68 Riviera Brake Issue

Been having a brake problem with my Riv, didn't want to have to resort to asking for help seeing as I should be able to resolve this on my own but as of this point I dont want to start throwing parts at it.
I have gone around the car, all wheel cylinders are working good and are dry, all shoes have at least 50% left, all shoes have been properly adjusted, drums are not scored up and do not appear to be warped, replaced all 3 brake hoses, entire brake system has been flushed/filled/bled with fresh fluid. While bleeding with engine off pedal feels great, start the car and pedal effort is decreased and the pedal goes almost to the floor, can feel brakes start to slightly slow the car down, push pedal any further and the front drums lock right up, my suspision is the master cylinder needs to be replaced but I would like to hear your guys thoughts, thanks.

 

I'd guess that was the first choice. I know you don't want to throw parts at it but those aren't too expensive and if it is very old, it is probably the issue. Are there any leaks around the base where it bolts to the booster?

 

How is the brake distribution block?

 

Does not appear to be wet anywhere, and I would probably just order the napa master/booster combo for $175 and be done with it, the "distribution block" like with the brake sensor in it? Was under the impression all that does is run the brake light and has no specific functions otherwise and no it is not wet either..

 

Have fun getting that booster off.

 

When I removed the master cylinder from my '72 GS back in 2002, I could tell that the master had never been flushed such that a valley was worn in the bottom of the bore.

 

Definitely appreciate your advice. I would be replacing both due to the factor of the booster alone costs almost as much as if were to buy master/booster combo, if I am replacing the master I have no problem spending the extra buck and getting a new booster, the more new parts under the hood the better it looks imo, I am fully aware on the function and testing of a master, but I am having a strange problem here, hence the seeking advice/comments, when I pump and hold the brake with the engine off the pedal is solid, could it be up higher from the floor.. maybe.. but it not by any means way down there near the floor, Now could it be possible that the seals for the rear in my master are so far gone it I am just getting front lock up with only minimal rear application?

 

If the pedal sinks to the floor with little or no braking action it really can only be a couple things assuming the system is bled properly.

• If the fluid is being pumped out of the master cylinder as it should, if no leaks it will move the wheel cylinders
• If wheel cylinders move but there is too much free play before the shoe makes contact with drum it can allow pedal to go to floor. You seemed confident all shoes are adjusted properly. Make 100% sure they are assembled correctly. Pull every drum to be sure if necessary if any doubt at all.
• When pedal goes to floor, if you pump the brakes, will it eventually pump up and stay? If so I would put greater emphasis on double checking the assembly and adjustment of shoes.
• If there is no problem with above or the pedal won't pump up hard no matter what, then the master is not pumping fluid like it should and instead it is leaking back past the cup seals on the piston instead of being pushed through the lines to the wheel cylinders. Replace master cylinder.

As stated the booster is a real pain to remove particularly getting the master cylinder rod eyelet off the brake pedal. Its a personal choice but I do not trust aftermarket replacement boosters and master cylinders. I send original boosters for rebuild and the master cylinder for a brass or stainless sleeve and rebuild unless the car has to be back on the road quickly.

 

The pedal does not sink, the pedal does not improve with pumping, all drums have been removed brakes cleaned and inspected and adjusted(3 times) properly, entire brake system flushed and gravity & then pressure bled with fresh clean fluid. After speaking more about this issue with you guys I am confident replacing the master cylinder will fix this issue, thanks for the advise reguarding the booster replacement and the having the master rebuilt apose to a jobber one, I have found master rebuild kits avaliable and I am more than qualified enough to do the rebuild myself and have a shop with all the tools you could dream of, is there a place or brand or type of master rebuild kit you would recommend? Thanks again.

 

I have never taken a master cylinder apart on an old car or a car that sat for years that I was comfortable rebuilding with just a kit. There is always some level of deterioration of the cylinder bore from moisture. Of course you can run a hone in the bore and put new piston seals in and it might work for awhile. If you are looking for a short term low budget fix that's OK and it just depends on your goal. Otherwise the brake system is not a place to cut corners.

When a master cylinder is sent out for sleeving with either stainless or brass you get a superior polished bore finish made from a material that is very resistant to corrosion for years to come. Whitepost Restorations and Apple Hydraulics are the main sleeving shops people use.

 

Right on thanks, there are few very good shops locally that could most likely do that sort of professional work for me, my work has a hydralic cylinder rebuilder that might help me out with it if sleeving is required, otherwise I mine as well send it out as you guys are recommending, its too bad there isn't a good replacement new master cyl. avaliable, no-one has luck with brand new jobber masters at all? or is this just a personal preference thing here...