Last night, a friend and I spent about an hour and a half trying to manually (foot on the brake pedal, crack open the bleeder valve) bleed the front disk brakes on my 69 Chevelle. Just when it looked like the air bubbles were subsiding, another round starts in. We finally concluded that air must be getting pulled into the system from someplace (?), so I pulled off the new master cylinder with the intention of returning it for another today. One thing I'm concerned about though is the metering valve located next to the master cyl. I have disassembled, cleaned and reassembled it. There is a rubber seal in the bore at the back of the valve and the rubber cover that snaps over the shaft (button) is cracked and no longer usable. Could air be getting sucked in past this seal? Would a missing rubber cover be allowing air in? I'm at the point now where I will get some sort of thresded fitting to by-pass this valve altogether as it doesn't have a very important function anyway. Can anyone help me out with this? I've got a cruise night on Saturday and a show in a couple of weeks and would sure appreciate any insights!
Thanks,
Rich

That's your proportioning valve I believe. The rubber cover is just a dust cover not a seal. You can try bypassing it to see if it's the problem but I would think you would have fluid coming out from the back of it if it were leaking air in. It's taken me a long time sometimes to properly bleed the brakes, especially if the lines were totally dry. When I converted from drums to discs and replaced all my forward lines a few years back I finally got sick of it and took it to my local shop and had them use their power bleeder.

Cheers,
Andy

 

OK, I'm doing two things different tonight: by-passing the metering valve with a solid brass block and plugging the rear brake line at the MC to isolate the front system. If, I'm able to eliminate the air from the fronts and it reappears after I reconnect the rears, I'll know I have a bad master cyllinder!
BTW, I checked the entire system this AM and found NO evidence of fluid leakage anywhere in the entire system.
Thanks,
Rich

 

you must bleed the master first! just by cracking open the fittings as your buddy is holding the pedal and let it go to the floor then close lines and let foot up. Repeat untill their is a stream of fluid with little bubbles, then go down to the calipers and wheel cyl. good luck should work or else you would have a leak in the system somwhere

 

Make a power bleeder from this site: http://www.bmw-m.net/TechProc/bleeder.htm
It also show a leak where the air is coming in.

It's cheap, easy, and great to use. With this, I replace and bleed my brakes once a year as regular maintenance. Couple of friends borrow it and return it with some good food or something. It's paid for itself many times over.

 

Make sure the master cylinder is bench bled before installation.

Make sure the front calipers have the bleeders pointing up or on the top or the pistons bore. You can tell this easily by looking at the back of the caliper.

If all that is good. Then you can take a few brake hose clamps and pinch them off to seal them shut from the caliper. You need 3 of these, one for each front wheel and one for the hose that runs to the diff. for the rear wheels. Before pinching them off, try to bleed the brakes normally first. Going from the furthest wheel back. (right rear, left rear, right front, left front.) If you dont get anywhere with that method. Then pinch off all 3 brake hoses and sit in the car and push the pedal down.....

If its solid...then you have air in one circiut. Still to the floor then the master possibly still has air in it. Or a possible leak before the pinched hoses.

Remove one (doesnt matter which one) clamp and push pedal down. If pedal goes down then you narrowed it to that circiut. (The pedal may go down a little bit =normal, shouldnt go down to the floor.) If it is solid pedal with one clamp removed then reinstall that clamp. You only want one clamp removed at a time for this, so remove one and push pedal then put clamp back on and try next clamp and try that one. Whatever clamp is off and you have a pedal that goes to the floor, you have a good start to the area where the potential problem occurs.

Do not use a vice grips or anything of the sort to pinch of brake hoses, they will get damaged. You can get brake hose clamps anywhere.

 

Finally got it! Removed the MC and metering valve, bench bled the Master again. Reinstalled the MC, left the metering valve off this time, by-passing it with a brass block threaded to accept the fittings. This was the first time I was able to get only small bubbles and then, within about 10-12 pedal pumps, a clean flow of fluid w/ no bubbles! The metering valve was obviously sucking air.(Went through about a gallon of fluid!) Now, I need to road test to see how everything works w/o this valve. Maybe I'll replace w/ a new one later. thanks for all the responses. I want to check that home-made pressure bleeder-that looks good.
Thanks,
Rich

 

Wow, that home made bleeder is slick. My shop will soon have one! I'm tied of listening to the wife complain about helping me bleed brakes!!

