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1976 Bus - Brakes Mysteriously Faded, Then Came Back -
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wagohn
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PostPosted: Tue Jan 12, 2021 4:10 pm    Post subject: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

Hello all,
After buying our bus in April '20, we replaced the rear shoes and cylinders and bled the system. Front pads seemed fine, as did hoses. We have driven the bus many miles since then with the brakes working well. My daughter took the bus to visit a neighborhood friend and reported that the brakes faded almost all the way to the floor. She was able to pump the brakes to stop. However, after the pumping the brakes were fine again.
On her return, I took the bus for a test on the exact route, no issues and the brakes were fine there and back. I also tested the booster by pressing the pedal while starting and, as expected, the pedal dropped slightly - but settled well over half the available travel, as its always been. Fluid is full with no apparent leaks.
Any ideas why seemingly good brakes would intermittently fade?
Thanks!
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PostPosted: Tue Jan 12, 2021 4:16 pm    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

Your Master cylinder could be the problem.
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PostPosted: Tue Jan 12, 2021 5:29 pm    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

wagohn wrote:
... but settled well over half the available travel, as its always been.


Hmm, wonder what that means? Normal braking action starts as soon as free play at pedal is taken up, and just
increases in force as pedal is pushed further down. It certainly does not drop halfway, which would sort of
suggest one of your brake circuits is kaput. Something that requires immediate attention, at any rate.
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PostPosted: Tue Jan 12, 2021 5:31 pm    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

master cylinder
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PostPosted: Tue Jan 12, 2021 5:46 pm    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

kreemoweet wrote:
wagohn wrote:
... but settled well over half the available travel, as its always been.


Hmm, wonder what that means? Normal braking action starts as soon as free play at pedal is taken up, and just
increases in force as pedal is pushed further down. It certainly does not drop halfway, which would sort of
suggest one of your brake circuits is kaput. Something that requires immediate attention, at any rate.

X2, good brakes should only go down less than 2" no matter how hard you push with the engine running, you might have more than one issue going on.
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PostPosted: Tue Jan 12, 2021 6:19 pm    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

Thanks everyone - perhaps "halfway" down was too pessimistic, probably closer to 15-25% before we get pushback. Brakes have always been excellent since we refreshed the shoes/rear cylinders. Stops on a dime.

As for the original question, thank you! Makes total sense that if the seals in the MC were on their way out that the odd "no pressure" scenario would occur.

We will order a new MC as I know my limitations and don't fancy refreshing the old. Any tips for the removal/install? I see references to bench bleeding in other threads but I'm not sure what that entails. I'm assuming filling the MC with fluid before install - wouldn't the fluid just pour out when unplugging the holes to fit the pipes? I'm assuming the MC can just be swapped out without any mating to the servo issues?

Thanks!
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PostPosted: Tue Jan 12, 2021 7:42 pm    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

wagohn wrote:
We will order a new MC as I know my limitations and don't fancy refreshing the old. Any tips for the removal/install? I see references to bench bleeding in other threads but I'm not sure what that entails. I'm assuming filling the MC with fluid before install - wouldn't the fluid just pour out when unplugging the holes to fit the pipes? I'm assuming the MC can just be swapped out without any mating to the servo issues?


There isn't really a prospect of "refreshing" the M/C, as rebuild kits are not available. I've never had the slightest trouble bleeding system with new M/C with no
"bench bleed" involved. After install and filling the reservoir, air in M/C will just naturally bubble up and out (assuming bus is level, and not at some weird angle).
Rarely, the internal pushrod in booster will be too long to suit the M/C, causing the M/C compensating port to be blocked with resulting eventual brake lockup.
You can somewhat feel that happening by just holding M/C (sans o-ring seal) onto booster in installed position. You should feel no resistance from booster pushrod
in doing so.

Inside of booster should be checked for leaked brake fluid, and cleaned out if present - not too easy if installed.

Take it easy when manipulating metal brakelines, as they will kink all too readily. The metal lines have to be aligned almost perfectly to be able to start the nuts, and
sometimes takes a deal of fiddling to get it right.
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PostPosted: Tue Jan 12, 2021 9:36 pm    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

kreemoweet wrote:

There isn't really a prospect of "refreshing" the M/C, as rebuild kits are not available. I've never had the slightest trouble bleeding system with new M/C with no
"bench bleed" involved. After install and filling the reservoir, air in M/C will just naturally bubble up and out (assuming bus is level, and not at some weird angle).
Rarely, the internal pushrod in booster will be too long to suit the M/C, causing the M/C compensating port to be blocked with resulting eventual brake lockup.
You can somewhat feel that happening by just holding M/C (sans o-ring seal) onto booster in installed position. You should feel no resistance from booster pushrod
in doing so.

Inside of booster should be checked for leaked brake fluid, and cleaned out if present - not too easy if installed.

Take it easy when manipulating metal brakelines, as they will kink all too readily. The metal lines have to be aligned almost perfectly to be able to start the nuts, and
sometimes takes a deal of fiddling to get it right.


Thank you, sir. Some great info here.
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PostPosted: Tue Jan 12, 2021 11:09 pm    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

I might add to suggestions that some very experienced air-cooled vehicle buffs recommend taking apart
brand-new brake cylinders to clean out factory debris. I've never done so, and not been stung. Yet.
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PostPosted: Wed Jan 13, 2021 10:16 am    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

wagohn wrote:


I'm assuming the MC can just be swapped out without any mating to the servo issues?

