1971 Beetle with weak breaks

JonzoDGreat · Posted: Tue Apr 28, 2015 8:20 pm Post subject: 1971 Beetle with weak breaks

I have a 1971 beetle, the brakes are weak and slow to stop. If I pump the breaks once or twice they get hard, but about a minute it loses most of its pressure. When I press the brakes all the way it takes about 4 seconds to stop at about 30mph.

So far I have:
-made sure the brake fluid was always full
-did proper brake bleeding order
-new (metal and rubber)lines and shoes in the back
-also new rear wheel cylinders
-adjusted all four break drums so that the are just making contact
-replaced master cylinder recently, but it was a cheap $19.99 one.

What is my next step? Are vw brakes usually weak? Could it the master cylinder?

Tim Donahoe · Posted: Tue Apr 28, 2015 8:52 pm Post subject:

$19.99 for a master cylinder?

That's probably where you went wrong.

Get a good German one--or at least, a Varga.

Also, 80% of your braking is done with the front brakes. You replaced a lot for the rears--but not so much up front.

Tim
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Let's do the Time Warp again!

Richard O'Brien

awreed · Posted: Tue Apr 28, 2015 8:54 pm Post subject:

VW drums don't make for the quickest of stops, but on a 1900 lb. car they should do just fine when properly maintained.
Have you replaced the front shoes? They may be glazed or nearly gone. Fronts do most of the work when stopping- breakdown is like 70-30. Replacing the rear shoes may not make any difference if they weren't worn out to begin with.
Losing break pressure is another problem altogether. A very serious one too. Have you removed the front drums to see if there are any fluid leaks? With the amount of pressure loss you're describing there should be a pretty large and messy leak. Brake fluid is damn caustic stuff and will ruin your wheels.

JonzoDGreat · Posted: Tue Apr 28, 2015 9:15 pm Post subject:

Thanks Tim for the info about cheap master cylinders, I will look into getting a better one.

My back brakes were weak so that was my motivation to fix those ones first. The front drivers side was a bit scored along with the drum. The left wasn't too bad. I found out the last owner neglected to include the connecting link to one of the rear brakes. Also there is no fluid leaking from anywhere(brake lines master or wheel cylinders, the reservoir is not draining in any way.

awreed · Posted: Tue Apr 28, 2015 9:22 pm Post subject:

Even a cheap new master cylinder should still work. At least at first. Maybe still air in the lines. You shouldn't have to pump the brakes for them to work.

JonzoDGreat · Posted: Tue Apr 28, 2015 9:27 pm Post subject:

I've bled the brakes until there was no more bubbles of air. I turned dirty fluid into clean fluid during the process.

TheAmazingDave · Posted: Tue Apr 28, 2015 9:37 pm Post subject:

A couple things come to mind.

1. Replacement wheel cylinders. I can say this from experience; if you bought replacement cylinders from Autozone or a similar parts store, they may be crap. Before I did a full brake system overhaul, I had a front cylinder pop and I replaced it with an Autozone part. It sucked, big time. I could pump the pedal for days and hardly build any pressure. I ended up taking the new cylinder apart, and immediately found that it was built like crap, and missing a spring that keeps the pistons out against the shoes when the pedal is let up. This spring was likely the whole problem, but I took the new piston seals out of the cheap new cylinder, and put the seals in my old cylinder, and it worked good as new, and lasted a few months until the full overhaul.

2. Brake shoe adjustment. Are you sure that you have both shoes at each wheel adjusted evenly? If you have one shoe out so that it's just dragging, but still a significant gap on the other, you waste precious pedal travel on those first few pumps just pushing out the shoes against the drums. Then once they close the gap, the brake pedal gets nice and solid. Might be worth double-checking.

3. Master cylinder. Even though you bought it "new" it could just be rebuilt crap. Don't rule out a potential problem with the new master, and consider replacing it with a better unit if everything else checks out.

DO NOT skimp on your brakes.
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awreed · Posted: Tue Apr 28, 2015 9:39 pm Post subject:

Sorry to hear about the problems. We've all been there with the trouble-shooting. It can be frustrating.

I guess maybe what Tim said might be the key. I don't even know where you found a $20 master cylinder for your car. The OEM ones I'm looking at are $100. Did you get a correct dual circuit one?

JonzoDGreat · Posted: Tue Apr 28, 2015 10:01 pm Post subject:

I adjusted the front breaks, although it has a slight pull to the right now, no pull before.

I bought German wheel cylinders for the rear, and German rubber hoses for the rear, added new metal lines in the rear, but I left the original long cab metal hose knowing how difficult it would to replace.

Yes correct duel circuit, bought it about four years ago, installed it then, but I never took the car out until now due to massive registration fees.

theKbStockpiler · Posted: Wed Apr 29, 2015 4:38 am Post subject:

60ragtop · Posted: Wed Apr 29, 2015 5:21 am Post subject:

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

Are all the adjusters installed right on the ~breaks~?
_________________
Rick
Certified Mechanic by the State of Michigan in 1977
ASA certified in 1987
Certified Hunter Wheel Alignment Master Technician 1986

JonzoDGreat · Posted: Wed Apr 29, 2015 8:42 am Post subject:

Yeah all the adjusters are installed properly, I guess I can try adding a little more drag on the left front and maybe the rear.

