Hello all. I'm working to get my car back on the road next and ran into a strange problem. I replaced the brake master cylinder, but then after installing the brand new one, my brake pedal just sunk to the floor when trying to bleed the lines. Then when I walked towards the front I heard air slipping out somewhere. Turned out to be the booster diaphragm, so I replaced that too. Problem now is the brakes hold pressure but not until REALLY far down. Like the pedal doesn't seem to be moving the pushrod at the right place. Does this sound right or could it still be my booster? I'm pretty sure the lines are bleed just fine.

Also when the car is off, the pedal is stiff but when I turn it on it's soft until the really far down.

What am I missing?

 

brake booster vaccum hose connected to intake manifold? otherwise bleed the brakes.

 

Vacuum lines connected. I don't have a split air pipe right now, but I don't think that should cause a leak should it? Will try to bleed again.

 

Does the vacuum line need to have the air valve in it. That only let's air get pulled into the booster? Im having the same issue. I switched my car from efi to carb and I'm just running a hose from the intake manifold to the booster.

 

Do you have drums? Did you mess around with the drums? There is an adjustment in the rod itself, but most of the time its the adjusters in the drums that can get out of whack and cause a "low" brake pedel.

 

I have discs on all fours with new calipers on all corners. The reason i think it is just an adjustment is because i replaced the booster which required removing the rod that connects the pedal to the booster/cylinder combo. I dont see anything saying the pedal should need adjustment tho after replacing the booster. Maybe i did more work than i needed to? does anyone have any information about adjusting the pedal rod

 

it can be adjusted but it appears that there is air on your lines.

 

I tried to bleed them again this afternoon and it didnt seem like there was air in the lines. I only tried for about ten minutes tho because my helper flaked on me. Im gonna give it a good go again tomorrow afternoon

 

Ok so had my helper today, bleed the brakes again. When the car is off the pedal is stiff all the way to the top. but as soon as i take it for a drive it sinks down to the floor again. Getting really frustrated with it. Dont see any fluid on anything and the level is fine so its not escaping as far as i can tell. When i bleed them today i was sure that it was ready and good to go but sure enough as soon as i turned it on to go for a drive, nothing again. Should i start replacing calipers? could there STILL be air in the lines? I dont feel like it should be this difficult, ive done this same job on pretty much every car i own and its only ever taking one maybe two bleeds to get it perfect.

Also i suppose another possibility is a bad booster? it was a reman from autozone. Has anyone tried one of these?

also for anyone that wants a laugh: i thought my exhaust sounded a bit loud so i took a peak under there. Oh man. The main cat is welded to the pipe that connects to the muffler at the hanger. No bolts holding it together, just welded on both sides at the hangers. sigh.

 

When the car is off the brakes should feel hard. When started with your foot on the brake pedal, it should
sink down if the booster is working. Sounds like your booster is working.

There is an adjustment needed of the rod out of the booster into the MC. Its documented in the FSM. If
its too short it may not be engaging the MC until very late in the stroke. If its too long it will cause the
MC to not fully bleed back and keep pressure on the brakes.

I bet you still have air in them. If you sit with the brake pedal pushed for a few minutes, is it sinking
(with car turned off). Press hard and hold and see if it starts to give, if it does - air still in lines.

 

have to bench bleed the master first, otherwise u push all that air thru the system.

 

Ah I didn't bench bleed the master. But I always thought that was one of those suggestive things that doesn't really matter?

Is there any good write up on adjusting the rod? I'll give it another go this afternoon

 

Double Post

 

Ok went at it again today. (my brake bleeder is getting pretty sick of it ) haha. Noticed a few things.

When i bleed the rears, The pedal feels rock hard (like it should) then when i get up to the fronts, its gets soft at the top again. Im going to replace both front calipers and see what happens. I yoinked the vacuum from the booster and now i can tell it is definitely doing SOMETHING. IE the brakes are super stiff. the pedal travel is still the same before the brakes engage, its just harder to push, so i dont think its the booster (which is good because i didnt want to deal with replacing it again). Ordering front calipers today so theyll be here in a couple days.

Engine seems to be idling kind of hard. but i need a new battery and probably a new alternator. Going to check timing and carb adjustment because god only knows the last time it was done.

Will update back in a day or so.

 

You said you had new calipers on all four corners earlier but now you are getting new ones again for the
front? Confused.

 

Ah derp! when i said new calipers the first time i meant new pads.

 

OK so got new calipers and rubber lines installed today. It seems to stop like it is supposed to which is good! I think there might still be a bit of air in the lines because it got dark and i wanted to get my core deposit back for the stack of stuff i have replaced on the dang thing. Im gonna give it one more final bleed tomorrow in the daylight and hopefully i will be good!