So I won't mention what vehicle this master cylinder is on and I think I know my answer but it always good to get a second opinion. Similar to performing a full frontal lobotomy on yourself. Get a second opinion and not from the squirrel running around in your head.

So I've sucked out the old fluid from the master (I think I just gave myself away) and the brakes are hard and stops the wagon "ahem" car on a dime. But as I'm stopped with my foot on the brakes the pedal goes to the floor. I'm using no fluid. What is wrong with my wagon, er sorry car? 

Views: 238

Reply to This

Replies to This Discussion

Master cylinder bypassing. Replace it.

Dang Russ you really know how to cheer a guy up. I was was hoping it was something I missed or a special kunnuter valve that needed adjusting. 

I messed it up by not putting a block of wood on the floor to stop peddle travel to the floor. It still would have needed to be done anyways. 

Sorry ol chap, but I have heard of not pushing the pedal all the way down on a used master cylinder. The crud is build up back where the piston doesn't normally travel, and you cut seals doing so.

Test it.  

Only two things can make a pedal fade without fluid loss;. trapped air in the lines or internal leakage in the master cylinder.    If the fluid wasn't disturbed or run empty, you can almost certainly rule out air in the lines.  If you're not sure about the fluid, you can test it logically.  

A quick check for air in the system is to have someone pump the brakes several times and then release the pedal.   If the fluid squirts in the air when the pedal is released, there is air in the system.  This happens because pumping the brakes will compress the air which will decompress quickly when the pressure is removed.   If there is only fluid, no compression can take place, so you will see only agitation in the reservoir with no squirt.

To test a master cylinder, get some plugs and install them in place of the lines.   Bleed the air and then check by pushing the pedal hard.   If it drops, then it must be the master cylinder is defective since you have isolated that component.   If it's hard as a rock, only moves a tiny amount and holds regardless of how hard you push it, it is ok. 

If neither test exposes the problem, u can pinpoint troubles with a pair of hose pinch off pliers.   Squeeze off each of the three rubber hoses one at a time at the front wheels and above the rear.  When the problem goes away, you know the trouble is in whatever the pinched hose supplies.

Finally, it isn't clear that what you describe isn't a bad vacuum feed to your booster.  You say the pedal is hard then drops slowly.   I'm not there to feel it, but that sounds like a sluggish vacuum booster that isn't building boost quickly enough.  So does the pedal fade with the engine off or only when driving?   If it's hard and steady when off, then the booster is at fault.

Enjoy

Now there's a great load of info. Thanks Mark. I have hydro boost not a vacuum system.

I'll give you a bit more back ground. 

I was doing some general maintenance and noticed the back master cylinder cup was almost empty. I topped it up and went looking for a leak. The brakes are at least 75 percent so that wasn't the problem.  I found the leak at the trailer brake controller under the dash. It's the old style with a line tapped into the front brakes. I took it apart and found the tiny hyd cylinder inside it leaking. I soaked the rubber cup in lacquer thinner and cleaned the old fluid out of it. All is good there now at least temporarily. I sucked the fluid out of the master and added fresh dot 3 and bled most of the old fluid out of the system including the trailer brake controller. My nephew did the pumping and I did the bleeding. Nice hard brakes and the trailer brake controller works better than ever. Sitting with my foot on the brakes and the hard paddle goes to the floor. My thought was that there was some gunk in the master and the extended travel of the peddle may have damaged the inner seals. Basically there may have been rust in the master just past its normal travel and I chewed up the seals by pumping them to the floor.

What's your thoughts with this added information. 

The brakes were fine prior to this event. They weren't as firm as they are now but 1970's firm and didn't feel unsafe. 

Would lacquer thinner not stuff the cup?

I'd be checking the stuff hasn't rooted the cup.

Brakes are for quitters... very overrated.

For you it is of course not necessary with brakes Kevin. As you are constantly up side down I guess you should worry more about falling off the planet. 

