Spongy Brake Pedal - '71 Super Beetle

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vwlover77
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Spongy Brake Pedal - '71 Super Beetle

Post by vwlover77 » Mon Feb 20, 2017 5:37 pm

I've bled the brakes on my '71 Super Beetle twice now, but I just can't get rid of the spongy pedal. I'm beginning to think I've somehow done it wrong both times, but I'm not new to this!

When first beginning to brake, the pedal seems reasonably high and braking seems OK, but then I realize I need more braking force and have to depress the pedal nearly to the floor to stop.

I tried a "panic stop" today from around 45mph. I quickly (and fairly easily) pushed the pedal all the way to the floor. The car stopped straight and even, but it didn't even seem close to locking a wheel, and seemed to take a long distance to stop.

If I maintain a constant pressure on the pedal, it does not sink to the floor.

Bleed them again and hope the third time is the charm, or is there something else to check?

Thanks!
Don

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Re: Spongy Brake Pedal - '71 Super Beetle

Post by asiab3 » Tue Feb 21, 2017 12:50 am

I always make sure the adjuster stars are at their optimum point of adjustment before bleeding. Any laziness in the shoe adjustment will eat up valuable pedal travel necessary for efficient bleeding.

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Re: Spongy Brake Pedal - '71 Super Beetle

Post by vwlover77 » Tue Feb 21, 2017 6:31 am

I did the last bleed by pressurizing the fluid reservoir to a few PSI with my air compressor and opening each bleeder valve in turn. (With frequent checks to make sure the reservoir was not going dry.)

Star adjustment would make no difference using that technique.
Don

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Re: Spongy Brake Pedal - '71 Super Beetle

Post by hambone » Wed Feb 22, 2017 12:36 pm

I've had better luck with the pumping pedal method.
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Re: Spongy Brake Pedal - '71 Super Beetle

Post by cegammel » Wed Feb 22, 2017 4:18 pm

Important things I learned on my super...

If there is leaky fluid on the shoes, no good brakes.
If the drums are worn down, hard to get firm pedal.
If the rears are not equally adjusted, no firm pedal...
If the master cylinder is leaking, even the slightest, the pedal will not be firm. My only indication was a drip from the front tunnel drain, as the mc was dripping in between the pan pieces...

I have a mityvac pump...pumping the pedal is far superior.

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Re: Spongy Brake Pedal - '71 Super Beetle

Post by vwlover77 » Thu Feb 23, 2017 7:10 am

Those are good things to know.....

The rear shoes were just replaced due to fluid leaked onto them, the fronts were replaced last Fall along with two corroded/sticky wheel cylinders. The repair last Fall is when the soft pedal started.

I just bought a Mityvac pump last night at Harbor Freight. Maybe I should return it before I use it........
Don

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Re: Spongy Brake Pedal - '71 Super Beetle

Post by vwlover77 » Thu Feb 23, 2017 7:11 am

Does anyone know how many pumps of the pedal it takes to get fluid from the master cylinder to the furthest wheel cylinder (right rear?) ?
Don

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Re: Spongy Brake Pedal - '71 Super Beetle

Post by Amskeptic » Thu Feb 23, 2017 8:41 am

vwlover77 wrote:Those are good things to know.....

The rear shoes were just replaced due to fluid leaked onto them, the fronts were replaced last Fall along with two corroded/sticky wheel cylinders. The repair last Fall is when the soft pedal started.

I just bought a Mityvac pump last night at Harbor Freight. Maybe I should return it before I use it........
MightyVacs suck dead donkeys. You need pressure from the reservoir to the bleeders.

You do know that new shoes can add to the spongy feeling until the lining have broken in, yes?

Recheck all of your work exhaustively. Unfortunately, that means pulling each drum, checking under the boots for any signs of liquid, checking the linings for contamination, checking the springs, checking the drums for glaze (that cross-hatch sanding that I am always going on about is to let the new linings apply their own glaze recipe to the drum friction surfaces), checking the ebrake cables for drama-free release, re-assembling everything, adjusting the stars to *very difficult to turn* THEN backing off to minor scraping, adjusting the ebrake cables to factory specified point . . . . . then bleed.
Yeppers, another Saturday bites the dust.
Colin
BobD - 1978 Bus . . . . . . . . . . .110,350 miles
Chloe - 1970 bus . . . . . . . . . . . 206,775 miles
Naranja - 1977 Westfalia . . . . 72,350 miles
Pluck - 1973 Squareback . . . . . 55,478 miles
Alexus - 1991 Lexus LS400 . . . 64,425 miles

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Re: Spongy Brake Pedal - '71 Super Beetle

Post by vwlover77 » Mon Feb 27, 2017 7:31 pm

I haven't done it all yet, but I did bleed the brakes again - the old fashioned way - and adjusted the shoes again (which are still breaking in on all 4 wheels now), and things are much improved.