There 6 ports in my master cylinder,
•2 coming in
•1 for the rear brakes and •1 for the front brakes, two breeder valves for each of these port which are located at the wheel cylinders, but what about the other two ports?
•2 for the back brake light, could there be air located here? I have the lights plugged in and the are working? With no bleeder valve I did not realize until now that there might be air trapped here. Could this be a problem?

theKbStockpiler · Posted: Wed Apr 29, 2015 10:10 am Post subject: Re: 1971 Beetle with weak breaks

Master cylinders have to be specifically bled on initial installation or if they go dry. Just because you bleed something at the very end Does Not mean the entire brake circuit is bled.Usually if you encounter a chronic brake problem It IS because there is air trapped in the master cylinder.
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My beetle is not competing with your beetle. I have the yellow beetle in my town. There is a red one, a green one ......
Use all safety devices including a mask. Smile

vernonc · Posted: Wed Apr 29, 2015 12:31 pm Post subject: Re: 1971 Beetle with weak breaks

theKbStockpiler · Posted: Wed Apr 29, 2015 4:48 pm Post subject:

vernonc · Posted: Wed Apr 29, 2015 7:33 pm Post subject: Re: 1971 Beetle with weak breaks

theKbStockpiler · Posted: Wed Apr 29, 2015 8:51 pm Post subject:

Generally I find that people that can not get their brakes bled have air trapped in the master cylinder. They get liquid out at the wheel cylinder or caliper and can't understand why their pedal is spongy.

I have never heard of anyone being able to get a firm brake pedal while using a mightvac or the master cylinder for pressure and not bleeding the master at the brake line ports or the bleeder located on the master cylinder it's self if the master has never been bled. Whether a master can be bleed with a pressure bleeder at the the wheel cylinders/calipers is beyond me because I have not as of yet been enticed to use a pressure bleeder. My go to method is to use a lisle hood prop between the pedal and the seat. Sometimes I use a mightyvac because they work well at getting fluid past a proportioning valve. This is the only use of gravity bleeding in my opinion.

So if a pressure bleeder will actually bleed the entire circuit at once I stand corrected. Using the master cylinder or a mightvac will never do this from my own experience.
_________________
My beetle is not competing with your beetle. I have the yellow beetle in my town. There is a red one, a green one ......
Use all safety devices including a mask. Smile

Tim Donahoe · Posted: Wed Apr 29, 2015 11:29 pm Post subject:

Strange!

A while back, I installed a new German MC, new soft lines, and a disc brake conversion on my 1974 Super Beetle. I did not bleed the master cylinder at all.

I simply gravity bled at the front brakes, first (dual circuit mc), then I gravity bled the rears. Then I had my daughter pump and hold as I did the final bleeds.

My brakes worked great--and still do.

So ... I have to go with Vern on this one--at least as far as my particular model is concerned.

Tim
_________________
Let's do the Time Warp again!

Richard O'Brien

vernonc · Posted: Thu Apr 30, 2015 4:07 am Post subject:

One last comment; 'vacuum bleeders'. Vacuum bleeders are not part of a 'proper bleeding technique'. They can, if used properly, sometimes, be successful. However, since the cups in the wheel cylinders are designed to 'seal in, only, one direction', the application of very much vacuum will draw air in past these cups. Therefore, this type of bleeder can, continuously, pull, both, fluid and air into the wheel cylinders. The result, spongy brakes. There have been multiple posts on here that will verify that fact.

I, truly, hope that my 'rant' on this subject will help some readers who face problems similar to that of the original poster.

mort
_________________
"Those who don't read newspapers are un-informed. Those who do read newspapers are mis-informed." Will Rogers

'69 sedan, low mileage, all original.....currently being 'freshened-up' for road trips and daily driving...just not every day

Freshening-up link http://www.thesamba.com/vw/forum/viewtopic.php?t=617386

theKbStockpiler · Posted: Thu Apr 30, 2015 4:35 am Post subject:

I try to get a completely rock hard pedal when I do hydraulic work. There really should be no sponginess at all even at the beginning of a pedals travel. To the non-believers of master bleeding; the next time you do hydraulic work and you believe the pedal is as good as it gets,go a head and bleed the master cylinder as well and see what happens. Feel the sponginess at the beginning of the pedal travel. Then, press the pedal 1/2 to the floor and give it short jabs with your foot. If you can move the pedal noticeably at 1/2 the pedals travel after you are sure the brakes should be locked,there is air still in the system. This is NOT the hoses expanding.It IS the air in the master compressing. The hoses expanding allow the pedal to move to almost no extent. I have worked in garages on and off throughout the years and there are lots of cars that have spongy brake pedals that are accepted as being 'good'.

In my experience , the only people that gravity bleed brakes is if and when they can't get fluid out past a proportioning valve.

Edit: If you view a diagram of a master cylinder ,the bore is much bigger than the diameter of the port that leeds to the wheel cylilnder/calipar. The air gets trapped from above this port to the top of the bore. Fluid goes right by and the air stays there.
_________________
My beetle is not competing with your beetle. I have the yellow beetle in my town. There is a red one, a green one ......
Use all safety devices including a mask. Smile


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