Of course, the symptoms are pointing to the master cylinder, but I don't like changing parts without seeing the failure first.   Take the master off and hone it, clean it like you did the trailer actuator, and replace the cups, they are too cheap to not just swap out.   

Mark, the rebuild kit was 34 and new master 70 at rockauto.com. I went with the new one, although they did have some rebuilt ones for 30 to 50 I decided to get a new one.

Kevin, I found an exact match to my brake controller on eBay, it's NOS. The one cleaned with lacquer thinner is still holding fine. I only soaked it long enough to soften it up and swell it a tiny bit. It was a stop gap repair to get me moving again but it is still holding up. Now I just want to see how long it will last LOL 

RSS

Photos

  • Add Photos
  • View All

Forum

64 tranny mount

Started by Ron Perry in 1963/64 Cadillac Specific Discussion 19 hours ago. 0 Replies

Hi Guys Hoping someone could recommend a vender where I can purchase a transmission mount for my 64 Sedan De Ville.  Thanks!Continue

Jason's September 26, 2022 Ramble - Gone Like a '64 Cadillac

Started by Jason Edge in General Discussion. Last reply by Jason Edge 19 hours ago. 2 Replies

Well, parts car #58 is history. Rear end came out late yesterday (1st Picture below), it was delivered to the metal yard this morning (2nd picture) and for the first time since I bought my 2013…Continue

Was there Originally Carpet Inside 1964 Eldorado Center Console?

Started by C. Van Tune in 1963/64 Cadillac Specific Discussion. Last reply by Bobby Brown yesterday. 6 Replies

Is there supposed to be carpet inside the '64 Eldo center console?There is carpet in mine, and it's a deeper pile than what's on the floor (which has probably been replaced.)Here's some pix of mine.…Continue

63 Lower Front Bumper Ends?

Started by Peter Greenway in Wanted to Buy. Last reply by Peter Greenway yesterday. 3 Replies

I'm looking for 2 good condition lower front bumper ends for a 1963 car. Can anyone help please?Continue

Blog Posts

electric fuel pump question on 63

Posted by Kim K Kaiser on September 27, 2022 at 11:30pm 0 Comments

I suffered another vapor lock today,  and im bout ready to go to electric.  It can get really hot and dry out here in MT and it was only 88 yesterday when I stalled.   car ran flawless all day..  got into my town, did some slow and idle driving, and temp on gauge got to about 195.   To get to my house, I have to climb a pretty steep hill, and as has happened on other occasions, has stalled about half way up.   I checked the bowl, it was at the bottom.  The fuel pump was HOT!!!,,,I had it…

Continue

Trunk Open and Lock Mechanism is in Closed Position

Posted by Chris Anderson on September 13, 2022 at 7:14pm 7 Comments

While working on my trunk lock on 64 Cadillac, I mistakenly closed the locking mechanism while the trunk was open.  Is there an easy way to manually release the lock back to the open position?

Thanks.

Fuel Pump Failure

Posted by Jon Shields on August 6, 2022 at 6:48am 4 Comments

Hello,

I'm located in Melbourne, Australia and my 64 sedan de ville is stuck in the garage due to failed mechanical fuel pump. The first after market mechanical fuel pump lasted a few years before it failed & left me stranded 5 hours from home. A hire car and tow got us home. On inspection, I noticed a valve not seated within the housing. I was optimistic, pressed it into place and assumed the pump was good to go. But alas, no. From what I can now determine, the diaphragm pushrod…

Continue

Renovation project 1964 Cadillac Deville convertible

Posted by Balachne on May 31, 2022 at 7:00am 3 Comments

Renovation project 1964 Cadillac Deville convertible

 

Introduction

To achieve an excellent result of vehicle restoration, it is essential to  manage this task as one manages an industrial project.

To do this we will use a certain formalism of project management and therefore start by defining the need. It is from this that we will deduce the scope, then the time of execution of the…

Continue

Videos

  • Add Videos
  • View All

© 2022   Created by Jason Edge.   Powered by

Badges  |  Report an Issue  |  Terms of Service