Today I test drove a basically stock mid-50's Chrysler with power brakes (all drums, obviously). The entire brake system had been replaced or rebuilt during the previous 2 years, and worked perfectly before being stored for the winter (this was its first drive since October). The only thing I can think of is a lack of vacuum to the booster, or a broken booster...neither seem likely to me. I've heard a couple stories about late-model cars where it turned out the brake booster had failed, but the symptoms in those cases were the pedal going to the floor and there being almost no braking power. Anyone have any ideas?
I'd take a vacuum reading at the booster to see if it is getting a signal at all..if so, the diaphram likely has ruptured. Might check to see if the pedal lingage has rusted up or gone over center or some weird ****..
Make sure your pedal is returning all the way to the top of its stroke. I have had to add a spring to similiar systems in order for it to retract fully. If the piston of the master cylinder does not fully return it will have the effect you describe.
Even with a failed booster you wouldn't have an extreme hard pedal, just more effort to apply brakes. I think Rocky's theory sounds good, but it's always been my experience that a hard pedal is the result of a collapsed brake hose. Sometimes you can't tell from looking at the outside of the hose for internal damage. If the car's been sitting for two years all manner of damage from brake fluid ****ing up water could've occured.
look for a pinched or incorrectly routed hose. Same thing happened when I was messing with my rear shocks and I got the rear hose wrapped around it by mistake!!
Ok, thanks for the info. If you can't tell if a brakeline spontaneously contracted from the outside, how do you figure out where the problem is, aside from totally replacing all the brake lines?
Jack it up and try spinning each wheel without the brakes applied. If one doesn't budge that's prolly it. If they all spin, then apply the brakes and try to spin them. If one does spin then that's prolly it. If more than one either spins or doesn't, its a connector line or master cylinder... My guess is one of the 2 rears will be locked up as this is where your pedal height comes from.
I'm with Nads on this one. Probrobly a collapsed rubber brake hose. try bleeding the brakes and if you cant get pressured fluid out, the rubber line feeding that wheel cyl. or cyl.s is most likely at fault. Billy
Damn Machinos, a "spontaneous contraction", sounds like somthing that would happen if your wife caught you with her best friend!....
Machinos Hard brake pedal almost ALLWAYS indicates a bad booster or lack of va*** to booster.A bad booster will not give you a low pedal, generally. A bad hose will either cause the car to pull badly to one side,due to extemely uneven brake pressure or the brakes will apply but will not release, this is common, the inside of the hose fails, brake pressure being applied pushed past bad spot but when pressure is released there is not enough force to allow fluid to flow back into master cylinder and brake stays on. Check that booster and ***ociated parts carefully.
wwwwwwwwwwwwwwwwwww[ QUOTE ] Ok, thanks for the info. If you can't tell if a brakeline spontaneously contracted from the outside, how do you figure out where the problem is, aside from totally replacing all the brake lines? [/ QUOTE ]
If the line has failed internally it will usually cause a wheel to lock up, spin wheels to determine seized one, then crack the bleeder ****** on wheel cylinder, if brakes free up then you can generally ***ume that hose is bad, of course you need to visually inspect brakes and make sure they are not sticking due to rusted/damaged mechanism or bad wheel cylinders..........if cracking wheel cylinder does not relieve pressure, work backwards up brake system, cracking lines until pressure is relieved. That point will tell you what is bad. If master cylinder is bad more than likely all the brakes would be locked up, if brakes lock up gradually as car is driven, check to make sure there is a teeny weeny bit of clearence between brake pedal pushrod and mastercylinder. It should be felt in pedal if moved by hand, 'bout a 1/4" of freeplay before pushrod contacts.
While you're looking at the brake hoses, look for the outer casing to be torn at flex points near the fittings. That's usually an indicator that the hose is weak there too, even though it will be a buldge in the hose. That usually causes brakes that grab, or won't release like they should...
I had the same problem with my 59 buick, i put in all new brakes from master cylinder to wheel cylinders, turns out the early model adjusting rod from the brake pedal has a thicker, cupped washer than the new master cylinder had been designed for, I had to remove the piston in the Master Cylinder to shave about 3/16" off the end of the piston so it would return back far enough to let the compensating port clear, if the port hole doesnt have room it will build pressure on the pedal until the brakes are hard as concrete and then it wil start applying the pressure to the wheels themselves and locking up the brakes, hope it helps
A quick check of power booster condition is easy test. Engine turned OFF, pump pedal slowly untill a solid pressure is felt. Now hold pedal (If pedal depresses slowly at this time a leak is occuring somewhere in the juice circuit). Back to the booster while still holding pedal pressure start engine. Now if vacuum is pulling a GOOD booster the pedal will go DOWN slightly. This happens because you are now being "***isted" in pushing the pedal. If the pedal does not feel like got "***isted" then you must check for problem. Got Vacuum? second use a vacuum pump to pull on booster. Good Luck--- It would be the ****'s not to stop any ride!
If its a treadle-vac,and I think it is,it may be surface rust in the booster house. Ive had the same trouble with a lincoln,witch use the same booster. just separate the house,clean it up,and lube it alittle. worth a try,if the va*** are ok.
