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1971 bus not stopping after full brake job
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fasty68
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PostPosted: Tue Sep 12, 2017 8:08 pm    Post subject: 1971 bus not stopping after full brake job Reply with quote

My buddy and I just finished a full brake job on his 1971 vw bay window. But now after bleeding the whole system we have no real break power. Also we got really good pressure when bleeding the rear but not on the front. All new hoses, calipers and brake pads on the front. All new hoses, cylinders and shoes and adjusted on the rear. We also tried with a new master cylinder but no luck.
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Danwvw
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PostPosted: Tue Sep 12, 2017 8:11 pm    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

Must not be bleed well enough yet. Did you bleed it where the fittings connect to the MC? That should help.
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PostPosted: Tue Sep 12, 2017 8:23 pm    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

What was your bleed method?
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Wasted youth
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PostPosted: Tue Sep 12, 2017 10:13 pm    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

fasty68 wrote:
....Also we got really good pressure when bleeding the rear but not on the front. All new hoses, calipers and brake pads on the front. All new hoses, cylinders and shoes and adjusted on the rear. We also tried with a new master cylinder but no luck.


There is an outside possibility that your Brake Regulator is fouled with muck and the steel ball inside is stuck. This will prevent correct flow to balance front and rear brakes. Its supposed to equalize pressure between front and rear brakes.

Brake Regulator might be inboard of outside frame rail on Driver's side. Just follow the brake lines from Master Cylinder if you are having trouble locating it.

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scrivyscriv
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PostPosted: Tue Sep 12, 2017 11:32 pm    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

bottom dollar says you didn't bleed it right. I don't care what anyone else says, the Bentley manual backs me on this, you need to PRESSURE BLEED your brakes at this point. Not pumping the brakes and holding, not gravity bleeding, not vacuum bleeding.

Look up DIY brake pressure bleeder, you can make one for under $20 with a garden sprayer and a brake fluid cap. You don't need much pressure to bleed them right, maybe 5 PSI.
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asiab3
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PostPosted: Wed Sep 13, 2017 12:35 am    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

Pumping the pedal IS pressure bleeding. Bentley 9.2 and 9.3 please. The cool thing about science, is that it's true weather or not you believe in it. Wink

Some front calipers on '71+ buses have two bleed ports; one is on top the other is lower. Which did you use?

Robbie
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SamboSamba22
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PostPosted: Wed Sep 13, 2017 1:43 am    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

Adjustment needed to the adjuster stars?
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PostPosted: Wed Sep 13, 2017 3:44 am    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

asiab3 wrote:
Pumping the pedal IS pressure bleeding. Bentley 9.2 and 9.3 please. The cool thing about science, is that it's true weather or not you believe in it. Wink
Robbie


Semantics aside, pedal pumping is not the same as using a pressure pot. Pressure pot bleeding forces air bubbles out of the master when they would otherwise be trapped.

What about this guy's situation when he has lines full of air? There is no hydraulic pressure generated using pedal pumping on a system that can't get a 'prime' in the master cylinder.
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Davydomes
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PostPosted: Wed Sep 13, 2017 4:57 am    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

Wasted youth wrote:
fasty68 wrote:
....Also we got really good pressure when bleeding the rear but not on the front. All new hoses, calipers and brake pads on the front. All new hoses, cylinders and shoes and adjusted on the rear. We also tried with a new master cylinder but no luck.


There is an outside possibility that your Brake Regulator is fouled with muck and the steel ball inside is stuck. This will prevent correct flow to balance front and rear brakes. Its supposed to equalize pressure between front and rear brakes.

Brake Regulator might be inboard of outside frame rail on Driver's side. Just follow the brake lines from Master Cylinder if you are having trouble locating it.

Image may have been reduced in size. Click image to view fullscreen.


We had a problem with the rears staying on. After much bleeding attempts we discovered the master cylinder had bits of perished seals in the bottle which must have passed into the system. After cleaning it and flushing out the whole system the problem remained. The only thing we had not split (because we were a bit nervous to be honest) was the pressure regulator. When we did it also had bits of perished seal blocking the holes. Once cleaned out and recharged the problem disappeared. Do you use any kit to help you bleed? Either a suction device or pump? We only used the tried and tested method and it worked.
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PostPosted: Wed Sep 13, 2017 6:49 am    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

fasty68 wrote:
My buddy and I just finished a full brake job on his 1971 vw bay window. But now after bleeding the whole system we have no real break power. Also we got really good pressure when bleeding the rear but not on the front. All new hoses, calipers and brake pads on the front. All new hoses, cylinders and shoes and adjusted on the rear. We also tried with a new master cylinder but no luck.
Does the servo function properly?
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TDCTDI
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PostPosted: Wed Sep 13, 2017 7:05 am    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

One of the reasons for pressure or vacuum bleeding is to avoid depressing the plunger in the master cylinder beyond the normal operating range of motion. Going beyond this introduces the seals to the unused rusted areas of the bore which tears & damages the seals & will cause the master cylinder to fail.
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Tcash
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PostPosted: Wed Sep 13, 2017 9:12 am    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

Did you bleed them per the service manual as far as in the correct order RF, LF, RR, LR?
If you replaced the Master cylinder you need to bleed that first.

Because the Master cylinder sits so low in the vehicle it is best to Pressure or Vacuum bleed the brakes.
Pressure bleed start Farthest from master cylinder.
Vacuum bleed start Closest from master cylinder.

