Brake issue ... rear well on MC draining - somewhere?

[czarcaustic]

My new toy hasn't stopped well since I got her last week - really soft pedal all the way to the floor, sounds like only the front discs were stopping her. So today I rebuilt the rear brakes. Filled the MC, bled the rear brakes, the brake light went off and they are working great!

Then I tested a hard stop. I locked them up. The brake light came back on and the brakes felt soft again. When I looked at the MC - it was dribbling fluid out from under the seal at the front well. When I opened the MC - the rear well was almost empty again. refilled ... pumped the brakes on a clean surface - no leaks that I can see, but the pedal isn't stiffening up again.

I seem to be losing fluid out of the rear well, the front well seems to be bubbling out of the gasket on the MC - but I can't find any evidence of a leak on the ground. Where on earth is the fluid going from that rear well!?!?

It is driving me NUTS. I plan to put new calipers and pads on the front next week. Should I be looking at a new MC as well?

[mr48chev]

If there isn't a leak in the line the rear half of the cylinder is leaking. Take the two bolts off and pull the master cylinder out a few inches and see if the back side of the piston is wet. New ones aren't very expensive and double master cylinders are one thing I don't rebuild myself or recommend rebuilding at home. I have flat never had any luck rebuilding double master cylinders and always replace them. Besides that, now the kit costs almost as much as a new mastercylinder.

The High buck Napa mastercyinder that fits my 71 GMC and I think fits your 72 1500 is 46.46 here locally so that's not a bank breaker.

[67 chevelle]

if you have a power booster thats where it is
if not maybe a wheel cylinder or blown line

[ole dollor]

power brakes would leak into the booster, non power would leak under dash inside firewall...

[czarcaustic]

There is a booster ... so I am filling that bad boy up with Dot 3, eh?

How on earth am I going to clean that mess up? Furthermore, can I rebuild that booster?

[ole dollor]

i would let it set untill i replaced the m c ...cheeper than fenders and grill.

[czarcaustic]

Originally Posted by ole dollor

i would let it set untill i replaced the m c ...cheeper than fenders and grill.

Yeah ... it is looking like I should go ahead and just rebuild the ENTIRE brake system.

I got the rear drums done today. My calipers get here Tuesday, and I guess I will be getting a MC as well.

Will the brake fluid in the Booster damage it? I know I should probably get out as much as possible, but I am unsure how to go about doing that. Any tips? Tricks?

[ole dollor]

i think it will burn out all by itself. will suck out through the intake , i have seen this a lot over the years, i do know its not good for brake fluid to be in there, i guess you could pull the booster and see if anything will drip out. do you know how long its been doing this. the booster may be ok if your peddle is not real hard.

[czarcaustic]

Unfortunately, I don't know how long it has been doing it. The guy I bought it from said "everything is running like a top!" Which is basically true, except for the brake light I noticed. He was unsure how long the brake light had been on, as he wasn't the daily driver. blah blah blah

Long story short. I have had it for a little over a week - the brake light has been on the entire time I have had it (driven lightly), except for a few moments this afternoon after I rebuilt the rear brakes and topped off the MC.

So - I will keep her off the road until I can pop that MC off and fix that little problem.

Thanks for all the feedback everyone.

[czarcaustic]

New MC installed (bled it on the truck, seems to have worked). Brake light off, no leaks, truck stops like a dream.

Thanks guys!

[ole dollor]

thats great...now its time to take it out and have fun with your new truck...