I never tried pumping the brakes at all, but the pedal was equally hard when it was just sitting, turned off. The car wasn't pulling at all to one side or the other when driving, does that eliminate all the hose-bulging possibilities? My guess is really that it has to be something that would occur while the car was sitting (it was under one of those "tarp garages" outside all winter). If any of the wheels were locked up, wouldn't that make it really hard to drive? It pulled itself right along (auto trans) when in drive. The "treadle-vac" thing sounds like a possibility, but I don't know what that is, actually. The booster and MC are rebuilt stock parts, BTW.
Hey, good news... On Wednesday I took it to work (picked it up Tuesday night), where there's a gigantic empty parking lot, so I figured I'd rev it up to 50 and hit the brakes as hard as I could to see if I could lock them up. I did just that, but at about 20mph the right front brake line blew up. Luckily I steered it into a secure area around back and didn't hit anything (in fact, I'm actually glad this happened now instead of later). I got a new brake line, installed it, and bled the brakes with my dad. They work even better than before now, the pedal travel seems much more "correct" and they seemed to stop better even though it was sleeting out a little at the time. So, this is good, but why did a brake line blowout (it was an all-at-once blowout by the way, definitely wasn't leaking, the hard line had been rubbing on the frame) fix the problem?
What did I tell you? Like I said these rubber brake lines can and do fatigue internally with no signs on the outside. My guess would be that it was moisture buildup reacting with the rubber that caused the failure. Now that you had one hose fail, you'd better replace the other two, because they're not far behind.
Great post. This should go to tech. May help the guys that are new to this build your own stuff. Would have saved the brand new grill I just installed on the first '62 pu I did when I was 18 and thought I knew it all. I had traded '72 frontend under there and kept having a hard pedal. Bleeding and bleeding and replacing, stayed the same. Hoses looked fine. Finally going to work one morning the left hose exploded. BANG into the rear of a mini van. Of course I didn't have an E brake, didn't need one. Told you, thought I knew it all.
I came back and resurrected this thread since I've driven the car so much since then, and spent a little time trying to get the booster apart tonight (despite what it looks like from under the hood, you've gotta unbolt the whole booster/MC ***embly from under the dash to get the MC off...bah). What's happening, and I'm quite sure of this now, is that the boost ***ist works for part of the way down through pedal travel, but soon gets much harder to push than even manual brakes. Some dumb*** ran a red left-turn arrow in front of me last week and it was a REAL close call because I didn't instantly remember that I had to use both legs to really push the pedal hard enough. A nice, leisurely stop in mild 30mph traffic is pretty much possible without going into the "super-hard" range of the pedal, but usually I do have to exert a bit much force. Still haven't been able to lock up the brakes, even with both legs. I know it's not a problem with the brakes rubbing or anything since the pads would be long gone by now if that were the case, pretty much positive it's the booster. And, uh, a couple months after I posted this I bought a gigantic shop manual (dictionary-sized for '55 ONLY, man it's big) but a month ago I misplaced it, and during the time I knew where it was I didn't think to look up the braking thing since I was driving my truck 99.9% of the time. I still think it might be surface rust in there as was suggested, but it's nearly impossible to get it unbolted under the dash, at least by myself, so I'm hoping to find my shop manual again and hopefully find a way to just get at the booster without taking the entire ***embly apart. For reference, the booster looks like the one in this pic (link may take a few tries to work): http://www.imperialclub.com/YearbyYear/1955/KTKeller/Pic12.jpg By the way, I do remember that it's a Kelsey-Hayes unit for sure.
Yeah, but like I said it wasn't the flex hose that blew, it was a weak spot in the hard line where it had gotten rusty. Flex hoses are good.
OK, one collapsed line makes a pull, not a hard brake. IF your car has a check valve at the booster, replace it, them get old and hard and the check valve acts as a vac*** block. If not, check the tube the hose hooks to for any block inside it. Run a pipe cleaner or short coat hanger piece through it. Otherwise, its rust inside, as stated before and the booster is not actuating.
I just took the whole stupid thing off and once I got the booster part open, it looks just fine inside. Still had the coating inside from the rebuild a few years ago (I believe) and the rubber bellows looks practically new, except for around the edge where it's a little rough due to brake fluid eating at it. So I'm pretty sure the problem is the master cylinder, which ****S because it's such a damn weird thing and I don't know what to do with it. I think the time now is to upgrade to a modern booster and dual MC... Oh, also: I checked the vacuum lines and they're fine. As for the check valve, I'm guessing it must be a part of the big fitting the vacuum line goes into, so I'm not sure how to check it other than knowing that air goes through there seemingly right.
Wouldn't that make the car pull one way or another when braking though? Brakes straight as an arrow currently.
Just thought I'd post an update, that I "fixed" it. I have no idea how or why it works now though A few days ago I took off the m/c and booster and it all seemed just fine. Finally tonight I put it all back on since I've gotta work tomorrow, and just resigned myself to not getting it fixed until I could replace the whole brake system at some point. Inexplicably, the brakes work great now. I can lock 'em up no problem and it stops EXTREMELY well. I slammed on the brakes at 45mph like 7 times in a row and they didn't seem to fade at all. I dunno why everyone's so down on drum brakes...
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