 

Ok, I looked at the power bleeder DIY thing, but I don't quite follow where you pump into? Someone mind explaining? it looks easy enough to make, I even think I have a spare garden sprayer at home.. I have to switch my master cylinder soon and I hate having to find someone to crack the bleeder/pump the brakes with, especially when doing all of them..
Plus this way I could flush the lines easier, it seems.

matt

 

MadMarv, I think the way this works is, when you pressurize the sprayer tank, it forces the brake fluid into the system when you open a bleeder on a wheel cylinder or caliper. That is when the pressure forces the fluid through the lines and out that bleeder, then into your catch bottle.

I too am going to build one of these. I am doing a drum to disk conversion. This will be a great tool to bleed the lines alone.

 

I understand the general theory here, but I'm looking at his pictures, and I'm not sure where you are forcing fluid into- As in I don't see where his nozzle fits into.

I guess I'm just confused. When I bleed brakes I usually keep the reservoir full, start at the pass side rear, and then crack the bleeder, have someone press the pedal, close the bleeder, and have them let up, and repeat, until no air is coming out. Every 4 or 5 pumps I pop the top off the MC and check to see it still has fluid..

Was I doing this wrong from the start? I just don't see where that nozzle would plug into in a conventional GM master cylinder..?

thanks
sorry for being a twit

matt

 

I think these websites might clear up some confusion. I found one site that has many different kits avaiable, depending on what you have for a braking system. This ranges from domestic and foreign cars, to motorcycles, to ATV's, to any other system that uses a fluid in a closed system for whatever.

http://www.pavementsucks.com/showcase/pressurebleeder.php

To make one of these kits, following the instructions, seems very easy and straight forward. Here is a Car Craft article that shows a plate to go ontop of the master cylinder, with the offset opening. Granted this article shows how to make one to use a compressor to force the fluid through the lines, but modifying it to use the hose fitting nipple and clear tubing should be simple. Here is that article :

http://www.carcraft.com/techarticles/85658/

I was at the hardware store last night and got a small sprayer for $11.00. I'm well on my way now

I hope this helps others to see what needs to be modified to make this device work on our cars. BTW the original article is for BMW cars.

 

Madmarv

I'm with you I think I will stick with the old fashioned way. I'm real cautious when adding or bleeding brakes about getting any on my $$$ paint job. Something about that one picture with the chains and hooks and pressurized brake fluid screams trouble to me.


Bob

 

From http://www.pavementsucks.com/showcase/pressurebleeder.php

"The system worked quite well. It safely forced the old fluid out and the new fluid in. It bleeds the master cylinder as well, so no need to bench bleed it if you ever need to replace it."

So this method also replaces the need to Bench Bleed a new Master Cylinder? Does this sound like it would be true?

 

Looking at the CC article, I like the idea of this setup, except that you would have to remove the c-clamp when you thought you needed more fluid and clamp it back up again. I'd prefer an external tank like the other link so you have a continuous supply of fluid. Having a countinuous 10 psi is nice too. I guess if you do enough bleeding jobs, you could merge the two ideas. How about utilizing the bales to hold the plate down? They;re alredy there and all that would be needed would be to make sure the plate wasn't too wide and then build up steel shims on top (weld in place) to maintain the downward force necessary. Connections for hoses to both reservoirs with a flip valve to supply the one you were working on......now I'm getting too involved.
Rich

 

I have a plate with a fitting just like the CC article. I C-clamp the plate to the Master Cylinder and fill the pump container with brake fluid. Pump up the pressure to about 8-10 lbs. Switch the plate around to do the fronts. Total time about 1/2 hour. Simple, clean, done.

 

I just finished building mine. Can't wait to try it out. It was very easy to assemble. The toughest part was cutting the plate to size, and removing the paint from that surface. Although I did have an issue with the 1/4 inch pipe/nipple. I couldn't find a drill bit big enough to use. I needed a .557 hole, 1/2 was too small, 9/16 was too big, I couldn't find a proper tap ....... I ended up drilling a 1/2 inch hole, then using a larger, conical dremel stone bit, to widen the opening until the piece fit like a glove !!! I woulnd up completely using up that stone, but it was only a buck. Any way, after that I just used a gasket/RTV goop, to fix the rubber sheeting to the face of the metal plate, after cutting a hole in it to clear the nipple opening, and clamped it to a piece of wood over night, to cure. It looks like it should work well for bleeding brakes alone. Later