick I have heard of for brakes that are stubborn to bleed: get a 2x4 or similar of just the right length, step on the brake pedal, and force it to stay down by jamming the 2x4 between it and the seat. Come back in the morning whereupon the air will supposedly have found its way back to the MC. Haven't tried that one myself.
Jim

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RSorak 71Westy
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Re: Bus master cylinder replacement

Post by RSorak 71Westy » Mon Sep 26, 2011 8:48 pm

A trick I have heard of for brakes that are stubborn to bleed: get a 2x4 or similar of just the right length, step on the brake pedal, and force it to stay down by jamming the 2x4 between it and the seat. Come back in the morning whereupon the air will supposedly have found its way back to the MC. Haven't tried that one myself.
I don't think this would work as the only time fluid can return to the master cyl. is when the piston is in the foot OFF the pedal position. Think about what it does and how it works. Do the brakes ever release while your foot is on the pedal?
Take care,
Rick
Stock 1600 w/dual Solex 34's and header. mildly ported heads and EMPI elephant's feet. SVDA W/pertronix. 73 Thing has been sold. BTW I am a pro wrench have been fixing cars for living for over 30 yrs.

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grandfatherjim
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Re: Bus master cylinder replacement

Post by grandfatherjim » Mon Sep 26, 2011 9:01 pm

I imagine a combination of compressed air and liquid in there, with the bubble of air slowly moving within the brake line i.e. there isn't really fluid returning to the MC. Having said this, I don't know why the air would "want" to return to the MC. But several people have sworn it worked, FWIW.
Maybe gravity plays a part. It does explain most things we can't otherwise understand.

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