Alright, this is bothering me. I swapped in my stainless brake lines on all 4 corners and replaced all my bleeder screws with russell speed bleeders. I've bled the brakes 3 times starting from RR to LR to FR to FL using the top bleeder screw. I used valvoline syn power brake fluid "exeeds dot 3 and dot 4 according to the bottle, and its compatible w/ conventional fluids.

The pedal is extremely firm when the car is off. It gets resistance with in the first inch of pushing the pedal. There is no air in the system that I can tell. Everytime I bled them only clean new fluid came out and no bubbles (bubbles came out the first and 2nd time, but not the third). Once I start up the car the pedal goes nearly to the floor. I haven't driven it yet, but before I swapped lines I don't tihnk it went down quite as far.

Any ideas? I have thought about replacing the master cylinder. I'm not loosing brake fluid anywhere I can see.

 

Sounds like something's screwy with the booster...

 

Is there a way to test it with out a vacuum booster like the fsm describes?

 

The exact same thing is happening to me right now.

I read a post in this section about a month ago about some adgustment needing to be made on the actual brake pedal - adjust the push-pin in the cylinder or some thing like that. I'll try to do a search for the actual thread.
-a

 

did you use teflon tape with the bleeders? Air sucks back in so fast with those bleeders i've found... Also, I had tightened my SS lines, and a week later they had come loose and were leaking... I tefloned those too...

 

You may be on to something there, Kenteth, but are you sure that teflon tape is chemically compatible with the brake fluid?

 

I don't know, but it helped keep the air from sucking back in when the bleeder is partially unscrewerd. Once its tight I don't care if the teflon disolves so long as I don't have air in the lines. This was done several months ago and it worked fine.

The problem we had is we couldn't get the bleeders to bleed without having them a good way unscrewed. To the point where you could touch the bleeder and it would move around. It was pretty obvious we were sucking air back in because the air bubles lasted forever. We took the bleeders back out, teflonned them, put them back in, and the air bubles were bled out in about 2 minutes. Spent over two hours trying to bleed air out and we were just sucking air back in the entire time.

 

heh... Out of curiosity, is the author of this thread using DOT5 synthetic brake fluid? If he is, thats the problem. DOT5 is controversial on older systems, it won't mix with DOT3 or DOT4, so you basicaly can only install it if you're installing an entirely new brake system *(All new compoents)*. Not to mention that Synthetic DOT5 will find a leak if there is ANY chance of there being one. While DOT3/4 might work great in the system, DOT5 might instantly find a place to suck air in at.

If you're using DOT5, well... I'm sorry. Your easiest fix in my opinion is stop buying $25/qt brake fluid, and put some $8/qt racing DOT4 brake fluid in. Of course... you'll have to make DAMN sure you get all that DOT5 out, cause like I said it won't mix.

DOT3/4 and DOT5 compress at different ratios. It makes braking FRIGGIN unstable and intermittent if you have the slightest mix in the system.

Goodluck, and hope you're not using dot5.

And YES, this is from experience and factual evidence from DOT5 manfuactuers.

 

there is a threaded rod connected to the brake pedal that adjusts the freeplay. There is a nut on this threaded rod and by turning this nut you can either increase or decrease the freeplay in the brakes. I can't remember which direction does which but its easy to tell once you start the car. It sounds like you have an airtight system. If there were leaks anywhere you would not get a firm pedal when the car was off.

However, since you get a firm pedal when the car is off, and a soft one when the car is down it sounds like it is your brake booster. If the master cyllinder was bad then you would have air bubbles coming out at random times while bleeding. If your lines were not in properly you would not be able to build pressure with the car off. I would guess it is the brake booster.

Although, when you say you can get a hard pedal with the car off do you mean that you can pump the pedal up until its solid wait 10 seconds and then push it and still have it solid? If the brakes need to be pumped up again after 10 or so seconds to get the pedal solid, with the car off, then you have a slow leak somewhere...

 

It sounded to me like he was using synthetic fluid, but not Dot 5...I've used that Valvoline stuff before, it seemed to work well...I used the Dot 5 stuff in my clutch system for a while with no problems, but went back to regular Dot 4 stuff when I rebuilt the master & slaves...

Another way to keep air from being sucked back in during bleeding is to just keep your finger on top of the bleeder screw. Works well for me. You shouldn't have to crack the bleeder open more than about 1/2 turn to bleed, or something's wrong...

 

Kenteth, that's some good info on the bleeder valves... good to know.

I wish there was a kind of "random facts" archive organized by part. This would definately be something to add to the brakes section of something like that.

--Bob

 

did you bleed both bleed valves on the rear brakes? there are two and i had this problem because i only bled one valve on the rear brakes... so there are 4 to bleed in the back and 2 to bleed in the front

 

The speed bleeders had some thread locker type stuff on them to prevent air from escaping or entering thru the threads.

According to the fsm you're only supposed to bleed the top bleeders on the brakes if you removed a line. And the bottom if you removed the caliper and rebuilt it or sumthing. Perhaps I should try to bleed them all.

The valvoline syn power was like 6 or 7 bucks, and it does not says it dot5, it just says it exceeds 3 and 4 and is compatible w/ either type.

I have adjusted the pedal freeplay and heights both up and down to spec per the fsm.

Sounds like I need to buy a vacuum booster thingy to check my power booster. Although Perhaps the piston is out of adjustment where the pin meets the cylinder on the booster side. Thanks for info so far.

 

RETeds website comes to mind