Update on Brakes Part 3

""Doc"" wrote in message news:M18cb.2733$ snipped-for-privacy@nwrddc01.gnilink.net...

#4) AIR in the REAR SYSTEM

Before you buy that valve I would "START OVER" and bleed the crap out of the rear. That combination valve is very simple(not much to fail, especialy since you checked it out.) Start at the master and have someone pump it slowly, (nothing in the system open) make sure they get full stroke ALL THE WAY DOWN. Watch for bubbles in the reservoir. If you see bubbles that means there is air in there. If air bubbles come out, fluid is going in to replace it. Pump it slowly (ALL THE WAY DOWN) till it quits air bubbling. Go to the right rear, remove the bleeder and make sure it is not plugged with shit, clean it out and re-install. Next, bleed: open the bleeder ALOT , BEFORE they start to push the pedal(ALL THE WAY DOWN.)Close the bleeder when they hit bottom. This way you dont have any back pressure on the rears until you get some fluid in there. REPEAT until you start to get good fluid flow out of the bleeder. Go to the left rear and do the same. Then bleed them holding the pedal down and then open the bleeder, then close it when they hit bottom. (ALL THE WAY DOWN) Keep in mind the proportioning valve could cut off the rears at any time. The light will tell you. It would probably be a good idea to put some vice grips on that tit on the prop valve while bleeding to hold it out(or in, depending on who you ask)( Im going with -out-.) P.S. Bottom line: THERE IS MOST LIKELY AIR IN THE REAR SYSTEM. Try bleeding anything connected to the rear(ABS VALVE or WHATEVER) if the above didnt work. Did I mention to have your assistant push ALL THE WAY DOWN on the pedal when bleeding? :) What I meant was: have your assistant push ALL THE WAY DOWN on the PEDAL while bleeding. Please read the above very carefully conserning the OPEN THE BLEEDER B E F O R E the pedal is pushed, close when they get to the bottom, until you get good fluid flow. GL Doc.

. Doc, have you tried clamping all the hoses, just to see what the pedal feels like with no apply parts moving?

Scrib

Doc,

I'm sorry, but I laughed out loud when I read your post because I can vision myself doing the EXACT same thing. The picture in my mind is priceless - I wish I could explain it!

More importantly, I wish I could help out with your brakes, but after following your last post, you seem to have covered all the bases my brain would have thunk up.

NO DOC!!!! NEVER ALL THE WAY DOWN. Pushing the pedal all the way down can allow the pistons in the master to travel past the seals!!!! Put a narrow piece of wood under the pedal to keep this from happening. Read this!

i'ma feel'n ig nored

Doc, if you want to make sure you get all the air out you are going to have to give it FULL stroke. If you get to the bottom and see no air come bubbling from the resevoir, great, move on. Usually that air will bubble at the bottom of the stroke. Sorry but thats the way it is.

the pin position:) I'm going with hold it IN now....Never actually had to do this myself, but it seems its the "correct" way to bleed the rears. GL

Excellent article Scrib! But mine defied all this logic!!! It is the curse of "White Devil" and now poor Doc has it.

I seem to recall doing a "bench bleed" on a new master cyl. You need to leave the screw-in plugs installed and fill it with fluid. Then actuate it with a few full stokes until all the air bubbles out of the cylinder. Or, some guys had special fittings with lines made up that just spit the fluid back into the reservoir. Then, when you attach the lines you need to get that new air pocket out of the line from one end or the other. I always preferred putting the "pressure" on from the wheel end of the line because air likes to float "upward". Mike

No offense Scott, I'm with you. I didnt know for sure if he used a new master. Just being safe since this IS brakes. We dont want to lose Doc. I still think something in those metal lines is deteriorating and allowing the fluid to pass but forming an air pocket. This is a simple braking system that is defying all logic and a few of us believe it now.

I have folllowed this with great interest, and I have learned a LOT about modern cheby brakes. And I thank you all.

I would like to make a small suggestion, concerning bleeding, I dont know if it is new to any of you, or how helpfull it is. The idea is from motorcycle brake bleeding.

"pull" the fluid out........ using a large syringe, one pulls the fluid, and hopefully, Air, rather than "push" it. This works well on Bike brakes. We tend to get Air trapped in the piston resevoir area, or so it seems. Also, we push the pads back into the resevoir to expel Air trapped there.

Again, thanks for the education. We had an 86 Astro with lots of pedal travel that between myself and 2 shops, could not get out. Now I know that none of us knew exactly what we were doing (wrong).

Well, I had the similar problem once and this logic may or may not apply. But who knows. My friend had this 1984 Fiero with a hydraulic clutch. He had changed out both clutch cylinders and could not get a stiff pedal to save his life. I got a hair brained idea that I dubbed "back bleeding" I took his sons medicine syringe and added a lenth of clear nylon hose. I then added brake fluid to the syringe and forced it back into the cylinder and up through the reservoir. Had many bubbles. It worked like a champ and had stiff pedal in about ten minutes. I tried the same trick on my 72 VW Beetle brakes with success. This took a little longer and I used a bigger syringe. I also know of a system that Sears used to use. It involves an air pressurized tank filled with brake fluid. It made an airtight seal at the master cylinder and then all the mechanic did was walk around the wheels and loosen the bleeder screws. Never saw that method fail.

--disclaimer-- I DO NOT ENDORSE SEARS AS A VIABLE GARAGE TO DO ANYTHING EXCEPT INSTALL BATTERIES OR TIRES...and I am leary about letting them do that, but I do not own a tire machine so someone has to do it. Now I do not know if the newer ABS have valves in them that prevent backward pressure. If they do, than this procedure may not work. BUT if they do not....who knows.

See, Doc didnt need your stupid link :) LOL

While I already knew the majority of what was in the linked page, it is an excellent resource for those who might be newer to the world of power brakes............

Doc

cause he posted it 3 times :)