Power Brake Help! Too much vacuum?

Just finished all the plumbing and stuff involved in putting a dual piston master cylinder and matching power booster for a 4 wheel drum 69 Caprice into my 60 LeSabre. This swap was done on a recommendation from Fraz who has done the same thing. I also replaced the front wheel cylinders. The problem I am now having is that with the car running when I press the pedal it goes easily to the floor and when I let go it only returns about an inch. With the car off the pedal feels okay, it can be pushed to the floor but it takes some effort. My question is this; do I have too much vacuum going to the booster or do I just need to keep bleeding everything? If it is too much vacuum how do I restrict it? I'm afraid it is just air in the lines but bleeding sucks and Ive already done the entire car about 3 times and Im sick of it so I figured I would consult with the experts.

 

Crack the bleeders on your wheels and go away for a day leaving them open then come back tighten them and see what you got . Three times around bleeding brakes on a new system doesn't sound so bad , I've done more ! Did you bench bleed the master before install ?

 

Not exactly an expert, but I'm pretty sure that you can't have too much vacuum (at least not from an auto engine). I'm going to speculate that you still have to bleed it some more (and yes, I know how much that sucks!)

Try a pressure (or vacuum) bleeder, it will make your life much easier.

 

Even with a pressure bleeder on a newly installed (bench bled) master cylinder and all new lines, it took about 3 times around for me to get all the air out. Try bleeding again. With all new lines, you could get no bubbles for a bit, and then all off a sudden a big pocket of air.

 

Yeah that sounds about right I guess. Ought to keep me out of trouble for the rest of today anyways...

 

Sounds like the master wasn't bench bled enough to me.

 

No such thing as TOO MUCH VACUUM !! One important point ... the pushrod going into the BOOSTER must be the CORRECT length !! If you used the same rod/adjustment as the manual master it is probably wrong.... check for how much depth is in the "cup" where the rod enters the booster ....then check the manual master cyl depth...... if they are not the same you gotta' adjust the rod to mate with the new cup......this rod sound be within 1/8" from bottoming out on the new booster cup... power boosters are usually have a DEEPER cup than manual master -- BUT NOT ALWAYS !! ......so ..... if bleeding, etc won't help ---take a LOOK !!

....... jersey Skip

 

I did bench bleed the master (plugged ports, stroked piston lots and lots of times) but it is very posssible that one or both reservoirs ran dry while I was chnging some lines around. If I just pull the lines coming from the master and plug the ports and bench bleed again will I also have to redo each wheel? I guess I'll just go try it and see where we get. Thanks guys.

 

I'm in agreement with the rest of the fellas, quintuple-check for air in the system somewhere.

 

Hey, Fraz. Thanks for the tips on the swap by the way. One question for you; Where did you put the washer fluid tank after you put on the bigger booster? I guess I could just ditch it and try to not get the windshield dirty.

 

If I just pull the lines coming from the master and plug the ports and bench bleed again will I also have to redo each wheel?

you MUST run the lines back INTO the master resivour ( NOT PLUGGED) and pump slowly until all bubbles are gone .........you can buy a "bench bleed kit" with adapters and plastic lines anywhere ...... you CAN NOT use PLUGS !!

...... jersey Skip

 

For bench bleeding make up a couple short lines that run from the ports and curve up and stick back into the master. I've found this works way better than the plugs. If you ran it dry you gotta start all over again.

Bill

 

Yeah thats what I have always seen too but the master was brand new and came with the plugs along with instructions for a "new and improved" bench bleeding technique. My buddy Mike also told me of this method and he has worked on more junk than anyone I know.

 

My washer tank was toast before the swap so when I tossed it. Also, the "new improved" technique is bullshit, cost me 3 trips to the parts store and half a gallon of brake fluid. I did it the way WildWilly describes, and no issues.

 

Don't forget the brake shoe adjustment. If the shoes aren't adjusted up right on 4 wheel drums you can get a lot of pedal travel just getting all the shoes out to where they start to really work in side the drums. It can be a problem not found on disc brake systems.

 

Not to Bogard your thread, but what about the rear brakes grabbing when you turn and your not braking?

 

Yup made sure the brakes were adjusted before I started today. Apparently no-one at any of the commie parts store chains even knows what a bench bleeding kit is, much less actually have one. I'll stop by one of the good places tomorrow. Man I really want to drive this beast...

 

Ok bench bled the master again, the right way this time, and started bleeding the rest of the car again. I noticed a "kissing" noise under the car but couldn't see any leaks. After an hour and a half and like 50 ounces of brake fluid with still a ton of bubbles coming out I checked the lines more carefully. The line going from the distrubution block to the hose on the torque tube has the world's smallest pinhole in it. Harldly seeps any fluid out bur apparently lets tons of air in. Looks like I know what I'm doing the next few evenings...

 

Ah yes, that pain inna ass lil shorty short line. A perusal through the local Autozone's stuff yielded one that was about 1/2" longer than the original. I think it was for like an 84 Dodge Aires or some such thing.

 

When redoing an old car brake system the hoses should be the first thing you replace, especially the rear one. If hoses ever get replaced on cars it is 99% of the time ONLY the front ones, so the rear should be a priority on all rebuilds.

 

Actually its the hardline leading up to the hose. All the hoses and literally every other pice of hardline was replaced when the car was "restored" a few years ago by the PO. I'm sure glad this happened now, if I had left the single pot master and driven it around all summer I probably would have planted it into a tree of the back of an f-250 by now.

 

Ooooh, I HATE that one! Had to replace that SOB on the Byooik too. Good thing you found that pinhole though, cuz you're right, stopping one of our monsters with smushy brakes is extremely not fun.

 

"Apparently no-one at any of the commie parts store chains even knows what a bench bleeding kit is, much less actually have one."

Matt, only place to go in Rochester is Schnabel's Auto Parts on Buffalo Rd. near West Ave. Real old time parts house (since 1946) with adult counter guys that know what you're talking about. They even look up parts in parts book - not on a computer !! I went in the other day and the guy behind the counter says "What the fuck do you want?" and then spent half an hour getting me the right stuff !!

 

Thanks, TagMan. Ive heard of that place before but have never been. Its even real close to my house. Ha, when I go into the local (Chili) autozone or advance lately they just slide the keyboard and mouse to me, wait for me to do my thing, then take my money and tell me it will be in on Tuesday. Ive found the napa in Honeoye Falls to be helpful, its run by a couple old-timers and its right across the street from where I work.