Thanks!


Make sure the servo is clean and dry inside. If it's wet it might be time to premptivly send it out for a rebuild.

Your daughter experienced a hydrulic system failure. Brake fade is a whole different animal and it sucks in a whole different way.
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PostPosted: Thu Jan 14, 2021 2:02 pm    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

I had a similar issue a couple of years ago. I had redone the front and rear brakes and felt I had a good system. I then had a workday with Colin (Itinerant Air-cooled) and when he drove my bus, he quickly identified that I had a bad master cylinder. What was strange to me is that when I applied the brakes, I felt I had good control - but I had learned to compensate by pushing the pedal down with a quick, last-minute foot move. Colin used a slower physical approach. So - I tried changing how I applied the brake and suddenly realized that I indeed had a problem. (see the write up from Colin's website: http://www.itinerant-air-cooled.com/viewtopic.php?...d1248fd48)

I was able to source a quality master cylinder and when Colin came for his next visit, we replaced it. It was a pretty do-able job and then not soon after, the servo failed. AND - so I had it rebuilt and now - I have much more confidence in my brake system.

From my experience and what others have written, it make sense to replace your Master Cylinder.
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PostPosted: Thu Jan 14, 2021 2:43 pm    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

Whaanga wrote:
I had a similar issue a couple of years ago. I had redone the front and rear brakes and felt I had a good system. I then had a workday with Colin (Itinerant Air-cooled) and when he drove my bus, he quickly identified that I had a bad master cylinder. What was strange to me is that when I applied the brakes, I felt I had good control - but I had learned to compensate by pushing the pedal down with a quick, last-minute foot move. Colin used a slower physical approach. So - I tried changing how I applied the brake and suddenly realized that I indeed had a problem. (see the write up from Colin's website: http://www.itinerant-air-cooled.com/viewtopic.php?...d1248fd48)

I was able to source a quality master cylinder and when Colin came for his next visit, we replaced it. It was a pretty do-able job and then not soon after, the servo failed. AND - so I had it rebuilt and now - I have much more confidence in my brake system.

From my experience and what others have written, it make sense to replace your Master Cylinder.


I was kind of away from thesamba for awhile having had twins a few years ago. Iíve been been back pretty regularly for a few months and have not seen any sign of Colin. Anyone know of his status? Hope heís well.
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PostPosted: Thu Jan 14, 2021 6:18 pm    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

Thanks all, New MC should be here tomorrow. I just soaked the brake pipe nuts in PB Blaster for the night in prep.

On a side note, I'm using newly purchased Harbor Freight 6" ramps, should have bought them years ago. Drive right on, rock solid, and lots of work room. Great deal for $45 and rated for 13000 lbs.
I'm getting older and need a little more room. Wink

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PostPosted: Thu Jan 14, 2021 7:46 pm    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

Start those brake line unions before you bolt up the MC, that lets you manipulate both to line them up. I find I can feel the threads engage when I have both in hand, vs one being bolted up.
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PostPosted: Thu Jan 14, 2021 9:37 pm    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

oscarsnapkin wrote:
Iíve been been back pretty regularly for a few months and have not seen any sign of Colin. Anyone know of his status?


He's taken the year off from his usual activities, as many of us have. He still posts (infrequently) on his website: https://www.itinerant-air-cooled.com, and
just last week put up a new site banner there.
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PostPosted: Fri Jan 15, 2021 8:54 am    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

Abscate wrote:
Start those brake line unions before you bolt up the MC, that lets you manipulate both to line them up. I find I can feel the threads engage when I have both in hand, vs one being bolted up.


Well now, that right there is a great tip!
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PostPosted: Fri Jan 15, 2021 9:34 am    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

It's been mentioned here before, but some new cylinders have the rear brake light switch mounted planar with the front switch, and that can get in the way of the handbrake cable. Good cylinders mount the switch at an angle. It's up to you if you want to try to return/exchange it, or make a chafe-guard for the cable; just look out for it!

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PostPosted: Fri Jan 15, 2021 9:41 am    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

airschooled wrote:
It's been mentioned here before, but some new cylinders have the rear brake light switch mounted planar with the front switch, and that can get in the way of the handbrake cable. Good cylinders mount the switch at an angle. It's up to you if you want to try to return/exchange it, or make a chafe-guard for the cable; just look out for it!

Robbie


Good to know, thanks. Unfortunately, delivery seems to be end-of-day, then a prior commitment tomorrow. I intend to at least remove the old one today.
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PostPosted: Fri Jan 15, 2021 1:52 pm    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

So I got the old MC off and everything came off fairly easily. The only possible issue was removing the filler tube. There appears to be a "shouldered, black rubber, inner insert at the inlet and the shoulder area is torn up or deteriorated. How crucial is this, can I reasonably use as pictured, and in the pic do I have it the right way around?

Inner booster was dry.

Thanks for your attention.


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PostPosted: Fri Jan 15, 2021 6:15 pm    Post subject: Re: 1976 Bus - Brakes Mysteriously Faded, Then Came Back - Reply with quote

I decided to go with the frayed black grommet in the pic. Other than the shoulder it was complete. I've ordered a new one and will fit when it arrives.

New MC is now on and holding fluid. Next step, bleed the brakes. Smile
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