~Cannot depress brake pedal, and seems like brakes are fully engaged~ I just put in a new dual master cylinder/bracket assembly from Chevs of the '40's today.....bled te brakes took a short ride up and down the block, around the neighborhood, everything seemed great. until...I take the car out an hour later for a 15 minute drive.... After I pull into my driveway, all of a sudden the pedal is rock hard, and it appears that brakes are engaged.!..? I put car into reverse, 1st....won't move..... I didn't have a chance to look into yet....any ideas?
check your pushrod between the booster and master. should have minimal play. if its too long it wont release the fluid back into the master and locks the brakes on.
okay, I will look into that.....does it make sense though that it worked fine on the first the first 'test ride"?
The pedal should move a small amount (I never measured it, but around a 1/4" or so) before the pushrod moves.
finger the push rod , if it rolls or has a lil play it is releasing . if it is a lil to long , it may work once then not let the fluid back into the res . is it adjustable ?
i had a 53 210 with a stock master cyl that the [bleed back] hole in the m/c was stopped up I could drive about 175 mi before the brakes locked down.then had to open the line at the mastercyl. to relieve pressure & would work ok for another 150-175 mi.
you check it a couple of ways. one, the depth of the old master push rod hole compared to the new one, or like what TagMan said check the play in the peddle 1/4' is a little much. you don't want the push rod to fall out of the master. most push rods usually are adjustable for this case. loosen the jamb nut and shorten it by turning it in to the cleaves until the peddle has some play.
Not going to be able to look at this until Tuesday, can any damage be done by leaving the system 'under pressure'? (checked again late last night, and it was still up, and could not be moved...)
brakes freed by chance today.... went for a very short test drive then the rain started coming down...didn't want to chance anything, I'll drive it some more tomorrow.....
Using a vehicle's hydraulic brake system, i.e. "line lock" etc., is strictly race car stuff and should not be used in place of a mechanically linked E brake system on the street, for very obvious reasons.
Additionally: Automotive braking components are designed for a short "spike" in hydraulic pressure, not continuous loads.
Hey worthop, is this a firewall mounted kit? With a booster or manual? My friend has a firewall mounted kit on his '53 with a booster, and it is disc front, drum rear and he is having the same problem. We shortened the rod as much as possible and it didn't really help, I'm starting to think that the master cylinder is screwed up somehow, not sure where it is made but probably Chinese junk. I'm not sure where he purchased the kit from.
It sounds like you may be trapping fluid. Make sure you have a separate spring that firmly returns the pedal. Do not rely on the internal master cylinder springs to return the pedal. (you did not mention a booster) With the pedal fully returned, you should have 1/16"-1/8" push rod free play, which will result in about 3/8"-3/4" pedal free play with a normal 6:1 manual pedal ratio.
I had a similar event on my Model A years aso. It turned out that when the brake pedal was released and touched the firewall it was still holding a tiny bit of pedal pressure on the system. It needed less than 1/8" of pedal adjustment. I also added a pedal return spring.
Ditto on the return spring. Also check the pedal for a bind, unlikely but worth a look. Your brakes probably locked up due to the fluid getting hot and expanding (free play in the rod compensates for this). If you pop a wheel cylinder bleeder and it spits, that's what's going on. Or crack a bleeder on the master if so equipped. Bob
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