Brake System Pressure/Bleeding Troubles

[vernonc]

[bluebus86]

[King_vw61]

Find the one man bleeder, They sell them at carquest. Daniel Folts does a lot of prep on off-road race cars that have 2 reservoirs and bleeding the air can be impossible. You use 2 of them, Right side of car front and rear then left side. They let no air in the system but you can see the bubbles coming out of the w/c's. He let me borrow them and was the best. I own a vacuum bleeder and I wont be using it anymore.

[Q-Dog]

[vernonc]

My blue Bentley (Official Service Manual...Beetle and Karmann Ghia 1966, 1967, 1968, 1969) says "When bleeding both circuits of the dual-circuit brake system, always start with the front one."

This makes sense because there is a spring between the two pistons in the master cylinder; the rear most one for the rear brakes and the front most one for the front brakes. If the shoes are adjusted 'tight' and all the air bleed from the rear circuit, there will be 'very little movement' of the rear piston when the pedal is depressed. Therefore, when trying to bleed the front, if there is very little movement of the rear piston, it cannot (via the spring between the pistons) push the forward piston sufficiently to expel fluid or air from the system. A little perhaps but not much.

However, if there is air in both circuits and the fronts bled first, the rear piston can move 'full stroke' thus pushing the forward piston 'full stroke' (via the spring between) thus pushing both fluid and air from the system. Once done, the spring between the two pistons will allow the rear piston to move 'full stroke' thus pushing both fluid and air from the rear circuit.

I hope I've explained this clearly enough to be understood.

Of course the drawback to this method is that all shoes must be tight or, at least, very close to the drums and it takes two persons to execute.

Personally, I use a Motive Power Bleeder and none of this is required.

Hope this helps.

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

[bluebus86]

Thanks for the excellent info.

I guess I got away with doing rears first cause usually the shoes Id tighten last, after all the fluid was purged of air. But doing fronts first does make sense now given your excellent explanation.

Bug On!
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[theKbStockpiler]

The bleeding order is bull sh.t.
I get better results from doing the closest wheel first and work to the furthest.

The far biggest brake system issue is air trapped in the master cylinder. Fluid will go right past parts where air is trapped like the rear part of the rear master cylinder bore because it cant bottom out in that bore. There is a rod that limits its stroke.
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[shiskabobnut]

Still having issues. Just to recap:

Replaced the master cylinder twice.

Replaced ALL existing lines, rubber and steel.

Adjusted brake pedal freeplay from over 1'' of play, to 1/4'' of play at the top of pedal.

Tried bleeding from front to back, as well as back to front, doesn't seem to make a difference. I still only have half a pedal.

I will try relieving pressure from the rear circuit, and bleeding the front first. The back seems to bleed but the front doesn't. I'll try anything!

[bluebus86]

[VW_Jimbo]

You are getting no fluid out of the front cylinders?
_________________
Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[shiskabobnut]

I will try swapping the feeder hoses to the master cylinder from reservoir.

I get some fluid from the front bleed screws along with much air. Never seems to be a steady push of fluid from the front screw.

[shiskabobnut]

The feeder hose from the reservoir to the master cylinder connects to the plastic nipples via a short piece of rubber tubing. This tubing connects to a metal line running up to the reservoir.

This Rubber Tube-Metal Line connection is a little loose. Could this be the culprit? How would this be any different than bleeding the system with the cap removed from the reservoir?

EDIT: I understand the system needs to be entirely closed, I assumed the feed hoses were gravity fed. Meaning they didn't have to be perfect, as long as the fluid would flow through to the master cylinder.

[bluebus86]

[VW_Jimbo]

There are three segments of brake fluid rated hose on both of the reservoir lines. You need to change them all.

Also, remove the reservoir and clean it out, with soap and water.

Remember, brake fluid is hygroscopic, so if you spill any wash it off very quickly with water.
_________________
Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[bluebus86]

new hose may be inorder, and assuming all are same age, wise to change them all, but for a test, maybe try a hose clamp on the loose end(s) and see if she bleeds correctly. however if hose is really rotted, it may be leaky at places other than only the connection.
If the hose clamp fixes it, then you should replace them anyway, as looseness is an indication the hose is failing.

bug on!

ps Or you could swap the front and rear hose from reservoir at the master and see if the master front now bleeds correctly, if so, then the hose is very likely the problem.
_________________
Help Prevent VW Engine Fires, see this link.....Engine safety wire information

Stop introducing dirt into your oil when adjusting valves ... https://www.thesamba.com/vw/forum/viewtopic.php?t=683022

[shiskabobnut]

After replacing the hoses connecting the Reservoir down to the Master Cylinder, I have determined I do not have front brakes. After proper bleeding, and proper adjustment of the shoes, I can still turn the drum after the brakes are applied.

I haven't changed the front wheel cylinders, but every other part in the system has been replaced. The cylinders aren't leaking.

[cocacoladodge]

Apologies up front, but I'm getting a little off your topic with my own...

In my Bradley GT (kitcar) I changed my rear drums out for disk a couple years ago, and still have drums up front now. I have changed the brake pressure sensor multiple times now, but still have to push the brake petal in as far as I can in order to barley get the lights to come on... I understand that the drum and disk combo does take a funkey PSI difference, but the brakes work great... is there some sensor that takes lower PSI to activate or should I look into a different master cylinder?

Thanks, Bob

[Cusser]

[Phat73]

put a hose on each bleeder, run it in to a small bottle of brake fluid. Then bleed your lines.

You will chase your ass in circles if you try to bleed without the end of the bleeder hose immersed in fluid.
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I succeed because I fail.

[cocacoladodge]

Thanks for the quick replies.

Why the back first, that's where the majority of the weight is and also the power... The front only would have just skidded since its so light, additionally the extra weight of the drums is about the only weight factor for the front end. So that's the reason for the drum front disk rear.

Yes I have correctly bleed out the brakes, with the help of another friend who has a few Manx buggies. He is stumped as well.

The only idea I have left if there is not a low pressure sensor is to change the master cylinder to the single output, and put in a distribution block, but I have more faith in the dual units than I do the single.