I think the other thing that might be fooling me is that the front shoes I replaced were both contaminated with fluid from previous cylinder leaks that I tried to remove with brake cleaner. I think they were "stickier" due to the contamination and made it feel like I had more braking power than these new shoes have ???? (They also locked up far too easily under moderate braking - which is why I replaced them.)
Don

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Re: Spongy Brake Pedal - '71 Super Beetle

Post by asiab3 » Mon Feb 27, 2017 7:48 pm

New shoes aren't exactly matched to the arc of the drum. They should get better with time. (Old school shops used to do this in-house before releasing your vehicle to the public roads…)

Locking up under moderate braking? That's the opposite problem most people seem to have. :)

I think a main problem with the vacuum bleed approach is leakage on the threads of the bleeder screws; air can seep into the vacuum stream that way and give a "false" bleed. I realized this when I was pressure bleeding, and the fluid seeped out of the bleeder threads if I opened the blender too far.

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Re: Spongy Brake Pedal - '71 Super Beetle

Post by vwlover77 » Mon Jun 19, 2017 8:50 am

I think I figured it out. I finally pulled the right front drum yesterday to have a look....

It's hard to see in the photos, but the linings on these Bosch brake shoes are thinner at the top. When I saw that, I remembered that's how they came, and thought at the time it would help them seat better. Nope. Only the middle third of the lining is touching the drum during braking. That part feels smooth while the bottom and top are still rough as they came out of the box. I think the spongy feeling is from trying to bend the top portion of the shoes to touch the drum. You can hear them creaking as I increase pedal pressure at a standstill!

I've ordered new Wagner shoes. Hopefully they'll be better.

Front shoe:
Image

Rear shoe:
Image

Notice the lining is thinner at the top - came out of the box that way:
Image
Don

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Re: Spongy Brake Pedal - '71 Super Beetle

Post by Amskeptic » Thu Jun 22, 2017 7:41 pm

vwlover77 wrote:
Mon Jun 19, 2017 8:50 am
I think I figured it out.


Let us know. Shoes *are* arc'ed to meet the drum's specified diameter, your do not look all that unusual, but your shoe contact area does look weird.
Colin
BobD - 1978 Bus . . . . . . . . . . .110,350 miles
Chloe - 1970 bus . . . . . . . . . . . 206,775 miles
Naranja - 1977 Westfalia . . . . 72,350 miles
Pluck - 1973 Squareback . . . . . 55,478 miles
Alexus - 1991 Lexus LS400 . . . 64,425 miles

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Re: Spongy Brake Pedal - '71 Super Beetle

Post by sgkent » Fri Jun 23, 2017 5:23 pm

I'd go thru the brake adjustment procedure again. Those look like possibly they were not well enough adjusted so the contact area is poorer than it could be. It is hard to know without laying the shoes in the drum before installing them to see how they fit. Also if the drums are way oversize that will cause it too. Did you have the drums measured when you had them turned? How close to the limit are they? Did anyone eyeball the shoes in the drums before committing them?
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Re: Spongy Brake Pedal - '71 Super Beetle

Post by vwlover77 » Wed Jul 26, 2017 8:26 am

The new Wagner brake shoes fixed the problem. They fit very nicely when laid in the drums with minimal rocking from end to end as compared to to the Bosch pads which rocked badly. The brake pedal is now firm which tells me the pad material at the wheel cylinder end of the shoe is contacting first. The braking power is much better now too as I don't think the "wedge effect" was happening with the ill-fitting shoes.
Don

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Re: Spongy Brake Pedal - '71 Super Beetle

Post by sgkent » Wed Jul 26, 2017 5:21 pm

awesome work - if they don't look like they fit right before installing them they sure won't when they are installed. I think somewhere in a thread here or TS Colin had problems with a set of shoes that were poorly fitting right out of the box. The last set I installed I put a respirator on in case there was any asbestos present and sanded the shoes in the drums to make them fit well. Used to be when these buses were new one would hand the shoes and the drums to a machinist / brake shop and he/she/they would measure them and arc the shoes until they fit right. Now it is one size fits all (which we know from this thread doesn't always work well.)
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