Another thing to consider. Is the brake shoes Arc. Sometimes the shoe Arc does not fit the brake drum Arc and it takes awhile and a few brake adjustment to bed them in. So the brake surface contact area increases as the shoes wear into the drums and braking improves.

Wasted youth wrote:

There is an outside possibility that your Brake Regulator is fouled with muck and the steel ball inside is stuck. This will prevent correct flow to balance front and rear brakes. Its supposed to equalize pressure between front and rear brakes.

The Brake Pressure Regulators, function is to reduce the pressure to the rear brake to prevent rear wheel skid in a hard application.
Brake Pressure Regulator t2 211 612 501

TDCTDI wrote:
One of the reasons for pressure or vacuum bleeding is to avoid depressing the plunger in the master cylinder beyond the normal operating range of motion. Going beyond this introduces the seals to the unused rusted areas of the bore which tears & damages the seals & will cause the master cylinder to fail.

Agreed, I can't tell you how many times people have reported bleeding their brakes followed by, now the master cylinder is leaking.
Not an issue in this case because the master has been replaced.

Good luck
Tcash
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PostPosted: Wed Sep 13, 2017 9:22 am    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

the bus has to be level to properly bleed it. If the nose is low the rear brakes are cut off. If you don't have a hard pedal then there is air in the lines. If you have a hard pedal and it still doesn't work the front calipers could be frozen. Spin each tire, hit the brake and see if you can feel good resistance. Then lift your foot off the brake and be sure the tire spins freely. If not then the calipers are frozen. Front must be bled from the top bleeder, not the bottom if it has two.

Regulator cuts off the rear brakes, not the front.
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PostPosted: Wed Sep 13, 2017 11:30 am    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

Keep it level!
Always best to bench bleed the master cylinder, just dunk it in fluid & pump
Always use the upper bleed screws on the calipers, lowers do NOTHING.
Gravity bleeding is acceptable, open the reservoir cap, crack the bleeder,
wait 10 -15 minutes if you want to be sure, 2-3 ounces per wheel should
come out, top off reservoir & on to the next cylinder or caliper.
Sequence: RR,LR,RF,LF

There are times when this fails, teflon tape on your bleeder screws may be
required along with a Mity Vac to get the brake fluid 'drawing' to your
container-the teflon plumbing tape helps seal the bleeder screw threads.
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fasty68
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PostPosted: Wed Sep 13, 2017 3:39 pm    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

Sorry for the late response guys (grave yard shift) ok so we just bled the system the old pump and hold way, RR LR FR FL. Like 4 or 5 times already, however we did not bench bled the master cylinder Embarassed we have already replaced everything but the proportioning valve but that isn't the issue since we have really strong pressure coming out the back but on the front we have fluid coming out but with no pressure. Also the pedal stops half way I'm guessing that's when the rear brakes come in. Help!
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PostPosted: Wed Sep 13, 2017 4:22 pm    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

I want a list of what you replaced before I reply. your "full brake job" and mine may (and probably will) vary wildly


the brake regulator/proportioning valve does absolutely NOTHING static...when working properly, it takes inertia and a huge nose dive for it to activate (providing it works) otherwise, it's just in line to the rears. if you have good flow out of it to the wheel cylinders it isn't a problem.

now, about that list.....
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fasty68
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PostPosted: Wed Sep 13, 2017 10:32 pm    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

Replaced master cylinder, servo, hard lines and rubber hoses front and rear, rotors and drums, calipers and rear wheel cylinders, shoes and pads and put new fluid in it. Everything was working fine prior to replacing all of the above, it was just worn out and old. Like I said good pressure on the rear (both breeders) but very little almost no pressure put of the calipers (single bleeder).
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PostPosted: Thu Sep 14, 2017 12:49 am    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

As a diagnostic cap off the front lines and see if you develop brake pressure then. Remove one at a time to see if you can identify the offending caliper or replace master cylinder if you can't get pressure capped off.

I know you did.

Cheap parts suck.
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asiab3
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PostPosted: Thu Sep 14, 2017 12:55 am    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

TDCTDI wrote:
One of the reasons for pressure or vacuum bleeding is to avoid depressing the plunger in the master cylinder beyond the normal operating range of motion. Going beyond this introduces the seals to the unused rusted areas of the bore which tears & damages the seals & will cause the master cylinder to fail.


I honestly think this is a myth perpetuated by those with water-saturated brake fluid and rusty master cylinders that need replacing anyway. Bentley tells us to push to the floor. There should be NO rust in a good brake system, no matter the cheapness of owners. Wink

Vacuum bleeding becomes problematic to me when we use negative pressure to bleed a system that spends its life at 10psi and above. What part of the vacuum bleeding process gets the residual pressure back to operating pressure? (The wheel cylinder/shoe springs of drum brakes and residual valves in the MC keep about 10psi in the lines at all times. Vacuum bleeders can't contribute to this.)

Once a master cylinder is bench-bled, (in the bus works for this, ironically, that's just an industry term,) there is no functional difference between pedal bleeding and pressure bleeding. The hydraulic lines and cylinders do not care if the pressure is coming from a Volkswagen pressure tool, a garden sprayer, or the pedal. The system can't tell anyway.

Robbie
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PostPosted: Thu Sep 14, 2017 1:05 am    Post subject: Re: 1971 bus not stopping after full brake job Reply with quote

The number of people who change brake fluid on two year intervals is pretty low. Not a bad Job to give an inspection station every other year to:

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Remember to do to it
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If you don't want to do it yourself.

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