I still haven't mastered the black art of brake bleeding. Or perhaps bleeding the brakes on 30 year old worn out cars isn't effective. In either case I can't get all the air out of my lines. I've got nice new rebuild calipers and I'd really like to put them to work. What are the tips and tricks? Here's what I've done so far.

1.) Pressure bleeding: I have a spare reservoir cap that I've drilled and put an air fitting in so that I can pressurize the reservoir and push fluid through the system. When I do this right now I get no bubbles. I did notice that one of the lines from the reservoir to the master cylinder has a bad grommet and when I pressurize it leaks from the top of the master cylinder.

2.) Partner method: I've had a partner push the brake pedal while I open and close the lines. This doesn't produce any bubbles either.

3.) Mityvac: I put the Mityvac on and I got a ton of bubbles, but I suspect they were sneaking in around the bleeder screw threads.

4.) Gravity bleeding: This has been the most optimistic method I've used. Just open the bleeder screw and the fluid flows out on its own and usually brings a small bubble or two. I suppose if I did this every day after I drove it I would eventually get them all, but I am really tired of taking all the wheels off.

So now the questions. Am I missing something? Could my master cylinder be bad? It doesn't lose pressure if I press on the pedal, which I though was the sign of a bad master cylinder. Could the leaking reservoir grommet be a problem?

Mark,

If you have both upper nd lower bleed valves on the calipers, you must bleed the upper valves before the lower, otherwise you will never get all the air out.

Just a shot in the dark.

Phil

My 2 cents:

1) I didn't see you mention the proportioning valve. Gotta and I mean GOTTA bleed that sucker.

2) You mentioned a bad gromett on the the MC. If it was bad enough it can siphon air in as the fluid is going by. I'd fix it.

Shannon

Is there a bleed valve on the MC? I had heard there was and you need to bleed it also. Just a thought.

Hey Mark,

I have one of those 1 man bleeder tools with the built in check valve.

You put the tool on the bleeder fitting and pump away.
You keep the tool end in a catch container so you don't create a chem/bio-hazard.If you use clear plastic you can eyeball for bubbles.

You can pump all the fluid through the system if you wish.
Give a call I'll come a runnin'.

I'll be doing mine soon, too.

I don't trust the Vacuum method too much. Unless your bleeder screws are perfectly sealed into the caliper some air will be sucked by the threads when you're drawing brake fluid out.

I built a vacuum pump to do this and noticed that I always had lots of bubble than when having a helper pum the brakes. I even tried wrapping the bleeder screw threads with teflon tape - still got bubbles. I would definitely go the Pressure bleed route next time. I would also imagine that those "one-man" bleeder screws would do the same thing unless the threads are perfectly sealed. Even if you used some sort of thread sealant, unscrewing and screwing them would increase the chances of air passing by the threads.

You can't go wrong with a pressure bleeder, just make sure your reservoir to MC grommets are good. Plus with a pressure bleeder you can "one-man" bleed the master cylinder and proportioning valve too.

Mark,
Ditch that prop valve and put a "T" fitting in its place and you should have no problem getting a good pedal. Of course you may want to put some bigger calipers up front

I've got a "T" fitting if you're interested. "If" you want to replace the proportioning valve...

The speed bleeders work great.

I was avoiding the proportioning valve because it didn't look like I would be able to get to it easily with a wrench.

Mark,

I use a combination of the above methods.

1. Like most things, it's always more fun (and effective) with a partner.
2. Speedbleeder screws rock.
3. Get the ass-end of the car as high in the air as you safely can.
4. While your Speedbleeders are open and your partner is pumping the pedal, try rapping on the proportioning valve with a rubber mallet.

If you've done all you can, and the pedal still feels only "okay"... take it around the block a few times or to the local In-and-Out . If it's safe enough to drive, then drive it a couple of days and then repeat the bleeding process. Sometimes using the system helps dislodge little bubbles.

-Rusty

This may be a bit late but you cannot use a vacuum bleeder due to the prop valve...it only works on systems without them.

Interesting newdeal2! I'm curious why a vacuum bleeder can't be used on a car with a proportioning valve. Please explain.

I read it recently in one of the tech articles when I was having the same problem. I will try to get you the info. Apprently the pressure method is best:

See:

http://www.pelicanparts.com/techarticles/9...leed_brakes.htm


Peter
74 2 Liter

OK...I found the quote in a tech article as follows:

The system works well, but can sometimes cause air bubbles to form in the lines. Particularly on cars with rear brake proportioning valves like the Porsche 914, the vacuum system can leave air trapped in these valves, giving a spongy pedal as a result.

Here's the link:

http://www.drivewerks.com/tech/mult_bleed_brakes2.htm

Hope this helps.

Peter

I did it! I beat it! I conquered!

Step 1 - Replaced reservoir to master cylinder grommets. Lesson learned? Slide grommets just barely onto tubes and then push into master cylinder then push tube down into master cylinder. I don't think I got perfect 100% engagement, but it didn't leak and they look very close to correct (95%?).

Step 2 - Buy a pressure bleeder. These things are just awesome. If for no other reason, then because they keep the master cylinder topped up. Gotta love that.

Step 3 - Know the system. Here's how I got pedal when nothing else would work. The proportioning valve (PV) needs a certain amount of pressure to operate. If you open up the bleeder valve a lot then you can't make any pressure and the PV doesn't move. So I cracked the bleed valves just enough to let a tiny tiny tiny trickle of fluid out (pressure bleeder is on too) and then push the pedal to make pressure in the system and make the PV move to free bubbles. Viola! Everything is nice and smooth now. I have "normal" pedal feel. I'm going to go back later and bleed a couple more times, but at least I have pedal now!!

Good! Now you can come a/x.

Maybe I will beg a brake bleeding when those calipers finally go on. You take payment in burgers, right?

Trek

Hell yeah!

Mark,

I really like that idea you have in Item #3. I haven't heard that one before. I'm going to try it tomorrow!



Shannon

Resurrecting the dead here, but I wanted to say thank you for the input. I just put my pressure bleeder to the car and couldn't figure out for the life of me why I got essentially nothing out.
I'll get back at it with my wife in the car to put a little pressure on the pedal (step 3 in @McMark's process).

I also add some big stomping on the brake pedal, with the bleeders closed, in order to actuate the PV. You should be able to hear it respond.

Bleeding mine was challenging too. The final thing that worked was the simple three pump two person method, but much more rapid pumps than I was conventionally used to doing.

A small mallet is always useful. Tapping gently several times will dislodge small bubbles trapped in the corners of the calipers. And I prefer a pressure bleeder over a vacuum bleeder anytime. Like it's been posted, air seeps in around the bleeders and gives false sense of too much air.

I've had best luck with helper, three hard pumps, hold and bleed down. Three to four times per caliper.

The proportion valve is the problem, it is not really difficult to bleed it.
It seems to be the highest point in the brake system.
Use a rag to cover the top fitting, use a flange wrench, with the system under about 8 lbs of pressure slightly crack open the fitting and close, do it twice, some fluid will escape (reason for the rag) now adjust the rear brake clearance, pedal will be high and firm.

Don't touch the lower valves...they exist for decoration only. Air rises, it needs to come outta the top.