brake master question

[hinkdart]

A couple months ago I purchased a 72 Dart that is in pretty good shape. Somebody put a lot of love in the car but then sold it to the guy I bought it from. He worked in his family business which was a little repair shop/stereo installation store. Every night he would park the car inside and pull it back out in the morning. Everything was gummed up but it ran well.

Brakes were very grabby when I first got it. After flushing out the brake fluid they instantly got much better. Fluid was literally like mud and I had to use brake clean in the master and vacuum out the junk before I flushed it. Fluid comes out clean and master now looks like new. Unfortunately now when the brakes get really hot as in after a lot of stop and go driving or spirted back road driving the pedal gets very soft and goes down almost to its stop before it starts to actually slow the car down. Its starting to get a little scary and last weekend on my way to a car show it did it as I was driving down town. I parked and removed the master cylinder cover and fluid leaked out onto the ground. Next day I checked it cold and the firewall side of the master was overfilled and radiator side was a little low. I spooned a little fluid over and took it for another ride yesterday. As soon as I got in stop and go driving the brake pedal went soft. I went 15 miles on the highway and by the time i got off the brakes were back to normal again.

Should I just get a new master cylinder? I can't think of anything else that it could be. Thanks

 

[67Dart273]

NEVER use brake clean internally in brake parts, unless you are down to "only" metal parts, IE completely taken apart

Might be time for "more than" just a new master. Explain "soft," which might be a subjective word

Does the pedal leak down to the floor? Or do you still have a hard pedal, the brakes don't stop well?

Or does the pedal just feel mushy? You might have air in the system, or left over brake clean, which was never designed to "be" brake fluid.

 

[RedFish]

If the fluid was as nasty as you claim, you could have problems in the proportion valve, etc.. Replace the master cylinder and cross your fingers.
Flushing in one direction will not thoroughly clean anything anyway. To prove this, disconnect heater hose at firewall and drape them over the right fender. Use a garden hose to flush in one direction until water runs out clear. Now change direction of flow and watch the water turn nasty again.
You can't back flush the entire brake system. Even if, it wouldn't fix anything, especially using parts cleaner.

 

[hinkdart]

k. I'll go pick up a new master. Just to clarify; i didn't use brake clean to flush the system. I had the mighty mite vacuum out the junk in the master as I used brake clean to loosen up the crud. Completely vacuumed the master till it was clean then added brake fluid and flushed the system.

It does not feel like air. I was hoping it wasn't anything with the booster but I'll try the master and see how it is. I just checked the master and it doesn't seem to have lost any fluid but there was slightly more on the firewall side than the radiator. Same as last time but not as severe. It was a slight amount.

another thing of note is that I drove the car for a day before I changed all the fluids. Couldn't help myself even though I found a ton of stuff that would scare you. The brakes felt better after the day of driving and less grabby. I flushed the brakes a month ago and the soft pedal just started last week. I usually drive it on long casual drives or short trips. I just recently started using it every day. I'll report back with what I find, thanks agian.

 

[hinkdart]

Bought a new Raybestos master and it showed up today. It was $75 and a rebuild from Autozone was $17 but they were backordered. I'm glad i went new and just took it for a spin. Brakes feel perfect and pedal is perfect. I wouldn't be surprised if the proportioning valve is gummed up as it took forever to flush the fluid.

 

[nm9stheham]

Keep an eye on the inside of the wheel backing plates and the insides of the tires to see if any brake fluid starts leaking. My concern is that the brake-clean has softened up the rubber piston seals in the wheel cylinders; this may be why the MC went so quickly (or may not). But as said, brake-clean should never be used inside the brake system, only fresh brake fluid.

With the old MC's condition, I would be planning on replacing the wheel cylinders anyway, as well as all the rubber brake lines; they can fail and lock up a wheel.

Yeah $15 for a rebuilt MC at a box store would make me shudder! New for brakes is good!

 

[YY1]

Next time try rockauto.

I just ordered a new M/C plus 4 new wheel cylinders, one axles worth of shoes and all three rubber lines.

Was less than $120 shipped for all that plus two door hinge re-pin kits.

Cost of M/C was $35, and they have several styles to choose from.
I got the most stock looking one with the bolt, but Now I remember how much fun those are, and I probably should have paid the $3 difference for the one with the spring bale clamp.

can also choose from Raybestos, Wagner, Dorman, Cardone, etc.

Agree about wheel cylinders. need to inspect and monitor real close.
They are about $5-$7 from rockauto, or $2 for the rebuild kit.

 

[BillGrissom]

Fluid was literally like mud and I had to use brake clean in the master and vacuum out the junk before I flushed it.

That "mud" is rust junk, and typical if someone never refreshes the glycol fluid (most owners). No more problems since I changed to DOT 5 silicone fluid in all my non-ABS cars. However, much fear-mongering about it, and getting rare, so decide for yourself.

As mentioned, brake cleaner is only to clean the metal rotor or drum faces. I think it will eat up rubber, so not for use where brake fluid is, and I would try to keep it off rubber dust covers on calipers and wheel cylinders.