Bad Master Cylinder?

**BattleBug** · #1 (**permalink**) 12-10-2006, 07:03 PM

Good News: I just rebuilt my brake system with new pads, rotors, braided lines, speedbleeders, and I even rebuilt the calipers.

Bad News: One week, one sore calf, and two gallons of fluid later, I still have air bubbles in the rear brake lines. I tried elevating the rear end, tapping on the calipers, and even the fabled "2x4" trick. Nothing helps to get the air out and firm up the pedal. I tried all permutations of bleeding sequences...nothing mattered.
I'm perplexed. I think the MC piston seal for the rear circuit has gone south. Puzzling because I had no issues with the MC beforehand. Anyone?
TIA

bianchi1 · #2 (**permalink**) 12-10-2006, 09:15 PM

'fabled 2x4 trick'?

**BattleBug** · #3 (**permalink**) 12-10-2006, 09:26 PM

Yeah...it's where you take a 2x4 and beat the ever living $hizzle out of the car for its transgressions against humanity. Actually, the hypothesis was that if the brake pedal was held down overnight with a 2x4 it would help to re-expand the seals in the MC.

It didn't help.

Alfajay · #4 (**permalink**) 12-11-2006, 03:49 PM

BattleBug:

Yea, I had the same problem 6 mo or so back. I did all the tricks you describe - also changed the MC, the pressure regulator, consulted the BB, etc.

In the end, I gave up and took it to my local repair shop. They said "oh, it is impossible for one person to bleed brakes - one guy has to work the pedal while the another works the bleed screws". Sure enough, they got a firm pedal after bleeding it their way.

Now before you all respond "BS!, I've done it solo many times", let me add that I too have successfully done it solo. Sure, put a tube from the bleeder into a partially filled bottle, bleed one front + one rear together, close the bleed screw with the tube still submerged in fluid, ... Yea, that technique has worked many times in the past for me. But for some reason, it didn't 6 mo ago. Has the composition of brake fluid changed? Some byproduct of global warming? Phase of the moon?

I recently popped for a set of "speedbleeders" for my next project. Haven't tried them yet, but am hoping they address this issue. Can anyone comment?

**Gubi** · #5 (**permalink**) 12-11-2006, 04:07 PM

Quote:

Originally Posted by Alfajay

I recently popped for a set of "speedbleeders" for my next project. Haven't tried them yet, but am hoping they address this issue. Can anyone comment?

**Tifosi** · #6 (**permalink**) 12-11-2006, 05:30 PM

Speed bleeders = kitties rectum (just being able to do the clutch slave alone is worth the price of admission)

They'll work when doing it solo or with a pressure bleeder, though it's doubtful a vacuum bleeder would have enough gumption to allow them to function.

Reversionary type bleeding/feeding/filling would be totally out of the question.

mrutkaus · #7 (**permalink**) 12-20-2006, 06:53 AM

What size, where to get the auto-bleeders for '85 Spider? I've seen some at Advance Auto, but never quite grasped the right size...

Mike

Alfajay · #8 (**permalink**) 12-20-2006, 08:08 AM

mrutkaus:

Centerline carries them. They are about $10 apiece.

**lowmileage** · #9 (**permalink**) 12-20-2006, 08:38 AM

Motive bleeder - just make sure it's attached correctly to the master before pumping (

as me how I know but at least it wasn't the Alfa

)
http://www.motiveproducts.com/

elite38868 · #10 (**permalink**) 12-28-2006, 01:35 AM

I had a similar problem with my mom's 164. Even after the brake MC was replaced. I gave up and took it to the local shop who had a fluid pump and pumped brake fluid through the open bleed screw and into fluid tank of the car. Reverse bleeding it's called. It seems to be working fine ever since.

**BattleBug** · #11 (**permalink**) 01-07-2007, 07:35 PM

Indeed, my MC was bad...scored piston, "ridged" bore and collapsed seals. R&R'd it before the h-days and all is (almost) well. Now if I could only stop...