Power drum brakes questions??

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pettybludart

pettybludart

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I was out for a drive in my 68 Barracuda today,when applying the brakes the peddle feels hard and the car seems like it,s loseing vacuum(low idle,seems like it,s running on 7 cyl??)I checked for vacuum leak,alls good.The brakes are all new and the power booster looks newer(holds pressure)The PO owner had all brakes,flex lines,drums replaced,so I,m a bit confused as to why the brakes feel the way they do after checking for vacuum leaks?Maybe the shoes need adjusting?I,m new to the power drum brakes,so any help would be appreaciated.Thanks.

Could it have something to do with the proportioning valve?
 
If the car has been sitting a while I'd change the brake fluid and check the adjust ment of the brakeshoes. That being said I'd also start looking for a front Disc conversion. Much like the change from a single cylinder to a dual cylinder no complains or tries to knock the car for safety reasons. I'd keep the original stuff just in case the next owner wants to put that back on it for what ever reason.
 
Put a vacuum gage on the intake. If not enough at idle, the power booster won't work. That is common problem for people that install a wild cam. I forgot what reading is needed but you can find in posts. If ~half pure vaccum on the gage, should work the booster fine (15 inHg?).

Unlikely you have a diagphragm leak since you can usually hear as a hissing near the brake pedal. Also, they usually get into a mode when the power brakes grab suddenly as you press it, when a crack in the rubber seals.

Next look at the fluid side. See if you can bleed from each wheel cylinder. You just need a little to prove the lines aren't clogged.

If not above, you are into the mode of replacing parts. I would start w/ the vacuum booster since the most likely culprit and not super hard to replace, especially since yours is probably on stand-off brackets like most Darts.
 
The car has been driven recently,as the PO replaced the brakes(drums,shoes,hoses,complete rearend to 8 3/4)The booster looks fairly new with surface rust??I guess I,ll start with bleeding the system,adjusting shoes,then check for vacuum in gear.Here,s a pic of the booster.Hmm,maybe the mastercylinder is Kapoot??
View attachment 1968 Barracuda Fastback 038.jpg
 
To check for a vacuum leak in the booster put a vacuum gauge on the intake manifold. Take a reading and write it down. Now remove the vacuum line (large one) going to the booster from the manifold, cap it off and take a new reading. Should be the same reading as the first one. If off by more than a inch or so you may have a leaking booster. While you are at it check the vacuum check valve on the booster-you can blow through it one way and not the other. The check valve is the black plastic part that the vacuum line plug on to at the booster. It pulls off the booster but takes a strong pull.
 
slant6/4speed said:
To check for a vacuum leak in the booster put a vacuum gauge on the intake manifold. Take a reading and write it down. Now remove the vacuum line (large one) going to the booster from the manifold, cap it off and take a new reading. Should be the same reading as the first one. If off by more than a inch or so you may have a leaking booster. While you are at it check the vacuum check valve on the booster-you can blow through it one way and not the other. The check valve is the black plastic part that the vacuum line plug on to at the booster. It pulls off the booster but takes a strong pull.
Click to expand...
I was limited for time before work,but took the nipple off the vacuum line(check valve)had 20lbs,then put in gear it dropped to 15lbs.Could this mean my booster is junk?:sad7:Thanks for any help.
 
I,m gonna do a 4 wheel bleed of the system to see if it,s a problem with my proportioning valve?Maybe air got in when the PO bled after installing new brakes?Who knows,worth a try.
 
Same exact situation happened to my 69 Swinger 340 car, and it turned out to be a tear in the rubber diaphram in the booster. It was the same booster that you have pictured. I could not find a replacement anywhere, from anyone, so I had to have my original repaired.
Good Luck bud!

George
 
If the pedal is hard, does not sink, it is not a bleeding problem. I think what one of the guys was getting at was just opening the bleeders "a little" to see if you were actually getting flow through all the system, not actually bleeding it.

I'd bet this is either a booster problem, or the shoes are glazed, or the drums have been turned out too big, which causes the shoes to touch only in the center, makes the center part of the lining get hot and glaze.
 
Sorry 67Dart273,when I mentioned the PO replaced all the brakes,I guess I forgot to mention drums also.The whole braking system looks to have been replaced not to long ago.I know this doesn,t mean much with todays faulty parts,but I,m hoping this is a $imple fix.I will check for brake fluid flow to each wheel cylinder.Thanks
 
George R said:
Same exact situation happened to my 69 Swinger 340 car, and it turned out to be a tear in the rubber diaphram in the booster. It was the same booster that you have pictured. I could not find a replacement anywhere, from anyone, so I had to have my original repaired.
Good Luck bud!

George
Click to expand...
George R,any idea what make this booster is?This way if I need to replace it,I know who to stay away from.Thanks
 
You could try pulling the vacuum line off the booster and plug the hose. See how the pedal feels that way....
 
O.K I,ve bled the whole system and got no change,so I,m guessing this booster has some type of vacuum leak?Are they,re kits to replace gaskets for these?Car is a 68 Barracuda 318 with A/C.Thanks for any help.

P.S Shoes,drums,wheel cylinders and all hoses are brand new.The booster and master cyl. don,t look to old(maybe 2 yrs old)with very little mileage(500 miles tops)
 
I would NOT screw with a booster. Find a qualified rebuilder. Even the small town of Spokane has an outfit that does vacuum booster work.
 
Rock Auto offers a return and rebuild service for around $145 plus shipping. Figure on almost 2 weeks from your door and back since it takes 5 business days for the repairs. They do the booster and the master cylinder. Now for the fly in the ointment. The listing was for disc brakes only, but they should be able to repair the booster since there is no difference between the disc or drum boosters. Contact them and see what happens. Hey, it's a shot.
 
67Dart273 said:
I would NOT screw with a booster. Find a qualified rebuilder. Even the small town of Spokane has an outfit that does vacuum booster work.
Click to expand...
I,m speaking with a member about getting a replacement booster.I can,t beleive this booster is gone,somebody paid around $300 for this?Anybody know where to get a rebuild kit for this one?
View attachment 1968 Barracuda Fastback 089.jpg
 
O.K the check valve works,so now I,ve just blocked of the vacuum line to engine.My peddle is there again,so guess I,ll just drive manual til I can have this booster checked out.Atleast now it feels like it has brakes again LOL
 
Hey Pettyblu, did you get this issue resolved? I have the same booster as you and I'm having the same difficulty.
 
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