power brakes

[knightrider]

Just got done doing the brakes on the 59. I had started on the rear and worked forward replacing all the wheel cylinders as well as the master cylinder. all of which were leaking
now it seems once the car starts the pedal moves way more towards the floor than prior. it now seems like the brakes are being applied with out applying pressure to the pedal. going to full manual and bypassing the power unit seems totally fine. I did try the pedal adjust but it did not seem to do much/ or anything. so now is the power unit bad too ????

johhny

[jopizz]

It's natural for the pedal to go down slightly when you start the car. Do you have the shoes adjusted correctly and all the air out of the system. Either of those will also cause low pedal. Are you still using the stock single master cylinder? A bad power unit will leak vacuum and will cause the opposite effect. There will be no pedal movement when the car is started.

John

[Frango100]

After i changed the master cylinder rebuild kit, my brake pedal also went almost to the floor. I removed the master cylinder again and found quite a big difference in depth of the old and new master cylinder piston where the brake rod enters. I put a small piece of metal in the new piston to compensate for the difference.

[simplyconnected]

... replacing all the wheel cylinders as well as the master cylinder.

...now it seems once the car starts the pedal moves way more towards the floor than prior. it now seems like the brakes are being applied with out applying pressure to the pedal...

There are a few things going on here. I'm not going to preach about bleeding all the air out but I always advise everyone to 'BENCH BLEED' any dry master cylinder before assembly.

When the M/C is fully retracted, all the fluid should return to the reservoir because shoe springs push wheel cylinders back. IF your booster is MAL-adjusted the brakes will apply themselves because the M/C never retracts far enough to open the port to the reservoir.

So, part of your new M/C setup should include the output jack screw on your booster. This is covered in the Shop Manual because it's so important. Most owners never run into this procedure because their M/C is already 'wet' and adjusted when they get the car. Each M/C is different and so are boosters.

With the master and booster separated, have someone step on the brake pedal as you watch the booster's output shaft come out. It will be self-evident. When the M/C and booster are bolted together, you can't see the adjustment (between them). I use a slice of American cheese (still in the wrapper). Place it in the hole of the M/C. Gently bolt the pair together, then unbolt them and notice the cheese. If the cheese is squeezed out in the center, back off the booster's jack screw. The final setting should put the booster very slightly touching the M/C piston when everything is bolted together. - Dave

[knightrider]

brakes

= master cylinder was bled on car with nothing attached. I did have a bear of a time bleeding in general...
- master cylinder was from napa and looked identical as I could tell, pulling boot off and looking at the cylinder.
- I haven't yet made any adjustments to the master cylinder rod on the top part of the pedal, I may try that next.
I really didn't want to pull the cylinder off again.......


thanks ALL!!!!

[simplyconnected]

Just to be clear, you do not need to disconnect the hydraulic line. I am talking about separating the master cylinder from the booster, not the firewall. It isn't hard and there are only four nuts. The pedal rod is the very last adjustment. Follow your Shop Manual.

BTW, it takes about 20 pumps before the M/C purges all the air out. - Dave

[jopizz]

If he has a '59 he most likely has the under dash booster. Very few 59's had the under hood booster. Also the MC for the under hood booster is not available.

John

[Woobie]

Basic test

Engine off. Depress and release brake pedal several times to remove vacuum from power unit.

Depress pedal and hold with light effort of 15-25 lbs., start engine.

If power unit is operating, pedal will fall slightly and then hold. Less effort will be needed to apply pedal.


Above is the test procedure from our shop manual for testing the power brake booster, Chrysler though.

[simplyconnected]

If he has a '59 he most likely has the under dash booster. Very few 59's had the under hood booster. Also the MC for the under hood booster is not available.

John

My mistake about the booster.
Johnny, you only get one adjustment; the pedal rod. Yours may be too tight.

[knightrider]

brakes

Yes mine is a 59 w/ an under dash booster. pedal has pressure and returns fine with booster/vacuum discoed. I now do recall having adjusted the rod out more when putting the new master on. I will try re adjusting that then go the later of pulling the master off again.

man I tell ya I have never had this much frustration doing the brakes!!

thanks all for the helpful suggestions as always